Enter Zoom Meeting

TS4.1

EDI
Active Tectonics and Geodynamics of the Mediterranean Region

The Mediterranean region holds a plate boundary zone undergoing final closure between two major plates, Africa and Eurasia. The active tectonics and geodynamics of the Mediterranean region result from the interaction of subduction and collision processes, deformation of the slabs, mantle flow, and extrusion of crustal blocks. These geodynamic processes have a transient nature and their changes affect the regional tectonics.

This session focuses on two aspects of the Mediterranean recent active tectonics and geodynamics:
(1) how (active) geodynamic mechanisms define the current structure and recent evolution of Mediterranean Arc systems.
(2) how the surface deformation is accommodated, both on fault local scale (e.g. the seismic cycle and kinematics of active faults) and in the larger (e.g. regional kinematics and relation the surface deformation to the deeper processes).

We welcome contributions from a wide range of disciplines including, but not limited to seismology, tectonic geodesy, remote sensing, paleoseismology, tectonic geomorphology, active tectonics, structural geology, and geodynamic modeling.

We strongly encourage the contribution of early career researchers.

This session is formed by merging of TS sessions: "Active tectonics and geodynamics of the Eastern Mediterranean" & "Recent geodynamic evolution and active tectonics of Mediterranean Arcs"

Co-organized by GD8/SM1
Convener: Ali Deger OzbakirECSECS | Co-conveners: Manel Prada, Patricia Martínez-GarzónECSECS, Jean-Philippe Avouac, David Fernández-BlancoECSECS, Laura Gómez de la Peña, Konstantinos Chousianitis, Gülsen Uçarkuş, Giovanni Luca Cardello
Presentations
| Wed, 25 May, 13:20–18:30 (CEST)
 
Room D1

Wed, 25 May, 13:20–14:50

Chairpersons: Manel Prada, Laura Gómez de la Peña, Patricia Martínez-Garzón

13:20–13:23
Introduction

13:23–13:30
|
EGU22-2092
|
ECS
|
On-site presentation
Penggao Fang et al.

        The Cenozoic geodynamic evolution of the Western Mediterranean is complex comprising subduction, slab roll-back, back-arc extension, collision, and lithosphere delamination. We investigate the subsidence of a regionally observed unconformity in the Valencia Trough of the Western Mediterranean, here referred to as the Miocene Unconformity, which separates Mesozoic from latest Palaeogene to Neogene sediments. The mechanisms controlling its subsidence are poorly understood.

        We show, using a dense grid of seismic reflection data, well data and 3D flexural backstripping, that the Miocene Unconformity in the SW Valencia Trough subsided by more than 1.5 km to the present day at an average rate of 90 m/Myr. The absence of Cenozoic extensional faults affecting the basement shown by seismic data indicates that this rapid subsidence is not caused by Cenozoic rifting or remaining Mesozoic post-rift thermal subsidence. Neither can this subsidence be explained by subduction dynamic subsidence or flexural loading related to the thin-skin Betic fold and thrust belt which only affects subsidence observed near the deformation front.

        We interpret the 1.5 km subsidence of the Miocene Unconformity as the collapse of a back-arc transient uplift event. Erosion during this uplift, resulting in the formation of the Miocene Unconformity, is estimated to exceed 4 km. Transient uplift was likely caused by heating of back-arc lithosphere and asthenosphere, combined with mantle dynamic uplift, both caused by segmentation of Tethyan subduction resulting in slab tear. Subsidence resulted from thermal equilibration and the removal of mantle flow dynamic support Tethyan subduction slab roll-back. We propose that our observations and interpretation of rapid back-arc km-scale uplift and collapse have global applicability for other back-arc regions experiencing subduction segmentation and slab tear during subduction slab roll-back.

How to cite: Fang, P., Tugend, J., Mohn, G., Kusznir, N., and Ding, W.: Rapid large-amplitude vertical motions generated by 3D subduction slab roll-back in the Valencia Trough, Western Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2092, https://doi.org/10.5194/egusphere-egu22-2092, 2022.

13:30–13:37
|
EGU22-5227
|
On-site presentation
Ivan Martin-Rojas et al.

SE Iberia Tectonics is presently dominated by the NNW-SSE convergence between the Eurasian and Nubian plates. Farther east, the eastern Spanish coast and the Valencia Trough are dominated by ENE-WSW extension related to thermal subsidence. This extension has been interpreted as the final stage of abort rift responsible for the ENE motion of the Balearic promontory. Our data from 11 CGNSS stations permit us to discuss the deformation partitioning in SE Iberia related to the two abovementioned processes.

We identify three kinematic domains: a relatively stable domain, a domain moving towards NNW and undergoing NNW-SSE shortening, and a third domain relatively moving towards ENE and experiencing ENE-WSW extension. Our results indicate that plate convergence-related NNW-SSE shortening is mainly absorbed by the Eastern Betic Shear Zone (EBSZ), in agreement with previous studies, but also show that a significant fraction of this shortening is accommodated south of the EBSZ.

We also identify and quantify for the first time ENE-WSW extension northeast of the EBSZ. We propose that this extension could be absorbed by basement normal faults whose surface expression is obscured due to decoupling of deformation between the basement and the cover. Our results shed light on the tectonic puzzle of SE Spain.

How to cite: Martin-Rojas, I., Sánchez-Alzola, A., Medina-Cascales, I., Borque, M. J., Alfaro, P., and Gil, A.: Present strain partitioning in SE Spain. Insights from CGNSS data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5227, https://doi.org/10.5194/egusphere-egu22-5227, 2022.

13:37–13:44
|
EGU22-5479
Frank García-Tortosa et al.

We here discuss the results of a local GNSS episodic network from the Baza sub-Basin (S Spain). This network including six sites, was established in 2008 and has been measured seven times since then. Our data permit us to present the first short-term slip rates for the two active faults in this area. The main active structure is the normal Baza Fault. We estimate slip rates for this fault ranging between 0.3±0.3 mm/yr and 1.3±0.4 mm/yr. For the strike-slip Galera Fault, we quantify the slip rate as 0.5±0.3 mm/yr. These values are higher than previously reported long-term slip rates. We postulate that the discrepancy for the Baza Fault between short-term and long-term slip rates could indicate that the fault is presently in a period with a displacement rate higher than the mean of the magnitude 6 seismic cycle. Moreover, the velocity vectors that we obtained also show the regional tectonic significance of the Baza Fault, as this structure accommodates one-third of the regional extension of the Central Betic Cordillera.

Our results also show that the Baza and Galera Faults are kinematically coherent and they divide the Baza sub-Basin into two tectonic blocks. This points to a likely physical link between the Baza and Galera Faults; hence, a potential complex rupture involving both faults should be considered in future seismic hazard assessment studies.

How to cite: García-Tortosa, F., Alfaro, P., Sánchez-Alzola, A., Martin-Rojas, I., Galindo-Zaldívar, J., Avilés, M., López Garrido, A. C., Sanz de Galdeano, C., Ruano, P., Martínez-Moreno, F. J., Pedrera, A., de Lacy, M. C., Borque, M. J., Medina-Cascales, I., and Gil, A. J.: Kinematic and tectonic analysis of the Baza and Galera Fault (S Spain). Insights from GNSS data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5479, https://doi.org/10.5194/egusphere-egu22-5479, 2022.

13:44–13:51
|
EGU22-7890
|
ECS
|
On-site presentation
Marcos Moreno-Sanchez et al.

We present the first results of the MORPHOMED project, in order to deepen the chronology, uplifting rate, and tectonic forcing of different sectors of the Betic Cordillera since the Pliocene. Our initial morphotectonic analysis in the Western Betics, at the active termination of the Betic dextral STEP fault, highlights the location of active orogen-parallel normal faults cutting Pliocene marine sediments, uplifted above 600 masl, and Quaternary alluvial fans. The morphometric study we carried out includes normalized river steepness (ksn) and other geomorphic indices calculated in GIS using our own code designed in python. The fieldwork developed comprises the identification of uplifted Pliocene marine deposits, faulted alluvial fans and remnants of uplifted planation surfaces. The alluvial fans are related to travertine deposits older than 350 ka, which would be associated with hot springs. Geochronological studies involve previous and new U-Th dating on travertines and speleothems from caves in the high areas. The preliminary morphometric analyses reveal the occurrence of knickpoints that coincide with normal faults affecting marine Pliocene deposits and alluvial fans. These fans show vertical displacement of more than 20 m and their age remains unknown albeit the associated travertines are being dated. These results support previous works concerning of active tectonics in the Central and Western Betic Cordillera and they will serve to define new active faults, driving tectonic uplift of the Western Betics, which are the key to understand the landscape evolution forced probably by deep mantle rooted tectonics like slab tearing and edge delamination.

