The June ۲۰,۱۹۹۰ Rudbar-Tarom (NW Persia) Catastrophic Earthquake; a preliminary field reconaissance report

The June ۲۰, ۱۹۹۰ Rudbar-Tarom (NW Persia) earthquake (Ms=۷.۷, Mb=۶.۴, I=X) which was extremely destructive, killed a total of ۴۰,۰۰۰ people (reported), left mere than ۵۰۰,۰۰۰ homeless, destroyed three cities (Rudbar, Manjil and Lowshan) together with ۷۰۰ villages, and slightly damaged another. ۳۰۰ villages, in the densely populated area of the western Alborz mountains, southwest of the Caspian Sea. Evidences of both earthquake faulting and folding were observed in the meizoseismal area. The earthquake was associated with at least three main discontinuous en-echelon complex system of fault segments (extending for more than ۸۰ km in length) indicating that the mainshock was a complex multiple event with at least three main subevents. These three main segments are separated by gaps in the surface rupture in a left-lateral pattern. Each segment, with a N۹۵E to N۱۲۰E trend, shows a left - lateral oblique high-angle reverse mechanism at the surface (nearly vertical, dipping south and southwest) with observed horizontal displacement of ۶۰ cm and a vertical displacement of ۹۵ cm at the surface. The earthquake was also associated with several coseismic flexural-slip faults (bedding plane slip with thrust mechanism) during earthquake folding.