Ugur Teoman - Academia.edu (original) (raw)
Papers by Ugur Teoman
Shear wave splitting measurements across the North Anatolian Fault (NAF) in Northern Turkey are c... more Shear wave splitting measurements across the North Anatolian Fault (NAF) in Northern Turkey are calculated from teleseismic SKS arrivals recorded by the dense temporary DANA seismological array to ...
1 School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT, 2 Department of Geolo... more 1 School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT, 2 Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, 3 Department of Geology and Geophysics, School of Geosciences, University of Aberdeen, King’s College, Aberdeen, AB24 3UE, United Kingdom, 4 Kandilli Observatory and Earthquake Research Institute, Department of Geophysics, Boğaçizi University, 34684 Cengelköy, Istanbul, Turkey, 5 Department of Geophysical Engineering, Sakarya University, Esentepe Campus, 54187, Sakarya, Turkey 6 COMET, School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT
Journal of Asian Earth Sciences, 2019
Eastern Anatolia is a ~2km high plateau shaped by the continent-continent collision of the Arabia... more Eastern Anatolia is a ~2km high plateau shaped by the continent-continent collision of the Arabian and Eurasian plates. The left lateral East Anatolian Fault Zone, the right lateral North Anatolian Fault Zone and the Bitlis fold-thrust belt are the major tectonic boundaries of this convergence zone. The Arabian-Eurasian collision has resulted in high volcanism and well recorded seismic activity in Eastern Anatolia and its surroundings. Karlıova Junction is located at the intersection of these major fault systems and contains secondary faults such as the Karakoçan fault and the Sancak-Uzunpınar fault. We processed high quality waveform data collected from a recent seismic activity in the proximity of the city of Bingöl where the largest event is the moderate-size earthquake (Mw = 5.3) occurred on 2 December 2015. This event is located to the west of Karlıova Junction and to the northwest of Sancak-Uzunpınar fault. The spatial distribution of the aftershocks points out unmapped faults with NNW-SSE alignment towards the west of Sancak-Uzunpınar fault. Aftershock depth distribution indicates a nearly 15 km deep brittle seismogenic zone. The relocated aftershock distributions and seismic moment calculations yield a rupture area 9 km in length and 5 km in width with an average 8 cm of slip. The latest four earthquakes preceding the 2015 Eq with magnitudes larger than Mw>6 enhanced the Coulomb stress failure in the 2015 Bingöl Earthquake rupture area. The ruptured fault plane is in-line with the optimally oriented right-lateral strike-slip faults.
Earth and Planetary Science Letters, 2015
Continental scale deformation is often localized along strike-slip faults constituting considerab... more Continental scale deformation is often localized along strike-slip faults constituting considerable 18 seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such Major continental strike-slip faults, such as the North Anatolian fault Zone (NAFZ) in Turkey or the 44 San Andreas Fault in the USA, are key elements in our understanding of plate tectonics. Such 45 faults are clearly defined at the surface but considerable uncertainty surrounds their structure in 46 the mid to lower crust and upper mantle, and specifically how deformation is focussed in shear 47 zones that are presumed to extend beneath seismically active fault planes (e.g., Handy et al., 2007; 48 Platt and Behr, 2011). An understanding of such fault systems (e.g., Pollitz et al., 2001) requires 49 characterisation of the structure and physical properties of the crust and upper mantle to 50 constrain the rheological parameters that determine how stress is redistributed during the 51 earthquake cycle (e.g., Hearn et al., 2009). Localized zones of relatively high or low viscosity can 52 have an important impact on this cycle (Yamasaki et al., 2014). 53 Modelling of geodetic deformation has provided some constraints on the physical variation of 54
Tectonophysics, 2015
With the aim of extensively investigating the crustal structure beneath the western segment of th... more With the aim of extensively investigating the crustal structure beneath the western segment of the North Anatolian Fault Zone where it splays into northern and southern branches, a temporary seismic network (Dense array for North Anatolia-DANA) consisting of 70 stations was deployed in early May 2012 and operated for 18 months in the Sakarya region during the FaultLab experiment. Out of 2437 events contaminated by explosions, we extracted 1371 well located earthquakes. The enhanced station coverage having a nominal station spacing of 7 km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8 km and 0.9 km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km. Using our current earthquake catalogue we obtained a b-value of 1. We also mapped the b-value variation with depth and observed a gradual decrease. Furthermore, we determined the source parameters of 41 earthquakes with magnitudes greater than 1.8 using P-wave first motion polarity method. Regional Moment Tensor Inversion method was also applied to earthquakes with magnitudes greater than 3.0. Focal mechanism solutions confirm that Sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique-slip motion character. Stress tensor analysis indicates that the maximum principal stress is aligned in WNW-ESE direction and the tensional axis is aligned in NNE-SSW direction.
Geophysical Research Letters, 2015
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Proceedings, 2013
ABSTRACT This study focuses on upper crustal studies such as earthquake locations (especially mic... more ABSTRACT This study focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), moment tensor inversions and receiver function analysis. Accurate earthquake locations will eventually lead to high-resolution seismic images of NAF including both the northern and the southern branches in the upper crust.In this study, 722 earthquakes within the time period of 09 May – 17 September 2012 were located. Furthermore, the crustal structure beneath the DANA Array is investigated using receiver functions obtained from the teleseismic recordings from a total of 73 broadband stations. Calculated Moho depth beneath the most of stations is between 33 and 36 km.