How to cite: Moreno-Sanchez, M., Ballesteros, D., Booth-Rea, G., Pérez-Peña, J. V., Pérez-Mejías, C., Reyes-Carmona, C., Azañón, J. M., Galve, J. P., and Ruano, P.: Knickpoints and faulted alluvial fans: evidence of orogen parallel active extension related to delamination in the Western Betics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7890, https://doi.org/10.5194/egusphere-egu22-7890, 2022.

13:51–13:58
|
EGU22-7451
|
ECS
|
Virtual presentation
Laura Gómez de la Peña et al.

The Alboran Basin is located in the westernmost Mediterranean Sea. This basin was formed during the Miocene, and since the late Miocene, has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. Thus, the Alboran Basin is a seismically active area, which hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which several small faults are accommodating the deformation.

Based on a modern set of active seismic data, we were able for the first time to quantify the total slip accommodated by the most prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin.

These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. Using the most complete dataset until the date, we performed a revision of the geometry and characteristics of the main fault systems offshore. Based on this data, we perform a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed.

How to cite: Gómez de la Peña, L., R. Ranero, C., Booth-Rea, G., Azañón, J. M., Gràcia, E., Maesano, F., Basili, R., and Romano, F.: A revision of the main active fault systems of the Alboran Basin: their significance in plate tectonics and a first appraisal of its seismogenic and tsunamigenic potential., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7451, https://doi.org/10.5194/egusphere-egu22-7451, 2022.

13:58–14:05
|
EGU22-4234
|
ECS
|
|
Virtual presentation
Pedro J. Gea et al.

The origin and tectonic evolution of the Western Mediterranean region, specifically the Gibraltar Arc system, is the result of a complex geodynamic evolution involving the convergence of the Eurasia and Africa plates and the dynamic impact of the Gibraltar slab observed in tomographic studies. Although geologic and geophysical data collected in the last few years have greatly increased our knowledge of the Gibraltar Arc region, it is still unclear the mechanical links between the Gibraltar slab and the past deformation of the overriding Alboran lithosphere as well as present-day motion shown in detailed GPS observations. In this work, we use the code ASPECT to model the geodynamic evolution of the Alboran slab in 2D over the last 20 million years. The initial model setup simulates a vertical WE section at a latitude of about 36oN and represents the situation at 20 Ma, when the trench had already fully rotated to the southwest and the predominantly westward rollback of the Gibraltar slab started taking place. We conduct a parametric study varying the rheological parameters and the initial slab properties (dip angle and length) to properly fit the robust current slab features, particularly, its position and its curved morphology extending eastward. We show how after 20 Myr of model evolution, i.e. at present time, the slab pull appears to have a still significant influence on surface velocities. We find a westward surface motion in the Gibraltar arc caused by the negative buoyancy of the slab. These velocities increase westwards from 1 to 4 mm/yr consistently with geodetic observations. Our models roughly reproduce the Alboran basin evolution, initially developing the West Alboran Basin and then the East Alboran Basin. Finally, preliminary 3D models further support these results and properly the main trends of the coupled dynamics of the Gibraltar slab and Alboran basin evolution during the last 20 Myr.

How to cite: Gea, P. J., Negredo, A., and Mancilla, F. D. L.: The Gibraltar slab dynamics and its influence on past and present-day Alboran domain deformation: Insights from thermo-mechanical numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4234, https://doi.org/10.5194/egusphere-egu22-4234, 2022.

14:05–14:12
|
EGU22-12611
|
ECS
|
Virtual presentation
Shaza Haidar et al.

The Algero-Balearic Basin (ABB) is an Oligo-Miocene back-arc basin resulting from a polyphase tectonic evolution involving Tethyan subduction retreat and bilateral slab tear propagation. The ABB was fully opened by the Tortonian, while the Gibraltar and Calabria arcs formed by the narrowing of retreating slab fragments. Since then, the Algerian margin has undergone a tectonic inversion, potentially preceding an incipient subduction as shown by the analysis of the on-offshore deformation distribution. In this work, we aim to shed light on the relationships between the large-scale structures inherited from the ABB opening and the recent margin inversion. For this purpose, we rely on two recent analyses, one addressing the ABB opening (Haidar et al., 2021) and the other mapping the inversion-related structures off-Algeria (Leffondré et al., 2021), both being constrained by a set of deep penetration multi-resolution seismic profiles cross-correlated with magnetic, gravimetric and bathymetric data. 

The deep ABB has been subdivided into 4 zones with relatively distinct geodynamic evolutions, as demonstrated by variations in pre-Messinian sedimentary infill thickness and basement depth : (1) the oldest, fan-shaped oceanic basin to the east (off-Jijel), formed during the Langhian-Serravallian after collision of the Kabylian blocks with the stretched African margin; (2) the shallower and younger Hannibal thinned continental domain (HD), intruded by intense post-collisional magmatic activity during the Upper Serravallian - Lower Tortonian; and ever-younger to the west, (3) the central-western (off-Algiers-Tipaza) and (4) westernmost zones, formed from the Tortonian to the Lower Messinian in response to the westward retreat of the Gibraltar slab and the concomitant migration of the Alboran block by propagation of vertical tears along a STEP (Subduction Transform Edge Propagator) type margins.

The tectonic inversion is characterised by long-wavelength of flexure (>100km) of the ABB towards the Algerian margin and/or buckling of shorter wavelengths (≈30km). The central (HD) and central-eastern (off-Jijel) zones are dominated by flexure, whereas buckling is dominant in the central-western zone. Further, the easternmost (off-Annaba) and westernmost zones exhibit a combination of flexure and buckling. Except in the westernmost zone, characterized by low deformation on a single fault, the margin toe consistently displays inversion-related faults systems consisting of 3 to 4 south-dipping and sub-parallel thrust faults.

By comparing the zonation of the deep ABB and the zones with different responses to inversion, we evidence a similar zonation of the margin, with only slight differences likely resulting from data density variations. To the east, the old and wide fan-shaped basin has favored the development of a significant flexural response, whereas the young westernmost zones, narrower and bordered by STEP-faults, evidence a combination of buckling and short-wavelength of flexure. The HD is a complex zone with a shorter wavelength of flexure compared to the eastern zone, probably related to magmatic activities affecting the potentially continental crust. Our results suggest that if initial zonation persists, several parameters may be involved in the control of the inversion mode. These parameters may include the opening-related structural inheritance, the oceanic lithosphere composition, as well as the age and former structures of the margin.

How to cite: Haidar, S., Leffondré, P., Déverchère, J., Graindorge, D., Klingelhoefer, F., Arab, M., Medaouri, M., and Beslier, M.-O.: New insights on the relationship between inherited structures of the opening of the Algero-Balearic basin and recent inversion of its southern margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12611, https://doi.org/10.5194/egusphere-egu22-12611, 2022.

14:12–14:22
|
EGU22-10619
|
ECS
|
solicited
|
Virtual presentation
Seifeddine Gaidi et al.

This work analyses the tectonic evolution of Northern Tunisia from the Late Miocene to Present. Two orthogonal extensional systems with ENE- and SE-directed transport produced the extensional collapse of the Tell and Atlas Foreland Thrust Belts (FTBs) in northern Tunisia during the Late Miocene to Pliocene in a context of NW-SE plate convergence between Africa and Eurasia. These systems produced the extensional denudation of the Tunisian Atlas and Tell foreland thrust belts, which we related to deep mantle tectonic mechanisms, known as a common feature in other FTB´s in the western Mediterranean, i.e. Betics, Rif, Calabria and Apennines. Low-angle normal faults have extended and reworked the Tunisian Tell external foreland thrust belt, exhuming midcrustal lower-greenschist metapelites and marbles with Triassic protholiths, and forming Late Miocene basins. This extension was followed by later Pliocene to Present tectonic inversion, developing the active shortening structures in Northern Tunisia. The main shortening structure is formed by different reverse and strike-slip fault segments, linked forming the 130 km long Alia-Thibar fault zone. Restored Plio-Quaternary deformation observed on reflection seismic lines indicates deformation rates around 0.6-0.8 mm/yr in the studied segments and larger amounts of shortening to the West of Northern Tunisia (16%) than to the East (7%), which suggests that tectonic inversion started earlier to the West and later propagated eastwards, reaching Northeastern Tunisia in the Late Pliocene. Due to the young age of this tectonic inversion, the present relief of Northern Tunisia is characteristic of a young thrust and fold belt, with dominating axial valleys along synforms and an incipient transverse drainage development propagating from West to East.

