Basement Seismicity in the Lurestan Arc of Zagros

One of the main issues in Zagros is the extent that basement and the thick sedimentary layer participate in the observed seismicity. During Nov. 2013, five magnitude ~5 Mw events hit a region in the western end of Lurestan arc of Simply Folded Belt (SFB) of Zagros. We used the Iran-China temporary network and data from regional permanent networks to relocate the events using a multiple event relocation method, calculate regional moment tensor and centeriod depths for the five moderate events and estimate a velocity model for the two nearby seismic stations using joint inversion of the receiver functions and dispersion curves. Our results show a seismic cluster of about 30 km long and 15 km width. The moment tensor solutions of the five moderate events indicate an almost pure thrust mechanism. The aftershock cloud indicate a low angle east dipping fault plane (i.e., , dip in the range of 23 o -39 o ) as the causative fault plane. The calculated centeroid of the five moderate events are about 14 km and the focal depth of all events calculated by multiple event relocation are about 10-16 km. The results indicate that the thickness of sedimentary column is less than 8 km and thus showing the whole seismic cluster happened within the basement. This observation proves wrong the hypothesis of vertical separation of mainshock and aftershocks in Ssimply folded belt FB of Zagros (Nissen et al. 2011) and implies that in the Lurestan arc the sedimentary layers are deformed aseismically.