Search

Based on the amplitude spectra of surface waves, the source parameters of the strong Turkish earthquakes on February 6, 2023 (Mw = 7.8 and Mw = 7.7) were calculated in two approximations: an instantaneous point source and an elliptical shear dislocation. As a result, fault planes were identified, data were obtained on the scalar seismic moment, moment magnitude, focal mechanism, and source depth of the considered seismic events, and the integral parameters characterizing the fault geometry and its development in time were estimated. It is shown that the sources of the earthquakes under study were formed under the action of the regional stress field and their focal mechanisms were sinistral strike-slips with a strike direction close to the strike of the East Anatolian fault zone for the first event and close to the strike of the Sürgü-Çardak fault system for the second one. For the first earthquake, our estimates of the rupture duration and its length (t = 52.5 s, L = 180 km) probably refer not to the entire rupture, but only to its main phase, confined to the northeastern segments of the East Anatolian Fault and characterized by maximum displacements and values of the released seismic moment. The values of t = 30 s and L = 180 km that we obtained for the second earthquake fully characterize the entire rupture. [ABSTRACT FROM AUTHOR]

Uzungöl settlement and Lake Uzungöl are located in the south of Çaykara, Trabzon, Eastern Black Sea region, and are an important tourist destination in Turkey, with natural beauty and rich flora. However, the settlement and the lake were formed by a historical landslide that covered the front of the Haldizen stream. Residential buildings, tourist facilities, transportation routes, and agricultural activities are located on ground that consists of the material that accumulated from the landslide. In this study, a geophysical investigation using integrated shallow seismic methods was carried out in Uzungöl settlement to provide detailed scientific imaging data on the structure of the subsurface, the physical properties of the soil and rock, the bedrock topography, and the vertical and lateral variation in the landslide deposits. For this purpose, seismic refraction and active and passive multichannel surface wave data were collected from 16 profiles in four separate zones designated according to the agricultural activity and geomorphology of the area. In addition, an electrical resistivity tomography survey of a profile was carried out to determine the reason for low-velocity anomalies such as cavities or man-made voids appearing in P-wave velocity–depth sections and underground water content. After applying basic processes including trace killing/editing, random noise filtering of the data, and amplitude balancing to all seismic data, 2D P-wave velocity–depth sections obtained by tomographic inversion, 1D S-wave velocity–depth profiles, and 2D S-wave velocity–depth sections were generated via analysis of MASW and ReMi data. P- and S-wave velocity–depth sections generally demonstrate three main lithological units in the area: the soil (Vp = 300–600 m/s, Vs = 195–350 m/s and H = 0–2.5 m), the landslide material (Vp = 600–2400 m/s, Vs = 350–680 m/s and H = 2.5–15 m), and the bedrock (Vp > 2400 m/s, Vs > 680 m/s and H ≥ 15 m). In particular, the landslide material exhibits variable thickness from profile to profile and represents the complexity of the subsurface. However, we observed that the deposit thickness increases close to the lake. It was determined that the high seismic velocities of the landslide deposits are attributable to the densely packed deposits and the primarily dry or very poor underground water, according to electrical resistivity tomography results. Moreover, the top of the bedrock is characterized by soft rock, and the deeper part of the bedrock is harder and more compact. We believe that this information will be a useful contribution to geotechnical project development and risk mitigation in the Uzungöl area. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the site characterization of the Senirkent Basin (Isparta) by using the microtremor (H/V) and surface wave analysis (ReMi) methods. Senirkent district, which is located on the foothill of the Kapi Mountain, are prone to seismic and landslide hazards. After the last landslip disaster (1995), the city has continued to develop on the alluvial basin. The microtremor data collected at 41 stations were analyzed. The predominant frequency and the amplification of the soil were found to be in the range of 1.8–6.6 Hz and 0.8–6.8, respectively. These are 4.0–6.8 Hz and 1–2.5 around the slope of the Kapi Mountain and 0.8–3.6 Hz and 3.0–6.6 at alluvium deposits of the valley. The ReMi data collected along 41 profiles were analyzed to obtain a Vs30 map. The soil classifications were done by using Vs30 values according to NEHRP soil classification criteria. The results showed that the southern area of the study had better soil conditions with Vs30 between 360–1160 m/s and soil class between C and B. The alluvium deposits on the north are relatively low with Vs30 in the range of 260–360 m/s and soil class D. [ABSTRACT FROM AUTHOR]

This study aims to reveal upper-crustal velocity structure of Inner part of Izmir Gulf by using ambient noise tomography. One-year noise data have been used from 17 stations belong to IzmirNET. Rayleigh wave group velocities which present good signal/noise ratio have been obtained from dispersion curves by using multiple filter technique. Results have been mapped for 2, 4 and 6 s period intervals. Then, shear wave velocities have been obtained from the inversion of group velocity by using local dispersion curves belongs to same periods. Low velocity areas representing alluvial deposits beneath Inner part of Izmir Gulf, have been precisely observed down to 3 km on group and shear wave maps. Added to this, it is also detected not only the existence of low velocities but also high values in the depth slices of inner part of the Gulf. This method may provide precise and high resolution images of crustal structure and upper mantle by using ambient noise tomography without seismic events. It can be applied in the future to the Aegean Region, Turkey or neighbouring countries by using broad-band data set. [ABSTRACT FROM AUTHOR]

Abstract: Waveforms of 50 teleseismic receiver functions and dispersion curves have been used to invert jointly for the 1D average crust and uppermost mantle seismic structure beneath GEOFON station ISP. The surface wave (Rayleigh and Love) dispersion curves were adopted from an earlier study and greatly help to stabilize the inversions by alleviating the deficiencies of inverting the receiver functions alone. The teleseismic receiver functions had a backazimuth distribution from which three stacks were created. All the stacks resulted in compatible inversions. Nine different influence factors ranging between 0.1 and 0.9 were employed and the influence factors around 0.5 were preferred for producing a reasonable seismic structure to represent the geology under station ISP. Three distinct crustal depth ranges are identified based on the inverted velocity-depth profile. The first corresponds to 0–5km where the velocity-depth profile has a positive gradient with an increase from 2.5kms−1 to 3.0kms−1. The second depth range is 5–10km and the velocity-depth profile shows a positive gradient between 3.0kms−1 and 3.20kms−1. A velocity jump from 3.20kms−1 to 3.62kms−1 tops the third depth range (10–20km), which is characterized by a constant velocity. There is another velocity drop at 20km depth from 3.62kms−1 to 3.40kms−1 and the low velocity therein is persistent down to 27.5km. Below this depth range, the shear velocity increases until 40km depth where the Moho discontinuity is estimated with Sn velocity of 4.4kms−1. In general, seismic velocities under SW Anatolia are considerably slower than those of the Preliminary Reference Earth Model (PREM). [Copyright &y& Elsevier]

We infer the lithospheric structure in eastern Turkey using teleseismic and regional events recorded by 29 broad-band stations from the Eastern Turkey Seismic Experiment (ETSE). We combine the surface wave group velocities (Rayleigh and Love) with telesesimic receiver functions to jointly invert for the S-wave velocity structure, Moho depth and mantle-lid (lithospheric mantle) thickness. We also estimated the transverse anisotropy due to Love and Rayleigh velocity discrepancies. We found anomalously low shear wave velocities underneath the Anatolian Plateau. Average crustal thickness is 36 km in the Arabian Plate, 44 km in Anatolian Block and 48 km in the Anatolian Plateau. We observe very low shear wave velocities at the crustal portion (30–38 km) of the northeastern part of the Anatolian Plateau. The lithospheric mantle thickness is either not thick enough to resolve it or it is completely removed underneath the Anatolian Plateau. The shear velocities and anisotropy down to 100 km depth suggest that the average lithosphere–asthenosphere boundary in the Arabian Plate is about 90 and 70 km in Anatolian block. Adding the surface waves to the receiver functions is necessary to constrain the trade-off between velocity and the thickness. We find slower velocities than with the receiver function data alone. The study reveals three different lithospheric structures in eastern Turkey: the Anatolian plateau (east of Karliova Triple Junction), the Anatolian block and the northernmost portion of the Arabian plate. The boundary of lithospheric structure differences coincides with the major tectonic boundaries. [ABSTRACT FROM AUTHOR]

Abstract: We have studied seismic surface waves of 255 shallow regional earthquakes recently recorded at GEOFON station ISP (Isparta, Turkey) and have selected these 52 recordings with high signal-to-noise ratio for further analysis. An attempt was made by the simultaneous use of the Rayleigh and Love surface wave data to interpret the planar crust and uppermost mantle velocity structure beneath the Anatolian plate using a differential least-square inversion technique. The shear-wave velocities near the surface show a gradational change from approximately 2.2 to 3.6 km s−1 in the depth range 0–10 km. The mid-crustal depth range indicating a weakly developed low velocity zone has shear-wave velocities around 3.55 km s−1. The Moho discontinuity characterizing the crust–mantle velocity transition appears somewhat gradual between the depth range ∼25–45 km. The surface waves approaching from the northern Anatolia are estimated to travel a crustal thickness of ∼33 km whilst those from the southwestern Anatolia and part of east Mediterranean Sea indicate a thicker crust at ∼37 km. The eastern Anatolia events traveled even thicker crust at ∼41 km. A low sub-Moho velocity is estimated at ∼4.27 km s−1, although consistent with other similar studies in the region. The current velocities are considerably slower than indicated by the Preliminary Reference Earth Model (PREM) in almost all depth ranges. [Copyright &y& Elsevier]