IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Poster presentation 2298
Crustal structure in South of Zagros, from the 2005 Qeshm Island
earthquake in Iran
Dr. Zohrehsadat Riazirad
Geophysics Azad University Science & Research branch M.Y.R.C IASPEI
Recently the seismic activity in south eastern extension of Zagros has been increased, remarkably.
Among the several moderate earthquakes, several have occurred in Qeshm Island about 60 km
southwest of Bandar-e-Abbas port city in south Iran. In this paper, the geology, including detailed fault
map, and the seismicity, including teleseismic and locally recorded earthquakes. Focal mechanism of
strong earthquakes were determined and discussed with the stress field in the region. The earthquakes
that have occurred during that past 3 year were shallow events. On 27th November 2005, an
earthquake occurred with Mb=6.2 in west of Qeshm about 57 km southwest of Bandar-e-Abbas and
produced damages and destructions in the area. The mainshock was followed by considerable
aftershock. According to this study the velocity of crust and under Moho and crustal depth is found. The
velocities of layers were obtained from the time-distance curves by a least squares method. The
apparent velocities for each event were obtained in a least squares manner. The average velocities for
the events in a distance range 175-240 km provided the upper mantle velocity. Similarly, the mean
value of apparent velocities for the distance range 120-145 km gave crust velocity. The best wave
velocity of the crust is Vpg=6.20.1 (km/s) and Vsg=3.550.05 (km/s). Wave velocity of the Moho is
Vpn=8.050.05 (km/s). In order to depth for Moho discontinuities were obtained 445 km in Bandar-e
abbas region. The computed curves for S arrivals by using several Vp/Vs ratios and comparison with the
observed S waves, suggested a value of 1.75 for Vp/Vs. The observed later phases on the records of
BNDS station were used as supplementary information.
Keywords: crust, qeshm island