Crustal Seismicity In and Around Turkey

Vertical and horizontal variations of the frequency of crustal earthquakes (h ≤ 35 km) that have occurred in and around Turkey are analyzed, using data from the Global Hypocenter Data Base and the IRIS data for the period 1964–1998. Fits of various magnitude scales to the observations have been used to construct a homogeneous catalogue. Depth distribution of the parameters derived from the Gutenberg–Richter relationship reveals that there is a depth dependence in the a- and b-values of the frequency distribution. It is observed that unknown focal depths (0, 10, 33 km) are dominant in the total seismicity reported, and give rise to substantial changes to the vertical distribution of these parameters. It is also observed that the parameters of either a or b alone may not be used as a measure of regional seismicity of the study area in which high and low seismic activity observed over short distances. In contrast, distribution of modal (a/b) values provides detailed images of the local areas presented by high and low seismic zones. This study presents evidence that low b-values are associated with major strike-slip faults, particularly exhibiting high apparent stresses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Deliniation of Weathering in the Çatalca Granite Quarry with the Very Low Frequency (VLF) Electromagnetic Method

Faulting and weathering can endanger quarry operations by decreasing the total reserve, quarry’s useful life and production value. We investigated weathering and faulting problems in the Çatalca granite quarry at Istanbul in Turkey, using the Very Low Frequency (VLF) method. VLF method is an electromagnetic method which is very successful in locating vertical discontinuities such as faults and fracture zones. This method measures the apparent resistivity of the rocks in the region, besides the electromagnetic parameters such as tilt angle and ellipcity. Apparent resistivity is a very sensitive parameter to water presence inside the pores and fractures of the rocks. This feature enables the VLF method to map the boundaries between the fresh and cracked granite and altered zones in the quarry. In this work we mapped the faults and weathered zones within the granite in Çatalca quarry and found a high resistivity zone at the central part of the survey area which may be suitable for production. This study also shows the efficiency of the VLF method in understanding the structural and textural features of a quarry and estimating zones with high quality rocks for production planning.     

Analysis of largest earthquakes in Turkey and its vicinity by application of the Gumbel III distribution

A study of the spatial distribution of seismicity parameters is undertaken along Turkey and its vicinity, using the Gumbel’s third asymptotic distribution of extreme values (GIII). The data set used spans of 111 years (1900–2010). The seismicity of the whole region is subdivided into equal area mesh of 1° lat. × 1° long. Various seismicity parameters examined, resulted from the application of the GIII method. The results show a quite good correlation between the seismicity parameters and the tectonic regime of the studied area. For instance high values concentrated around North Anatolian Fault. The x ²-test is applied throughout the whole process and in every stage of GIII, in order to check the accuracy of the obtained results. The spatial distribution of upper-bound (ω) formed a W-shape pattern, which shows the difference in the mechanical structure of the materials in the examined area.     

Performance evaluation of disaster monitoring systems

Understanding the performance of disaster monitoring systems is a key to understanding their success; therefore, various qualitative and quantitative measures and metrics can be applied in the characterization and analysis of such systems. Through evaluation studies, problems that impede a disaster monitoring system performance can be identified. The results can be used for system design, control, and capacity planning. Previous studies address technical performance analysis metrics for analyzing monitoring systems leaving out human and organizational dimensions of such systems. Thus, the primary objective of this study is to identify and describe a set of metrics that may be employed to evaluate such systems. This study may be valuable to researchers and practitioners involved in disaster and emergency response studies in planning the transportation of vital first-aid supplies and emergency personnel to disaster-affected areas and in improving chances of survival after a disaster.     

