C. Berk Biryol | University of North Carolina at Chapel Hill (original) (raw)
Papers by C. Berk Biryol
Geosphere
The central Anatolian plateau in Turkey is a region with a long history of subduction, continenta... more The central Anatolian plateau in Turkey is a region with a long history of subduction, continental collision, accretion of continental fragments, and slab tearing and/or breakoff and tectonic escape. Central Anatolia is currently characterized as a nascent plateau with widespread Neogene volcanism and predominantly transtensional deformation. To elucidate the present-day crustal and upper mantle structure of this region, teleseismic receiver functions were calculated from 500 seismic events recorded on 92 temporary and permanent broadband seismic stations. Overall, we see a good correlation between crustal thickness and elevation throughout central Anatolia, indicating that the crust may be well compensated throughout the region. We observe the thickest crust beneath the Taurus Mountains (>40 km); it thins rapidly to the south in the Adana Basin and Arabian plate and to the northwest across the Inner Tauride suture beneath the Tuz Gölü Basin and Kırşehir block. Within the Central Anatolian Volcanic Province, we observe several low seismic velocity layers ranging from 15 to 25 km depth that spatially correlate with the Neogene volcanism in the region, and may represent crustal magma reservoirs. Beneath the central Taurus Mountains, we observe a positive amplitude, subhorizontal receiver function arrival below the Anatolian continental Moho at ~50-80 km that we interpret as the gently dipping Moho of the subducting African lithosphere abruptly ending near the northernmost extent of the central Taurus Mountains. We suggest that the uplift of the central Taurus Mountains (~2 km since 8 Ma), which are capped by flat-lying carbonates of late Miocene marine units, can be explained by an isostatic uplift during the late Miocene-Pliocene followed by slab breakoff and subsequent rebound coeval with the onset of faster uplift rates during the late Pliocene-early Pleistocene. The Moho signature of the subducting African lithosphere terminates near the southernmost extent of the Central Anatolian Volcanic Province, where geochemical signatures in the Quaternary volcanics indicate that asthenospheric material is rising to shallow mantle depths.
Geosphere
Using finite-frequency teleseismic P-wave tomography, we developed a new three-dimensional (3-D) ... more Using finite-frequency teleseismic P-wave tomography, we developed a new three-dimensional (3-D) velocity model of the mantle beneath Anatolia down to 900 km depth that reveals the structure and behavior of the subducting African lithosphere beneath three convergent domains of Anatolia: the Aegean, Cyprean, and Bitlis-Zagros domains. The Aegean slab has a relatively simple structure and extends into the lower mantle; the Cyprean slab has a more complex structure, with a western section that extends to the lower mantle with a consistent dip and an eastern section that is broken up into several pieces; and the Bitlis slab appears severely deformed, with only fragments visible in the mantle transition zone and uppermost lower mantle. In addition to the subducting slabs, high-amplitude slow velocity anomalies are imaged in the shallow mantle beneath recently active volcanic centers, and a prominent fast velocity anomaly dominates the shallow mantle beneath northern Anatolia and the southern Black Sea. As a whole, our model confirms the presence of well-established slow and fast velocity anomalies in the upper mantle beneath Anatolia and motivates two major findings about Eastern Mediterranean subduction: (1) Each of the slabs penetrates into the lower mantle, making the Eastern Mediterranean unique within the Mediterranean system, and (2) the distinct character of each slab segment represents different stages of subduction termination through progressive slab deformation. Our findings on the destructive processes of subduction termination and slab detachment have significant implications for understanding of the post detachment behavior of subducted lithosphere.
