Patterns of historical earthquake rupture in the Iranian plateau

The Iranian plateau accommodates the 35 mm/yr convergence rate between the Eurasian and Arabian plates by strike-slip and reverse faults with relative ly low sig rates in a zone 1000 km across. although these faults have only locally been the subject: of paleoseismological studies, a rich historical and archeological record spans several thousand years, long enough to estab lish recurrence intervals of 1000 to 5000 yr on individual fault segments. Several clusters of earthquakes provide evidence of interaction among rever se and strike-slip faults, probably due to adjacent faults being loaded by individual earthquakes. The Dasht-e-Bayaz sequence of 1936 to 1997 includes earthquakes on left-lateral, right-lateral, and reverse faults. The Neysha bur sequence: of four earthquakes between 1209 and 1405 respected the segme nt boundary between the Neyshabur and Binalud reverse fault systems. The tw o pairs of earthquakes may have ruptured different faults in each segment, similar to the 1971 and 1994 San Fernando, California, earthquakes. The 197 8 Tabas reverse-fault earthquake was preceded. by the 1968 Ferdows earthqua ke, part of the Dasht-e-Bayaz sequence, The North Tabriz fault system ruptu red from southeast to northwest in three earthquakes from 1721 to 1786; a p revious cluster may have struck this region in 855 to 958. The Mosha fault north of Tehran ruptured in three earthquakes in 958, 1665, and 1830, Five large earthquakes struck the Tehran region from 743 to 1177, but only two t hat large have struck the area since 1177. Other earthquakes occurred in pa irs in the Talesh Mountains near the Caspian Sea (1863, 1896),the Iran-Turk ey border (1844 1843), and the Nayband-Gowk fault system (both in 1981). Ot her historical events did not occur as parts of sequences. The historic seismic moment release in Iran accounts for only a small part of the plate convergence rate, which may be due to aseismic slip or to the Iranian historical record, long as it is, being too short to sample long-te rm deformation across the plateau. Na historic earthquakes of M greater tha n or equal to 8 have struck Iran. However, several long, straight strike-sl ip faults (Doruneh, West Neh, East Neh, and Nayband) have not sustained lar ge historical earthquakes, raising the possibility that these long faults c ould produce earthquakes of M greater than or equal to 8, thereby removing at least part of I-he apparent slip deficit. An increased understanding of Iran's seismic hazard. could be obtained by a n extensive paleoseismology program and space-geodetic arrays, supplementin g the abundant historical and archaeological record.