Source Parameters of The 26 April 2007 Bam Earthquake Obtained By The Near Field Accelerograms Data



On 26 December 2003 at 05:26LT (01:26GMT), a catastrophic earthquake Mw 6.6, seismic moment (6 – 9 ×10 Nm) struck the city of Bam in the Kerman province of southeast Iran. The intense shaking in the city caused the complete collapse of nearly every building in the central parts of the city including many of the newer buildings, killing about 40000 people officially. The city lies to the east of the Nyband – Gowk – Sarvestan fault system and on which several powerful earthquakes have occurred over the past 23 years [Berberian et al., 1984; Berberian and Qorashi, 1994; Berberian et al., 2001]. There are no recorded historical earthquakes at Bam. Most of the citadel of Arg-e-Bam, one of world heritage sites inscribed by UNESCO, which was constructed by mud brick about 2000 years ago was destroyed in this earthquake.
Four powerful earthquakes (M>6) since 1981 have occurred near the Gowk fault zone [Berberian et al., 1984, 2001]. The Gowk fault zone, a predominantly right–lateral strike–slip zone that extends from 50 km west of Bam northward [Walker and Jackson, 2002], has also been associated with several large historical earthquakes [Ambraseys and Melville, 1982; Berberian and Yeats, 1999].
After 26 December 2003 many aftershocks and earthquakes have occurred in Bam, southeast Iran. The last event with M=4.9 (NEIC) occurred on 26 April 2007. In this study, we calculated the ground motion parameters of the latest event using digital accelerograms of the Building and Housing Research Center (BHRC). We calculated seismic Moment (Mo) and Moment magnitude (Mw) of the 03/26/2007 Bam earthquake. For acceleration, Velocity and Displacement diagrams; we determined flat portion (K) and corner frequency (fc) by correction of base line and band pass filtering of Fourier spectrum. We calculated average seismic Moment (Mo=3.6×1016 Nm) and Mw 5; the answers conform to the results by other methods computation. We determined the location of the epicenter, our motivation for these computations was the determination of the difference of epicentral location with Maximum 36 km. In this study, we determined the focal mechanism of this earthquake; strike angle (N51?W), Dip89 ? westwards and Rake 138?, by using first P motion of the accelerograms and seismograms Data.
The occurrence of a strong earthquake such as that of the 26 April 2007 indicates that the Bam region is still seismically active.