Geochemistry, Geophysics, Geosystems, 2016
Geochemistry, Geophysics, Geosystems, 2016
The Central Andean Plateau, the second-highest plateau on Earth, overlies the subduction of the N... more The Central Andean Plateau, the second-highest plateau on Earth, overlies the subduction of the Nazca Plate beneath the central portion of South America. The origin of the high topography remains poorly understood, and this puzzle is intimately tied to unanswered questions about processes in the upper mantle, including possible removal of the overriding plate lithosphere and interaction with the flow field that results from the driving forces associated with subduction. Observations of seismic anisotropy can provide important constraints on mantle flow geometry in subduction systems. The interpretation of seismic anisotropy measurements in subduction settings can be challenging, however, because different parts of the subduction system may contribute, including the overriding plate, the mantle wedge above the slab, the slab itself, and the deep upper mantle beneath the slab. Here we present measurements of shear wave splitting for core phases (SKS, SKKS, PKS, and sSKS), local S, and source-side teleseismic S phases that sample the upper mantle beneath southern Peru and northern Bolivia, relying mostly on data from the CAUGHT experiment. We find evidence for seismic anisotropy within most portions of the subduction system, although the overriding plate itself likely makes only a small contribution to the observed delay times. Average fast orientations generally trend roughly trench-parallel to trench-oblique, contradicting predictions from the simplest two-dimensional flow models and olivine fabric scenarios. Our measurements suggest complex, layered anisotropy beneath the northern portion of the Central Andean Plateau, with significant departures from a two-dimensional mantle flow regime.
Journal of Geophysical Research: Solid Earth, 2016
The lithospheric structure of the Southeastern United States is a product of earlier episodes of ... more The lithospheric structure of the Southeastern United States is a product of earlier episodes of continental collision and breakup. The region is located in the interior of the North American Plate, away from active plate margins. However, there is ongoing tectonism in the region with multiple zones of seismicity, uplifting arches, and Cenozoic intraplate volcanism. The mechanisms controlling this activity and the state of stress remain enigmatic. Two important factors are plate strength and preexisting, inherited structures. Here we present new tomographic images of the upper mantle beneath the Southeastern United States, revealing large-scale structural variations in the upper mantle. Examples include the relatively thick lithospheric mantle of stable North America that abruptly thins beneath the Paleozoic Appalachian orogeny, and the slow upper mantle of the Proterozoic Reelfoot rift. Our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering. This provides a viable explanation for seismicity, uplifting, and young intraplate volcanism. We postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin. Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere. Ongoing lithospheric foundering beneath the eastern margin of stable North America explains significant variations in thickness of lithospheric mantle across the former Grenville deformation front.
Geophysical Journal International, 2015
The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamate... more The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamated during the closure of the Paleotethys Ocean and Neotethys Ocean along a subduction margin. Using ambient noise tomography, we investigate the crustal and uppermost mantle shear wave velocity structure of the Anatolian Plate. A total of 215 broad-band seismic stations were used spanning 7 yr of recording to compute 13 778 cross-correlations and obtain Rayleigh wave dispersion measurements for periods between 8 and 40 s. We then perform a shear wave inversion to calculate the seismic velocity structure of the crust and uppermost mantle. Our results show that the overall crustal shear wave velocities of the Anatolian crust are low (∼3.4 km s −1), indicative of a felsic overall composition. We find that prominent lateral seismic velocity gradients correlate with Tethyan suture zones, supporting the idea that the neotectonic structures of Turkey are exploiting the lithospheric weaknesses associated with the amalgamation of Anatolia. Anomalously slow shear wave velocities (∼3.15 km s −1 at 25 km) are located in the western limb of the Isparta Angle in southwestern Turkey. In the upper crust, we find that these low shear wave velocities correlate well with the projected location of a carbonate platform unit (Bey Daglari) beneath the Lycian Nappe complex. In the lower crust and upper mantle of this region, we propose that the anomalously slow velocities are due to the introduction of aqueous fluids related to the underplating of accretionary material from the underthrusting of a buoyant, attenuated continental fragment similar to the Eratosthenes seamount. We suggest that this fragment controlled the location of the formation of the Subduction-Transform Edge Propagator fault in the eastern Aegean Sea during rapid slab rollback of the Aegean Arc in early Miocene times. Lastly, we observe that the uppermost mantle beneath continental Anatolia is generally slow (∼4.2 km s −1), indicating higher than usual temperatures consistent with the influx of asthenosphere to shallow depths as a result of the segmentation and break-up of the subducting African lithosphere.
