Relocation and Assessment of Seismicity in the Iran Region

We have relocated Iranian earthquakes occurring between 1909 and 2005. The image of seismic activity occurring at the boundaries between distinct tectonic blocks is sharpened, and - most significantly - event depths are refined. ISC locations throughout Iran (especially in the Zagros) tend to be in the lower crust or upper mantle. Our results suggest that the vast majority of Iranian events occur in the upper crust, consistent with focal depths of available local seismic network hypocenters. Most confirmed lower crustal events are located in the Oman line region. Mantle events are associated with the Makran subduction zone in southern Iran and incipient subduction across the central Caspian north of the south Caspian Basin. Iranian seismicity is the result of the early stages of continent/continent collision (25-35mm/yr of northwards overall shortening) between the Arabian Peninsula and Eurasia. This shortening across Iran results in thrust and strike-slip faulting. Distinct tectonic blocks respond to the nascent collision through relative motion, resulting in seismicity at the boundaries. Areas of heightened strain (collision with the Oman Peninsula and drastic variations in crustal structure around the southern Caspian) result in seismicity in the lower crust.