Investigation of Seismotectonics of Eastern South Caspian Basin Using Earthquakes Focal Mechanism and Geomorphological Investigations

Nemati, M; Hollingsworth, J; Ghassemi, M.R

doi:10.22071/gsj.2015.43393

Investigation of Seismotectonics of Eastern South Caspian Basin Using Earthquakes Focal Mechanism and Geomorphological Investigations

Document Type : Original Research Paper

Authors

M Nemati ¹

J Hollingsworth ²

M.R Ghassemi ³

¹ Assistant Professor, Department of Geology, Faculty of Sciences and Earthquake Research Center, Shahid Bahonar University of Kerman, Kerman, Iran

² Assistant Professor, Division of GPS, California Institute of Technology, Pasadena, USA

³ Associate Professor, Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran

10.22071/gsj.2015.43393

Abstract

Our research focuses on the seismotectonics of the north of Eastern Alborz and southeast of the Caspian Sea. Eastern part of the Caspian fault, and seismological active plain situated in north of the area have been studied. The seismological data of microearthquakes (M_L>4.5) recorded by the local network of the Geological Survey of Iran (installed during 2009 and 2010) and regional seismicity located by seismological networks of the Geophysics Institute of University of Tehran and International Institute of Earthquake Engineering and Seismology of Iran were used. Also geomorphological evidences in the area and dynamic parameters of the 1985 Gorgan earthquake, M_S=6.0, are included for getting a better justification. Although deep thrust mechanisms of the 1999, 2004 and 2005 earthquakes indicate N-S compressional regime at depth and normal component of shallow earthquakes (M_L>4.5) shows extensional regime at near surface in southeast of the Caspian Sea. The morphological evidences confirm this normal kinematics. In addition, the dynamical parameters of the 1985 Gorgan earthquake and its focal mechanism introduce the Caspian fault as the source of this thrust earthquake. All evidences confirm probable underthrusting of southeast of the CaspianBasin beneath the Eastern Alborz.

Keywords

Caspian Sea

Earthquake

Thrusting

Moho discontinuity

Local Network

Seismotectonics