Study area, the Eskipazar Basin, is located in the western part of the North Anatolian Fault Syst... more Study area, the Eskipazar Basin, is located in the western part of the North Anatolian Fault System. It is a 3-5 km wide, 10 km long and NWSE trending depression, bounded by a complex array of oblique-slip normal faults and strike-slip faults. The Eskipazar Basin is interpreted to be a superimposed basin. The basin fill is composed of two different units deposited under the control of different tectonic regimes, namely the paleotectonic and the neotectonic regimes. The latest paleotectonic fill of the basin is the fluvio-lacustrine deposits of the paleotectonic Eskipazar formation. This formation is unconformably overlain by a group of neotectonic units namely, the Budaklar, the Karkýn and the Ýmanlar formations. The unconformity in between these paleotectonic and neotectonic units represents the time interval during which the paleotectonic period comes to end and the neotectonic period started. Thus, onset age of the strike-slip neotectonic regime in the study area is Late Pliocene...
A large earthquake (Mw 8.1) followed by a tsunami took place in the southeast Pacific along the N... more A large earthquake (Mw 8.1) followed by a tsunami took place in the southeast Pacific along the New Britain subduction zone on April 1, 2007. This region displays a complex tectonic nature where 4 plates intersect. Along the Solomon Island convergent margin the relatively small Woodlark and Solomon plates enter into the subduction zone side-by-side with the much larger Australia plate and the boundaries of these three plates are defined by transform faults. On a regional scale this subduction zone plate boundary is characterized by the occurrence of large earthquake doublets in 1971, 1974, 1975, 1977 and 2000. We investigated the source process of the April 1, 2007 earthquake using three different faulting patterns; (1) fixed thrust mechanism over the entire extend of the fault, (2) varying slip directions over the area of rupture and (3) varying focal mechanisms along the faulted region. The teleseismic body wave inversion technique that we used in our analysis of the source parame...
A variety of complex tectonic processes are active in Anatolia. Collision related plateau formati... more A variety of complex tectonic processes are active in Anatolia. Collision related plateau formation dominates the present lithospheric deformation toward the east and slab roll-back related back-arc extension takes place toward the west. The two zones are connected at the northern part of the region by strike-slip faulting along the right-lateral North Anatolian Fault. Recent seismological studies show that the Eastern Anatolian Plateau (EAP) is supported by hot asthenosphereric material that was emplaced beneath the plateau following the detachment of subducted Arabian lithosphere. The westward continuation of the deeper structure of Anatolia is less well constrained due to the lack of geophysical observations. In order to study how the deeper lithosphere and mantle structure evolves spatially from east to west, we used teleseismic P-wave tomography and data from several temporary and permanent seismic networks deployed in the region. A major part of the data comes from the North A...
The depth extent of continental strike-slip faults and associated lower crustal deformation are s... more The depth extent of continental strike-slip faults and associated lower crustal deformation are still much debated. Scientific literature is recently centered on two competing models. In the first model the transition from brittle to ductile deformation occurs within the crust where strike-slip faults become a broad shear zones in the lower crust. This model predicts lack of Moho offset, spatial variation of displacement and resultant seismic anisotropy in the lower crust. In the second model, lower crust and mantle lithosphere are rigid and strike-slip faults cut the entire crust as narrow shear zones. This deformation style may create Moho offset across faults that juxtapose two crustal blocks with different thicknesses. Determining which of these two models most accurately describes the lithospheric deformation has important tectonic implications. In this respect, teleseismic receiver functions (RFs) are very powerful on determining Moho structure, possible Moho offsets and crust...
The complex and sinusoidal pattern of subduction zones of the Mediterranenan region plays an impo... more The complex and sinusoidal pattern of subduction zones of the Mediterranenan region plays an important role in controlling the current tectonic framework of the Alpine-Himalayan orogenic belt. The Anatolian region is part of this belt and it displays the complex characteristics of the interplay between continent collision in the east and subduction-rollback related backarc extension in the west. The ongoing northward subduction of the African Plate beneath the Anatolian Plate contributes significantly to the emergence of the current tectonic setting of this region. Despite its crucial effect on the tectonics of Anatolia, there are only a few studies that focus on the deeper extent of this zone. In this study we provide higher resolution tomographic images of the subducting African lithosphere beneath Anatolia. Our approach is based on analysis of teleseismic body-wave travel-time data using a finite-frequency seismic tomography algorithm. The data for our analysis comes from multipl...
In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has res... more In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32°-44°E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismic stations in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at perio...
