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Two large earthquakes (Mw = 7.7 and Mw = 7.6) that occurred in Turkey on February 6, 2023, affected a very extent region and caused a lot of loss of life and property. This paper presents preliminary results from geophysical measurements (Seismic Refraction Tomography-SRT, Multi-Channel Surface Wave Analysis-MASW and Microtremor-MT) on eight profiles in four provinces (Kahramanmaraş, Hatay, Malatya, Gaziantep) to understand the relationship between subsurface properties and the destruction that occurs immediately after earthquakes. By analyzing the geophysical data, the dynamic-elastic properties of ground and the soil classification according to Vs30 were determined. It is generally understood that the near-surface (< ~ 10–15 m) units in the measurement areas are very loose, and the deeper ones (≥ ~ 15–20 m) have a very porous/fractured structure. Soil classes were defined as ZD (Malatya-1, Hatay-1 and Kahramanmaraş-1) and ZC (Malatya-2, Hatay-2, Gaziantep-1,2 and Kahramanmaraş-2). In addition, by evaluating the information of strong ground motion station closest to the measurement profiles, it is observed that the PGA values versus epicenter distances are higher at stations in the zone parallel to the direction of both faults than those in the perpendicular zones. This leads directivity effect in the propagation of earthquake waves. The results indicate that one of the basic reasons for the damages is that the earthquake-ground-structure relationship has not been fully and accurately reflected in building designs. Therefore, future researches involving more geophysical data and PGA values will provide more information about the structural, physical and geotechnical properties of subsurface and definitive results. [ABSTRACT FROM AUTHOR]

A strong earthquake with Mw 6.6 occurred on 20 July, 2017 in Gökova Bay at the southwest part of the Turkey, accompanied by a local tsunami which impacted Bodrum (Turkey) and Kos (Greece). This paper presents simulation of strong ground motions from this earthquake to visualize the extent of spectral acceleration over the region. A stochastic finite fault method based on a dynamic corner frequency is utilized as a simulation tool. For validation of simulation, strong motion recordings from 10 closest stations within 76 km are used. Horizontal to vertical spectral ratio and near surface attenuation parameter (kappa) of shear waves at strong motion recording stations are calculated to account for site effects. The most suitable source parameters; stress drop and pulsing area percentage are found as 2.5 MPa with 30–36% based on the residuals analyses. In general, an acceptable level of consistency is found between observed and simulated ground motions. Simulation is more successful at frequencies of 2 Hz and above. Distribution of spectral accelerations at a larger region is calculated with the best validated model parameters and compared with ground motion prediction equations. In spite of significant scatter of synthetics particularly in the near fault region, at longer epicentral distances the median values of Turkish empirical prediction better approximates the synthetics. The current results and further scenario simulations for the region are believed to complement normal faulting synthetic strong ground motion library of Turkey. [ABSTRACT FROM AUTHOR]

The seismic vulnerability index (Kg) is a parameter that depends on the dynamic properties of soil. With this parameter, it is possible to evaluate the vulnerability of a point-based site under strong ground motion. Since it is related to the natural vibration period and amplification factor, the parameter can be calculated for both soil and structure. In this study, HVSR microtremor measurements are recorded at more than 200 points in the Van region to generate a seismic vulnerability index map. After generating the map, it is determined that the hazard potential and seismic vulnerability index is high at the sites close to Van Lake and at the densely populated city center. Damage information of the buildings investigated after the 2011 Van earthquakes (Mw = 7.1) are placed on the seismic vulnerability index map and it is realized that there may be a correlation between the damage and the seismic vulnerability index. There is a high correlation, approximately 80 percent, between the damage rate map based on the damaged building data and the Kg values. In addition, vulnerability indexes of buildings are calculated and the eff ect of local soil conditions and building properties on the damage levels are determined. From the results of this study and the site observations after the 2011 Van earthquakes, it is found that structural damage is not only structure-dependent but is also related to the dynamic behavior of soil layers and local soil conditions. [ABSTRACT FROM AUTHOR]

Completing the earthquake recurrence period of the Marmara segment, one of the two seismic gaps of the northern Anatolian fault zone, necessitates earthquake hazard studies for Istanbul, considering the population density. This study focuses on determining the soil properties of the study area in the Maltepe district of Istanbul. The Maltepe, with its large population density, stands very close to this fault zone and is vulnerable to earthquake damage. The soil properties such as Vs 30 , dominant period (T 0), and amplification ratio (A 0) were determined with the MASW from surface wave analysis methods at 48 points and the HVSR approach of microtremor analysis methods at 26 points. These point-based properties were mapped in the GIS environment, and spatial distribution maps were prepared. In addition, seismic vulnerability (Kg) and effective shear strain (γ e) calculations for different acceleration values were carried out to detect deformation-failure on the surface. It was understood from the maps and the 2D cross-sections produced to examine the lateral and vertical changes that the soil conditions in the study area developed under the control of the Maltepe Beykoz fault (MBF). Accordingly, the two sides of the MBF lineament were determined with different geophysical outputs by their different geological origins. Namely, the alluvial part in the coastal part was defined by low Vs 30 , high period, and Kg values; on the contrary, the more rigid parts located at high elevations were described by relatively high Vs 30 , low period, and Kg values. In addition, it was understood that the deltaic sediments spread loosely and undulated in the alluvium at the SE part of the MBF lineament. These results obtained in the study are significant for predicting disaster damages and taking precautions before disasters. In addition, the scientific data potential of the outcomes of this study will make future studies, which are carried out to determine other parameters to be used during the taking of the precautions, more accessible. • The study includes the assessment of the integrated HVSR (Nakamura technique) and MASW method. • The soil properties of the Maltepe district of Istanbul were determined. • Vulnerability and effective share strain were obtained from acceleration scenarios. • The outcomes of each method were compared and mapped GIS environment. • According to the results, the evolution of the area was shaped under the control of en-echelon NW-SE trending MBF. [ABSTRACT FROM AUTHOR]

The horizontal to vertical spectral ratios of microtremor (HVSR) analysis of Yüksekova and its surroundings is carried out using the results of field investigations, local soil conditions and seismotectonic features of the region. Soil-structure interaction is one of the most important reason for building damage ratio. The effects of soil conditions on probably damaged building units were determined, by conducting HVSR microtremor measurements. In this study data collection is handled during 30 min using three component seismograph measurements at 40 points in the Yüksekova region. HVSR peak period map shows that the fundamental period range between 0.4 and 1.6 s in the soft sediments units. Rock sites of the northern coast of Yüksekova period range between 0.1 and 0.2 s. HVSR peak amplitude values are in the interval 1.5–6.0. [ABSTRACT FROM AUTHOR]