Browsing by Author "Toker, Mustafa"

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The 3-D Strain Patterns in Turkey Using Geodetic Velocity Fields From the Rtk-Cors (Tr) Network
(Pergamon-elsevier Science Ltd, 2016) Kutoglu, Hakan Senol; Toker, Mustafa; Mekik, Cetin
This study presents our use of GPS data to obtain and quantify the full continuous strain tensor using a 3D velocity field in Turkey. In this study, GPS velocities improve the estimation of short-term strain tensor fields for determining the seismic hazard of Turkey. The tensorial analysis presents different aspects of deformation, such as the normal and shear strains, including their directions, the compressional and extensional strains. This analysis is appropriate for the characterizing the state of the current seismic deformation. GPS velocity data from continuous measurements (2009-2012) to estimate deformations were processed using the GAMIT/GLOBK software. Using high-rate GPS data from permanent 146 GNSS stations (RTK-CORS-TR network), the strain distribution was determined and interpolated using a biharmonic spline technique. We show the strain field patterns within axial and plane form at several critical locations, and discuss these results within the context of the seismic and tectonic deformation of Turkey. We conclude that the knowledge of the crustal strain patterns provides important information on the location of the main faults and strain accumulation for the hazard assessment. The results show an agreement between the seismic and tectonic strains confirming that there are active crustal deformations in Turkey. (C) 2015 Elsevier Ltd. All rights reserved.
The 3-D Strain Patterns in Turkey Using Geodetic Velocity Fields From the Rtk-Cors (Tr) Network (Vol 115, Pg 246, 2016)
(Pergamon-elsevier Science Ltd, 2016) Kutoglu, Hakan Senol; Toker, Mustafa; Mekik, Cetin
The Array Analyzing of the High Quality Glacial Seismic Events Active in Greenland Using Long-Period Surface (Rayleigh) Wave Detection by the German Regional Seismic Network
(2018) Toker, Mustafa
This study reports on four high quality glacial events in Greenland, M 4.9, 2007-07-04; M 4.8, 2007-07-09; M 4.7, 2007-07-09; M 4.7, 2007-07-20 detected using thelong-period surface waves (Rayleigh wave) recorded at the stations of the German RegionalSeismic Network (GRSN) array (German-GR and Geofon-GE programs). The waveformpatterns of the detected slow events for Greenland updated through 2008 were monitoredto analyze this new class of low-frequency earthquakes in the context of the array processingtechnique and array parameters using the software Seismic Handler Motif (SHM).The array geometry of GRSN was defined by seven stations and processed to associateseismic phase arrivals to define glacial events. Two stations of GRSN were assigned the roleof reference sites. The long-period surface wave characteristics of the event signals withmagnitudes M 4.9, M 4.8, M 4.7, and M 4.7 were detected using filtering, beamforming,and location-relocation steps; then, the results were updated using SHM. The event datawere filtered with a Butterworth band pass filter of 35s-70s with a common amplification.Using the array-beamforming technique, the beam traces were computed to calculate thebeam-slowness (the apparent velocity) and the beam-azimuth of incoming wavefronts forparticular time intervals to further analyze the observed glacial events. Then, the detectedevent signals were relocated and used to estimate array parameters; beam-slowness andbeam-azimuth. Finally, in this study, the array processing technique was used with arrayparameters computed from the SHM to detect and analyze the slow glacial events using thearray installation data from GRSN.
Crustal Poisson's Ratio Tomography and Velocity Modeling Across Tectono-Magmatic Lake Regions of Eastern Anatolia (Turkey): New Geophysical Constraints for Crustal Tectonics
(Pergamon-elsevier Science Ltd, 2019) Toker, Mustafa; Sahin, Sakir
The tomography of the Poisson ratio structures based on the Vp/Vs ratio provides much tighter constraints on the crust and uppermost mantle than Vp or Vs alone. In this study, high-resolution crustal tomography beneath tectono-magmatic lake regions (Lakes Van and Ercek) of Eastern Anatolia (Turkey) was used to estimate Poisson's ratio from the Vp and Vs structures through the joint inversion analyses of the travel times of Vp and Vs using the station records of the permanent network of Kandilli Observatory and Earthquake Research Institute (KOERI, Turkey). The results of Poisson's ratio anomaly reveal distinct and substantial variations in the different tectonic units and show a prominent, continuous and dense high Poisson's ratio anomalies in the range of 0.27 to 0.30 for the lowermost crust/the uppermost mantle beneath the regions of Lakes Van and Ergek and comparably low average Poisson's ratio (similar to 0.23) anomalies for the brittle crust in several local areas. High Poisson's ratios (over similar to 0.29) in the basins of Lakes Van and Ercek and in the vicinity of their boundary faults appear to be due to partial melts. Low Poisson's ratios (similar to 0.23) near seismogenetic faults at similar to 14 km depth beneath the lake regions suggest weaker and more easily deformable crust. The high and low Poisson's ratio structures suggest a strongly fault-controlled and highly heterogeneous crustal architecture beneath the lake regions. High Poisson's ratios at variable depths suggest that the mafic content beneath the lake regions is higher than has ever been expected, thus indicating the existence of intrusive materials of possible mantle origin, interacting with faulted crustal rocks. The regional extent of the high Poisson's ratios (0.27-0.30) of the lowermost crust/the uppermost mantle proposes strong interaction of partial melts with active tectonics in the basins of Lakes Van and Ercek. Key constraints from the estimated Poisson's ratios and V-anomalies indicate the diverse and interactive nature of crustal deformations beneath the lake regions where the underplating of the mantle magma scenario is proposed to exert a key control on tectono-magmatic evolution of the regions of Lakes Van and Ergek and serves as a working hypothesis for further studies.