How to cite: Gaidi, S., Melki, F., Booth-Rea, G., Marzougui, W., Pérez-Peña, J. V., Ruano, P., Galve, J. P., Chouaieb, H., Azañón, J. M., and Zargouni, F.: Neogene to recent geodynamic evolution of Northern Tunisia foreland thrust belt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10619, https://doi.org/10.5194/egusphere-egu22-10619, 2022.

14:22–14:29
|
EGU22-9955
|
ECS
|
Virtual presentation
Giuseppe Vico and Giovanni Luca Cardello

The Apennine Tyrrhenian margin records the evolutionary steps of the back-arc basin developed at the rear of a E-ward migrating fold-and-thrust belt. As well-documented in literature, the counterclockwise rotation of the Apennines is related to the southward increase of the roll back-related subduction of the Adria slab. This led first to the progressive incorporation of thrust sheets within the Apennine prism in the upper plate and later to its subsequent back-arc extension that is contemporaneous with the continuate inarching of the Apennine front towards the Adriatic and Ionian seas. Uncertainties arise on the structural style and timing in the internal Apennines between the orogenic and post-orogenic stages, that are respectively represented by thrust-sheet implacement, and crustal thinning.

We hereby propose a combined 2D seismic and field data review that allows identifying the geodynamic processes preceding the crustal stretching of the Apennine Tyrrhenian margin with new insights from on- and off-shore seismic lines. In particular, the construction of a new geotraverse across the margin, which is stretched over 100 km between the internal Central Apennines belts and the Pontian escarpment, allows to roughly estimate: i) the Late Miocene - Earliest Pliocene shortening with its change of the basal decollement depth through time; in particular, subsurface data highlighted stacked thrust sheets that were involved in an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We also distinguish late backthrusts related to the formation of triangle zones that are more deeply rooted moving to the western chain interior. ii) The amount of crustal stretching and subsidence; Back arc-related orogenic collapse is preceded by initial orogen uplift and erosion in the internal sectors. iii) The onset of at least two magmatic cycles; in this frame, the lateral slab tearing and retreat is tracked by E-rejuvenated volcanic activity in the upper plate along the Volsci Volcanic Field and the Palmarola-Vesuvius lineaments. Those volcano-tectonic trends are favoured by a series of transtensive structures that progressively reflect the arc expansion in the rear. In this frame, the NE-dipping crustal detachment(s) may have played into crustal thinning during the Pliocene, driving and occasionally hampering magma emplacement, while high-angle faults have locally driven monogenetic eruptions. Finally, we report on field and seismic evidence of neo-tectonics, supporting ongoing extension occurring on the margin.

How to cite: Vico, G. and Cardello, G. L.: From thrusting to back-arc extension: seismic structure and field evidence of the Apennine Tyrrhenian margin (Central Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9955, https://doi.org/10.5194/egusphere-egu22-9955, 2022.

14:29–14:36
|
EGU22-8132
A Probabilistic Assessment of the Causes of Active Deformation in the East Central Mediterranean Using Spherical Finite Element Models
(withdrawn)
Rob Govers et al.
14:36–14:43
|
EGU22-5335
|
ECS
|
On-site presentation
Taco Broerse et al.

Tearing of the lithosphere at the lateral end of a subduction zone is a consequence of ongoing subduction. The location of active lithospheric tearing is known as a Subduction-Transform-Edge-Propagator (STEP). The transcurrent plate boundary system lengthens with time and is referred to as the STEP Fault. Lithospheric tearing was taken to start at the trench in the classical STEP model of Govers and Wortel (2005). They show that active STEPs and STEP Faults can be found alongside many subduction zones. However, recent seismicity studies show results near the active STEPs that are difficult to reconcile with the classical STEP model: there is significant and deep seismicity along the STEP Fault near to the west of Trinidad in the southeast Caribbean; a Wadati-Benioff zone perpendicular to the Pliny-Strabo trenches (the STEP Fault) in the eastern Mediterranean reaches 180 km depth; STEP Fault perpendicular earthquake slip vectors are observed along the northern termination of the South Sandwich trench. We seek to understand these discrepancies by studying the tearing process.  

We show results of new physical analog lab models that aim to elucidate what controls lithospheric tearing and the resulting geometry of the lithospheric STEP. We study the ductile tearing in the process of STEP evolution, which is dynamically driven by the buoyancy of the subducting slab. In our experiments, the lithosphere as well as asthenosphere are viscoelastic media in a free subduction setup. A stress-dependent rheology plays a major role in localization of strain in tearing processes of lithosphere such as slab break-off. 

We find that complete tearing of the lithosphere typically occurs later than in the classical model, at 100-150 km depth. The slab is consequently highly curved near the lateral end of the trench. However, not all STEPs show evidence for such delay, e.g., the north end of the Tonga trench. In our model experiments we therefore investigate the influence of age and integrated strength of the lithosphere and its contrasts across the passive margin, on the timing, depth, and the degree of localization of the tearing process. Furthermore, we relate the tearing at depth to deformation at the surface along and across the STEP fault and we discuss potential consequences for STEP evolution for a number of subduction zones worldwide. Delayed lithospheric tearing explains the observations qualitatively. 

How to cite: Broerse, T., Govers, R., and Willingshofer, E.: Delayed lithosphere tearing along STEP Faults , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5335, https://doi.org/10.5194/egusphere-egu22-5335, 2022.

14:43–14:50
|
EGU22-8675
|
Virtual presentation
Nicolò Bertone et al.

The eastern Mediterranean is shaped by the interaction between the African, Arabian, and Eurasian plates resulting in a complex tectonic framework. The Hellenic subduction is well documented and studied but, the northeast corner of the eastern Mediterranean Sea remains enigmatic. It is a tectonically active region where different plate boundary conditions coexist (i.e., oceanic subduction, continental collision, extension, and strike-slip movements). An active and tsunamigenic system has been interpreted west and east of Cyprus by using deep seismic reflection lines. Vintage deep-penetrating seismic reflection profiles of the Mediterranean Sea project (MS project) - acquired during the ’70 - were re-analyzed and merged with a synthesis of available subsurface data from the scientific literature. This study focuses on two transects (MS53 and MS56) that cross the major offshore structures (i.e., Florence Rise, Latakia Ridge, and Kyrenia Ridge) from north to south. The western transect (MS53) shows the Herodotus oceanic crust subducting northward beneath the Eurasian plate. The Florence Rise is the leading edge of the system, and the Antalya Basin is its forearc basin. Close to the Turkish coast, a buried block seems to act as a backstop for the offshore system, and north of it, some out-of-sequence thrusts have been interpreted. The strain is partitioned between the Florence Rise and the Taurides front. The eastern transect (MS56) crosses the Latakia Ridge, i.e., the northern boundary of the Levant Basin, where shortening is greater than in the western area. The seismic line continues northward into the Cyprus – Latakia Basin, crossing the Kyrenia Ridge, and reaching the Turkish coast. On the seismic section, we interpreted the Mesozoic subduction front now hindered by strike-slip movements on the Latakia Ridge. Another prominent transpressive structure is the Kyrenia Ridge, which is interpreted as an active structure with a well-imaged thrust system in front of it. The seismic sections were depth converted to provide a regional geologic model for the northeastern Mediterranean Sea. Active subduction fronts, which are only partially imaged, were structurally modeled and then crosschecked with previous studies to better constrain their geometry. In the northeastern Mediterranean Sea, a plate boundary is buried offshore with active subduction west of Cyprus and mainly transpressional tectonics to the east. A better understanding of its nature and kinematics would be useful to assess the tsunami hazard in this area.

How to cite: Bertone, N., Bonini, L., Colin, E., Del Ben, A., Brancatelli, G., Camerlenghi, A., Forlin, E., and Pini, G. A.: Subduction hints from the northeastern Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8675, https://doi.org/10.5194/egusphere-egu22-8675, 2022.

Wed, 25 May, 15:10–16:40

Chairpersons: Ali Deger Ozbakir, Patricia Martínez-Garzón, David Fernández-Blanco

15:10–15:17
|
EGU22-7780
|
ECS
|
On-site presentation
Violeta veliz borel et al.

