HR: 1340h
AN: T13E-1626    [Abstracts]
TI: Observations of Frequency-Dependent Sn Blockage in Northern Tibet
AU: * Barron, J A
EM: jaab3@cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences, Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AU: Priestley, K F
EM: keith@madingley.org
AF: University of Cambridge, Department of Earth Sciences, Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AB: We present new observations of the frequency-dependent propagation efficiency of the seismic phase S_n over the Tibetan plateau. Our measurements are the ratio of the S_n amplitude to the P_coda amplitude on Tibetan regional seismograms. 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 S_n blockage identified by previous studies to be better constrained. An important result is that at low frequencies (0.2 Hz), S_n propagates efficiently over the entire plateau, while at higher frequencies, S_n is blocked for a region of the northern plateau. The area of inefficient \rm S_n propagation extends farther southward as higher frequencies (between 0.2 and 1.0 Hz) are brought into consideration. The observation that low frequency S_n propagates efficiently across the whole plateau suggests that the lithosphere beneath Tibet is still intact and has not delaminated as previously proposed. The observation that high frequency S_n does not propagate beneath northern Tibet suggests that the Tibetan upper mantle has been heated and possibly contains partial melt.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7218 Lithosphere (1236)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting