Sn Attenuation in the Iranian and Tibetan Plateaus

Abstract:

The Iranian and Tibetan plateaus are both part of the Alpine-Himalayan mountain belt and both formed as a result of the continental collision (between Arabian plate, Indian plate and Eurasia plates). The two plateaus illustrate many of the same processes but at different stages of development. The Iranian plateau is a much less mature continental plateau than the Tibetan plateau with about half the elevation and a much thinner crust. In order to better understand the nature of the lithosphere mantle and origin of the measure seismic velocity anomalies we have made detailed measurements of the uppermost mantle attenuation using the high frequency regional phase Sn.

In order to measure Sn attenuation. We have collected a large data set consisting of 18 years (1995-2012) of waveforms recorded by 305 permanent and temporary stations in Iran and 3 years (2007-2009) of waveforms recorded by 136 permanent and temporary stations in Tibet separately. We used a bandpass filter (0.1-0.5Hz) to identify efficient longer period Sn phases. In order to determine Sn Q we applied a Two Station Method (TSM) and Reverse Two Station Method (RTM) to eliminate the source effects. We have used the LSQR algorithm to tomographically map Sn attenuation tomography across the Iranian plateau.

Our results show moderately low Q values beneath the Iranian plateau (~250) and high Q values beneath the south Caspian sea (~400) and Arabian shield (~400). The pattern we observe is roughly consistent with previous studies. We also observe high Q values beneath the Zagros mountains (~450) that is consistent with the Arabian plate underthrusting beneath the Eurasia plate. In Tibet we find high Q values beneath the Qaidam basin (~500) and low Q values beneath much of the Kunlun fault (~200). We also observe high Q values beneath the Bangong-Nujiang suture (~400) which can be explained that the Indian plate is underthrusting beneath the Eurasia plate. Comparing the Sn Q values beneath the Iranian and Tibetan plateaus, we find they are about the same.