Karpathos is a roughly north-south oriented island that emerges between Crete and Rhodes in the forearc of the eastern Hellenic subduction system. It extends for ~60 km to the north of the 40 km contour of the plate interface depth. Further, the northern part of the island is confined to a N-S trending Horst bounded by two large normal faults that shape the seafloor off both, the eastern and western shore.  Furthermore, many normal faults, mainly in the north, strike parallel to the Horst and shape the topography onshore. Given the location and the structural configuration of the island, we expect that multiple processes are reflected in both the sedimentary and morphological record of vertical movement. Marine terraces and paleo-cliffs are observed all around the island recording its vertical movements over the last ~1 Ma. Moreover, sedimentary basins in the southern and central parts of the island are excellent archives of long-term uplift interrupted by subsidence over the last ~4.5 Ma. Twenty-five samples were collected at elevations between 1 and ~310 masl. We have gathered six (n=6) age/elevation data-points obtained by Sr-isotope dating, and nineteen (n=19) age/elevation data-points by radiocarbon dating. We explored the likelihood of different hypotheses on what drives the uplift:  whether it is driven by upper-crust normal faults, megathrust earthquakes, underplating, or a combination of these phenomena. We present preliminary results on both the temporal and spatial fluctuations of the vertical movement of Karpathos.

How to cite: veliz borel, V., Oncken, O., Mouslopoulou, V., Begg, J., and Glodny, J.: The vertical movement of Karpathos: Competing hypotheses  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7780, https://doi.org/10.5194/egusphere-egu22-7780, 2022.

15:17–15:24
|
EGU22-9804
|
ECS
Plate boundary deformation of the eastern Hellenic arc inferred from analysis of lineaments, Island of Rhodes, Greece 
(withdrawn)
Malu Ferreira and Ulrich Riller
15:24–15:34
|
EGU22-13052
|
solicited
Sylvain Barbot and Jonathan Weiss

The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African, and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction, but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geologic structures. We find that tectonic escape is facilitated by a plate-boundary-like, trans-lithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north-south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts, including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa-Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8 mm/yr in a largely trench-normal direction, except near eastern Crete where variably-oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy-Pliny-Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback, and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea, and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation.

How to cite: Barbot, S. and Weiss, J.: Connecting subduction, extension, and shear localization across the Aegean Sea and Anatolia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13052, https://doi.org/10.5194/egusphere-egu22-13052, 2022.

15:34–15:41
|
EGU22-2986
|
ECS
|
|
On-site presentation
Jonas Preine et al.

Many of the most hazardous volcanoes lie in rift systems, where tectonics often seems to exert control on magma emplacement. However, our current knowledge of the interplay between volcanism and tectonics is immature due to the lack of observations on geological time scales. Located in the southern Aegean Sea, the Christiana-Santorini-Kolumbo (CSK) volcanic field lies in a prominent continental rift zone caused by back-arc extension along the Hellenic Arc. Covered by numerous geophysical surveys, this area offers the unique possibility to reconstruct a volcanic rift in time and space. Previous studies have revealed that the CSK volcanic field developed during four distinct volcanic phases, which initiated in the Pliocene and only recently matured to form the vast Santorini edifice. Here, we combine P-wave velocity tomography models and high-resolution reflection seismic data to reveal the internal architecture and the spatio-temporal evolution of the rift basins as well as their relation to the evolution of the CSK volcanoes. Our joint analysis reveals a distinct NE-SW-directed horst-structure separating the volcanic rift into a volcanically active northwestern zone and a volcanically inactive southeastern zone. Using a refined seismo-stratigraphic framework of the internal architecture of the rift basins, we identify four distinct phases of the rift system that correspond to the volcanic phases of the CSK field. These phases reflect the gradual development of a Pliocene-Pleistocene NE-SW oriented fault system overprinting an older Miocene-Pliocene ESE-WNW oriented fault system. The latest volcanic phase, during which volcanism focussed on Santorini and became highly explosive, corresponds to a distinct shift in the tectonic behavior of the rift system after which enhanced subsidence at the Santorini-Anafi and Amorgos faults occurred that was rapidly filled up by thick volcano-sedimentary deposits. We conclude that the volcanism of the CSK field is fundamentally controlled by NE-SW-directed rifting, which lies parallel to the Pliny and Strabo trends of the southeastern Hellenic Arc. This volcanic system is bounded to the southeast by the Akrotiri-Anhydros horst, which seems to be a deep-rooted structural boundary for the volcanic plumbing system. The shift from ESE-WNW directed faulting to NE-SW directed faulting is an indication that the dominant direction of slab-rollback driving the extension of the CSK rift shifted from the southwestern to the southeastern Hellenic Arc with Santorini lying at the hinge of these trends.

How to cite: Preine, J., Hübscher, C., Karstens, J., Hooft, E., and Nomikou, P.: This Rift is on Fire: Volcano-Tectonic Evolution of the Christiana-Santorini-Kolumbo volcanic field, Aegean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2986, https://doi.org/10.5194/egusphere-egu22-2986, 2022.

15:41–15:48
|
EGU22-164
|
On-site presentation
Bernhard Grasemann et al.

Although damaged speleothems have been widely investigated to study paleo-earthquake records in caves, only few reports could directly link damages to specific recent earthquakes. We mapped before the 2017 Mw 6.6 Bodrum–Kos earthquake the so-far unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece), which is located at the transition between the Aegean and Anatolian region and is known for its strong seismicity. The cave formed along an active normal fault and records numerous broken columns and flowstones sealed by younger speleothems. New 230Th/U-ages show that paleoseismic events occurred since the formation of the cave, which is older than the limit of the dating method. During a cave visit 2 months after the 2017 Mw 6.6 Bodrum–Kos earthquake we noted that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, have been chipped off by movements along the fractures and were lying on flowstones covered by greenish biofilms. Removal of the broken fragments demonstrated that the chlorophyll pigment below the position of the fragments did not show a colour difference to the surrounding area, which is exposed to the daylight of the cave entrance. The preservation of the photoautotrophic biofilm, which can survive only a few months without daylight, suggests that the stalactites have been broken by the 2017 Mw 6.6 Bodrum–Kos earthquake, which also caused the collapse of several buildings on the island of Kos only 4 km S of Pserimos. We conclude that earthquake capable of causing small shear displacements on fractures can damage speleothems. However, other delicate speleothems including long and slim stalactites remained undamaged.

How to cite: Grasemann, B., Plan, L., Baron, I., and Scholz, D.: Speleothem deformation due to the 2017 Mw 6.6 Bodrum–Kos earthquake in a cave on Pserimos (Dodecanese, Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-164, https://doi.org/10.5194/egusphere-egu22-164, 2022.

15:48–15:55
|
EGU22-11846
|
Virtual presentation
Ian Bastow et al.

The eastern Mediterranean hosts, within the span of a few hundred kilometres, extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Widespread Miocene-Recent volcanism and ~2km uplift has been attributed to mantle processes such as delamination, dripping and/or slab tearing/break-off. We investigate this complex region using a variety of broadband seismological techniques, with new P- and S-wave tomographic images in Kounoudis et al. (2020), seismic anisotropy constrained via an updated dataset of SKS shear-wave splitting observations in Merry et al. (2021), and crustal structure imaged by quality-controlled H-κ stacking of receiver functions in Ogden & Bastow (2021). Overall, seismic anisotropy and crustal structure are more spatially variable than previously recognised, and such variations correspond well with variations in mantle structure shown by the tomography. In general, Moho depth is poorly correlated with elevation, suggesting crustal thickness variations do not fully explain topographic differences, and residual topography calculations indicate the requirement for a mantle contribution to Anatolian Plateau uplift. Evidence for such a contribution exists in central Anatolia, where an imaged horizontal tear in the Cyprus slab spatially corresponds with volcanism, a residual topographic high, and a region of reduced splitting delay times and nulls, all consistent with upwelling of asthenospheric material through the tear. Anisotropic fast directions are consistent with flow through the imaged gap between the Cyprus and Aegean slabs, again correlating roughly with both volcanism and high residual topography. Slow uppermost‐mantle wave speeds below active volcanoes in eastern Anatolia, and ratios of P-to-S wave relative traveltimes, indicate a thin lithosphere and melt contributions. Elsewhere, there is more evidence for slab processes controlling mantle flow, with anisotropic fast directions diverted at the edges of imaged slabs and consistent with flow towards the retreating Hellenic trench in the Aegean. The North Anatolian Fault is revealed to be a deep, plate-scale structure: whilst there are no clear changes in Moho depth across the fault, deep velocity contrasts suggest a 40­-60km decrease in lithospheric thickness from the Precambrian lithosphere north of the fault to a thinned Anatolian lithosphere in the south. Moreover, short-length-scale variations in anisotropy and backazimuthal variations in splitting parameters at the fault indicate fault-related lithospheric deformation, with seismic fast directions either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low-strained transcurrent mantle shear zone. Upper mantle structure thus exerts a strong influence on uplift, volcanism and deformation in Anatolia.

