Field Survey and Simulation of the 1990 Rudbar Earthquake Tsunami Along the Iranian Coast of the Caspian Sea

Abstract:

The occurrence of tsunamis on the Southern coast of the Caspian Sea is reported historically, and constitutes potentially significant hazard, due to modern development and a locally high population density. In the Summer of 2012, we conducted a field survey motivated by Rikhter (1961)'s claim of an episode of inundation in 1960, but could not verify it from the testimony of older witnesses. Rather, we documented that the 1990 Rudbar earthquake (Mw = 7.4) was definitely followed by a tsunami reaching a run-up amplitude of ~2 m along a ~30 km stretch of the coast, from Kiashahr to Jafrood, and which to our our knowledge, had not been previously reported. A dataset of 29 witness reports was compiled using standard investigative techniques for post-tsunami surveys.

Hydrodynamic simulations using the MOST algorithm and various published models of the earthquake's rupture fail to reproduce the fundamental characteristics of the inundation, notably its lateral concentration along the coast. The alternative model of an underwater landslide, presumably triggered along a steep segment of the Caspian Sea floor, provides an acceptable fit to the distribution of the tsunami along the shoreline of the Caspian Sea, and suggests that landslides could be the primary source of tsunami hazard in the area.