Decoupled Co-Seismic Deformation and Stress Changes During the 2021 (Mw 6.0, 6.4) North Bandar Abbas Doublet Earthquakes in Fin Region, Se-Syntaxis of Zagros, Iran: New Insights Into the Tectonic Deformation Decoupling Process
(Springer, 2023) Toker, Mustafa; Durmus, Hatice; Utkucu, Murat
The co-seismic properties of the Mw 6.0 (12:07:03 UTC) and Mw 6.4 (12:08:06 UTC) doublet earthquakes that took place on 14 November 2021, N-Bandar Abbas Syntaxis (Fin region), SE-Zagros Simply Folded Belt (SFB), Iran, are thoroughly examined. Understanding the earthquake ruptures and their relationship to the co-seismic deformations, critical to our knowledge about the earthquake source mechanisms, has provided a singular chance to interpret the details of the rupture procedure of these two interrelated earthquakes, to complement previous studies of seismicity. Here, using finite-fault source inversion, we first estimated the co-seismic source models and then the co-seismic displacements during the earthquakes, differentiated into vertical/horizontal components. We inverted the observed tele-seismic broadband P velocity waveforms of the earthquakes to simultaneously estimate the finite-fault rupture process, the slip distribution, the fault geometry and the stress changes. We found that the earthquakes were typical blind thrust-fault types along NW-SE and NE-SW striking fault lengths of similar to 40-50 km, widths of similar to 25-30 km, at a depth range of similar to 3-16 km and similar to 3-15 km, respectively, with co-seismic surface folding (similar to 7-10 km) to NE controlled by a salt decollement layer at a depth range of similar to 10-12 km. We also found that the earthquakes consisted of relatively fast rupture sources (V-R 3.3 km/s); an initial pure thrust faulting bilateral rupture at a depth of 12 km with a maximum slip of 30 cm and a dip angle of 32 degrees, which was followed by a bilateral rupture with an oblique-slip left-lateral thrust faulting at a depth of 10 km, with a maximum slip of 80 cm and a dip angle of 24 degrees propagated towards the NE. The joint interpretation of estimated Coulomb stress changes imparted by proposed variable slip rupture models, and the salt layer indicated that the stress increased load, triggered the fault planes of both events and influenced along-strike co-seismic strain distribution, providing evidence for the SW-NE trending activation of the stress decoupling between the ruptures, corresponding to the salt decollement. The initial pure thrust motion ruptured and mobilised the salt layer, then triggered and activated the bilateral rupture that generated the co-seismic detachment folds subparallel to the decollement. The weak salt, co-seismically ruptured and rapidly activated, compensated co-seismic strain through lateral thickness changes from SW to NE and obliquely accommodated the folding in the shallow cover. Thus, basal ductile shear facilitated the change from pure thrust faulting in the basement to oblique thrust faulting in the cover. This finding clarifies differences in rupturing properties and deformation styles of such low-angle thrust faults.
Discrete Characteristics of the Aftershock Sequence of the 2011 Van Earthquake
(Pergamon-elsevier Science Ltd, 2014) Toker, Mustafa
An intraplate earthquake of magnitude Mw 7.2 occurred on a NE-SW trending blind oblique thrust fault in accretionary orogen, the Van region of Eastern Anatolia on October 23, 2011. The aftershock seismicity in the Van earthquake was not continuous but, rather, highly discrete. This shed light on the chaotic non-uniformity of the event distribution and played key roles in determining the seismic coupling between the rupturing process and seismogeneity. I analyzed the discrete statistical mechanics of the 2011 Van mainshock-aftershock sequence with an estimation of the non-dimensional tuning parameters consisting of; temporal clusters (C) and the random (RN) distribution of aftershocks, range of size scales (ROSS), strength change (an), temperature (T), P-value of temporal decay, material parameter R-value, seismic coupling x, and Q-value of aftershock distribution. I also investigated the frequency-size (FS), temporal (T) statistics and the sequential characteristics of aftershock dynamics using discrete approach and examined the discrete evolutionary periods of the Van earthquake Gutenberg-Richter (GR) distribution. My study revealed that the FS and T statistical properties of aftershock sequence represent the Gutenberg-Richter (GR) distribution, clustered (C) in time and random (RN) Poisson distribution, respectively. The overall statistical behavior of the aftershock sequence shows that the Van earthquake originated in a discrete structural framework with high seismic coupling under highly variable faulting conditions. My analyses relate this larger dip-slip event to a discrete seismogenesis with two main components of complex fracturing and branching framework of the ruptured fault and dynamic strengthening and hardening behavior of the earthquake. The results indicate two dynamic cases. The first is associated with aperiodic nature of aftershock distribution, indicating a time-independent Poissonian event. The second is associated with variable slip model, varying loading rates and high seismic coupling along the ruptured area. This study concludes that the aperiodic statistical behavior of the Van aftershock sequence is one of the results of the time-independent Poissonian seismic deformation in the 2011 Van earthquake. (C) 2014 Elsevier Ltd. All rights reserved.