References

Kounoudis, R., I.D. Bastow, C.S. Ogden, S. Goes, J. Jenkins, et al.,  (2020), Seismic Tomographic Imaging of the Eastern Mediterranean Mantle..., G3, 21(7), doi:10.1029/2020GC009009.

Merry, T.A.J., I.D. Bastow, R. Kounoudis, C.S. Ogden, R.E. Bell, & L. Jones (2021), The influence of the North Anatolian Fault and a fragmenting slab architecture on upper mantle seismic anisotropy... ,G3, 22, doi:10.1029/2021GC009896.

Ogden, C.S., & I.D. Bastow (2021), The Crustal Structure of the Anatolian Plate from Receiver Functions..., GJI, doi:10.1093/gji/ggab513.

How to cite: Bastow, I., Merry, T., Kounoudis, R., Ogden, C., Bell, R., Goes, S., Jenkins, J., Jones, L., Grant, B., and Braham, C.: Mantle origins of topography, volcanism and the North Anatolian Fault in Anatolia: constraints from seismic tomography, seismic anisotropy and crustal structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11846, https://doi.org/10.5194/egusphere-egu22-11846, 2022.

15:55–16:02
|
EGU22-10193
|
ECS
|
Virtual presentation
Efe Turan Ayruk et al.

The North Anatolian Fault (NAF) is a one of the major dextral strike-slip faults of Turkey which forming the boundary between the Eurasian - Anatolian plates. From 1939 to 1999, significant earthquakes occurred as showing a westward migration. Several studies are being conducted due to this seismic activity along the NAF. However, none of these are sufficiently dense to understand the behaviour of the fault. Here we present our block modelling results obtained from combine that published GNSS velocity datasets to determine strain accumulation along the NAF with TDEFNODE software (McCaffrey,1995). Our study area separates to 3 blocks, starts from east of the Sapanca Lake and includes the Karliova Triple Junction on the east, extends over the Black Sea on the north and 130 kilometers from the fault on the south. Checkerboard method is used to test the resolution of the dataset, then node distribution on the NAF is optimized and Wang’s model is used for inversion solution (Wang,2003). Euler Pole and block strain are estimated with inversion solution for Eurasia/Anatolia plates and the slip deficit variations are estimated for NAF. Under the constrain of the dense GNSS networks, we displayed that some segments of NAF are creeping up to shallow part of the crust and some other segments are locked at deeper region. Herein to better understand latest circumstance of complex slip deficit pattern of the NAF, estimated by our model, we evaluated our results under the complementary present and paleo-seismological datasets.

Keywords: NAF, block modelling, GNSS

How to cite: Ayruk, E. T., Özarpacı, S., Özdemir, A., Özbey, V., Ergintav, S., and Doğan, U.: Determining Strain Accumulation Along NAF with Block Modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10193, https://doi.org/10.5194/egusphere-egu22-10193, 2022.

16:02–16:09
|
EGU22-459
|
ECS
|
|
Virtual presentation
Havva Neslihan Kiray et al.

Continental transform faults are generally known to have widely distributed structures and sparse seismicity, in opposite to their oceanic counterparts. The North Anatolian Shear Zone (NASZ) is an ideal example, where the total deformation is shared between multiple structures especially during its evolutionary stages. The North Anatolian Fault (NAF), the most prominent member of the NASZ, started to form of about 11 Ma in the east and propagated to the west, reaching to the Marmara Sea only a few hundred thousand years ago. This principal displacement zone generally extends as a single strand from its easternmost tip to the west until Bolu for about 900 km. To the west of Bolu, it bifurcates into two branches, Düzce and Mudurnu Valley segments, delimiting the Almacık Flake (AF) respectively to the north and south. Although there is a considerable number of multi-disciplinary studies on the kinematics and history of active faulting within and around the AF, we still have gaps in our knowledge on (a) the ratio of strain distribution, (b) time of formation of bounding fault segments and (c) their evolutionary stages.

In order to fulfil some parts of this gap, we studied the major morphometric indices, including hypsometric curve and integral (HI), asymmetry factor (Af), channel concavity (θ), chi (χ) and knickpoint analyses on drainage basins across the whole AF and all surrounding fault segments. Our goal is not only to document the comparative tectonic effect of the bounding fault segments on the topography, but also to test any potential cumulative morphological response to pre- and post-peak structures, especially along the Düzce Segment. Almost all of 83 extracted drainage basins yield high HI values, usually ranging between 0.4 and 0.72, and suggest a rejuvenating morphology compatible with the general ‘uplift hypothesis’ for the AF. In more details, θ and χ values point out the strong and confined effect of the active bounding faults. Moreover, knickpoints do not show evidence for any pre-peak structures rather than recent active faulting. This may be result of limited size, thus ages, of drainage basins, which are cut by bounding faults at both sides of the AF. Alternatively, these fault segments may be older than previous assumptions, whereas the effect of pre- and post-peak shear structures on topography has already been erased mainly by external processes. On the other hand, χ values, based on 0.45 reference θ, suggest a high incision along the western sections of the Mudurnu Valley Segment, which may indicate a strain transfer from north to south. Nevertheless, the breach of a landslide dam of about 5750 years ago and the strong incision of the Mudurnu River following this event to the south of the AF, as suggested by previous studies, can be another reason for this anomaly. Briefly, our preliminary results suggest a strong tectonic control on the AF’s topography mainly due to the activity of the bounding structures. We do not see any morphometric evidence for the secondary (pre- and post-peak) faults in the near past of the NASZ around the AF.

How to cite: Kiray, H. N., Sançar, T., and Zabcı, C.: Spatial strain distribution along continental transform faults: insights from morphometric analyses of the Düzce and Mudurnu Valley segments (North Anatolian Fault, NW Turkey), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-459, https://doi.org/10.5194/egusphere-egu22-459, 2022.

16:09–16:16
|
EGU22-5475
|
On-site presentation
Naiara Fernandez et al.

The North Anatolian Fault Zone (NAFZ) extends for about 1500 km in the Eastern Mediterranean region, from eastern Anatolia to the northern Aegean. The NAFZ is characterized by strong and frequent seismic activity, increasing the seismic hazard in the region. In the Sea of Marmara area (NW Turkey), the North Anatolian Fault splits into three main branches. The northern branch of the fault, the Main Marmara Fault (MMF), has produced several major earthquakes (M7+) in the past, with a recurrence time of about 250 years. At present, there is a 150 km seismic gap along the MMF which has not ruptured since 1766. The observed fault segmentation, with creeping and locked segments, is indicative of along-strike variability in the fault strength along the seismic gap.

Previous modeling studies in the Sea of Marmara have revealed how crustal heterogeneities effectively affect the thermal and mechanical states of the lithosphere and can likely explain the observed fault segmentation in the area. Therefore, constraining the 3D structure of the deeper crust and upper mantle below the Sea of Marmara is crucial to better assess the mechanical stability of the fault and the possible seismic hazards in the area. In this study, we make use of seismic tomography models and forward gravity modelling to gain insights into the 3D lithospheric structure below the Sea of Marmara. Two tomographic models are used to compute a 3D density model of the area relying on two distinct approaches for the crust and the lithospheric mantle. The results showcase a heterogeneous and rather complex crustal density distribution in the study area[m1] . The 3D density distributions are used in a second step to forward model the gravity response. The results from this new tomography-constrained 3D gravity modelling are then compared to published gravity data and iteratively corrected to fit the overall gravity signals. The final 3D lithospheric-scale density model of the study area will be the basis for thermo-mechanical modeling experiments aimed at improving our current understanding of the present-day geomechanical state of the Sea of Marmara and the MMF and its implications for the seismic hazard of the region.

How to cite: Fernandez, N., Scheck-Wenderoth, M., Bott, J., Cacace, M., and Gholamrezaie, E.: Insights into the 3D lithospheric structure below the Sea of Marmara region from seismic tomography and forward gravity modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5475, https://doi.org/10.5194/egusphere-egu22-5475, 2022.

