Site Effect Evaluation in Qeshm Island (Iran) Using Earthquake Recording and Microtremor Measurments

Abstract eng:
Un earthquake of Mw =6.0 struck the central part of Qeshm Island, the greatest Iranian island in the Persian Gulf in November 27, 2005 (13:52 local time) after a relatively long period of seismic silence during 20th century in the region. This earthquake caused some of causalities and important damages to rural areas. This leads the Qeshm free zone organization and International Institute of Earthquake Engineering and Seismology (IIEES) to conduct a comprehensive study on the surface ground motion characteristics and earthquake geotechnical engineering in this Island. This paper shows some of the results obtained using earthquake data and Microtremors measurements. In this regards, the data of a seismological network consisting of 17 stations, installed after the earthquake (from 2005 December 2 to 2006 February 26) and 49 single station Microtremors measurements were used. More than 100 seismic events have been extracted for each station to estimate site effect by conventional methods such as Standard Spectral Ratio (SSR), General Inversion (GI) and horizontal/vertical spectral ratio (HVSR) Methods. Microtremor measurements were mostly focused on the 2 important city of the region, Qeshm and Dargahan. The comparison of the results with the destruction map of 2005 Qeshm Island earthquake show a moderate level of amplification for some of the localities severely damaged during Earthquake, specially in the Tomban and Gavarzin villages due to the existence of loose sandy-silty soils. However for most part of the seismological stations we do not observed a significant amplification, despite of the existence of weak geological formations.

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