An Integrated Critical Approach To Off-Fault Strike-Slip Motion Triggered by the 2011 Van Mainshock (Mw 7.1), Eastern Anatolia (Turkey): New Stress Field Constraints on Subcrustal Deformation
(Pergamon-elsevier Science Ltd, 2021) Toker, Mustafa; Pinar, Ali; Hoskan, Nihan
In this study, we retrieved the finite source characteristics of the October 23, 2011 Van earthquake (Mw 7.1) using the teleseismic waveforms to focus on the source location. The outstanding off-fault aftershock sequence of the Van mainshock was readily explained by calculating the Coulomb stress changes imparted to the surrounding crust. This may be accomplished through finite source modelling to examine the stress interaction between the fault, ruptured by the Van mainshock, and the surrounding fault(s) triggered by the same mainshock. In addition, to provide further support for the Coulomb failure stress changes in the off-fault area, centroid moment tensor (CMT) inversion of the off-fault aftershocks was performed and stress tensors were derived from their focal solutions. This identified the dominant fault slip, the constraints of the crustal stress fields and illuminated the crustal nature of the stress interaction. The off-fault aftershocks showed a strike-slip stress regime in rotational (to NW) and non-rotational (to N) stress fields of the upper and lower crusts, respectively. However, this was inconsistent with a horizontal compressional stress direction striking to the north. This suggests that a local source and/or rotation of lateral variation in stress magnitudes in crustal and sub-crustal structures strongly perturbed the regional stress field. It was also evident that these strike-slip aftershocks increased the intensity of stress in an off-fault area, NE of the source rupture. This revealed a uniquely triggered strike-slip motion, activated and rooted in the weak lower crust. We conclude that the Van mainshock rupture source area, associated with the stress changes imparted to the surrounding crust, had undergone anomalous modifications to generate distinctive off-fault aftershock responses in the entire crust, and also triggered and loaded the weak lower crust. We hypothesize that the strike-slip motion, the so called "transfer fault", as a distinctly triggered slip event, was generated or selectively activated by subcrustal ductile processes in the absence of mantle lid beneath the study area. However, local slab fragmentation, tearing and cold mantle beneath the study area lead to paradigm changes in interpreting the strike-slip motion and subcrustal deformation. The presence of a small piece of oceanic lithosphere, consistent with fragmented, torn slab and cold mantle, may be an alternative hypothesis that remains to be tested. The Van earthquake, combined with careful examination of associated off-fault aftershocks, revealed new information about stress field constraints on subcrustal deformation. This investigation also provided insights into an important role of stress interaction, with a newly discovered transfer fault within the offfault area, which extends through the entire crust beneath Lakes Van and Ercek areas.
Long-Term Ion Hydration Process and Lithosphere-Atmosphere Coupling Following the 2021 Fagradalsfjall Volcanic Eruption Using Remotely Sensed Data
(Elsevier Sci Ltd, 2023) Senturk, Erman; Adil, Muhammad Arqim; Toker, Mustafa; Iban, Muzaffer Can; Akyurek, Ozer
After a series of earthquakes, the Reykjanes peninsula in Iceland faced a volcanic eruption for the first time in 800 years. This vol-canism of the 2021 Fagradalsfjall started on March 19, 2021, and lasted until September 18, 2021. In this study, the vestiges of the mutual interplay of Earth's different geophysical shells due to the local lithospheric changes around the Fagradalsfjall were extensively investi-gated with the help of satellite-based remotely sensed datasets. Firstly, the regional surface deformations caused by the pre-eruption seis-mic activity are determined using interferometric image pairs, and horizontal and vertical displacement rates are analyzed. Secondly, the satellite observations revealed that the land surface temperature of the entire area increased to a maximum of 40 degrees C during the maximum phase of lava discharge by the end of May 2021. Moreover, we observed that the surface mass concentrations of SO2 and CO trace gases started to ascend in parallel with the lava discharge after the initial eruption, where their concentrations were doubled in April before reaching their maximum phases (three to four times more than the initial eruption) in May 2021. The cumulative concentrations of the trace gases in the atmosphere emitted from the Fagradalsfjall volcano pushed the regional atmospheric balance into a non-equilibrium state by creating air ionization through various chemical reactions with other atmospheric gases. These ion clusters underwent an ion hydration process that changed the electric conductivity of the atmospheric boundary layer, which covers the first two kilometers of the atmosphere. Finally, our observations showed a sharp decrease in the atmospheric relative humidity that led to an increase in the atmospheric air temperature due to this ion hydration process. The large ion clusters in the atmospheric boundary layer produced a ver-tical electric field that penetrated over the affected region and brought long-term changes in the ionosphere layer. This unique phe-nomenon of the simultaneous interaction of different geophysical layers was specifically observed during the maximum phase of the lava discharge and increased ion concentrations in the atmosphere. The used data sets cover the first three months of the volcanism, and this interval seemed to be sufficient to reveal the atmospheric traces. Our comprehensive study provides an important contribution to the theory of the coupling of volcanism and the Earth's atmospheric dynamics. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.
Multiple Segmentation and Seismogenic Evolution of the 6th February 2023 (Mw 7.8 and 7.7) Consecutive Earthquake Ruptures and Aftershock Deformation in the Maras Triple Junction Region of Se-Anatolia, Turkey
(Elsevier, 2023) Toker, Mustafa; Yavuz, Evrim; Utkucu, Murat; Uzunca, Fatih
On 6th February 2023 (UTC), two consecutive and catastrophic earthquakes with moment magnitudes (Mw) 7.8 and 7.7 struck the Maras Triple Junction (MTJ) region in SE Anatolia along with dozens of aftershocks, causing numerous casualties and significant building damage, and generating the most complex and longest surface ruptures ever observed in Turkey. The main driving mechanisms of this complex double event are still unresolved and remain controversial, even though they are likely linked with conventional fault activations, recurrence intervals and seismic gaps. Here, the aim was to gain insight into the source regimes and rupture processes of both events and their relationship with resolved fault focal solutions for the observed aftershocks, and to present an interpretation that accounts for the most puzzling aspects of the fault rupture models. In line with this, the coseismic slip distributions of these two events were examined by joint analyses of centroid moment tensor (CMT) and finite-fault source inversions using regional and teleseismic broadband observations. Inversion results indicate that both earthquakes were left-lateral strike-slip events, and the main ruptures extended mainly from close to NNE to SSW and E to W, with maximum slips of -6.5-10 m, mostly confined to a shallow depth range of <= -10-15 km and extending to the surface, indicating bilateral source processes with an average rupture velocity of -3.5-5.5 km/s. The estimated total seismic moment range was 4.94-8.22 x 1020 N m, associated with -352-152 km long (along strike) and - 25 km wide (along dip) fault planes at focal depth of -10 km. Regional CMT results indicate nearly pure normal-slip and left-lateral normal oblique-slip focal mechanisms and shallow centroid depths (<= -15 km) for the early aftershock distribution that are obviously complementary with the coseismic bilateral rupture propagations. This result highlights that double pull-apart branching of focal mechanisms for aftershock occurrence implies interacting fault ruptures embedded in the MTJ area, where two sub-/ supershear-rupturing faults meet, thus explaining multiple segmentation and seismogenic evolutions of two interrelated mainshocks, i.e. "triple junction earthquakes". The results reveal that the MTJ tends to migrate to the SSW and likely drives the SSW-stepping of the left-lateral strike-slip shear (-136 km). This accounts for the peak slips, long co-seismic fault ruptures and the associated faulting styles. Hence, the co-seismic faulting apparently distributed across the MTJ may reflect triple junction migration, and thus large extension at the core of the Anatolian-Arabian plates, leading to very high seismic hazard in similar junction regions of the country.
New Insight Into the 24 January 2020, Mw 6.8 Elazig Earthquake (Turkey): an Evidence for Rupture-Parallel Pull-Apart Basin Activation Along the East Anatolian Fault Zone Constrained by Geodetic and Seismological Data
(Ist Nazionale Di Geofisica E Vulcanologia, 2021) Irmak, Tahir Serkan; Toker, Mustafa; Yavuz, Evrim; Senturk, Erman; Guvenaltin, Muhammed Ali
In this study, we investigated the main features of the causative fault of the 24 January 2020, M-w, 6.8 Elazig earthquake (Turkey) using seismological and geodetic data sets to provide new insight into the East Anatolian Fault Zone (EAFZ). We first constrained the co-seismic surface deformation and the rupture geometry of the causative fault segment using Interferometric Synthetic Aperture Radar (InSAR) interferograms (Sentinel-1A/B satellites) and teleseismic waveform inversion, respectively. Also, we determined the centroid moment tensor (CMT) solutions of focal mechanisms of the 27 aftershocks using the regional waveform inversion method. Finally, we evaluated the co-seismic slip distribution and the CMT solutions of the causative fault as well as of adjacent segments using the 27 focal solutions of the aftershocks, superimposed on the surface deformation pattern. The CMT solution of the 24 January 2020Elazig earthquake reveals a pure strike-slip focal mechanism, consistent with the structural pattern and left-lateral motion of the EAFZ. The rupture process of the Elazig event indicated that the rupture is started at 12 km around the hypocenter, and then propagated bilaterally along the NE-SW but mainly toward the southwest. The rupture slip has initially propagated toward the southwest (first 10 s) and northeast (4 s), and again toward the southwest (9 s). Maximum displacement is calculated as 1.3 m about 20 km southwest of the hypocenter at 6 km depth (centroid depth). The rupture stopped to down-dip around 20 km depth toward the southwest. The distribution of the slip vectors indicates that the rupture continued mostly through a normal oblique movement. Most of the moment release was released SW of the hypocenter and the rupture reached up to around 50 km. The focal mechanisms of analyzed 27 aftershocks show strike-slip, but mostly normal and normal oblique-slip faulting with an orientation of the tensional axes (NNE-SSW), indicating a normal oblique-slip, "transtensional" stress regime, parallel-subparallel to the strike of the EAFZ, consistent with SW-rupture directivity and coseismic deformation pattern. Finally, based on the co-seismic surface deformation compatible with the distributional pattern of normal focal solutions, normal and normal oblique-slip focals of the aftershocks evidence the rupture-parallel pull-apart basin activation as a segment boundary of the left-lateral strike-slip movement of the EAFZ.