16:16–16:23
|
EGU22-8142
|
On-site presentation
Dirk Becker et al.

The occurrence of earthquake-repeaters, i.e. co-located seismic events of comparable magnitude with highly similar waveforms breaking the same fault patch with an almost identical mechanism, is generally regarded as an indication that the fault surrounding the earthquake asperity is (aseismically) creeping. Earthquake repeaters can either occur during transient loading, e.g. within the afterslip of large earthquakes, or during the constant tectonic loading of tectonic faults. In this study we consider the latter.

The Main Marmara Fault (MMF) belongs to the western part of the North Anatolian Fault Zone (NAFZ) between the Anatolian and Eurasian plates and runs close to the population centre of Istanbul below the Marmara Sea. While the main NAFZ branches to the east and west of the MMF ruptured in M>7 earthquakes in the last century, the MMF itself is regarded as a seismic gap with the potential to host an M>7 event in the near future. Knowledge about the amount of aseismic creep of the off-shore MMF strand is important for a better seismic hazard assessment for the city of Istanbul and is heavily debated.

Building on earlier studies that identified repeating earthquakes in the western part of the MMF, we investigate a newly compiled seismicity catalogue of the Sea of Marmara for repeating events along the complete MMF. The catalogue spans the time period 2006-2020, comprises almost 14,000 events in the magnitude range M0.3-M5.7 and was compiled from regional permanent stations operated by AFAD and KOERI. Phase onset times were automatically picked with a two-step procedure using higher-order statistics and an AIC-representation of the waveforms for crude and fine-tuned estimation of the P- and S-onsets. The resulting onset-times were used in the Oct-tree location algorithm of the probabilistic NLLoc software using a regional velocity model and station corrections to obtain the final hypocentres.

To search for earthquake repeaters, we divide the MMF into overlapping segments and perform a station-wise cross-correlation analysis for all available event waveforms in each segment. Correlated waveforms start 1 s before the P-wave arrival and include the complete waveform including the S-wave coda. Waveforms were bandpass filtered between 2 and 20Hz to retain a rather wide frequency spectrum. We apply strict selection criteria and identify repeating events only as those with a normalized cross-correlation coefficient larger than 0.9 at at least 3 stations and a temporal separation of more than 30 days to exclude bursts of highly similar events in aftershock sequences or earthquake swarms.

The highest density of repeating earthquakes is found below the western Marmara Sea (Central Basin and Western High) with a systematic decrease of repeaters towards the east (Kumburgaz Basin) and none at all in the presumably locked Princess Islands section of the MMF immediately south of Istanbul. These results for the first time provide a consistent image of the amount of creep along the entire overdue Marmara section of the NAFZ derived from permanent onshore stations refining earlier results obtained from individual spots using local seafloor deployments.

How to cite: Becker, D., Martínez-Garzón, P., Wollin, C., and Bohnhoff, M.: Systematic variations of fault creep along the Marmara seismic gap, north-western Turkey, based on the observation of earthquake repeaters obtained from a high-resolution regional earthquake catalogue, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8142, https://doi.org/10.5194/egusphere-egu22-8142, 2022.

16:23–16:30
|
EGU22-9541
|
ECS
|
On-site presentation
Jorge Jara et al.

Recent observations suggest that seismogenic faults release elastic energy not only during sudden earthquakes but also aseismically. Slow slip can be persistent, lasting for years, or episodic. Aseismic slip is thought to be influenced by the presence/migration of fluids, stress interactions through fault geometrical complexities, or fault material heterogeneities. However, slow slip events have mostly been captured by regional GNSS networks in subduction zones, and the finest details of the nucleation, propagation, and arrest of such events have not been observed yet. Therefore, continental creeping faults are ideal targets for tackling such observational gaps and focusing on the sub-daily behavior of such slow slip events.

 

The central segment of the North Anatolian Fault is known to be creeping at least since the 1950s. This region was struck by the Mw 7.3 Bolu/Gerede earthquake in 1944, and since then, no earthquake of magnitude greater than 6 has been recorded. During the 1960s, aseismic slip was discovered as a wall built across the fault in 1957 was being slowly offset. Geodetic studies (InSAR, GNSS, and creepmeters) focused on capturing and analyzing aseismic slip around the village of Ismetpasa. Creepmeter measurements during the 1980s and 2010s, along with InSAR time series analysis, suggest that aseismic slip occurs episodically rather than persistently. However, no permanent GNSS stations were available close enough to the fault to study the details of such slow slip events.

 

Within the scope of a French-Turkish collaboration, we installed 17 GNSS stations (ISMENET) in 2019 to survey the spatio-temporal evolution of aseismic slip rate and characterize the physical properties of the fault zone. A creepmeter array located in the Ismetpasa village reported the occurrence of a significant slow slip event between December 2019 - January 2020. We analyze the GNSS record to search for small aseismic slip episodes and describe their behavior. We use a combination of Multivariate Singular Spectrum Analysis (MSSA) and Geodetic Template Matching (GTM) to extract the signature of aseismic slip and characterize its source. Results are compared to creepmeter measurements, as well as the historical earthquakes, fault geometrical complexities, and kinematic coupling. Our results confirm that aseismic slip in the region is not permanent. Therefore, even though the aseismic slip rate in the long-term seems to be constant, such a rate might result from the contribution of many aseismic slip episodes as the one detected in this work.

How to cite: Jara, J., Ozdemir, A., Dogan, U., Jolivet, R., Çakir, Z., and Ergintav, S.: Slow slip events captured by GNSS  along the Central Section of the North Anatolian Fault, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9541, https://doi.org/10.5194/egusphere-egu22-9541, 2022.

16:30–16:37
|
EGU22-3939
|
Virtual presentation
Simone Racano et al.

The Central Pontide orogenic belt marks the northern margin of the Central Anatolian Plateau and is the result of several geodynamic processes, including the subduction of the Neo-Tethys crust, the opening of the Black Sea, the continental collision between the southern Eurasian margin and the Anatolide-Tauride block, and the development of the North Anatolian Fault (NAF). Transpressional deformation and crustal thickening along the North Anatolian fault zone are thought to have generated rock-uplift rates of 0.2 – 0.3 km/Myr since ca. 400 ka within the Central Pontides based on Quaternary marine and river terraces. Moreover, data from low-temperature thermochronology suggest that an enhanced exhumation phase in the Central Pontides occurred within the last 11 Mya. However, the precise onset of this faster uplift phase, which likely reflects the timing of the development of the NAF in the Central Pontides, is poorly constrained.

In this work we define the spatiotemporal pattern of rock-uplift rates within the Central Pontides over the last ca. 10 Myr by performing linear inversions of river profiles that drain the northern, external margin of the Central Pontides. We analyze 19 different catchments that drain from the Sinop Range to the Black Sea, first applying a non-dimensional inversion on the chi-plots of the selected stream channels. We then use 21 new basin-averaged denudation rates derived from 10Be concentrations in river sands to calibrate an erodibility parameter, which we use in turn to scale our chi-transformed river profiles. Our results document an increase in rock-uplift rates after 8 Ma, with peak uplift rates of around 0.15 – 0.25 km/Myr occurring between 4 and 2 Ma. Moreover, the spatiotemporal pattern of uplift suggests that faster rock uplift started first in the eastern part of the Sinop Range and migrated westward over a period of ca. 2 to 2.5 Myr. Overall, these results provide important new constraints on the timing of topographic development in the Central Pontides and the westward migration of the NAF from eastern Turkey.

How to cite: Racano, S., Schildgen, T., and Ballato, P.: Timing of rock-uplift and of the North Anatolian Fault development in the Central Pontides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3939, https://doi.org/10.5194/egusphere-egu22-3939, 2022.

Wed, 25 May, 17:00–18:30

Chairpersons: Ali Deger Ozbakir, Patricia Martínez-Garzón, Giovanni Luca Cardello

17:00–17:07
|
EGU22-10145
|
ECS
|
Virtual presentation
İlay Farımaz et al.