The North Anatolian Fault (NAF) is one of the world's largest active continental strike-slip ... more The North Anatolian Fault (NAF) is one of the world's largest active continental strike-slip faults, and forms the northern margin of the Anatolian plate. Although its geologic and geomorphologic features are well defined, crustal deformation and associated seismicity around central segment of the NAF is relatively less-known. In this study, we analyzed locations and focal mechanisms of over hundred events with magnitude >= 3, which are recorded by 39 broadband seismic stations deployed by the North Anatolian Passive Seismic Experiment (2005-2008). The distribution of the events shows that the local seismicity in the area is widely distributed, suggesting a widespread continental deformation in the southern block. For the entire data set, P- and S- arrival times are picked and events are relocated using the HYPOCENTER program. Then, relocated events which have a good azimuthal coverage with a maximum gap of 120 and at least 13 P- wave readings are selected and 1-D inversion a...
Journal of Geophysical Research: Solid Earth, 2013
ABSTRACT
Geophysical Journal International, 2013
In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has res... more In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian Plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32 • to 44 • E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Passive Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismographs in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at periods ranging from 8 to 40 s. At all periods, the phase velocity maps are similar for winter and summer subsets of the data, indicating that seasonal variations in noise sources do not bias our results. Across the study area, we invert the phase velocity estimates for shear velocity as a function of depth. The shear velocity model, which extends to 50 km depth, highlights tectonic features apparent at the surface: the Eastern Anatolian Plateau is a prominent low-velocity anomaly whereas the Kırşehir Massif has relatively fast velocities. There is a large velocity jump across the Inner Tauride Suture/Central Anataolian Fault Zone throughout the crust whereas the North Anatolian Fault does not have a consistent signature. In addition, in the southeastern part of our study area, we image a high velocity region below 20 km depth which may be the northern tip of the underthrusting Arabian Plate.
Geophysical Journal International, 2012
P-wave velocity structure and V p /V s variations in the crust along the North Anatolian Fault Zo... more P-wave velocity structure and V p /V s variations in the crust along the North Anatolian Fault Zone (NAFZ) in north-central Anatolia were investigated by the inversion of local Pand S-wave traveltimes, to gain a better understanding of the seismological characteristics of the region. The 3-D local earthquake tomography inversions included 5444 P-and 3200 S-wave readings obtained from 168 well-located earthquakes between 2006 January and 2008 May. Dense ray coverage yields good resolution, particularly in the central part of the study area. The 3-D V p and V p /V s tomographic images reveal clear correlations with both the surface geology and significant tectonic units in the region. We observed the lower limit of the seismogenic zone for north-central Anatolia at 15 km depth. Final earthquake locations display a distributed pattern throughout the study area, with most of the earthquakes occurring on the major splays of the NAFZ, rather than its master strand. We identify three major high-velocity blocks in the mid-crust separated by theİzmir-Ankara-Erzincan Suture and interpret these blocks to be continental basement fragments that were accreted onto the margin following the closure of Neo-Tethyan Ocean. These basement blocks may have in part influenced the rupture propagations of the historical 1939, 1942 and 1943 earthquakes. In addition, large variations in the V p /V s ratio in the mid-crust were observed and have been correlated with the varying fluid contents of the existing lithologies and related tectonic structures.
Geophysical Journal International, 2010
The North Anatolian Fault Zone (NAFZ) is a transform structure that constitutes the boundary betw... more The North Anatolian Fault Zone (NAFZ) is a transform structure that constitutes the boundary between the Anatolian Plate to the south and the Eurasia Plate to the north. We analysed the properties of the upper-mantle strain field and mantle anisotropy in the vicinity of NAFZ via splitting of SKS and SKKS phases. We used data from the North Anatolian Fault (NAF) passive seismic experiment. This is the first study that analyses the upper-mantle anisotropy in this region and our results indicate that the observed upper-mantle strain field is uniform underneath the array with consistent NE-SW polarization directions for fast split waves. The measured lag times between the arrivals of the fast and slow split waves varies from 0.5 to 1.6 s for the study area. Smaller lag times are obtained consistently in the eastern part of the array. However, we do not observe any significant variation in either the polarization directions or the delay times across the plate boundary (NAFZ). The uniformity of the fast polarization directions throughout the study area and the strength of anisotropy favour an asthenospheric source for the anisotropy. The regional tectonic framework favours a SW direction of asthenospheric flow due to the forces acting on the upper-mantle exerted by the slab-roll-back taking place along the Aegean and the Cyprean Subduction Zones.
Geosphere
The central Anatolian plateau in Turkey is a region with a long history of subduction, continenta... more The central Anatolian plateau in Turkey is a region with a long history of subduction, continental collision, accretion of continental fragments, and slab tearing and/or breakoff and tectonic escape. Central Anatolia is currently characterized as a nascent plateau with widespread Neogene volcanism and predominantly transtensional deformation. To elucidate the present-day crustal and upper mantle structure of this region, teleseismic receiver functions were calculated from 500 seismic events recorded on 92 temporary and permanent broadband seismic stations. Overall, we see a good correlation between crustal thickness and elevation throughout central Anatolia, indicating that the crust may be well compensated throughout the region. We observe the thickest crust beneath the Taurus Mountains (>40 km); it thins rapidly to the south in the Adana Basin and Arabian plate and to the northwest across the Inner Tauride suture beneath the Tuz Gölü Basin and Kırşehir block. Within the Central Anatolian Volcanic Province, we observe several low seismic velocity layers ranging from 15 to 25 km depth that spatially correlate with the Neogene volcanism in the region, and may represent crustal magma reservoirs. Beneath the central Taurus Mountains, we observe a positive amplitude, subhorizontal receiver function arrival below the Anatolian continental Moho at ~50-80 km that we interpret as the gently dipping Moho of the subducting African lithosphere abruptly ending near the northernmost extent of the central Taurus Mountains. We suggest that the uplift of the central Taurus Mountains (~2 km since 8 Ma), which are capped by flat-lying carbonates of late Miocene marine units, can be explained by an isostatic uplift during the late Miocene-Pliocene followed by slab breakoff and subsequent rebound coeval with the onset of faster uplift rates during the late Pliocene-early Pleistocene. The Moho signature of the subducting African lithosphere terminates near the southernmost extent of the Central Anatolian Volcanic Province, where geochemical signatures in the Quaternary volcanics indicate that asthenospheric material is rising to shallow mantle depths.
Geosphere
Using finite-frequency teleseismic P-wave tomography, we developed a new three-dimensional (3-D) ... more Using finite-frequency teleseismic P-wave tomography, we developed a new three-dimensional (3-D) velocity model of the mantle beneath Anatolia down to 900 km depth that reveals the structure and behavior of the subducting African lithosphere beneath three convergent domains of Anatolia: the Aegean, Cyprean, and Bitlis-Zagros domains. The Aegean slab has a relatively simple structure and extends into the lower mantle; the Cyprean slab has a more complex structure, with a western section that extends to the lower mantle with a consistent dip and an eastern section that is broken up into several pieces; and the Bitlis slab appears severely deformed, with only fragments visible in the mantle transition zone and uppermost lower mantle. In addition to the subducting slabs, high-amplitude slow velocity anomalies are imaged in the shallow mantle beneath recently active volcanic centers, and a prominent fast velocity anomaly dominates the shallow mantle beneath northern Anatolia and the southern Black Sea. As a whole, our model confirms the presence of well-established slow and fast velocity anomalies in the upper mantle beneath Anatolia and motivates two major findings about Eastern Mediterranean subduction: (1) Each of the slabs penetrates into the lower mantle, making the Eastern Mediterranean unique within the Mediterranean system, and (2) the distinct character of each slab segment represents different stages of subduction termination through progressive slab deformation. Our findings on the destructive processes of subduction termination and slab detachment have significant implications for understanding of the post detachment behavior of subducted lithosphere.
