Seismicity, Velocity Structure and Tectonics of the Arabian Plate

Hafidh A. A. Ghalib & Ghassan I. Aleqabi
Array Information Technology, 5130 Commercial Drive, Suite B, Melbourne, FL 32940, USA
Washington University in Saint Louis, Campus Box 1169, One Brookings Drive, Saint Louis, MO 63130, USA


Abstract

The deployment of the North Iraq Seismographic Network (NISN) and of the array
KSIRS and the implementation of the virtual Middle East Seismographic Network
(vMESN) produced a wealth of unprecedented data for use in studying the seismicity,
velocity structure and some aspects of the tectonic activities associated with the Arabian
plate dynamics. Recent studies using stationary Global Positioning System (GPS)
stations in the region clearly show the northeast trending transitional and
counterclockwise rotational motions of the plate. Most of the seismicity is occurring in
the crust along the Zagros and Taurus mountain ranges and their foothills, along the
Dead Sea transform fault and along the rift zones in the Red Sea and the Gulf of Aden.
Earthquakes with magnitude greater than 5 mb are not frequent. Likewise, intermediate
and deep earthquakes are uncommon in the region. The great majority of the
earthquakes occur as a result of the continental collision between the Arabian plate and
the Iranian and Turkish plateaus. Preliminary analysis of the earthquakes’ spatial
distribution suggests likely alignment with the faults in the region. Moment tensor
analysis of the larger events, carried out as part of the routine data processing, suggests
their focal mechanisms vary from normal, reverse to strike-slip depending on the local
stress pattern and the event’s location relative to the Zagros and Taurus suture zones.
The three-dimensional crustal seismic velocity structure of the Arabian plate and
surrounding regions estimated from the dispersion of Rayleigh surface waves reflects the
impact of the overlying 5-10 km thick sedimentary column on the morphology of the
crystalline basement, the Conrad and Moho discontinuities whose depths range from 20-
25 km and 40-50 km, respectively. The teleseismic P-wave receiver function analysis
provided an independent verification of the velocity models beneath the various stations
used in the study of the region. In summary, the resulting models show remarkable
correlation between the distribution of shear velocities and the major physiographic and
tectonic provinces of the Arabian plate, Turkish and Iranian plateaus. It also helped
delineate the extent of the Red Sea rift and the roots of the Zagros and Taurus mountain
ranges.

Key Words:
Arabian Plate
Seismicity
Velocity Structure
Source Mechanism


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