To extensively investigate the upper crustal structure beneath the western segment of the North A... more To extensively investigate the upper crustal structure beneath the western segment of the North Anatolian Fault Zone (NAFZ) in Sakarya and the surroundings, a temporary seismic network consisting of 70 stations (with nearly 7km station spacing) was deployed in early May 2012 and operated for 18 months during the Faultlab experiment encompassing both the northern and southern strands of the fault in between the area of 1999 İzmit and Düzce mainshock ruptures. With the help of this new and extensive data set, our main objective is to provide new insights on the most recent micro-seismic activity and the velocity structure beneath the region. Out of 2437 events contaminated by the explosions, we extracted 1344 well located earthquakes with a total of 31595 P and 18512 S phase readings which lead to an avarage Vp/Vs ratio of ~1.82 extracted from the wadati diagram. The enhanced station coverage decreased the magnitude threshold to 0.1 where the horizontal and vertical location errors di...
Deformation along major strike-slip faults is typically focussed into narrow damage zones at the ... more Deformation along major strike-slip faults is typically focussed into narrow damage zones at the surface, but the distribution at greater depths is more enigmatic. For instance, deformation in the lower crust beneath these faults is often attributed to much broader ductile shear zones. Deciphering how strain is distributed throughout the crust and lithospheric mantle is important because it has ramifications on the earthquake loading cycle. In order to better understand the structure of these systems at depth, we investigate the North Anatolian Fault Zone (NAFZ) as part of a multidisciplinary project entitled FaultLab. This fault system extends ~1200km across Turkey and has shown a clear west-east progression in seismicity over the last century, culminating in 2 catastrophic earthquakes located close to the population centers of Izmit and Duzce in 1999. In this contribution, we will present new data from a dense seismic array (Dense Array for North Anatolia, DANA, a 6x11 grid with a...
Shear-wave splitting from local earthquakes provides valuable knowledge on anisotropy of the uppe... more Shear-wave splitting from local earthquakes provides valuable knowledge on anisotropy of the upper crust. Upper-crustal anisotropy is widely interpreted as due to aligned fluid-filled cracks or pores. Differential stress is thought to close cracks aligned perpendicular to the maximum principal stress and leaves cracks open that are aligned perpendicular to the minimum horizontal compressional stress. In other cases local shear-wave splitting has been found to be aligned with regional faulting. Temporal variations in local splitting patterns might provide hints of changes in stress orientation related to earthquakes or volcanoes. North Anatolian Fault Zone (NAFZ) is a large-scale continental strike slip fault system originating at the Karlıova Junction in the east where it intersects the East Anatolian Fault (EAF) and extends west cutting across the entire Northern Turkey towards the Aegean Sea and the mainland Greece. Our primary focus is to provide constraints on the crustal anisot...
ABSTRACT North Anatolian Fault (NAF) is one of the major strike slip fault systems on earth compa... more ABSTRACT North Anatolian Fault (NAF) is one of the major strike slip fault systems on earth comparable to San Andreas Fault some ways. Devastating earthquakes have occurred along this system causing major damage and casualties. In order to comprehensively investigate the shallow and deep crustal structure beneath the western segment of North Anatolian Fault (NAF), a temporary dense seismic network consisting of 73 broadband sensors was deployed in early May 2012 with support from The Natural Environment Research Council (NERC) and partial support from Bogazci University Research Fund. This joint project involves researchers from University of Leeds, UK and Bogazici University, Kandilli Observatory and Earthquake Research Institute (KOERI). In addition to the 63 sensors provided by SEIS-UK instrument pool and three permanent KOERI sites in the region, another seven stations of KOERI-Department of Geophysics were installed surrounding the rectangular grid with the aim of further enhancing the detection capability of this dense seismic array (map). Six months of seismic data have been collected and initial analysis underway. This research focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), moment tensor inversions and ambient noise correlations. Accurate earthquake locations will eventually lead to high resolution seismic images of NAF including both the northern and the southern branches in the upper crust. In order to put additional constraints on the active tectonics of the western part of NAF, we determined fault plane solutions using Regional Moment Tensor Inversion (RMT) and P wave first motion method. For the analysis of high quality fault plane solutions, data from KOERI and the DANA project were merged. Furthermore, detailed Moho topography will be revealed via receiver function method. Iterative time domain deconvolution was used to obtain receiver functions and H-K stacking was applied to calculate crustal thickness values. The preliminary results indicate that Moho is located at roughly 26 - 28 km depth with Vp/Vs ratios higher than 1.98. We also present the observed Moho depth variations along N-S and E-W profiles beneath the western segment of NAF.