Using the Wiener–Levinson algorithm to suppress ground-roll

In land seismic surveys, the seismic data are mostly contaminated by ground-roll noise, high amplitude and low frequency. Since the ground-roll is coherent with reflections and depends on the source, the spectral band of seismic signal and ground-roll always overlap, which can be clearly seen in the spectral domain. So, separating them in time or frequency domain commonly causes waveform distortions and information missing due to cut-off effects. Therefore, the combination of these factors leads to search for alternative filtering methods or processes. We applied the conventional Wiener–Levinson algorithm to extract ground-roll from the seismic data. Then, subtracting it from the seismic data arithmetically performs the ground-roll suppression. To set up the algorithm, linear or nonlinear sweep signals are used as reference noise trace. The frequencies needed in creating a reference noise trace using analytical sweep signal can be approximately estimated in spectral domain. The application of the proposed method based on redesigning of Wiener–Levinson algorithm differs from the usual frequency filtering techniques since the ground-roll is suppressed without cutting signal spectrum. The method is firstly tested on synthetics and then is applied to a shot data from the field. The result obtained from both synthetics and field data show that the ground-roll suppression in this way causes no waveform distortion and no reduction of frequency bandwidth of the data.     

A quantitative appraisal of earthquake hazard parameters computed from Gumbel I method for different regions in and around Turkey

Useful information concerning the earthquake hazard parameters distributed in Turkey and the adjacent areas are estimated in the present work. Based on Gumbel’s I distribution parameters we are able to estimate the hazard values of the investigated area which are the mean return periods, the most probable maximum magnitude in the time period of t-years and the probability for an earthquake occurrence of magnitude ≥M during a time span of t-years. Figures concerning the spatial distribution of probabilities and the return periods are plotted and we considered them of particular interest for mapping the earthquake hazard in Turkey and the surrounding areas. These figures effectively produce a brief earthquake hazard atlas. The quantitative appraisal of the hazard parameters is useful for engineers, planners, etc., because it provides a tool for earthquake resistant design.     

An Evaluation of Earthquake Hazard Potential for Different Regions in Western Anatolia Using the Historical and Instrumental Earthquake Data

We applied the maximum likelihood method produced by Kijko and Sellevoll (Bull Seismol Soc Am 79:645–654, 1989; Bull Seismol Soc Am 82:120–134, 1992) to study the spatial distributions of seismicity and earthquake hazard parameters for the different regions in western Anatolia (WA). Since the historical earthquake data are very important for examining regional earthquake hazard parameters, a procedure that allows the use of either historical or instrumental data, or even a combination of the two has been applied in this study. By using this method, we estimated the earthquake hazard parameters, which include the maximum regional magnitude $ \hat{M}_{\max } , $ the activity rate of seismic events and the well-known $ \hat{b} $ value, which is the slope of the frequency-magnitude Gutenberg-Richter relationship. The whole examined area is divided into 15 different seismic regions based on their tectonic and seismotectonic regimes. The probabilities, return periods of earthquakes with a magnitude M?≥?m and the relative earthquake hazard level (defined as the index K) are also evaluated for each seismic region. Each of the computed earthquake hazard parameters is mapped on the different seismic regions to represent regional variation of these parameters. Furthermore, the investigated regions are classified into different seismic hazard level groups considering the K index. According to these maps and the classification of seismic hazard, the most seismically active regions in WA are 1, 8, 10 and 12 related to the Alia?a Fault and the Büyük Menderes Graben, Aegean Arc and Aegean Islands.     

A Probabilistic Assessment of Earthquake Hazard Parameters in NW Himalaya and the Adjoining Regions

The maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of NW Himalaya and the adjoining regions. For this purpose, we have prepared a reliable, homogeneous and complete earthquake catalogue during the period 1500–2010. The technique used here allows the data to contain either historical or instrumental era or even a combination of the both. In this study, the earthquake hazard parameters, which include maximum regional magnitude (M _max), mean seismic activity rate (λ), the parameter b (or β?=?b/log e) of Gutenberg–Richter (G–R) frequency-magnitude relationship, the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900–2010. The uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters. The earthquake hazard in the whole NW Himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level, tectonics and focal mechanism. The annual probability of exceedance of earthquake (activity rate) of certain magnitude is also calculated for all seismogenic source zones. The obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters. It is observed that seismic hazard level is high in Quetta-Kirthar-Sulaiman region in Pakistan, Hindukush-Pamir Himalaya region and Uttarkashi-Chamoli region in Himalayan Frontal Thrust belt. The source zones that are expected to have maximum regional magnitude (M _max) of more than 8.0 are Quetta, southern Pamir, Caucasus and Kashmir-Himanchal Pradesh which have experienced such magnitude of earthquakes in the past. It is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity.