Source Study of some Large Earthquakes Occurred in South Eastern Iran

We examine the source parameters of the March ۱۴, ۱۹۹۸ (Mw ۶.۶); March ۴, ۱۹۹۹ (Mw ۶.۶); February ۱۴, ۲۰۰۳ (Mw ۵.۶); December ۲۶, ۲۰۰۳ (Mw ۶.۶); February ۲۸, ۲۰۰۶ (Mw ۶.۰); earthquakes by analyzing body waveform seismograms and compiled source time function of June ۱۱, ۱۹۸۱ (Ms ۶.۷); July ۲۸, ۱۹۸۱ (Ms ۷.۱); November ۲۰, ۱۹۸۹ (mb ۵.۶) events, obtained from body waveform modeling. The results from waveform modeling for the March ۱۴, ۱۹۹۸; December ۲۶, ۲۰۰۳ events indicate that source depth was changed between ۴ and ۶ km and that the mechanism was right-lateral strike-slip. Evaluation of slip vector azimuths (assuming that the west-dipping nodal plane is the fault plane) of earthquakes occurred along the Gowk and Bam faults system (changed between ۱۴۲o-۱۸۴o) confirm the govern tension in this area and the dominant direction of basement is northward. The source depth of earthquakes (March ۴, ۱۹۹۹; February ۱۴, ۲۰۰۳; February ۲۸, ۲۰۰۶ events) in southern part of study area was changed from ۲۲ km to ۲۶ km and that the mechanism was dip-slip. They probably reflect the lower crust subducted zone dipping NNE direction with a low angle beneath the central Iran in this area and suggest a seismogenic layer of > ۲۰ km thick under the deposit layers sequence. The main purpose of this study is to evaluate fault rupture, and prepare information about displacement time history on the fault. The major pulse duration of each event was determined from source time function and used to determine rupture length. Seismic moments deduced from the body wave synthetics are used for calculating displacement and stress drop. Minimum and maximum displacement and stress drop is changed from ۰.۱۵ m to ۳.۵ m, ۳.۲ bars to ۷۹ bars, respectively. Varying the seismic moment along total duration of source time function is direct related to varying the source velocity structure did have an effect on centroid depth and seismic moment.

Keywords:

Source Parameters , Source Time Function , Waveform Modeling , Southeast Iran