Regional seismic wave propagation (Lg and Sn) and Pn attenuation in the Arabian Plate and surrounding regions

Abstract

S U M M A R YContinuous recordings of 17 broadband and short-period digital seismic stations from a newly established seismological network in Saudi Arabia, along with digital recordings from the broadband stations of the GSN, MEDNET, GEOFON, a temporary array in Saudi Arabia, and temporary short period stations in Oman, were analysed to study the lithospheric structure of the Arabian Plate and surrounding regions. The Arabian Plate is surrounded by a variety of types of plate boundaries: continental collision (Zagros Belt and Bitlis Suture), continental transform (Dead Sea fault system), young seafloor spreading (Red Sea and the Gulf of Aden) and oceanic transform (Owen fracture zone). Also, there are many intraplate Cenozoic processes such as volcanic eruptions, faulting and folding that are taking place.We used this massive waveform database of more than 6200 regional seismograms to map zones of blockage, inefficient and efficient propagation of the Lg and Sn phases in the Middle East and East Africa. We observed Lg blockage across the Bitlis Suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. This is probably due to a major lateral change in the Lg crustal waveguide. We also observed inefficient Lg propagation along the Oman mountains. Blockage and inefficient Sn propagation is observed along and for a considerable distance to the east of the Dead Sea fault system and in the northern portion of the Arabian Plate (south of the Bitlis Suture). These mapped zones of high Sn attenuation, moreover, closely coincide with extensive Neogene and Quaternary volcanic activity. We have also carefully mapped the boundaries of the Sn blockage within the Turkish and Iranian plateaus. Furthermore, we observed Sn blockage across the Owen fracture zone and across some segments of the Red Sea. These regions of high Sn attenuation most probably have anomalously hot and possibly thin lithospheric mantle (i.e. mantle lid). A surprising result is the efficient propagation of Sn across a segment of the Red Sea, an indication that active seafloor spreading is not continuous along the axis of the Red Sea. We also investigated the attenuation of Pn phase (Q Pn ) for 1-2 Hz along the Red Sea, the Dead Sea fault system, within the Arabian Shield and in the Arabian Platform. Consistent with the Sn attenuation, we observed low Q Pn values of 22 and 15 along the western coast of the Arabian Plate and along the Dead Sea fault system, respectively, for a frequency of 1.5 Hz. Higher Q Pn values of the order of 400 were observed within the Arabian Shield and Platform for the same frequency. Our results based on Sn and Pn observations along the western and northern portions of the Arabian Plate imply the presence of a major anomalously hot and thinned lithosphere in these regions that may be caused by the extensive upper mantle anomaly that appears to span most of East Africa and western Arabia.

Local Site Effects Estimated from Ambient Vibration Measurements at Aqaba City, Jordan

“…The seismic hazard for the city of Aqaba, for the hilly rocky sites, may be related to earthquakes epicentered in the city or around with DF greater than 2.7 Hz. While the earthquakes, that epicentered in the Gulf of Aqaba (i.e., around 100 km away from the city) such as the Gulf of Aqaba 1995 event, may affect more the Wadi's and near shore sites that characterized by thick alluvium sediments with dominant peak frequencies range between 0.3 and 1.8 Hz, such observation is supported by previous studies for the area such as Al-Damigh et al [2004] and Al-Tarazi [2000].…”

Crustal structure of the Arabian plate: new constraints from the analysis of teleseismic receiver functions

“…This is partially documented in western Arabia based on the recent tomographic results of high attenuation and low velocity uppermost mantle [7,48,49].…”

“…It appears that the Red Sea consists of both oceanic and attenuated/thinned continental crust [6,7]. Neogene and Quaternary volcanics are present along the western part of the Arabian plate [8].…”

Evidence of magma activation beneath the Harrat Lunayyir basaltic field (Saudi Arabia) from attenuation tomography

“…Attenuation tomography has been successfully used in many studies of crustal and mantle structures. Regional attenuation structures in the mantle beneath the Arabian Plate surrounding the studied region were investigated together with Pn and Sn velocities by Al-Damegh et al (2004). They found a presence of a large mantle anomaly beneath western side of the Arabian Plate which is interpreted as a zone of thinner lithosphere and hot asthenosphere.…”