New Strain Configuration of Convergence in the Arabia-Eurasia Collisional Zone: a Comprehensive Analysis of Large Shear Zones Inferred From Geodetic and Seismic Observations
(Pergamon-elsevier Science Ltd, 2024) Toker, Mustafa; Pinar, Ali
A new strain configuration is presented concerning the ongoing convergence deformation field in the TurkishIranian High Plateau (TIHP), E Anatolia-NW Iran. The strain configuration is derived from the contribution of geodetic strain-rate fields using GPS velocity data to reveal new constraints not documented previously in the region. This provides good evidence for novel "highland shear strain zones" by analysis of the combination of interpolated GPS velocity fields and seismological observations with maximum principal strain axes. Both the strain-rate fields and rotational elements of the estimated geodetic deformation exhibit juxtaposed, patchy strain rate partitioning in E Anatolia-NW Iran. These comprise both compressional strain lobes combined with local extensional areas and large shear strain fields in the core of the collision where the rotation rate fields present an unexpected propagation zone of continuous, counterclockwise rotation towards the W. The main results define approximately N-S- and W-E-trending, large, continuous, diagonal shear strain patterns with high total strain rate and maximum shear strain rate, consistent with right-lateral strike-slip and normal focal mechanisms. These are the Longitudinal Shear Zone (LSZ) extending from S to N and dividing the TIHP into the E Anatolia and NW Iran blocks, and the right-lateral Transcurrent Shear Zone (TSZ) extending from E (NW Iran) to W (E Anatolia). These differential movements of the inconsistent LSZ and TSZ shape both the highly buoyant plateau topography and the area, which undergoes migration to the W with respect to stable Eurasia by means of plateau push. Geodetic deformation compatible with fault focal data indicates that the LSZ and TSZ, in the framework of thermal and mechanical changes in the structure of the lithospheric thickness beneath the TIHP, are invaded and shaped by flowing mantle material that triggers and drives lateral escape of convergent crustal blocks, and configures the convergence with a shear-dominated deformation regime. The shear regime is primarily driven by NE- and NWdirected mantle flow fields and associated buoyancy forces due to slab fragmentation and tears in the region, exerting dominant control over the differential evolution of the LSZ and TSZ patterns. The new strain configuration for this convergence illuminates "the highland tectonics of large shear zones" resulting from slab thinning or its absence, and challenges conventional tectonic strain models in the TIHP.
Shallow Seismic Characteristics and Distribution of Gas in Lacustrine Sediments at Lake Ercek, Eastern Anatolia, Turkey, From High-Resolution Seismic Data
(Springer, 2021) Toker, Mustafa; Tur, Huseyin
The high-resolution analysis of single-channel, seismic reflection data from Lake Ercek (Eastern Anatolia) revealed a wide range of shallow gas anomalies consisting of enhanced reflections, seismic chimneys, acoustic blanking/acoustic turbidity, strong reflectors, and pockmarks, including both surface and buried pockmarks. The enhanced reflections are represented by the higher amplitude reflection patterns resulting from high acoustic impedance variations. They are mostly clustered in the NW-corner of the lake. Seismic chimneys are represented by vertical and thinned columnar disturbances of amplitude blanking and mostly occurred in deep basinal and faulted sections in the West and East of the lake. Some seismic chimneys, occurring together with pockmarks, represent vertical vent activations. Acoustic gas masking was represented by chaotic and diffuse seismic reflection patterns, including acoustic blanking and acoustic turbidity. As diffuse acoustic turbidity indicates gas-charged sediments, columnar disturbances showing acoustic blanking indicate degassing of the sediments. These features extend from SE to NW, coinciding with the deep basin morphology of the lake. A very local strong reflector was identified in the W-section of the lake, simulating the lake floor. This reflector is due to extended enhanced reflections, suggesting shallow free gas. Pockmarks observed in the lake are structurally classified into the two distinct types; surface (active) pockmarks found in the SE-part of the lake and buried (passive) pockmarks found in the NW. The former enlarge through deeper gas reservoir feedback, as the layering is impermeable, while the latter have resulted from a cessation of the reservoir feedback mechanism and/or permeable layering. In the lake, shallow gas distribution is controlled by faults, that provide the faulting-driven depositional control and earthquakes, that provide the seismicity-driven overpressure control. The shallow gas is then vertically-horizontally distributed and shaped by asymmetric depositional-stratigraphic factors. This study of Lake Ercek presents complementary information about a possible tectono-thermal origin of observed shallow gas.
