Crustal structure of central Tibet as derived from project INDEPTH wide-angle seismic data

Citation
W. Zhao et al., Crustal structure of central Tibet as derived from project INDEPTH wide-angle seismic data, GEOPHYS J I, 145(2), 2001, pp. 486-498
Citations number
48
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
GEOPHYSICAL JOURNAL INTERNATIONAL
ISSN journal
0956-540X → ACNP
Volume
145
Issue
2
Year of publication
2001
Pages
486 - 498
Database
ISI
SICI code
0956-540X(200105)145:2<486:CSOCTA>2.0.ZU;2-A
Abstract
In the summer of 1998, project INDEPTH recorded a 400 km long NNW-SSE wide- angle seismic profile in central Tibet. from the Lhasa terrane across the B anggong-Nujiang suture (BNS) at about 89.5 degreesE and into the Qiangtang terrane. Analysis of the P-wave data reveals that (1) the crustal thickness is 65+/-5 km beneath the line; (2) there is no 20 km step in the Moho in t he vicinity of the BNS, as has been suggested to exist along-strike to the east based on prior fan profiling: (3) a thick high-velocity lower crustal layer is evident along the length of the profile (20-35 km thick, 6.5-7.3 k m s(-1)); and (3) in contrast to the southern Lhasa terrane, there is no ob vious evidence of a mid-crustal low-velocity layer in the P-wave data, alth ough the data do not negate the possibility of such a laver of modest propo rtions. Combining the results from the INDEPTH III wide-angle profile with other se ismic results allows a cross-section of Moho depths to be constructed acros s Tibet. This cross-section shows that crustal thickness tends to decrease from south to north, with values of 70-80 km south of the middle of the Lha sa terrane, 60-70 km in the northern part of the Lhasa terrane and the Qian gtang terrane, and less than 60 km in the Qaidam basin. The overall northwa rd thinning of the crust evident in the combined seismic observations, coup led with the essentially uniform surface elevation of the plateau south of the Qaidam basin, is supportive of the inference that northern Tibet until the Qaidam basin is under lain by somewhat thinner crust. which is isostati cally supported by relatively low-density, hot upper mantle with respect to southern Tibet.