ABSTRACT The Caucasus-Caspian region is part of the Alpine-Himalayan collision belt and is an are... more ABSTRACT The Caucasus-Caspian region is part of the Alpine-Himalayan collision belt and is an area of complex structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region little is known about the lithospheric structure. Using data from 25 new broadband seismic stations in the region, a unified velocity structure is developed using teleseismic receiver functions and surface waves. Several distinct regions are recognized: the Greater Caucasus, the lesser Caucasus and the Caspian/Kura Depression. Depth(h)-Vp/Vs(k) stacks of the receiver functions suggest crustal thicknesses of 45-50 km in the Lesser and Greater Caucasus with relatively high crustal velocities (Vs=3.4 km/s). Variations of the receiver functions with back-azimuth indicate 3D variations in structure in the Greater Caucasus. Crustal thickness in the Kura Depression and at the edge of the Caspian is less well constrained due to pronounced multiples associated with thick sedimentary layers but the preferred results suggest a Moho depth of 38 to 48 km and lower crustal velocities (Vs=3.1 km/s). Love and Rayleigh surface waves dispersion curves have been derived from using both event-based analysis and ambient noise correlation. Short-period surface waves outline the sedimentary structure of the region, while longer periods highlight crustal velocity, crustal thickness, and upper mantle velocity. Joint inversion of the receiver functions with the surface wave dispersion curves to determine absolute shear wave velocity is ongoing.
ABSTRACT The primary objective of this study is to obtain the lithospheric structure of Anatolian... more ABSTRACT The primary objective of this study is to obtain the lithospheric structure of Anatolian-African Subduction zone including the Isparta Angle (IA) from Phase velocity inversion of Rayleigh waves and subsequent Shear wave velocity inversions. The ongoing subduction of the African Plate under Anatolian Plateau results in a highly complex tectonic structure beneath Southwestern Turkey and the surroundings. IA is seismically quite active and formed by the intersection of two very different subduction zones: The Hellenic arc to the west and the Cyprian arc to the east. The geometric difference between Hellenic Arc (relatively steep retreating subduction) and Cyprus Arc (shallower subduction) might be indicating a tear or gap in the subducting African Lithosphere beneath the Anatolian Plate responsible for the active deformation. A temporary seismic network consisting of 10 3-component BB stations were installed in August 2006 with the support from University of Missouri and 9 more stations in March 2007 in addition to the 21 existing permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI) and two from Süleyman Demirel University (SDU). 8 stations from Geofon Network were also included to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitude larger than 5.5. Depending on the signal to noise ratio, azimuthal coverage of events, and coherence from station, 68 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li (2003) to simultaneously solve for the incoming wave field and phase velocity. This relatively simpler representation of a more complex wavefield provided the pattern of amplitude variations effectively in many cases. To begin with, an average phase velocity dispersion curve (35 -140 seconds) was obtained and used as an input for 2-D inversions. Updated 2-D tomographic maps of phase velocities were constructed along with the resolution tests. Phase velocities can only tell us integrated information about the upper mantle. Furthermore, we inverted phase velocities for shear wave velocities in order to obtain direct information at various depths (35- ~300 km) that can be interpreted in terms of temperature anomalies, the presence of melt or dissolved water, etc.,
ABSTRACT The African and Anatolian collision zone belt in southwestern Turkey consists of subduct... more ABSTRACT The African and Anatolian collision zone belt in southwestern Turkey consists of subducting African oceanic crust beneath Anatolian plate. Within the convergent plate margin there are two principle arcs: the Hellenic and Cyprean arcs. The region between the intersection of the Hellenic and Cyprean arcs is named the Isparta Angle(IA). In order to image the crustal variation, we applied joint inversion of receiver functions & surface wave group velocities and h-k stacks to the receiver functions which were obtained from teleseismic events recorded by forty three broad band stations which are combination of nineteen temporary and B.U. KOERI's permanent stations deployed in the region. Receiver functions are sensitive to compressional and shear wave velocity contrast and vertical travel times while surface wave dispersion curves are sensitive to shear wave velocity averages. Combining these different properties allow us to constrain the lithospheric shear wave velocities. H-K staking leads us to calculate Moho variation along the collision zone. We found that average mid crustal shear velocity is 3.49 km/s however the mid crustal velocities directly above IA is ranging between 3.47 km/s and 3.53 km/s. The average upper mantle P velocity is 7.53 km/s which is a little higher comparing to stations above IA which are varying between 7.08 km/s to 7.30 km/s. Both of the upper mantle P velocities are very low which are comparible with the Pn velocity tomography studies in southwestern Turkey. Moho variations beneath southwestern Turkey indicate a crustal thickness anomaly between the IA and the surrounding regions. The southwestern end of the region has a thinner crust (26 - 28 km) compared to southeastern end of region (30 - 34 km). We have observed that west of the IA has a 38 km thick crust but east of the IA has a crustal thickness of 32 km. In addition to this, south of the IA has 43 km Moho depth thereby suggesting the crust thickens towards the plate boundary (i.e. southward). This research is supported by Bogazici University Research Fund under contract number 07T203.
