Abstract
The Arabian Gulf is adjacent to the Zagros Mountains, one of the most seismically active regions in the world. We observe that broadband seismic records of Zagros earthquakes recorded on the Arabian side of the Gulf display long-duration surface waves. While shorter periods (<1 s) are attenuated from crossing the deep sediments (>10 km) of the Gulf basin, the long-period energy is enhanced and transmitted efficiently. Consequently, large earthquakes in the Zagros could result in amplified ground motions at long periods (2–10 s) relative to average behavior. Such ground motions are of concern for large engineered structures, such as tall buildings and long bridges with resonant periods in the same period range. Here we present results of investigations of the characteristics of ground motions recorded on the western shore of the Gulf from selected earthquakes in the Zagros Mountains region. Exceptionally, long-duration seismic waves, as compared with standard models, are shown to occur with periods of 2–10 s. This may be due to waveguide effects in the deep sedimentary basin structure of the Arabian Platform. In addition to analyzing recorded ground motion we performed 3D wave propagation simulations using a finite difference method and experimental velocity models of the Gulf, with different shallow sedimentary layers structures. The simulation results confirm our hypothesis that long-period waves with extremely long duration and relatively large amplitudes are caused by the geometry of the basin sedimentary layers and, to some extent, by shallow earthquake depths. Combined effects of basin edge geometry with sharp velocity contrasts and shallow sources (<10 km) on the eastern side of the Arabian Gulf can cause large long-period ground motion on the western side of the Gulf. In contrast, the short-period content of ground motion (<2 s) at long distances is relatively weak. This is mainly due to wave propagation scattering and attenuation in the shallow sedimentary layers of the Gulf basin.
Highlights
The Persian/Arabian Gulf lies near the boundary of the Arabian and Eurasian Plates
Acceleration Response Spectra We used ground motions from several earthquakes in the Zagros thrust belt recorded at stations on the west coast of the Gulf to investigate the effects of the Gulf basin structure on long period wave propagation
This study is an attempt to analyze ground motion characteristics observed in the western side of the Arabian Gulf from earthquakes in the Zagros Mountains using comparisons with GMPEs and ground motion simulation
Summary
The Persian/Arabian Gulf (hereafter referred to as the Arabian Gulf, or Gulf) lies near the boundary of the Arabian and Eurasian Plates. While the Gulf is mostly aseismic, the Arabian Peninsula is surrounded by regional seismic sources in the tectonically active areas of Iran and Turkey to the northeast, the Red Sea Rift bordering the Shield to the southwest, and the Dead Sea Transform fault zone to the north (JOHNSON 1998; AL-AMRI 2013). The Zagros Mountains, which are located on the northeast side of the Arabian Gulf, is a very seismically active region Large earthquakes in this region are capable of producing significant ground motion on the southwest side of the Gulf. We investigate structural effects on ground motion by modeling 3D anelastic wave propagation using a finite difference method
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