The Structural Elements and Tectonics of the Lake Van Basin (Eastern Anatolia) From Multi-Channel Seismic Reflection Profiles
(Pergamon-elsevier Science Ltd, 2017) Toker, Mustafa; Sengor, A. M. Celal; Schluter, Filiz Demirel; Demirbag, Emin; Cukur, Deniz; Imren, Caner; Niessen, Frank
This study analyzed multi-channel seismic reflection data from Lake Van, Eastern Anatolia, to provide key information on the structural elements, deformational patterns and overall tectonic structure of the Lake Van basin. The seismic data reveal three subbasins (the Tatvan, northern and Ahlat subbasins) separated by structural ridges (the northern and Ahlat ridges). The Tatvan basin is a tilted wedge-block in the west, it is a relatively undeformed and flat-lying deep basin, forming a typical example of strike-slip sedimentation. Seismic sections reveal that the deeper sedimentary sections of the Tatvan basin are locally folded, gently in the south and more intensely further north, suggesting a probable gravitational "wedge-block" instability, oblique to the northern margin. The northern subbasin, bounded by normal oblique faults, forms a basin-margin graben structure that is elongated in a northeast-southwest direction. The east-west trending Ahlat ridge forms a fault-wedged sedimentary ridge and appears to offset by reverse oblique faults forming as a push-up rhomb horst structure. The Ahlat subbasin is a fault wedged trough fill that is elongated in the west-east direction and appears as a horst-foot graben formed by the normal oblique faults. The northeast-southwest directed northern ridge is a faulted crestal terrace of a sublacustrine basement block. Its step-like morphology, in response to the downfaulting of the Tatvan basin, as well as its backthrusted appearance, indicates the normal oblique nature of the bounding faults. The lacustrine shelf and slope show distinctive stratigraphic features; progradational deltas, submerged fluvial channels, distorted and collapsed beddings and soft sediment deformation structures, characterizing a highly unstable nature of shelf caused by strong oblique faulting and related earthquakes. The faulting caused uplift of the carpanak spur zone, together with the northeastern Erek delta, deformation of deltaic structures and subsequently exposing the shelf and slope areas. The exposed areas are evident in the angular unconformity surface of the carpanak basement block with the northeastern Erek delta and thinned sediments. The uplift resulted in the asymmetric depositional emplacement of the southeastern delta that is controlled by a series of ramp anticlines/low angle reverse faults. The Deveboynu subbasin and Varis spur zone form wide fault-controlled depressions with thick sediments that are elongated in the north-south direction. These subbasins appear as a small pull-apart boundary formed by normal oblique faults at the western end of the southeastern delta. (C) 2017 Elsevier Ltd. All rights reserved.
Structural Patterns of the Lake Ercek Basin, Eastern Anatolia (Turkey): Evidence From Single-Channel Seismic Interpretation
(Springer, 2018) Toker, Mustafa; Tur, Huseyin
This study presents an analysis of the single-channel high-resolution shallow seismic reflection data from Lake Ercek, eastern Anatolia, to provide key information on the deformational elements, on the fault patterns and on the overall tectonic structure of the Lake Ercek Basin. High-resolution seismic data reveal major structural and deformational features, including N-S trending normal faults and W-E trending reverse faults bounding the Lake Ercek Basin, basement highs and folded structures along the marginal sections of the lake. The N-S trending normal faults asymmetrically control the steep western margin and the gentle eastern deltaic section, while the W-E trending reverse faults appear at the northern and southern margins. The N-S trending normal faults, half-graben structure, and the gradual thickening of sediments in the Ercek Basin toward the fault scarps strongly suggest an extensional tectonic regime resulting from an N-S compression. The Ercek Basin is an extension-controlled depocenter; it is a relatively undeformed and flat-lying deep Basin, forming a typical example of the half-graben structure. The N-S trending normal faults appear to be currently active and control the lake center and the E-delta section, resulting in subsidence in the lake floor. In the N- and S-margins of the lake, there is evidence of folding, faulting and accompanying block uplifting, suggesting a significant N-S compressional regime that results in the reverse faulting and basement highs along the marginal sections. The folding and faulting caused strong uplift of the basement blocks in the N- and S- margins, subsequently exposing the shelf and slope areas. The exposed areas are evident in the erosional unconformity of the surface of the basement highs and thinned sediments. The tilted basement strata and subsequent erosion over the basement block highs suggest prominent structural inversion, probably long before the formation of the lake. New high-resolution seismic data reveal the fault patterns and structural lineaments of the Lake Ercek and provide strong evidence for an ongoing extension and subsidence. The present study provides new structural insights that will support future tectonic and sedimentary studies and the development of strategies related to active earthquake faults and major seismic events in the region of Lake Ercek.