January 24, 2020 Sivrice earthquake (Mw 6.8), which is the largest along the East Anatolian Fault (EAF) over the last century, is providing a wealth of information on the mechanics of transform faulting and for monitoring the different phases of the last seismic cycle. In this study, we aim to estimate coseismic and postseismic surface deformation along the Sivrice earthquake rupture and determine the strain accumulations on Pütürge segment by combining InSAR and GNSS measurements. The area was described one of the major seismic gaps along the EAF and we have started to study from Palu to Sivrice segments of the EAF, since 2015. Near field survey GNSS network has been established since 2015 and measured two times in a year, until 2021. Besides, after the earthquake, we surveyed 60% of near field sites to contain the coseismic field within 2-3 days. This dataset analyzed with continuous GNSS stations around the region to control the far field of the deformation field. Additionally, this dataset is densified by InSAR deformation field. For this purpose, the stack of interferograms have been interpreted from descending orbit Sentinel-1 dataset, composed of 6 days interval SAR acquisitions that starts from January 2020 to June 2020 which covers the earthquake time. As a result, significant differences between the pattern of strain accumulation before and after earthquake are documented with both GNSS and InSAR data. Moreover, the signature of the postseismic deformations is presented for 6 months.  

This study was supported by TUBITAK 1001 project no. 114Y250 and 118Y435.

Keywords: Sivrice earthquake, EAF, coseismic, postseismic, InSAR, GNSS

How to cite: Farımaz, İ., Özarpacı, S., Özdemir, A., Erkoç, M. H., Ayruk, E. T., Ergintav, S., Doğan, U., and Çakır, Z.: Coseismic and Postseismic Deformation of the January 24, 2020 Sivrice (Elazig) Earthquake Under the Constrain of Geodetic Observations , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10145, https://doi.org/10.5194/egusphere-egu22-10145, 2022.

17:07–17:14
|
EGU22-5691
|
ECS
|
On-site presentation
Lasha Sukhishvili et al.

Since the Plio-Pleistocene, southward migration of shortening in the Eastern part of the Greater Caucasus (GC) into the Kura foreland basin has formed the Kura fold–thrust belt (KFTB) and Alazani piggyback basin between the GC and KFTB, modifying the drainage network within the southern foreland. The northern, eastern and south-eastern flanks of the Western KFTB (Gombori range) expose the predominantly alluvial Alazani series, while the central (highest) part of the range is covered by Tsivi suite. The base of the Alazani series is estimated to be 2.7-2.5 Ma and deposition spanned the Akchagyl and Apsheronian regional stages. The KFTB likely initiated during the Akchagyl-Apsheronian period, and thus the paleocurrents of the alluvial Alazani series sediments represent potential archives for tracking resulting drainage reorganization within the foreland. Previous measurements of paleocurrents from the Alazani series revealed a reversal from south to north flow directions, but the measurements were limited to the northern flank of the Gombori range. Here we present new observations from the central and southern flanks of the Gombori. Results from the eastern and southeastern regions are consistent with the currents from the northern flank, but paleocurrents from the Tsivi suite are more complex and raises additional questions regarding its depositional context and age. The new results help to build a more complete picture of fluvial dynamics driven by Quaternary tectonic deformations within the GC foreland.

How to cite: Sukhishvili, L., Boichenko, G., Merebashvili, G., Javakhishvili, Z., Forte, A., and Godoladze, T.: Reconstruction of tectonically driven Quaternary fluvial dynamics of the Western Kura Fold-Thrust Belt (Eastern Caucasus, Georgia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5691, https://doi.org/10.5194/egusphere-egu22-5691, 2022.

17:14–17:21
|
EGU22-10062
|
ECS
|
On-site presentation
Neill Marshall et al.

The 1948 M 7.3 Ashgabat earthquake, killing over 38,000 people, occurred in the dextral strike-slip Kopeh Dagh fault zone in the Iran-Turkmenistan border region. Previously, it has been debated which fault(s) it occurred on and whether this earthquake was a thrust/reverse, strike-slip, or multi-fault earthquake, as published focal mechanisms suggest it had a reverse mechanism. We relocated the hypocentre using historical seismograms and present a new strike-slip focal mechanism. We used Pleiades satellite stereo imagery to produce Digital Elevation Models of part of the ruptured area. These data reveal clear strike-slip faults where surface ruptures were mapped in 1948. The earthquake did not rupture the Main Kopeh Dagh fault, but instead these subsidiary faults, highlighting the importance of considering lesser faults in seismic hazard models.

How to cite: Marshall, N., Walker, R., Ou, Q., and Gruetzner, C.: A re-evaluation of the 5th October 1948 M7.3 Ashgabat earthquake (Turkmenistan) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10062, https://doi.org/10.5194/egusphere-egu22-10062, 2022.

17:21–17:28
|
EGU22-1972
|
|
Virtual presentation
Ali Nasiri and Mahtab Aflaki

The NW-striking North Tabriz Fault is one of the most important basement faults in the northwest of the Iranian ‎plateau. This fault defines the boundary between the two tectonic ‎blocks with different stress regimes in its northern and southern parts as characterized with NW-SE and NE-SW direction of maximum horizontal compression, respectively. In the southern ‎termination of the North Tabriz fault, part of deformation is concentrated along its EW-striking splay faults extending along northern and southern boundaries of the Bozqush Mountains. The occurrence of medium-magnitude earthquakes, as ‎well as morphotectonic evidence reveal that modern deformation is dominantly concentrated along ~EW-striking dextral/reverse dextral and NNE-striking sinistral faults in the southern flank of the Bozqush Mountains. It is still not known to what extent the deformation is also accomodated in the northern flank of the Bozqush Mountain. The approach of this research is to ‎answer the question by studying the state of stress along the northern border of the Bozqush Mountains by applying the inversion method on the fault slip data measured during the field studies, studying their related ‎morphotectonic evidence, and comparing the results with ‎the state of stress and the morphotectonic evidence reported throughout the southern flank of the Bozqush Mountains. Fault kinematic data were collected at 35 sites ‎along the northern boundary of the Bozqush Mountains. Evidence of the modern NW-SE stress regime is found at five sites measured within the Quaternary detrital deposits in the western part of the study area. At the other ‎sites, evidence of the older stress regime, with NE-SW direction of maximum horizontal ‎compression is obtained. Also, the systematic deflection of the stream channels, especially in the eastern part of the region, ‎indicates the sinistral displacement along the EW-striking faults, consistent with the old ‎stress regime in the region. Evidence of dextral deflection was observed along few EW-striking faults cutting the Quaternary deposits only in the western parts of the region. Therefore, ‎by comparing these kinematic data and morphotectonic evidences with those reported from the southern flank of the Bozqush Mountains, it can be concluded that the modern deformation is dominantly absorbed along the splay faults in the southern flank of the Bozqush.‎

 

​Key Words: North Tabriz fault, Modern stress state, NW Iran, Northern flank of Bozqush Mountains, Stress inversion

How to cite: Nasiri, A. and Aflaki, M.: ​Studying the active tectonic in the northern flank of the Bozqush Mountains, NW Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1972, https://doi.org/10.5194/egusphere-egu22-1972, 2022.

17:28–17:35
|
EGU22-6407
|
ECS
|
|
Virtual presentation
Aram Fathian et al.

The Zagros Mountains accommodate intense seismicity due to the ongoing deformation; however, surface faulting has been rarely observed and/or documented. The earthquakes of Furg (November 6th, 1990) and Qir-Karzin (April 10th, 1972) are unique events in the Zagros associated with a surface rupture. We use tectonic geomorphology and paleoseismology to document a previously unknown outcropped fault within the Zagros. This ~ 20 km fault zone lies between the Khormuj and Khaki anticlines, where the Simply Folded Belt (SFB) of the Zagros is physiographically known as the coastal Zagros as well. The Khormuj anticline, located in the northeast of the city of Khormuj, was previously linked to the Main Front Fault (MFF) on the southern limb of the anticline. Further to the south, the oblique-slip Khormuj fault zone with a strike of N120°–N125° cut the Quaternary sediments and displaced the streams and ridges laterally and vertically. Opposite to the dip of the MFF, the Khormuj fault dip is inclined to the southwest—approximately 75°—where the southern block is uplifted and marks an obvious trace on the ground. We carried out a kinematic GPS survey along the deflected ridges to measure the horizontal and vertical components. Our observations indicate significant dextral strike-slip displacements compared to the dip-slip offset. We observed a sequence of fluvial risers in three different levels along the Khormuj fault. We additionally studied a paleoseismological trench perpendicular to the Khormuj fault scarp evidencing at least two paleoearthquakes. The OSL age of the bottom of the colluvium wedge correlated with the older event indicates the latest event is younger than 25±8 ka considering the fault cuts these deposits up to the ground surface.