ABSTRACT The ongoing subduction of the African Plate under western Anatolia results in a highly c... more ABSTRACT The ongoing subduction of the African Plate under western Anatolia results in a highly complex tectonic structure especially beneath Isparta Angle (IA) and the surroundings where the Hellenic and Cyprian slabs with different subduction geometries intersect. The primary objective is to accurately image the lithospheric structure at this convergent plate boundary and further understand the reasons responsible for the active deformation. Data was gathered from a temporary seismic network consisting of 10 broadband stations that was installed in August 2006 with the support from University of Missouri and nine more stations deployed in March 2007 with the support from Bogazici Research Fund (project ID:07T203). In addition, 21 permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI) and two from Süleyman Demirel University (SDU) together with five stations from IRIS/Geofon Network were also included to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitudes larger than 5.5. Depending on the signal to noise ratio, azimuthal coverage of events, and coherence from station, 81 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li (2003) to simultaneously solve for the incoming wave field and phase velocity. This relatively simpler representation of a more complex wavefield provided quite stable patterns of amplitude variations in many cases. To begin with, an average phase velocity dispersion curve was obtained and used as an input for tomographic inversions. Two-dimensional tomographic maps of isotropic and azimuthally anisotropic phase velocity variations were generated. Phase velocities can only tell us integrated information about the upper mantle. Furthermore, we inverted phase velocities for shear wave velocities (Saito,1988) in order to obtain direct information at a depth range of 30-300 km that can be interpreted in terms of major tectonic processes such as extension, slab detachment/tearing, STEP faults, volcanism, temperature anomalies, the presence of melt or dissolved water, etc. Resulting tomograms along horizontal and vertical depth sections provided valuable insights on the crustal and upper mantle structure beneath Southwestern Turkey down to almost 300 km.
ABSTRACT Anatolian Plateau-Caucasus-Caspian region is an area of complex structure accompanied by... more ABSTRACT Anatolian Plateau-Caucasus-Caspian region is an area of complex structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region little is known about the detailed lithospheric structure. Using data from 29 new broadband seismic stations in the region, a unified velocity structure is developed using teleseismic receiver functions and surface waves. Love and Rayleigh surface waves dispersion curves have been derived from event-based analysis and ambient-noise correlation. We jointly inverted the receiver functions with the surface wave dispersion curves to determine absolute shear wave velocity and important discontinuities such as sedimentary layer, Moho, lithospheric-asthenospheric boundary. We combined these new station results with Eastern Turkey Seismic Experiment results (29 stations). Caspian Sea and Kura basin underlained by one of the thickest sediments in the world. Therefore, short-period surface waves are observed to be very slow. The strong crustal multiples in receiver functions and the slow velocities in upper crust indicate the presence of thick sedimentary unit (up to 20 km). Crustal thickness varies from 34 to 52 km in the region. The thickest crust is in Lesser Caucasus and the thinnest is in the Arabian Plate. The lithospheric mantle in the Greater Caucasus and the Kura depression is faster than the Anatolian Plateau and Lesser Caucasus. This possibly indicates the presence of cold lithosphere. The lower crust is slowest in the northeastern part of the Anatolian Plateau where Holocene volcanoes are located.
The Isparta Angle (southwestern Turkey) lies at the intersection of Hellenic and Cyprus arcs rela... more The Isparta Angle (southwestern Turkey) lies at the intersection of Hellenic and Cyprus arcs related to the collision of the African and Anatolian plates and possesses a complex structure. To further understand this complexity, we deployed a temporary network consisting of nineteen broad band instruments in addition to permanent seismic stations in the region. Crustal velocity and Moho depth variations were estimated along two profiles (N-S, and E-W) formed by the fourteen temporary and permanent stations. Crustal and lithopheric velocities and Moho depths were estimated in two ways: h-k stacks and the joint inversion of receiver functions and surface wave group velocities. Receiver functions are sensitive to shear wave velocity contrast and vertical travel times while surface wave dispersion curves are sensitive to shear wave velocity averages. Combining these different properties of shear waves ensures a more robust result. We found that upper crustal shear velocities are higher b...
Pure and Applied Geophysics, 2012
We estimate Lg wave attenuation using local and regional seismic phases in the Isparta Angle and ... more We estimate Lg wave attenuation using local and regional seismic phases in the Isparta Angle and the Anatolian Plateau (Turkey). The Isparta Angle (IA) is a tectonically active zone forming the boundary between the African Plate and the Anatolian Plateau, and is currently undergoing N–S extensional deformation. The Anatolian Plateau contains many intra-continental faults including the North Anatolian Fault Zone and the East Anatolian Fault Zone as well as the Menderes Massif. A large waveform data set was compiled from a variety of local and regional seismic networks including 121 digital seismic stations (broad-band and short period) between 1999 and 2008 spanning the IA, the Anatolian Plateau and Azerbaijan. The data set was used to determine the nature of Lg wave propagation and characterize the nature of seismic attenuation within the crust of these regions. Lg waveforms were used to calculate the frequency-dependent Lg-Qo and Lg-eta\etaeta. A wide range of Lg-Qo values was obtained between ~52 ± 6 and 524 ± 227. Low Lg-Qo values (~90–155) are calculated towards the north of IA, Iskenderun Gulf and its vicinity, Bingöl-Karlıova, Izmit and its vicinity. Lg-Qo values are especially low (<90) along the Menderes Massif and the Aksehir-Simav Fault Zones. This may be due to intrinsic attenuation of Lg associated with the partially molten crust and young volcanism. The high Lg-Qo values (~350) are probably caused by the crust not being subject to large amounts of extensional deformation like the Antalya Gulf and apparently being thick enough to support Lg propagation. Relatively higher values along the border of this subduction zone and plate boundary might be related to the Taurus Mountain belts and Bitlis-Zagros Suture Zone. The lateral frequency dependency Lg-eta\etaeta is also consistent with high tectonic activity in this region.
