NON-DOUBLE COUPLE COMPONENT OF 2006/03/09, MW 4.9 EARTHQUAKE IN EASTERN IRAN

Harvard CMT solution reported a low double-couple percentage (DC %) for the 2006/03/09 Mw 4.9 east of Iran earthquake, of about 38%. Near-regional waveforms, carefully analyzed in this paper for the DC% of moment tensor of this earthquake. Our study suggested a higher DC%,ranging from 60 to 100, dependent on the frequency used in the inversion. We try to model this earthquake with single and two point sources, but the fit of near-regional data cannot be improved when considering two-event model (we consider the probability of source complexity for this earthquake). However, two features make the two-event model unlikely: The second subevent changes drastically in its focal mechanism (based on the frequency used) and temporal separation (6 to 10 s) between first and second subevent is larger than the expected of this earthquake.In these tests we also investigate the dependence of DC% and frequencies used in the inversion. We also run deviatoric and pure double couple MT inversion for this earthquake in order to see the changes in DC percentage of the moment tensor. Our MT inversion (deviatoric) for waveforms using frequency range between 0.02 to 0.11 Hz show high DC% for this earthquake and reveal a stable mechanism in both deviatoric and pure DC inversions for frequencies > 0.1. Final preference is given to the simple interpretation, most clearly supported by the nearregional data, that this earthquake was an almost pure-shear event.

Keywords:

Moment Tensor , Non Double Couple Earthquakes , CMT Solution