Body Waveform Modeling of Five Moderately Earthquakes in the Zagros Fold Thrust Belt
Mehrdad Mostafazadeh , Omer Alptekin and Ali Osman Oncel
The generalized linear inverse technique has been applied to the problem of determining earthquake source models for five moderately large earthquakes in the Zagros Fold Thrust Belt (ZFTB). These earthquakes occurred in the southeastern (29 April 1987, m b =5.9, 12 July 1983, m b =5.8), central (12 July 1986, m b =5.6), northwestern (28 May 1983, m b =5.1, 18 December 1980, m b =5.8) parts of the ZFTB. Propagation and instrumental effects are deconvolved from the long period P and SH wave records of GDSN stations to obtain the teleseismic source time function using a damped least squares inversion. The inversion has the additional constraint that the source time function is positive everywhere. A comparison of source time function of these events show that the average source duration of earthquake along the strike-slip Kazerun fault is greater than the other parts of the region. Generally slow earthquakes have long source duration. Slow risetime presumably results from a very low stress drop. Focal mechanisms of the earthquakes are thrust in the southeastern ZFTB,and have strike-slip components in the central and northwestern ZFTB. Depth values of these events are estimated to vary between 5-15km. Considering the depths and observed emergent moment release, we speculate that these events occurred beneath the sedimentary sections near to the detachment horizon. The slip vectors along the Zagros zone that are computed on the basis of compiled focal mechanism solutions in this and previous studies show a similarity with direction of convergence between the Arabian plate and the Iranian plateau.