Preliminary Earthquake Report ۲۰۱۲-Aut.-۱۱ M ۶.۲ & ۶.۰ Ahar-Varzaghan Earthquakes

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Ahar-Varzaghan Earthquakes


SEISMOTECTONIC & SEISMOLOGY GROUP GEOLOGICAL SURVEY OF IRAN  Preliminary Earthquake Report 2012-Aut.-11   M 6.2 & 6.0 Ahar-Varzaghan Earthquakes East Azarbaijan Province Saturday, Ayg. 11, 2012-08-11 12:23:18.0 UTC Fast View The 6.2 and 6.0 magnitude earthquakes Saturday 11 Aug hit the towns of Ahar,and Varzaqan in East Azerbaijan province at 4:53 p.m. Unfortunately, the quakes killed more than 200 people and injured more than 2000 others. The epicenter of the quakes and their aftershocks were a region between Ahar and Haris, about 59 kilometers northwest of Tabriz and 482 kilometers the northwest capital, Tehran. At least 13 aftershocks affected the same area. The aftershocks were felt in a wide region, through the East Azerbaijan province and the Caspian Sea. The seismic events caused panic among the population. Iran is located on seismic fault lines and is prone to earthquakes. It experiences at least one earthquake every day on average. The northwest of Iran (include East Azerbaijan province) is one of the most seismically active region. Through this active area, the North Tabriz Fault is a major seismogenic fault. Toward north, the Ahar fault is another master seismogenic fault. Here the faults have a clear rupture along their strikes. Many geologists suggest that the convergence of 22±2 mm yr-1 between the northward motions of the Arabian Plate relative to Eurasia at N8° ±5° E is accommodated by a combination of thrust and strike-slip faults in different parts of Iran, as well as seismic area at the NW of Iran. NW of Iran has been studied by several geologists (e.g. Berberian & Arshadi, 1976; Karakhanian et al., 2001; Hessami et al., 2003). Berberian and Arshadi (1976) mentioned to the some traces of dextral movement mechanism along the North Tabriz Fault. Minimum slip rate ~2 mm/yr is estimated for this fault (Karakhanian et al.; 2001).   In this work the degree of ground shaking (MSK intensity) was constrained through the study area. Intensity in MSK scale was determined from observation of the earthquake’s effect on people, structures, and the earth’s surface at a given locality. But here to have a fast view the seismic Intensity was evaluated using B-cube methode. Our preliminary evaluation show that the Imax for the first event should be 9 in MSK scale (IX, a~200 gal).  

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