Symptomatic Discretization of Small Earthquake Clusters Reveals Seismic Coupling To 2017 Bodrum Earthquake (Mw 6.6) in the Gulf of Gokova (Sw Corner of Turkey): Viscous-Compliant Seismogenesis Over Back-Arc Setting
(Pergamon-elsevier Science Ltd, 2021) Toker, Mustafa
In this study, the small relocated "same and/or similar size events" repeated in each observed cluster are deduced from temporal and spatial statistics of microseismicity. Microseismicity not exceeding Mw 5.0 that occurred in the years from 2010 to 2014 and were recorded by the network of the Turkish General Directorate of Disaster Affairs were investigated. In the Gulf of Gokova (SW corner of Turkey), the November 26, 2012 Bozburun mainshock (Mw 4.8) was evaluated with its small events, together with its accompanying aftershock sequences that occurred in three discrete areas (Bozburun, Ula, Bodrum) of the gulf: the May 16, 2013 Ula aftershock (Mw 4.6), the March 25, 2014 Bozburun aftershock (Mw 4.0), and the May 1, 2014 Bodrum aftershock (Mw 4.0). Statistical analysis was accomplished by subdividing temporal distribution of microseismicity and resorting to a number of temporal clusters that allowed the mainshock-aftershock sequence to be placed into subgroups, and thus resulted in five clusters of various sizes linked to spatial clusters. The successive occurrence and clustering of small events into distinct discrete domains in time and space allowed reliable constraints on the stress state of the study area and suggested an interaction of the clusters. The interacting clusters offered an opportunity to evaluate the seismic coupling to 2017 Bodrum earthquake (Mw 6.6) in the study area. Our portrayal of the clusters inferred from small relocated events provide an important contribution to Bozburun, Ula and Bodrum: (1) a symptomatic discretization that is "peaked-like statistical behaviors" of clusters of small relocated events through time and space is an anomalously conspicuous feature, (2) this feature proposes a process of the inevitable interaction and triggering of the discrete clusters, indicating transient acceleration of aseismic slip on surrounding, uncoupled sections of the study area, and (3) this process reveals an evidence of the viscous-compliant seismicity as a principal objective of the cluster interaction, and hence a matter of seismic coupling scenario of the clusters to 2017 Bodrum earthquake (Mw 6.6) in the study area. These conclusions highlight the importance of the seismic-aseismic slip partitioning, arresting and balancing in the co-seismic source regions of the seismically active extensional grabens in driving the large earthquakes near the future and the viscous-compliant seismogenesis over back-arc setting of the Gulf of Gokova that provides an opportunity to understand the seismic coupling processes and the current stress state of the study area. This study implicates for the extensional back-arc graben basins in the Aegean region and WSW-Turkey that require a knowledge of the linkage between upper mantle flow processes and shallow, thin crustal dynamics in the region.
Time-Dependent Analysis of Aftershock Events and Structural Impacts on Intraplate Crustal Seismicity of the Van Earthquake (Mw 7.1, 23 October 2011), E-Anatolia
(versita, 2013) Toker, Mustafa
The Van earthquake (M (W) 7.1, 23 October 2011) in E-Anatolia is typical representative of intraplate earthquakes. Its thrust focal character and aftershock seismicity pattern indicate the most prominent type of compound earthquakes due to its multifractal dynamic complexity and uneven compressional nature, ever seen all over Turkey. Seismicity pattern of aftershocks appears to be invariably complex in its overall characteristics of aligned clustering events. The population and distribution of the aftershock events clearly exhibit spatial variability, clustering-declustering and intermittency, consistent with multifractal scaling. The sequential growth of events during time scale shows multifractal behavior of seismicity in the focal zone. The results indicate that the extensive heterogeneity and time-dependent strength are considered to generate distinct aftershock events. These factors have structural impacts on intraplate seismicity, suggesting multifractal and unstable nature of the Van event. Multifractal seismicity is controlled by complex evolution of crustal-scale faulting, mechanical heterogeneity and seismic deformation anisotropy. Overall seismicity pattern of aftershocks provides the mechanism for strain softening process to explain the principal thrusting event in the Van earthquake. Strain localization with fault weakening controls the seismic characterization of Van earthquake and contributes to explain the anomalous occurrence of aftershocks and intraplate nature of the Van earthquake.
Upper-To Mid-Crustal Seismic Attenuation Structure Above the Mantle Wedge in East Anatolia, Turkey: Imaging Crustal Scale Segmentation and Differentiation
(Elsevier, 2022) Toker, Mustafa; Sahin, Sakir
Multi-frequency P-and S -wave attenuation tomography models of Lake Van area (East Anatolia) have been obtained by estimating coda-normalized wave spectra of 3027 local earthquakes (2.0 < Mw < 7.1). The 6998 waveforms sampled from surface to a depth of 25 km, and were recorded from 2004 to 2020 at seven broadband, three-component digital seismic stations operated by Kandilli Observatory and Earthquake Research Institute (KOERI). We adopted a two-point ray-bending method to trace rays in a 3-D velocity model. We applied the coda normalization (CN) method to P- and S-wave data sets. We inverted the spectral data with a multiple resolution seismic attenuation (MuRAT) approach to obtain final tomographic models. On average, high (low) attenuation corresponds to low (high) velocity anomalies. The P-and S -wave attenuation contrasts delimit four well-known geological zones. High frequency-short wavelength attenuation contrasts constrain the 5-km-deep zone of interaction between magma and sediments within the Lake Van basin. Low frequency-long wavelength attenuation anomalies mark the central section of Lake Van between depths of 10 km and 20 km. This zone coincides with a rigid stable shear zone overlying a possible weak-ductile lower crust, interpreted as a detachment. Both low (5-15 km depth) and high attenuation (> 20 km) anomalies mark the area of maximum seismic energy release during the Van event. Their contrast highlights the maximum seismogenetic depth above weak-warm, unstable materials. High attenuation in the SE-part of the Lake Van area coincides with a large hydrothermal and/or magmatic folding-overthrusting, interpreted as a suture-metamorphic complex between depths of 10-15 km. Other minor high-attenuation zones deeper than 5 km focus on complex shear zones in the area damaged by the Van event. The paired attenuation structure of the Lake Van area appears linked to multiple tectonic processes of crust-magma interaction better constrains subsurface segmentation structures and differential deformation types at upper-middle crustal depths.
Van Gölü Bölgesinde 2011 Yılı Depremlerinin Artçı Şok Serisi Kırılma Karmaşığına Yapısal Bağlantı (DOĞU Anadolu, Türkiye)
(2021) Toker, Mustafa
Bu çalışma, Van Gölü alanında gerçekleşen, 23 Ekim Van (Mw 7.1) ve 9 Kasım Edremit (Mw 5.6) 2011 yılı depremleriyle, artçışok kırılma karmaşığına bağlı olarak, anaşok sonrası oluşan küçük deprem kümelerinin ve genel sismik hareketliliğin, azimuta bağlı değişimini dikkate alarak kurulan yapısal ilişkinin bir analizini sunmaktadır. Her iki anaşoktan sonra oluşan artçışok serileri, Van Gölünün altında bulunan kabuk kökenli faylarla ilişkilendirilmiş ve ardarda olmak üzere, sıradışı yıkıcı bir etki oluşturarak, bölgede çok önemli bir zarara neden olmuşlardır. Bu nedenle, çalışmamızın temel amacı, 23 Ekim 2011 artçışok odak derinliklerinin zamana, mekana ve azimuta bağlı olarak dağılımını ve dağılım sürecini göstermek ve aynı zamanda, artçışok odak derinliklerini kullanarak, artçışok serilerinin yapısal karakterini anlamaktır. Bu çalışmada, yaklaşık 10.000 artçışok verisi, 23 Ekim 2011 ve 17 Mart 2014 tarihleri arasında 3 yıl süreyle kaydedilen, sinyal gürültü oranı yüksek deprem katalogundan elde edilmiştir. Bu artçışok veri seti, 2011 Kasım ve 2014 Mart tarihleri arasında yeniden yersel olarak konumlandırılmış ve bu çalışmanın ilk aşamasını teşkil eden, yaklaşık 5000 adet artçışok verisi, derinlikuzaklık profil kesitlerinde, deprem kümelenmelerini tespit edebilmek için kullanılmıştır (Kasım 2011-Mart 2012). Böylece, artçışok kümelenmelerinin derinlik dağılımı, deprem odak derinliklerin hareketi ve küçük deprem kümelenmelerinin analizi gerçekleştirilmiştir ve ayrıca, artçışok odak derinliklerinin geometrik dağılımı kullanılarak, tespit edilmiş deprem kümelenmelerinin dağılım geometrilerinin analizi yapılmıştır. Artçışokların zamanda ve mekandaki dağılımları, Van depremini oluşturan fayın derinlerdeki kırılma karmaşasına dair, çok ilginç temel özelliklerini açıkça göstermiştir. Bu çalışma, ilk kez, deprem odağı analizi detaylı gözlem sonuçlarını vermektedir ve bu veri sonuçları, çalışma alanında, gelecekteki olması muhtemel deprem hasar analizleri için çok önem arz etmektedir.
Van Gölü Havzası ve Civarının Depremselliğine Genel Bir Bakış
(2023) Toker, Mustafa; Akkaya, İsmail; Alkan, Hamdi
Bu çalışma kapsamında, Van Gölü Havzası ve civarı için özellikle aletsel dönemde meydana gelmiş depremler ve bunların artçı şok verileri kullanılarak yapılan çalışmalardan elde edilen sonuçlar değerlendirilmiştir. Farklı sismolojik parametrelerin kullanıldığı bu çalışmaların bulguları derlenerek, bölgenin gelecekteki deprem riski/tehlikesi karşısındaki durumu ortaya koyulmaya çalışılmıştır. Aletsel ve tarihsel dönemde büyüklüğü 5.0 ve üzerinde olan birçok depremin meydana geldiği bölgede, son olarak 23 Ekim 2011 (Mw=7.1) ve 09 Kasım 2011 (Mw=5.8) tarihlerinde Van şehir merkezi civarında meydana gelen yıkıcı/hasar verici iki deprem bölgenin farklı özelliklerdeki aktif fay mekanizmalarına sahip olduğunu göstermiştir. Sonuç olarak, özellikle Van Gölü’nün hemen doğusu ile Çaldıran, Muradiye, Özalp, Saray ve Erciş civarında yakın gelecekte deprem tehlikesi diğer bölgelere göre büyük olarak ifade edilebilir. Ayrıca, Van Gölü Havzası ve civarının gerek jeofizik yöntemlere gerekse yapısal incelemelere dayalı farklı parametreler (zemin büyütmesi ve sismik hasar indisi gibi) kullanılarak zemin mühendislik özellikleri ve yapı-zemin etkileşimi açısından değerlendirmesi de bu çalışmada incelenmiştir.