SUMMARY
Information on fault zone structure is essential for our understanding of earthquake mechanics, continental deformation and seismic hazard. We use the scattered seismic wavefield to study the ...subsurface structure of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 İzmit and Düzce ruptures using data from an 18-month dense deployment of seismometers with a nominal station spacing of 7 km. Using the forward- and back-scattered energy that follows the direct P-wave arrival from teleseismic earthquakes, we apply a scattered wave inversion approach and are able to resolve changes in lithospheric structure on a scale of 10 km or less in an area of about 130 km by 100 km across the NAFZ. We find several crustal interfaces that are laterally incoherent beneath the surface strands of the NAFZ and evidence for contrasting crustal structures either side of the NAFZ, consistent with the presence of juxtaposed crustal blocks and ancient suture zones. Although the two strands of the NAFZ in the study region strike roughly east–west, we detect strong variations in structure both north–south, across boundaries of the major blocks, and east–west, parallel to the strike of the NAFZ. The surface expression of the two strands of the NAFZ is coincident with changes on main interfaces and interface terminations throughout the crust and into the upper mantle in the tomographic sections. We show that a dense passive network of seismometers is able to capture information from the scattered seismic wavefield and, using a tomographic approach, to resolve the fine scale structure of crust and lithospheric mantle even in geologically complex regions. Our results show that major shear zones exist beneath the NAFZ throughout the crust and into the lithospheric mantle, suggesting a strong coupling of strain at these depths.
A review on the historical evolution of seismic hazard maps in Turkey is followed by summarizing the important aspects of the updated national probabilistic seismic hazard maps. Comparisons with the ...predecessor probabilistic seismic hazard maps as well as the implications on the national design codes conclude the paper.
The North Anatolian Fault (NAF) is one of the most well-known continental strike slip faults, however, the details related to the geodynamic processes and the extent of deformation in the crust ...remain poorly understood. Within the context of the Dense Array for North Anatolia (DANA) project, a comprehensive data set was gathered from a dense temporary seismic network consisting of 70 stations that were deployed in early May 2012 and operated for 18 months in the Sakarya region and the surroundings. With the aim of further exploring the crustal deformation near the fault mainly caused by the strike slip motion also resulting in the alignment of minerals, the crustal seismic anisotropy beneath the western segment of NAF was investigated by local shear wave splitting analysis. Out of 1371 events, 90 well located earthquakes were extracted with magnitudes >1.4 corresponding to a total of 645 splitting measurements. This method makes use of earthquakes nearby or directly below each station benefiting from the fast polarization direction and the relevant delay time parameters as the main output. Despite the scattered patterns, the fast orientations are dominantly E-W parallel to the fault strike. Delay times between the fast and slow components of the shear wave vary between 0.01 and 0.3 s clearly revealing the existence of crustal anisotropy. In particular, measurements at each station exhibits spatial variations across the fault where it splays into two main branches beneath the study area separating different geologic units. A strong correlation could not be established between small scale faults and azimuthal anisotropy. The measurements presented here constrain crustal anisotropy above the deepest earthquakes at approximately 15 km depth.
•The extent of crustal anisotropy beneath the western segment of North Anatolian Fault.•Fast direction and delay time measurements revealed and scattering highlighting this structural complexity of active tectonic units.•Based on the observations, it might be suggested that there is not a strong coupling between mantle and crustal anisotropy.
A tsunami warning system providing services in the Eastern Mediterranean, Aegean, Marmara and Black Seas under the UNESCO Intergovernmental Oceanographic Commission (IOC)—Intergovernmental ...Coordination Group (ICG) for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and Connected Seas (NEAMTWS) framework was established in Turkey by the Kandilli Observatory and Earthquake Research Institute (KOERI) (Özel et al., 2011). KOERI’s Regional Earthquake and Tsunami Monitoring Center (RETMC) was established on the foundations of the legacy KOERI National Earthquake Monitoring Center (NEMC) by adding observation, analysis and operational capability related to tsunami early warnings after an extensive preparatory period during 2009 and 2011. The center initiated its test-mode 7/24 operational status as a national tsunami warning center in 2011, and after a one year period it became operational as a candidate tsunami warning center for NEAMTWS on 1 July 2012, together with CENALT (Centre d’Alerte aux Tsunamis—France) and followed by the NOA (National Observatory of Athens—Greece) on 28 August 2012, INGV (Instituto Nazionale di Geofisica e Vulcanologia—Italy) on 1 October 2014 and IPMA (Instituto Português do Mar e da Atmosfera—Portugal) on 1 February 2018, completing full coverage of the tsunami-prone regions monitored by NEAMTWS. In this paper, an overview of the progress and continuous improvement of KOERI’s tsunami early warning system will be presented, together with lessons learned from important tsunamigenic events, such as the 20 July 2017 Bodrum–Kos Mw 6.6 and 30 October 2020 Samos–Izmir Mw 6.9 earthquakes. Gaps preventing the completion of an effective tsunami warning cycle and areas for future improvement are also addressed.