Shear wave splitting measurements across the North Anatolian Fault (NAF) in Northern Turkey are c... more Shear wave splitting measurements across the North Anatolian Fault (NAF) in Northern Turkey are calculated from teleseismic SKS arrivals recorded by the dense temporary DANA seismological array to ...
1 School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT, 2 Department of Geolo... more 1 School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT, 2 Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, 3 Department of Geology and Geophysics, School of Geosciences, University of Aberdeen, King’s College, Aberdeen, AB24 3UE, United Kingdom, 4 Kandilli Observatory and Earthquake Research Institute, Department of Geophysics, Boğaçizi University, 34684 Cengelköy, Istanbul, Turkey, 5 Department of Geophysical Engineering, Sakarya University, Esentepe Campus, 54187, Sakarya, Turkey 6 COMET, School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT
Journal of Asian Earth Sciences, 2019
Eastern Anatolia is a ~2km high plateau shaped by the continent-continent collision of the Arabia... more Eastern Anatolia is a ~2km high plateau shaped by the continent-continent collision of the Arabian and Eurasian plates. The left lateral East Anatolian Fault Zone, the right lateral North Anatolian Fault Zone and the Bitlis fold-thrust belt are the major tectonic boundaries of this convergence zone. The Arabian-Eurasian collision has resulted in high volcanism and well recorded seismic activity in Eastern Anatolia and its surroundings. Karlıova Junction is located at the intersection of these major fault systems and contains secondary faults such as the Karakoçan fault and the Sancak-Uzunpınar fault. We processed high quality waveform data collected from a recent seismic activity in the proximity of the city of Bingöl where the largest event is the moderate-size earthquake (Mw = 5.3) occurred on 2 December 2015. This event is located to the west of Karlıova Junction and to the northwest of Sancak-Uzunpınar fault. The spatial distribution of the aftershocks points out unmapped faults with NNW-SSE alignment towards the west of Sancak-Uzunpınar fault. Aftershock depth distribution indicates a nearly 15 km deep brittle seismogenic zone. The relocated aftershock distributions and seismic moment calculations yield a rupture area 9 km in length and 5 km in width with an average 8 cm of slip. The latest four earthquakes preceding the 2015 Eq with magnitudes larger than Mw>6 enhanced the Coulomb stress failure in the 2015 Bingöl Earthquake rupture area. The ruptured fault plane is in-line with the optimally oriented right-lateral strike-slip faults.
Earth and Planetary Science Letters, 2015
Continental scale deformation is often localized along strike-slip faults constituting considerab... more Continental scale deformation is often localized along strike-slip faults constituting considerable 18 seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such Major continental strike-slip faults, such as the North Anatolian fault Zone (NAFZ) in Turkey or the 44 San Andreas Fault in the USA, are key elements in our understanding of plate tectonics. Such 45 faults are clearly defined at the surface but considerable uncertainty surrounds their structure in 46 the mid to lower crust and upper mantle, and specifically how deformation is focussed in shear 47 zones that are presumed to extend beneath seismically active fault planes (e.g., Handy et al., 2007; 48 Platt and Behr, 2011). An understanding of such fault systems (e.g., Pollitz et al., 2001) requires 49 characterisation of the structure and physical properties of the crust and upper mantle to 50 constrain the rheological parameters that determine how stress is redistributed during the 51 earthquake cycle (e.g., Hearn et al., 2009). Localized zones of relatively high or low viscosity can 52 have an important impact on this cycle (Yamasaki et al., 2014). 53 Modelling of geodetic deformation has provided some constraints on the physical variation of 54
Tectonophysics, 2015
With the aim of extensively investigating the crustal structure beneath the western segment of th... more With the aim of extensively investigating the crustal structure beneath the western segment of the North Anatolian Fault Zone where it splays into northern and southern branches, a temporary seismic network (Dense array for North Anatolia-DANA) consisting of 70 stations was deployed in early May 2012 and operated for 18 months in the Sakarya region during the FaultLab experiment. Out of 2437 events contaminated by explosions, we extracted 1371 well located earthquakes. The enhanced station coverage having a nominal station spacing of 7 km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8 km and 0.9 km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km. Using our current earthquake catalogue we obtained a b-value of 1. We also mapped the b-value variation with depth and observed a gradual decrease. Furthermore, we determined the source parameters of 41 earthquakes with magnitudes greater than 1.8 using P-wave first motion polarity method. Regional Moment Tensor Inversion method was also applied to earthquakes with magnitudes greater than 3.0. Focal mechanism solutions confirm that Sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique-slip motion character. Stress tensor analysis indicates that the maximum principal stress is aligned in WNW-ESE direction and the tensional axis is aligned in NNE-SSW direction.
Geophysical Research Letters, 2015
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Proceedings, 2013
ABSTRACT This study focuses on upper crustal studies such as earthquake locations (especially mic... more ABSTRACT This study focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), moment tensor inversions and receiver function analysis. Accurate earthquake locations will eventually lead to high-resolution seismic images of NAF including both the northern and the southern branches in the upper crust.In this study, 722 earthquakes within the time period of 09 May – 17 September 2012 were located. Furthermore, the crustal structure beneath the DANA Array is investigated using receiver functions obtained from the teleseismic recordings from a total of 73 broadband stations. Calculated Moho depth beneath the most of stations is between 33 and 36 km.