Geochemistry, Geophysics, Geosystems, 2016
Geochemistry, Geophysics, Geosystems, 2016
The Central Andean Plateau, the second-highest plateau on Earth, overlies the subduction of the N... more The Central Andean Plateau, the second-highest plateau on Earth, overlies the subduction of the Nazca Plate beneath the central portion of South America. The origin of the high topography remains poorly understood, and this puzzle is intimately tied to unanswered questions about processes in the upper mantle, including possible removal of the overriding plate lithosphere and interaction with the flow field that results from the driving forces associated with subduction. Observations of seismic anisotropy can provide important constraints on mantle flow geometry in subduction systems. The interpretation of seismic anisotropy measurements in subduction settings can be challenging, however, because different parts of the subduction system may contribute, including the overriding plate, the mantle wedge above the slab, the slab itself, and the deep upper mantle beneath the slab. Here we present measurements of shear wave splitting for core phases (SKS, SKKS, PKS, and sSKS), local S, and source-side teleseismic S phases that sample the upper mantle beneath southern Peru and northern Bolivia, relying mostly on data from the CAUGHT experiment. We find evidence for seismic anisotropy within most portions of the subduction system, although the overriding plate itself likely makes only a small contribution to the observed delay times. Average fast orientations generally trend roughly trench-parallel to trench-oblique, contradicting predictions from the simplest two-dimensional flow models and olivine fabric scenarios. Our measurements suggest complex, layered anisotropy beneath the northern portion of the Central Andean Plateau, with significant departures from a two-dimensional mantle flow regime.
Journal of Geophysical Research: Solid Earth, 2016
The lithospheric structure of the Southeastern United States is a product of earlier episodes of ... more The lithospheric structure of the Southeastern United States is a product of earlier episodes of continental collision and breakup. The region is located in the interior of the North American Plate, away from active plate margins. However, there is ongoing tectonism in the region with multiple zones of seismicity, uplifting arches, and Cenozoic intraplate volcanism. The mechanisms controlling this activity and the state of stress remain enigmatic. Two important factors are plate strength and preexisting, inherited structures. Here we present new tomographic images of the upper mantle beneath the Southeastern United States, revealing large-scale structural variations in the upper mantle. Examples include the relatively thick lithospheric mantle of stable North America that abruptly thins beneath the Paleozoic Appalachian orogeny, and the slow upper mantle of the Proterozoic Reelfoot rift. Our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering. This provides a viable explanation for seismicity, uplifting, and young intraplate volcanism. We postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin. Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere. Ongoing lithospheric foundering beneath the eastern margin of stable North America explains significant variations in thickness of lithospheric mantle across the former Grenville deformation front.
Geophysical Journal International, 2015
The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamate... more The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamated during the closure of the Paleotethys Ocean and Neotethys Ocean along a subduction margin. Using ambient noise tomography, we investigate the crustal and uppermost mantle shear wave velocity structure of the Anatolian Plate. A total of 215 broad-band seismic stations were used spanning 7 yr of recording to compute 13 778 cross-correlations and obtain Rayleigh wave dispersion measurements for periods between 8 and 40 s. We then perform a shear wave inversion to calculate the seismic velocity structure of the crust and uppermost mantle. Our results show that the overall crustal shear wave velocities of the Anatolian crust are low (∼3.4 km s −1), indicative of a felsic overall composition. We find that prominent lateral seismic velocity gradients correlate with Tethyan suture zones, supporting the idea that the neotectonic structures of Turkey are exploiting the lithospheric weaknesses associated with the amalgamation of Anatolia. Anomalously slow shear wave velocities (∼3.15 km s −1 at 25 km) are located in the western limb of the Isparta Angle in southwestern Turkey. In the upper crust, we find that these low shear wave velocities correlate well with the projected location of a carbonate platform unit (Bey Daglari) beneath the Lycian Nappe complex. In the lower crust and upper mantle of this region, we propose that the anomalously slow velocities are due to the introduction of aqueous fluids related to the underplating of accretionary material from the underthrusting of a buoyant, attenuated continental fragment similar to the Eratosthenes seamount. We suggest that this fragment controlled the location of the formation of the Subduction-Transform Edge Propagator fault in the eastern Aegean Sea during rapid slab rollback of the Aegean Arc in early Miocene times. Lastly, we observe that the uppermost mantle beneath continental Anatolia is generally slow (∼4.2 km s −1), indicating higher than usual temperatures consistent with the influx of asthenosphere to shallow depths as a result of the segmentation and break-up of the subducting African lithosphere.
Study area, the Eskipazar Basin, is located in the western part of the North Anatolian Fault Syst... more Study area, the Eskipazar Basin, is located in the western part of the North Anatolian Fault System. It is a 3-5 km wide, 10 km long and NWSE trending depression, bounded by a complex array of oblique-slip normal faults and strike-slip faults. The Eskipazar Basin is interpreted to be a superimposed basin. The basin fill is composed of two different units deposited under the control of different tectonic regimes, namely the paleotectonic and the neotectonic regimes. The latest paleotectonic fill of the basin is the fluvio-lacustrine deposits of the paleotectonic Eskipazar formation. This formation is unconformably overlain by a group of neotectonic units namely, the Budaklar, the Karkýn and the Ýmanlar formations. The unconformity in between these paleotectonic and neotectonic units represents the time interval during which the paleotectonic period comes to end and the neotectonic period started. Thus, onset age of the strike-slip neotectonic regime in the study area is Late Pliocene...
A large earthquake (Mw 8.1) followed by a tsunami took place in the southeast Pacific along the N... more A large earthquake (Mw 8.1) followed by a tsunami took place in the southeast Pacific along the New Britain subduction zone on April 1, 2007. This region displays a complex tectonic nature where 4 plates intersect. Along the Solomon Island convergent margin the relatively small Woodlark and Solomon plates enter into the subduction zone side-by-side with the much larger Australia plate and the boundaries of these three plates are defined by transform faults. On a regional scale this subduction zone plate boundary is characterized by the occurrence of large earthquake doublets in 1971, 1974, 1975, 1977 and 2000. We investigated the source process of the April 1, 2007 earthquake using three different faulting patterns; (1) fixed thrust mechanism over the entire extend of the fault, (2) varying slip directions over the area of rupture and (3) varying focal mechanisms along the faulted region. The teleseismic body wave inversion technique that we used in our analysis of the source parame...
A variety of complex tectonic processes are active in Anatolia. Collision related plateau formati... more A variety of complex tectonic processes are active in Anatolia. Collision related plateau formation dominates the present lithospheric deformation toward the east and slab roll-back related back-arc extension takes place toward the west. The two zones are connected at the northern part of the region by strike-slip faulting along the right-lateral North Anatolian Fault. Recent seismological studies show that the Eastern Anatolian Plateau (EAP) is supported by hot asthenosphereric material that was emplaced beneath the plateau following the detachment of subducted Arabian lithosphere. The westward continuation of the deeper structure of Anatolia is less well constrained due to the lack of geophysical observations. In order to study how the deeper lithosphere and mantle structure evolves spatially from east to west, we used teleseismic P-wave tomography and data from several temporary and permanent seismic networks deployed in the region. A major part of the data comes from the North A...
The depth extent of continental strike-slip faults and associated lower crustal deformation are s... more The depth extent of continental strike-slip faults and associated lower crustal deformation are still much debated. Scientific literature is recently centered on two competing models. In the first model the transition from brittle to ductile deformation occurs within the crust where strike-slip faults become a broad shear zones in the lower crust. This model predicts lack of Moho offset, spatial variation of displacement and resultant seismic anisotropy in the lower crust. In the second model, lower crust and mantle lithosphere are rigid and strike-slip faults cut the entire crust as narrow shear zones. This deformation style may create Moho offset across faults that juxtapose two crustal blocks with different thicknesses. Determining which of these two models most accurately describes the lithospheric deformation has important tectonic implications. In this respect, teleseismic receiver functions (RFs) are very powerful on determining Moho structure, possible Moho offsets and crust...
The complex and sinusoidal pattern of subduction zones of the Mediterranenan region plays an impo... more The complex and sinusoidal pattern of subduction zones of the Mediterranenan region plays an important role in controlling the current tectonic framework of the Alpine-Himalayan orogenic belt. The Anatolian region is part of this belt and it displays the complex characteristics of the interplay between continent collision in the east and subduction-rollback related backarc extension in the west. The ongoing northward subduction of the African Plate beneath the Anatolian Plate contributes significantly to the emergence of the current tectonic setting of this region. Despite its crucial effect on the tectonics of Anatolia, there are only a few studies that focus on the deeper extent of this zone. In this study we provide higher resolution tomographic images of the subducting African lithosphere beneath Anatolia. Our approach is based on analysis of teleseismic body-wave travel-time data using a finite-frequency seismic tomography algorithm. The data for our analysis comes from multipl...
In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has res... more In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32°-44°E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismic stations in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at perio...
The North Anatolian Fault (NAF) is one of the world's largest active continental strike-slip ... more The North Anatolian Fault (NAF) is one of the world's largest active continental strike-slip faults, and forms the northern margin of the Anatolian plate. Although its geologic and geomorphologic features are well defined, crustal deformation and associated seismicity around central segment of the NAF is relatively less-known. In this study, we analyzed locations and focal mechanisms of over hundred events with magnitude >= 3, which are recorded by 39 broadband seismic stations deployed by the North Anatolian Passive Seismic Experiment (2005-2008). The distribution of the events shows that the local seismicity in the area is widely distributed, suggesting a widespread continental deformation in the southern block. For the entire data set, P- and S- arrival times are picked and events are relocated using the HYPOCENTER program. Then, relocated events which have a good azimuthal coverage with a maximum gap of 120 and at least 13 P- wave readings are selected and 1-D inversion a...
Journal of Geophysical Research: Solid Earth, 2013
ABSTRACT
Geophysical Journal International, 2013
In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has res... more In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian Plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32 • to 44 • E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Passive Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismographs in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at periods ranging from 8 to 40 s. At all periods, the phase velocity maps are similar for winter and summer subsets of the data, indicating that seasonal variations in noise sources do not bias our results. Across the study area, we invert the phase velocity estimates for shear velocity as a function of depth. The shear velocity model, which extends to 50 km depth, highlights tectonic features apparent at the surface: the Eastern Anatolian Plateau is a prominent low-velocity anomaly whereas the Kırşehir Massif has relatively fast velocities. There is a large velocity jump across the Inner Tauride Suture/Central Anataolian Fault Zone throughout the crust whereas the North Anatolian Fault does not have a consistent signature. In addition, in the southeastern part of our study area, we image a high velocity region below 20 km depth which may be the northern tip of the underthrusting Arabian Plate.
Geophysical Journal International, 2012
P-wave velocity structure and V p /V s variations in the crust along the North Anatolian Fault Zo... more P-wave velocity structure and V p /V s variations in the crust along the North Anatolian Fault Zone (NAFZ) in north-central Anatolia were investigated by the inversion of local Pand S-wave traveltimes, to gain a better understanding of the seismological characteristics of the region. The 3-D local earthquake tomography inversions included 5444 P-and 3200 S-wave readings obtained from 168 well-located earthquakes between 2006 January and 2008 May. Dense ray coverage yields good resolution, particularly in the central part of the study area. The 3-D V p and V p /V s tomographic images reveal clear correlations with both the surface geology and significant tectonic units in the region. We observed the lower limit of the seismogenic zone for north-central Anatolia at 15 km depth. Final earthquake locations display a distributed pattern throughout the study area, with most of the earthquakes occurring on the major splays of the NAFZ, rather than its master strand. We identify three major high-velocity blocks in the mid-crust separated by theİzmir-Ankara-Erzincan Suture and interpret these blocks to be continental basement fragments that were accreted onto the margin following the closure of Neo-Tethyan Ocean. These basement blocks may have in part influenced the rupture propagations of the historical 1939, 1942 and 1943 earthquakes. In addition, large variations in the V p /V s ratio in the mid-crust were observed and have been correlated with the varying fluid contents of the existing lithologies and related tectonic structures.
Geophysical Journal International, 2010
The North Anatolian Fault Zone (NAFZ) is a transform structure that constitutes the boundary betw... more The North Anatolian Fault Zone (NAFZ) is a transform structure that constitutes the boundary between the Anatolian Plate to the south and the Eurasia Plate to the north. We analysed the properties of the upper-mantle strain field and mantle anisotropy in the vicinity of NAFZ via splitting of SKS and SKKS phases. We used data from the North Anatolian Fault (NAF) passive seismic experiment. This is the first study that analyses the upper-mantle anisotropy in this region and our results indicate that the observed upper-mantle strain field is uniform underneath the array with consistent NE-SW polarization directions for fast split waves. The measured lag times between the arrivals of the fast and slow split waves varies from 0.5 to 1.6 s for the study area. Smaller lag times are obtained consistently in the eastern part of the array. However, we do not observe any significant variation in either the polarization directions or the delay times across the plate boundary (NAFZ). The uniformity of the fast polarization directions throughout the study area and the strength of anisotropy favour an asthenospheric source for the anisotropy. The regional tectonic framework favours a SW direction of asthenospheric flow due to the forces acting on the upper-mantle exerted by the slab-roll-back taking place along the Aegean and the Cyprean Subduction Zones.