HR: 17:20h
AN: S44A-05 INVITED     [Abstracts]
TI: Joint receiver function, wide-angle reflection and P and S teleseismic delays approaches to image the lithosphere of Himalaya-South Tibet
AU: * Galve, A
EM: agalve@ija.csic.es
AF: Dpt de Ciencias de la Terra IJA, CSIC, calle Lluis Sole i Sabaris, Barcelona, 08028 Spain
AU: Hirn, A
EM: hirn@ipgp.jussieu.fr
AF: Dpt de Sismologie, IPGP, 4 place Jussieu, Paris, 75005 France
AU: Gallart, J
EM: jgallart@ipgp.jussieu.fr
AF: Dpt de Ciencias de la Terra IJA, CSIC, calle Lluis Sole i Sabaris, Barcelona, 08028 Spain
AU: Sapin, M
EM: sapin@ipgp.jussieu.fr
AF: Dpt de Sismologie, IPGP, 4 place Jussieu, Paris, 75005 France
AU: Diaz, J
EM: jdiaz@ija.csic.es
AF: Dpt de Ciencias de la Terra IJA, CSIC, calle Lluis Sole i Sabaris, Barcelona, 08028 Spain
AU: Jiang, M
EM: meij@public3.bta.net.cn
AF: Chinese Academy of Geological Sciences, Baiwanzhuang road, Beijing, 100029 China
AU: Laigle, M
EM: laigle@ipgp.jussieu.fr
AF: Dpt de Sismologie, IPGP, 4 place Jussieu, Paris, 75005 France
AB: A sino-french experiment in 1981-82 has deployed stations to record wide-angle reflections from Nepal to the centre of Tibet (Qang Tang) in order to image the north-south structural variation of the lithosphere (Hirn et al., 1984). This experiment was designed to image the Moho topography which appear complex with Moho segmentation and overlapping. In 1992, 24 broad-band 3-component stations were deployed along the same line than 10 years earlier. This array has recorded teleseismic earthquakes that we have processed to obtain an image from receiver functions. The general aspects of the Moho architecture are similar with a Moho which depth range from 50 to 90 km. These two images were obtained from two sets of data completely independent, highlighting the Moho. Indeed we here observe the response of the crust-mantle discontinuity to P-wave wide-angle reflections and to conversion of teleseismic P waves to SV waves.Since the main characteristics observed using the different methods agree in general, we have attributed them to the same structural elements and combine these two images to constrain physical parameters as the north-south variation of the velocity ratio in the crust. The matching in depth between the two images can be obtained by a decrease of the S-wave velocity north of the Indus Tsangpo suture (ITS). This is consistent with another type of observation made on the line: the P and S teleseismic delays. Indeed, the delay time of P-wave first arrival decrease northwards while the corresponding S-wave delay time increase strongly. This is consistent with a decrease of the crustal thickness north of ITS, as we see it on the image, as well as a decrease of the S-waves velocity, consistent with the presence of partial melt (Kind et al., 1996) and/or water (Makovsky and Klemperer, 1999). These two images do not join the idea of a continuous and smooth Moho. It appears to be made of segments that dip, overlap or superpose each other and imply to propose an alternative type of evolution model of Himalaya-Tibet.
DE: 0540 Image processing
DE: 0935 Seismic methods (3025, 7294)
DE: 7218 Lithosphere (1236)
DE: 9320 Asia
SC: Seismology [S]
MN: Fall Meeting 2005