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To determine the location and extent of buried geological structures, evaluation of gravity potential field data using edge detection methods is widely used, such as total horizontal derivative, tilt angle, the vertical derivative's tilt angle and analytical signal methods. In the interpretation process of anomalies obtained from these methods, users do need additional physical parameters. So, in the first step of this study, results of the edge detection methods have been examined via synthetic models to put forward the availabilities of each method. Synthetic data studies show that the increase in noise level plays a direct role in determining the structure boundaries. The results obtained from the tilt angle application for high noise ratios give more inadequate results than other applications. Especially for high noise ratios, the most accurate structure boundaries are obtained with the total horizontal derivative (THD) applications. The data collected from Dikili, Çandarlı, Foça regions at 840 stations showed the presence of five remarkable Bouguer gravity anomaly localizations in the part of Bakırçay and Gediz graben. After that, according to the obtained findings, the methods have been applied to the field data and discussed. The location of the alluvial reservoir between Foça and Menemen was able to detect residual complete Bouguer anomaly map, Çandarlı volcanic intrusion is clearly seen on THD and analytical signal (AS) maps, Foça volcanics and Dumanlıdağ volcanic center were detected on tilt angle (TA) map. All these outputs of the area were interpreted in the scope of geological literature. Finally, these results were examined by combining them with the obtained 3-dimensional bedrock topography. 3-D bedrock inversion results clearly showed that the volcanic intrusion at the Çandarlı region is a reason for the recent topographical shape of the area, which also helps us to define the surface of the Bakırçay Graben's related to hanging wall and its slope changes. [ABSTRACT FROM AUTHOR]

This study aimed to reveal the soil properties in the research area by using various geophysical methods. Physical parameters determining soil characteristics give us a chance to approach how the soil behaves during an earthquake. Thus, precautions can be taken to minimize earthquake damage. Also, safe construction against earthquake effects is important. The studied area is a tectonically and geothermally active area. İzmir Fault zone is passing through the investigation area and trending E–W direction. To investigate soil parameters at this active tectonic region, microtremor method data were recorded and the multichannel analysis of surface waves (MASW) method at 27 profiles was implemented in the study area. Additionally, these methods were supported by the spatial auto correlation (SPAC) method in center spot. Shear wave velocities up to 30 m, soil classification according to the National Earthquake Hazards Reduction Program (NEHRP), site amplification, predominant site period, amplification factor, ground vulnerability index, and shear wave velocity changes up to 300 m were obtained by evaluating the data collected from the applied geophysical methods. VS30 values varied between 700 and 1100 m/s in the southernmost part of the study area, corresponding to a C and B type as soil classification. While the predominant period values were taken as the lowest value of 0.2 s, it was observed to increase up to 5.5 s on the alluvial unit in the northern parts of the study area. The ground vulnerability index, which is directly related to the probability of earthquake damage, was found to be quite high in some parts of the study area. In this paper, we propose microzonation maps for the Balçova district, based on the variation of the soil dynamic parameters. [ABSTRACT FROM AUTHOR]

Structural damage which occurs during earthquakes is related to both the soil dynamic behavior attributes and soil response spectrums. Therefore, soil characterization based of S-wave velocity (Vs) is one of the prime factors to estimate damage and hazards. In this study, multi-channel analysis of surface waves (MASW) and refraction microtremor (ReMi) methods have been applied to estimate Vs values of the area located east of Izmir Bay. Based on the estimated Vs values, two- and three-dimensional shear-wave velocity and the maximum shear modulus maps at various depths down to 50 m were prepared. To study the relationship between the predominant period of the soil and shear-wave velocity values, a horizontal-to-vertical (H/V) spectral ratio method using Nakamura's technique has been applied. Groundwater level, standard penetration test (SPT-N30) and Poisson ratio values were also obtained from previous geotechnical borehole data in the study area. In addition, we calculated building periods using the empirical relationship between height (or number of floors) of buildings and predominant period of the buildings to examine soil-structure resonance. According to the National Earthquake Hazard Reduction Program (NEHRP; 1997) soil classification, the study site consists of B-, C- and F-type soils. Risk maps were created using dynamic properties of the soil. [ABSTRACT FROM AUTHOR]

The site effect plays very important role for planning design of structures and estimating seismic damage of existing structures, especially in seismicity active regions. Aliağa, located in the northern region of the İzmir City, is high seismically active region in western Turkey. We identified the dynamic properties of shallow soil for Aliağa district (western Turkey) in terms of the average shear-wave velocity for the top 30 m of soil (Vs), predominant period ( T ) and vulnerability index (Kg). We created the microzonation map that classes the shallow soil according to National Earthquake Hazards Reduction Program (NEHRP). Shear-wave velocity (Vs) was evaluated using the 1-D multichannel analysis of surface waves at 34 sites. The microtremor measurements were taken at 58 stations with a grid spacing of 1000 m in Aliağa district. The acquired HVSR results show that the T values change from 0.1 to 1.9 s, while the amplification factor ( A ) values change between 1.5 and 12. Soil classification results illustrate that northern part of the study area, located in alluvial unit, has lower Vs values. These values are observed within the range of 100-300 m/s. This part was classified as the D and E types according to NEHRP. In addition, the weak zones of the study area due to the local site effects were indicated by the Kg values which vary from 5 to 55. The northern part of the study area is high vulnerability index zone (Kg > 20). Last of all, we can mention that the northern part of our study area is the weakest zone according to the results of geophysical and geological data. [ABSTRACT FROM AUTHOR]

An earthquake record is needed on engineering bedrock to perform soil deformation analysis. This record could be obtained in different ways (seismographs on engineering bedrock; by the help of the soil transfer function; scenario earthquakes). S-wave velocity ( V ) profile must be known at least till engineering bedrock for calculating soil transfer functions true and completely. In addition, 2D or 3D soil, engineering-seismic bedrock models are needed for soil response analyses to be carried out. These models are used to determine changes in the amplitude and frequency content of earthquake waves depending on the seismic impedance from seismic bedrock to the ground surface and the basin effects. In this context, it is important to use multiple in situ geophysical techniques to create the soil-bedrock models. In this study, 2D and 3D soil-bedrock models of Bornova plain and its surroundings (Western Turkey), which are very risky in terms of seismicity, were obtained by combined survey of surface wave and microgravity methods. Results of the study show that the engineering bedrock depths in the middle part of Bornova plain range from 200 to 400 m and the southern and northern parts which are covered limestone and andesite show the engineering bedrock ( V > 760 m/s) feature. In addition, seismic bedrock ( V < 3000 m/s) depth changes from 550 to 1350 m. The predominant period values obtained from single station microtremor method change from 0.45 to 1.6 s while they are higher than 1 s in the middle part of Bornova plain where the basin is deeper. Bornova Plain has a very thick sediment units which have very low V values above engineering bedrock. In addition, it is observed sudden changes at the interfaces of the layer in horizontal and vertical directions. [ABSTRACT FROM AUTHOR]