Observations of frequency-dependent propagation in Northern Tibet

Barron, J. and Priestley, K. (2009) Observations of frequency-dependent propagation in Northern Tibet. Geophysical Journal International, 179 (1). pp. 475-488. DOI 10.1111/j.1365-246X.2009.04318.x

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Abstract

We present new observations of the frequency-dependent propagation efficiency of the seismic phase Sn over the Tibetan Plateau. Our measurements are the ratio of the Sn amplitude to the Pg coda amplitude on Tibetan regional seismograms, and we map the lateral variation in the maximum and mean values of this ratio across the Plateau. Good path density and azimuthal coverage allow the area of Sn blockage identified by previous studies to be better constrained. An important result is that at low frequencies (∼0.2 Hz), Sn propagates efficiently over the entire Plateau, whereas at higher frequencies (∼1 Hz), Sn is blocked for a region of the northern Plateau. As we take measurements at higher frequencies, we find that the southern boundary of the region of inefficient propagation migrates to the south. The observation that low frequency Sn propagates efficiently across the whole Plateau suggests that at the length-scales sampled by these waves, the upper mantle has an overall positive shear velocity gradient, which could indicate that the high-velocity seismic lid, or seismic lithosphere, beneath Tibet is still intact, and has not delaminated as some researchers have previously proposed. The observation that high frequency Sn does not propagate beneath northern Tibet suggests that at the shorter length-scales sampled by the higher frequency waves, the upper mantle has a negative shear velocity gradient. This could indicate that at shallow depths the sub-Moho upper mantle is hot and may contain some melt.

Item Type: Article
Uncontrolled Keywords: 09AREP; IA58;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Geophysical Journal International
Volume: 179
Page Range: pp. 475-488
Identification Number: 10.1111/j.1365-246X.2009.04318.x
Depositing User: Sarah Humbert
Date Deposited: 10 Oct 2009 10:25
Last Modified: 23 Jul 2013 09:55
URI: http://eprints.esc.cam.ac.uk/id/eprint/1187

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