How to cite: Fathian, A., Nazari, H., Shokri, M. A., Talebian, M., Ghorashi, M., and Reicherter, K.: Morphological and paleoseismic evidence of surface faulting in the coastal Zagros, southwestern Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6407, https://doi.org/10.5194/egusphere-egu22-6407, 2022.

17:35–17:42
|
EGU22-3591
|
On-site presentation
Yariv Hamiel and Oksana Piatibratova

Crustal deformation and seismic activity in the Levant is mainly related to the interplate Dead Sea Fault (DSF) and the intraplate Carmel-Gilboa Fault System (CGFS). In this study we analyze the interseismic deformation along these fault systems using 23 years of GPS measurements obtained from 209 campaign and 60 continuous stations. This GPS dataset is the longest record and the densest dataset for the DSF and the Levant region. We use this dataset to investigate the spatial variations of slip and creep rates along the southern and central sections of the DSF and the CGFS. Our inversion model results indicate that part of the tectonic motion is transferred from the DSF to the CGFS. We find that the left-lateral strike-slip motion along the DSF decreases in a rate of 0.9±0.4 mm/yr, from 4.8±0.3 mm/yr south to the intersection with the CGFS, to 3.9±0.4 mm/yr north to this intersection. Along the CGFS the left-lateral strike-slip motion ranges between ~0.3-0.5 mm/yr and the extension rate between ~0.6-0.7 mm/yr, indicating a total slip rate vector of 0.8±0.4 mm/yr in the DSF direction, in agreement with the reduction of slip rate along the DSF near the intersection with the CGFS. Shallow creep is found along the southern and central sections of the Dead Sea basin and the northern Jordan Valley section of the DSF, with creep rates of 3.4±0.4 and 2.3±0.4 mm/yr, respectively. These creeping sections were identified as areas with thick salt layers at the shallow subsurface. We suggest that shallow creep behavior along the DSF is govern by the presence and mechanical properties of the salt layers, which probably allows plastic deformation and the transition to velocity strengthening at the shallow subsurface and promotes creep.

How to cite: Hamiel, Y. and Piatibratova, O.: Spatial variations of slip and creep rates along the Dead Sea Fault and the Carmel-Gilboa Fault System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3591, https://doi.org/10.5194/egusphere-egu22-3591, 2022.

17:42–17:49
|
EGU22-9537
|
On-site presentation
Roi Granot et al.

The tectonic nature of the Sinai Microplate's western boundary is clouded with uncertainties. Early studies suggested that the western edge of Sinai is fully connected to the African Plate, thus concluding that Sinai is a sub-plate. Later, bathymetric analyses of prominent lineated faults straddling across the western edge of the Levant Basin have suggested that, in fact, this area is a plate boundary that accommodates dextral motion between the African Plate and the Sinai Microplate. However, this inference contradicts geological and geophysical observations across the Gulf of Suez, the southern continuation of the same plate boundary. Here we present preliminary results from a recent geophysical cruise aboard the R/V Bat Galim. We focused our investigation on one of the major faults, oriented in an NW-SE direction (located ~80 km southwest of the Eratosthenes Seamount), creating the plate boundary. We collected high-resolution shallow multichannel seismic reflection data complemented with multibeam bathymetry data. We also acquired two piston cores near the trace of the fault. These observations unravel the shallow three-dimensional structure of the fault system whereby several curved and steeply dipping normal fault segments are splayed from the main fault trace in a westerly direction. These secondary faults display a back-tilted and step-like morphology. This structure is best explained by a sinistral motion acting along the master fault. Independently, we present an updated Africa-Sinai Euler pole based on the motion of GPS stations recorded between 1996 and 2019. The results suggest that Sinai is moving in a northwesterly direction with respect to Africa (1.7-1.9±0.9 mm/yr). Focal mechanism solutions calculated for recent earthquakes occurring in this region (Mw>4.5) agree with the geodetic constraints of a sinistral relative motion.

Overall, these observations suggest that the western boundary of Sinai has been, and still is, accommodated sinistral motion relative to Africa. This conclusion implies that the Sinai Microplate is moving faster with respect to Eurasia relative to the motion of Africa with respect to Eurasia. This, in turn, seems to be in conflict with the notion that subduction of the oceanic lithosphere north of the Sinai Microplate (i.e., east of Cyprus) has recently ceased. We speculate that the downgoing slab might still promote the relatively fast northward motion of Sinai and/or a northward drag force induced by large-scale mantle flow related to the Afar plume could also contribute to the motion of the Sinai Microplate.

How to cite: Granot, R., Katz, O., Kanari, M., Hyams, O., and Hamiel, Y.: New constraints on the kinematics of the western Sinai Microplate: geodynamic implications , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9537, https://doi.org/10.5194/egusphere-egu22-9537, 2022.

17:49–17:59
|
EGU22-1692
|
solicited
|
Virtual presentation
Vasiliki Mouslopoulou et al.

Slow slip events (SSEs) in subduction zones can precede large-magnitude earthquakes and may therefore serve as precursor indicators, but the triggering of earthquakes by slow slip remains poorly understood. Here we report on a multidisciplinary dataset that captures a synergy of slow slip events, earthquake swarms and fault-interactions during the ~5 years leading up to the 2018 Mw 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). We find that this long-lasting preparatory phase was initiated by a slow-slip event that released, over a period of 4-months, aseismic slip equivalent to a ~Mw 6.4 earthquake on the Hellenic plate-interface. This SSE, which is the first to be reported in the HSS, was associated with mild Coulomb failure stress changes (≤3 kPa) that were nevertheless sufficient to destabilize faults in the overriding plate. Tectonic instability was evidenced by a prolonged (~4 years) period of suppressed b-values (<1), an associated increase in upper-plate seismicity rates on discrete thrust, normal and strike-slip faults, including an earthquake swarm in the epicentral area of the Mw 6.9 earthquake, and another episode of slow-slip immediately preceding the Zakynthos mainshock. We show that this second SSE in 2018 caused stress changes up to 25 kPa in the epicentral area immediately prior to the mainshock, affecting a highly overpressured and mechanically weak forearc, whose state of stress fluctuated between horizontal deviatoric compression and tension during the years preceding the Zakynthos Earthquake. We conclude that this configuration facilitated episodes of aseismic and seismic deformation that ultimately triggered the Zakynthos Earthquake and may characterise other subduction zones globally.

How to cite: Mouslopoulou, V., Saltogianni, V., Bocchini, G. M., Cesca, S., Bedford, J., Dielforder, A., Oncken, O., Gianniou, M., and Petersen, G.: Slow-slip events destabilize upper-plate and trigger large-magnitude earthquake at the western-end of the Hellenic Subduction System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1692, https://doi.org/10.5194/egusphere-egu22-1692, 2022.

17:59–18:06
|
EGU22-1477
|
ECS
|
Virtual presentation
David Fernández-Blanco and César R. Ranero


We propose that lithospheric collision of Africa and Eurasia is incipient throughout the entire East Mediterranean. Our evidence confirms the incipient continent-continent collision that has been recently proposed for the Cyprus Arc and showcases how collision is expressed at depth and across the Hellenic Arc. We provide evidence of basin-wide lithospheric-scale collision by coupling, at tectonic scale (1.5M km2), quantitative joint analysis of submarine and terrestrial relief, and the interpretation of a compilation of regional vintage multichannel seismic data (>46.000 km), reprocessed with modern techniques. No megathrust surface marking a subduction interplate contact is imaged in any seismic line, and the relief across sedimentary piles is not shaped as mechanically-accreted wedges. Instead, continent-continent collision is expressed across plates in two modes along longitude. In the offshore regions south of Cyprus and Crete, submarine thrust systems with no frontal structure nor imbrication, and lacking latitudinal continuation, record collision stacking basin sediments vertically. Onshore, concurrent uplift and extension are recorded by uplifting strandlines, hanging valleys, and normal faulting, in both continents, and neatly so in the African margin in front of Crete. Joint plate deformation at lithospheric scale is further inferred as wavelengths of relief coherent across both plates. Regions located latitudinally to these collisional sites extrude away obliquely, either rigidly along transpressional systems, as immediately east of Cyprus and Crete, or through flow and halokinesis of Messinian salts, as on the eastern and western sectors of the Mediterranean Ridge. Our evidence typifies incipient lithospheric collision as expressed throughout the East Mediterranean.

How to cite: Fernández-Blanco, D. and R. Ranero, C.: Incipient lithospheric collision throughout the East Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1477, https://doi.org/10.5194/egusphere-egu22-1477, 2022.

18:06–18:30
Discussion