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

Khaled Al-Damegh,Eric Sandvol,Ali Al-Lazki,Muawia Barazangi

doi:10.1111/j.1365-246x.2004.02246.x

Khaled Al-Damegh, Eric Sandvol + Show 2 more

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https://doi.org/10.1111/j.1365-246x.2004.02246.x

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Abstract

Continuous 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 (QPn) 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 QPn 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 QPn 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.

Highlights

The Arabian plate is surrounded by diverse plate boundaries (Figure 1)
The main tectonic area where efficient Lg propagation is clearly observed is along the Arabian shield, consistent with other studies (e.g. Sandvol et al 2001; Mellors et al 1999; Cong & Mitchell 1998)
West of the Arabian shield and across the Red Sea we observed another Lg efficient zone spreading from southern Egypt to northern Ethiopia and connected to the Arabian shield across the Red Sea

Summary

Introduction

The Arabian plate is surrounded by diverse plate boundaries (Figure 1). To the southwest and south the Arabian plate is bounded by sea floor spreading along the Red Sea, the Gulf of Aden, and the Arabian Sea (McKenzie et al 1970). To the east and north, the Arabian plate is colliding with the Eurasian plate along the Zagros and Bitlis sutures (McKenzie 1976). The Dead Sea fault system is located along the northwestern boundary of the plate. The fault is leftlateral with a minor component of rotation that results in the development of pull-apart basins, such as the Dead Sea rift basin (Garfunkel 1981). The interior of the plate is dominated by the late Proterozoic Arabian shield and the Arabian Phanerozoic platform. The platform is affected by numerous intraplate tectonism throughout the Mesozoic and Cenozoic time, such as the Palmyrides and Euphrates fault system within the northern part of the platform (Brew et al 2001; Hempton 1987)

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