•Arabian-Eurasian collision zone consists of East -North Anatolian Faults and Bitlis thrust belt.•The seismogenic zone is approximately confined in the upper 15 km of the crust.•The fault plane is ...aligned in NW-SE direction and aftershocks mark an unmapped fault.•Coulomb Stress Changes revealed areas of increased stress that might trigger future quakes.
Eastern Anatolia is a ∼2 km 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.
Continental scale deformation is often localised along strike-slip faults constituting considerable seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such ...faults, key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard, are poorly constrained in the mid to lower crust. Using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake we map previously unknown small-scale structure in the crust and upper mantle along this part of the North Anatolian Fault Zone (NAFZ). We show that lithological and structural variations exist in the upper, mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle. The surface expression of the NAFZ in this region comprises two major branches; both are shown to continue at depth with differences in dip, depth extent and (possibly) width. We interpret a <10 km wide northern branch that passes downward into a shear zone that traverses the entire crust and penetrates the upper mantle to a depth of at least 50 km. The dip of this structure appears to decrease west–east from ∼90° to ∼65° to the north over a distance of 30 to 40 km. Deformation along the southern branch may be accommodated over a wider (>10 km) zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the Moho. Layers of anomalously low velocity in the mid crust (20–25 km depth) and high velocity in the lower crust (extending from depths of 28–30 km to the Moho) are best developed in the Armutlu–Almacik block between the two shear zones. A mafic lower crust, possibly resulting from ophiolitic obduction or magmatic intrusion, can best explain the coherent lower crustal structure of this block. Our images show that strain has developed in the lower crust beneath both northern and southern strands of the North Anatolian Fault. Our new high resolution images provide new insights into the structure and evolution of the NAFZ and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km.
•A dense array recorded high resolution seismological data across a continental strike slip fault.•P wave receiver function images show complex crustal structure beneath the North Anatolian Fault.•Lithology varies over <10 km and <20 km in the crust and upper mantle, respectively.•A narrow (7–10 km) northern fault branch extends below the Moho (>50 km) and dips 65–90°N.•A more diffuse (>10 km) southern fault branch terminates within the crust.
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 18months 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 7km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8km and 0.9km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15km. Using our current earthquake catalog 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.
•High precision location of earthquakes detected by a dense seismic array•Discrimination of possible quarry blasts and identifying their locations•b-Value analysis•Determination of focal mechanism solutions and orientations of principal stresses
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•Present day stress tensor is determined from seismic fault plane solutions.•The present-day stress regime is extensional with a NNE-SSW direction.•Earthquakes migrated in SSW ...direction along stepped-synthetic normal faults.•The extension is caused by both the Anatolian extrusion and the African subduction.
The west to southwestward motion of the Anatolian block results from the relative motions between the Eurasian, Arabian and African plates along the right-lateral North Anatolian Fault Zone in the north and left-lateral East Anatolian Fault Zone in the east. The Biga Peninsula is tectonically influenced by the Anatolian motion originating along the North Anatolian Fault Zone which splits into two main (northern and southern) branches in the east of Marmara region: the southern branch extends towards the Biga Peninsula which is characterized by strike-slip to oblique normal faulting stress regime in the central to northern part. The southernmost part of peninsula is characterized by a normal to oblique faulting stress regime. The analysis of both seismological and structural field data confirms the change of stress regime from strike-slip character in the center and north to normal faulting character in the south of peninsula where the earthquake swarm recently occurred. The earthquakes began on 14 January 2017 (Mw: 4.4) on Tuzla Fault and migrated southward along the Kocaköy and Babakale's stepped-normal faults of over three months. The inversion of focal mechanisms yields a normal faulting stress regime with an approximately N-S (N4°E) σ3 axis. The inversion of earthquakes occurring in central and northern Biga Peninsula and the north Aegean region gives a strike-slip stress regime with approximately WNW-ESE (N85°W) σ1 and NNE-SSW (N17°E) σ3 axis. The strike-slip stress regime is attributed to westward Anatolian motion, while the normal faulting stress regime is attributed to both the extrusion of Anatolian block and the slab-pull force of the subducting African plate along the Hellenic arc.
We analyzed the waveforms of the small- to moderate-sized earthquakes that took place in the northern part of the inner Isparta Angle (IA) to retrieve their source parameters and combine these ...results with the focal mechanism solutions of the larger events that occurred in 2007 in Eğirdir Lake at the apex of IA. In total, source mechanisms of 20 earthquakes within the magnitude range 3.5 <
M
< 5.0 were calculated using a regional moment tensor inversion technique. The inversion of the focal mechanisms yields an extensional regime with a NNE–SSW (N38°E) trending
σ
3
axis. Inversion results are related to a mainly WNW–ESE oriented normal fault beneath Eğirdir Lake. The
R
value of a NNE–SSW extensional regime is 0.562 showing a triaxial stress state in the region. The current stress regime results from complex subduction processes such as slab pull, slab break-off, roll-back and/or retreating mechanism along the Hellenic and Cyprus arcs and the southwestward extrusion of the Anatolian block since the early Pliocene.
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