To extensively investigate the upper crustal structure beneath the western segment of the North A... more To extensively investigate the upper crustal structure beneath the western segment of the North Anatolian Fault Zone (NAFZ) in Sakarya and the surroundings, a temporary seismic network consisting of 70 stations (with nearly 7km station spacing) was deployed in early May 2012 and operated for 18 months during the Faultlab experiment encompassing both the northern and southern strands of the fault in between the area of 1999 İzmit and Düzce mainshock ruptures. With the help of this new and extensive data set, our main objective is to provide new insights on the most recent micro-seismic activity and the velocity structure beneath the region. Out of 2437 events contaminated by the explosions, we extracted 1344 well located earthquakes with a total of 31595 P and 18512 S phase readings which lead to an avarage Vp/Vs ratio of ~1.82 extracted from the wadati diagram. The enhanced station coverage decreased the magnitude threshold to 0.1 where the horizontal and vertical location errors di...
Deformation along major strike-slip faults is typically focussed into narrow damage zones at the ... more Deformation along major strike-slip faults is typically focussed into narrow damage zones at the surface, but the distribution at greater depths is more enigmatic. For instance, deformation in the lower crust beneath these faults is often attributed to much broader ductile shear zones. Deciphering how strain is distributed throughout the crust and lithospheric mantle is important because it has ramifications on the earthquake loading cycle. In order to better understand the structure of these systems at depth, we investigate the North Anatolian Fault Zone (NAFZ) as part of a multidisciplinary project entitled FaultLab. This fault system extends ~1200km across Turkey and has shown a clear west-east progression in seismicity over the last century, culminating in 2 catastrophic earthquakes located close to the population centers of Izmit and Duzce in 1999. In this contribution, we will present new data from a dense seismic array (Dense Array for North Anatolia, DANA, a 6x11 grid with a...
Shear-wave splitting from local earthquakes provides valuable knowledge on anisotropy of the uppe... more Shear-wave splitting from local earthquakes provides valuable knowledge on anisotropy of the upper crust. Upper-crustal anisotropy is widely interpreted as due to aligned fluid-filled cracks or pores. Differential stress is thought to close cracks aligned perpendicular to the maximum principal stress and leaves cracks open that are aligned perpendicular to the minimum horizontal compressional stress. In other cases local shear-wave splitting has been found to be aligned with regional faulting. Temporal variations in local splitting patterns might provide hints of changes in stress orientation related to earthquakes or volcanoes. North Anatolian Fault Zone (NAFZ) is a large-scale continental strike slip fault system originating at the Karlıova Junction in the east where it intersects the East Anatolian Fault (EAF) and extends west cutting across the entire Northern Turkey towards the Aegean Sea and the mainland Greece. Our primary focus is to provide constraints on the crustal anisot...
ABSTRACT North Anatolian Fault (NAF) is one of the major strike slip fault systems on earth compa... more ABSTRACT North Anatolian Fault (NAF) is one of the major strike slip fault systems on earth comparable to San Andreas Fault some ways. Devastating earthquakes have occurred along this system causing major damage and casualties. In order to comprehensively investigate the shallow and deep crustal structure beneath the western segment of North Anatolian Fault (NAF), a temporary dense seismic network consisting of 73 broadband sensors was deployed in early May 2012 with support from The Natural Environment Research Council (NERC) and partial support from Bogazci University Research Fund. This joint project involves researchers from University of Leeds, UK and Bogazici University, Kandilli Observatory and Earthquake Research Institute (KOERI). In addition to the 63 sensors provided by SEIS-UK instrument pool and three permanent KOERI sites in the region, another seven stations of KOERI-Department of Geophysics were installed surrounding the rectangular grid with the aim of further enhancing the detection capability of this dense seismic array (map). Six months of seismic data have been collected and initial analysis underway. This research focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), moment tensor inversions and ambient noise correlations. Accurate earthquake locations will eventually lead to high resolution seismic images of NAF including both the northern and the southern branches in the upper crust. In order to put additional constraints on the active tectonics of the western part of NAF, we determined fault plane solutions using Regional Moment Tensor Inversion (RMT) and P wave first motion method. For the analysis of high quality fault plane solutions, data from KOERI and the DANA project were merged. Furthermore, detailed Moho topography will be revealed via receiver function method. Iterative time domain deconvolution was used to obtain receiver functions and H-K stacking was applied to calculate crustal thickness values. The preliminary results indicate that Moho is located at roughly 26 - 28 km depth with Vp/Vs ratios higher than 1.98. We also present the observed Moho depth variations along N-S and E-W profiles beneath the western segment of NAF.
ABSTRACT The Caucasus-Caspian region is part of the Alpine-Himalayan collision belt and is an are... more ABSTRACT The Caucasus-Caspian region is part of the Alpine-Himalayan collision belt and is an area of complex structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region little is known about the lithospheric structure. Using data from 25 new broadband seismic stations in the region, a unified velocity structure is developed using teleseismic receiver functions and surface waves. Several distinct regions are recognized: the Greater Caucasus, the lesser Caucasus and the Caspian/Kura Depression. Depth(h)-Vp/Vs(k) stacks of the receiver functions suggest crustal thicknesses of 45-50 km in the Lesser and Greater Caucasus with relatively high crustal velocities (Vs=3.4 km/s). Variations of the receiver functions with back-azimuth indicate 3D variations in structure in the Greater Caucasus. Crustal thickness in the Kura Depression and at the edge of the Caspian is less well constrained due to pronounced multiples associated with thick sedimentary layers but the preferred results suggest a Moho depth of 38 to 48 km and lower crustal velocities (Vs=3.1 km/s). Love and Rayleigh surface waves dispersion curves have been derived from using both event-based analysis and ambient noise correlation. Short-period surface waves outline the sedimentary structure of the region, while longer periods highlight crustal velocity, crustal thickness, and upper mantle velocity. Joint inversion of the receiver functions with the surface wave dispersion curves to determine absolute shear wave velocity is ongoing.
ABSTRACT The primary objective of this study is to obtain the lithospheric structure of Anatolian... more ABSTRACT The primary objective of this study is to obtain the lithospheric structure of Anatolian-African Subduction zone including the Isparta Angle (IA) from Phase velocity inversion of Rayleigh waves and subsequent Shear wave velocity inversions. The ongoing subduction of the African Plate under Anatolian Plateau results in a highly complex tectonic structure beneath Southwestern Turkey and the surroundings. IA is seismically quite active and formed by the intersection of two very different subduction zones: The Hellenic arc to the west and the Cyprian arc to the east. The geometric difference between Hellenic Arc (relatively steep retreating subduction) and Cyprus Arc (shallower subduction) might be indicating a tear or gap in the subducting African Lithosphere beneath the Anatolian Plate responsible for the active deformation. A temporary seismic network consisting of 10 3-component BB stations were installed in August 2006 with the support from University of Missouri and 9 more stations in March 2007 in addition to the 21 existing permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI) and two from Süleyman Demirel University (SDU). 8 stations from Geofon Network were also included to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitude larger than 5.5. Depending on the signal to noise ratio, azimuthal coverage of events, and coherence from station, 68 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li (2003) to simultaneously solve for the incoming wave field and phase velocity. This relatively simpler representation of a more complex wavefield provided the pattern of amplitude variations effectively in many cases. To begin with, an average phase velocity dispersion curve (35 -140 seconds) was obtained and used as an input for 2-D inversions. Updated 2-D tomographic maps of phase velocities were constructed along with the resolution tests. Phase velocities can only tell us integrated information about the upper mantle. Furthermore, we inverted phase velocities for shear wave velocities in order to obtain direct information at various depths (35- ~300 km) that can be interpreted in terms of temperature anomalies, the presence of melt or dissolved water, etc.,
ABSTRACT The African and Anatolian collision zone belt in southwestern Turkey consists of subduct... more ABSTRACT The African and Anatolian collision zone belt in southwestern Turkey consists of subducting African oceanic crust beneath Anatolian plate. Within the convergent plate margin there are two principle arcs: the Hellenic and Cyprean arcs. The region between the intersection of the Hellenic and Cyprean arcs is named the Isparta Angle(IA). In order to image the crustal variation, we applied joint inversion of receiver functions & surface wave group velocities and h-k stacks to the receiver functions which were obtained from teleseismic events recorded by forty three broad band stations which are combination of nineteen temporary and B.U. KOERI's permanent stations deployed in the region. Receiver functions are sensitive to compressional and shear wave velocity contrast and vertical travel times while surface wave dispersion curves are sensitive to shear wave velocity averages. Combining these different properties allow us to constrain the lithospheric shear wave velocities. H-K staking leads us to calculate Moho variation along the collision zone. We found that average mid crustal shear velocity is 3.49 km/s however the mid crustal velocities directly above IA is ranging between 3.47 km/s and 3.53 km/s. The average upper mantle P velocity is 7.53 km/s which is a little higher comparing to stations above IA which are varying between 7.08 km/s to 7.30 km/s. Both of the upper mantle P velocities are very low which are comparible with the Pn velocity tomography studies in southwestern Turkey. Moho variations beneath southwestern Turkey indicate a crustal thickness anomaly between the IA and the surrounding regions. The southwestern end of the region has a thinner crust (26 - 28 km) compared to southeastern end of region (30 - 34 km). We have observed that west of the IA has a 38 km thick crust but east of the IA has a crustal thickness of 32 km. In addition to this, south of the IA has 43 km Moho depth thereby suggesting the crust thickens towards the plate boundary (i.e. southward). This research is supported by Bogazici University Research Fund under contract number 07T203.
ABSTRACT The ongoing subduction of the African Plate under western Anatolia results in a highly c... more ABSTRACT The ongoing subduction of the African Plate under western Anatolia results in a highly complex tectonic structure especially beneath Isparta Angle (IA) and the surroundings where the Hellenic and Cyprian slabs with different subduction geometries intersect. The primary objective is to accurately image the lithospheric structure at this convergent plate boundary and further understand the reasons responsible for the active deformation. Data was gathered from a temporary seismic network consisting of 10 broadband stations that was installed in August 2006 with the support from University of Missouri and nine more stations deployed in March 2007 with the support from Bogazici Research Fund (project ID:07T203). In addition, 21 permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI) and two from Süleyman Demirel University (SDU) together with five stations from IRIS/Geofon Network were also included to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitudes larger than 5.5. Depending on the signal to noise ratio, azimuthal coverage of events, and coherence from station, 81 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li (2003) to simultaneously solve for the incoming wave field and phase velocity. This relatively simpler representation of a more complex wavefield provided quite stable patterns of amplitude variations in many cases. To begin with, an average phase velocity dispersion curve was obtained and used as an input for tomographic inversions. Two-dimensional tomographic maps of isotropic and azimuthally anisotropic phase velocity variations were generated. Phase velocities can only tell us integrated information about the upper mantle. Furthermore, we inverted phase velocities for shear wave velocities (Saito,1988) in order to obtain direct information at a depth range of 30-300 km that can be interpreted in terms of major tectonic processes such as extension, slab detachment/tearing, STEP faults, volcanism, temperature anomalies, the presence of melt or dissolved water, etc. Resulting tomograms along horizontal and vertical depth sections provided valuable insights on the crustal and upper mantle structure beneath Southwestern Turkey down to almost 300 km.
ABSTRACT Anatolian Plateau-Caucasus-Caspian region is an area of complex structure accompanied by... more ABSTRACT Anatolian Plateau-Caucasus-Caspian region is an area of complex structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region little is known about the detailed lithospheric structure. Using data from 29 new broadband seismic stations in the region, a unified velocity structure is developed using teleseismic receiver functions and surface waves. Love and Rayleigh surface waves dispersion curves have been derived from event-based analysis and ambient-noise correlation. We jointly inverted the receiver functions with the surface wave dispersion curves to determine absolute shear wave velocity and important discontinuities such as sedimentary layer, Moho, lithospheric-asthenospheric boundary. We combined these new station results with Eastern Turkey Seismic Experiment results (29 stations). Caspian Sea and Kura basin underlained by one of the thickest sediments in the world. Therefore, short-period surface waves are observed to be very slow. The strong crustal multiples in receiver functions and the slow velocities in upper crust indicate the presence of thick sedimentary unit (up to 20 km). Crustal thickness varies from 34 to 52 km in the region. The thickest crust is in Lesser Caucasus and the thinnest is in the Arabian Plate. The lithospheric mantle in the Greater Caucasus and the Kura depression is faster than the Anatolian Plateau and Lesser Caucasus. This possibly indicates the presence of cold lithosphere. The lower crust is slowest in the northeastern part of the Anatolian Plateau where Holocene volcanoes are located.
The Isparta Angle (southwestern Turkey) lies at the intersection of Hellenic and Cyprus arcs rela... more The Isparta Angle (southwestern Turkey) lies at the intersection of Hellenic and Cyprus arcs related to the collision of the African and Anatolian plates and possesses a complex structure. To further understand this complexity, we deployed a temporary network consisting of nineteen broad band instruments in addition to permanent seismic stations in the region. Crustal velocity and Moho depth variations were estimated along two profiles (N-S, and E-W) formed by the fourteen temporary and permanent stations. Crustal and lithopheric velocities and Moho depths were estimated in two ways: h-k stacks and the joint inversion of receiver functions and surface wave group velocities. Receiver functions are sensitive to shear wave velocity contrast and vertical travel times while surface wave dispersion curves are sensitive to shear wave velocity averages. Combining these different properties of shear waves ensures a more robust result. We found that upper crustal shear velocities are higher b...
Pure and Applied Geophysics, 2012
We estimate Lg wave attenuation using local and regional seismic phases in the Isparta Angle and ... more We estimate Lg wave attenuation using local and regional seismic phases in the Isparta Angle and the Anatolian Plateau (Turkey). The Isparta Angle (IA) is a tectonically active zone forming the boundary between the African Plate and the Anatolian Plateau, and is currently undergoing N–S extensional deformation. The Anatolian Plateau contains many intra-continental faults including the North Anatolian Fault Zone and the East Anatolian Fault Zone as well as the Menderes Massif. A large waveform data set was compiled from a variety of local and regional seismic networks including 121 digital seismic stations (broad-band and short period) between 1999 and 2008 spanning the IA, the Anatolian Plateau and Azerbaijan. The data set was used to determine the nature of Lg wave propagation and characterize the nature of seismic attenuation within the crust of these regions. Lg waveforms were used to calculate the frequency-dependent Lg-Qo and Lg-eta\etaeta. A wide range of Lg-Qo values was obtained between ~52 ± 6 and 524 ± 227. Low Lg-Qo values (~90–155) are calculated towards the north of IA, Iskenderun Gulf and its vicinity, Bingöl-Karlıova, Izmit and its vicinity. Lg-Qo values are especially low (<90) along the Menderes Massif and the Aksehir-Simav Fault Zones. This may be due to intrinsic attenuation of Lg associated with the partially molten crust and young volcanism. The high Lg-Qo values (~350) are probably caused by the crust not being subject to large amounts of extensional deformation like the Antalya Gulf and apparently being thick enough to support Lg propagation. Relatively higher values along the border of this subduction zone and plate boundary might be related to the Taurus Mountain belts and Bitlis-Zagros Suture Zone. The lateral frequency dependency Lg-eta\etaeta is also consistent with high tectonic activity in this region.