Seismic Hazard Assessment of the City of Khoy and Its Vicinity, NW of Iran

Seismic Hazard Assessment of the City of Khoy and Its Vicinity, NW of Iran

Davood Fereidooni (School of Earth Sciences, Damghan University, Damghan, Iran)
Copyright: © 2015 |Pages: 13
DOI: 10.4018/IJGEE.2015010102
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Abstract

Analyses have been carried out considering the occurred earthquakes, geologic and seismotectonic conditions of the region covering a radius of 100 Km keeping Khoy as the center. The major seismic sources are small and large faults identified in the study area mostly directed in NW-SE. The MCE and PGA were measured based on both DSHA and PSHA approaches. The results of DSHA show that the MCE and PGA evaluated values are 6.8 Richter and 0.31g, which might be created by Chahar-Sotoon and Askar-Abad faults, respectively. The results of PSHA show that the MCE evaluated value is 6.1 Richter for a 0.64 probability in a 50- year period. Seismic hazard parameters have been evaluated considering the available earthquake data using Gutenberg-Richter relationship method. The ‘a' and ‘b' parameters were estimated 6.03 and 0.94, respectively. For earthquakes with magnitudes equal or greater than 6.1 Richter, the values of returning period (TR) and annual occurrence probability (PT) were obtained 112 and 0.009, respectively. The results obtained from two mentioned methods are matched to each other.
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1. Introduction

The increase in the Iranian cities’ population, together with the growth of high buildings and big towns, causing compacting of population, contributes to the increase of damages due to seismic hazards. The rupture along a fault plane causes earthquake and the generated seismic waves propagate through underlying bedrock and reach the earth’s surface. In the 20th century, more than 1,100 massive earthquakes occurred, causing more than 1,500,000 casualties, most of which are due to buildings collapsing, which constitutes almost 90% of direct deaths (Lantada et al. 2009). Furthermore, the performance of lifelines such as transportation systems, water and gas pipelines, communication and power transmission systems after a major earthquake is particularly vital for a community because of the emergency services that are usually required after such events (Selcuk and Yucemen 2000).

Khoy is one of the major cities in the north of West Azerbaijan province, NW of Iran, with a population of about 300,000 people. The presence of different faults in the city and its vicinity regions demonstrates the necessity of seismic study and risk assessment for this region. Based on occurred earthquakes in the study area, these faults have been caused earthquakes with magnitude more than 6 Richter in about every 41 years. The main purpose of the present research is to conduct a seismic hazard analysis for the mentioned city. Seismic Hazard Assessment (SHA) plays an important role in the earthquake resistant design of structures by providing a rational value of input hazard parameters such as Peak Ground Acceleration (PGA) or the response spectrum amplitudes at different natural periods (Ramanna and Dodagoudar (2014a).Therefore, assessment of seismic hazards in urban areas and the related mitigation measures as well as the assignment of priorities has become of crucial importance. The evaluation of potential damage is an essential stage of the planning process but the problems that may be encountered in conducting vulnerability analyses should not be underestimated. The evaluation of earthquake risk in an area needs to geological studies as well as identification of active faults (Burchfiel and Wang 2003). On the other hands, the identification and characterization of active faults as earthquake sources are essential parts of seismic hazard evaluation because they enable forecasts to be made of locations, recurrence intervals, and sizes of future large earthquakes (Aoudia et al. 2000). The seismic hazard analysis can be quantified using either Deterministic or Probabilistic Seismic Hazard Assessment (DSHA and PSHA) based on regional, geological, and seismological information (Reiter 1990; Anbazhagan et al. 2009). Identification and characterization of the seismic source is the very first step in SHA no matter whether the methodology adopted is deterministic or probabilistic. Such seismic sources are in the form of point, line or area (Ramanna and Dodagoudar (2014b). The deterministic approach is used in order to design of maximum earthquake that will produce maximum ground motion at a particular site. Whereas, the probabilistic method advocate that likelihood of occurrence should also be considered in view of the fact that the life of a structure is very short compared to the recurrence intervals of large events (Rafi et al. 2012). This method is a subject that has seen rapid methodological developments since it was first introduced just over 40 years ago. The pace at which developments continue is still rapid, and practices that might have seemed acceptable just 10 years ago would now be frowned upon. This has been particularly true in the ground motion modeling community, and one can point to the way in which this aspect of PSHA has been transformed in recent years (Musson 2012). Both approaches use the same data sets, which include earthquake sources, occurrence frequencies, and ground motion-attenuation relationships (Joshi and Mohan 2010).

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