Deep structure of southern Tibet inferred from the dispersion of Rayleigh waves through a long-period seismic network

Jobert, N.; Journet, Bernard; Jobert, Georges; Hirn, A.; Zhong, Shisheng

doi:10.1038/313386a0

Cited by 50 publications

(26 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our results already show that southern Tibet, near the Zangbo suture and the Himalayas, is a region of relatively high velocities, in comparison to the rest of the plateau. This result agrees with that of JOBERT et al (1985) obtained with instruments in southern Tibet. As regards the interior of the plateau, it appears that the plateau has a bowl shaped Moho with its bottom in central Tibet.…”

Section: Figuresupporting

confidence: 83%

Rayleigh Wave Group Velocity Tomography of Siberia, China and the Vicinity

Levshin

Кожевников

1997

Pure and Applied Geophysics

View full text Add to dashboard Cite

Rayleigh waves are used in a tomographic inversion to obtain group velocity maps of East Asia (40°E-160°E and 20°N-70°N). The period range studied is 30 to 70 seconds. Seismograms used for this study were recorded at CDSN stations, at a temporary broadband seismic array in Tibet, at several SRO stations, and Kirnos-equipped stations established in Asia by the former Soviet Union, in Siberia, in the Sakhalin and in Mongolia. Altogether more than 1200 paths were available in the tomographic inversion. The study area includes the Angara craton, the geologically ancient core of Asia, and the subsequently accreted units, the Altaids (a Paleozoic collision complex), the Sino-Korean platform (a chain of Archaen terranes separated by belts of active structures), the south China platform (a collage of Precambrian, Paleozoic and Mesozoic metamorphic and igneous terranes), as well as the Tibetan plateau (an active tectonic feature created in late Cenozoic through collision of the Indian subcontinent and the Asian continent). Many of these main units are recognizable in the tomographic images as distinctive units; Tibet appears as a prominent low velocity (about −15% from the average) structure, with western and central Tibet often appearing as the areas with the lowest velocities, the Central Asian fold-belt, and the Angara craton are consistently high group velocity areas. Some lesser tectonic features are also recognizable. For example, Lake Baikal is seen as a high velocity feature at periods greater than 40 seconds. However, the high group velocity feature does not stop near the southern end of Lake Baikal; it extends south-southwestward across Mongolia. The North China Plain, a part of the platform where extensional tectonics dominate, is an area of high velocities as a result of relatively thin crust. The south China block, the least tectonically active region of China, is generally an area of high velocity. For periods longer than 40 seconds, a NNE trending high group velocity gradient clearly exists in eastern China; the velocities are noticeably higher in the east. From the group velocity maps, average dispersion curves at twelve locations were determined and inverted to obtain velocity structures. Main results of group velocity inversion include: (1) a Tibetan crust of around 60 km thick, with low crustal and upper mantle shear velocities, at 3.3 km/s and 4.2 km/s, respectively; (2) with the Moho constrained at 40-43 km, the Angara craton and the Central Asian foldbelt have a V S in excess of 4.6 km/s; (3) relatively low shear velocities are obtained for tectonically active areas. In many parts of the study area, where Precambrian basement is exposed, the process in the crust and upper mantle due to recent tectonic activities have modified the crust and upper mantle velocity structures under the Precambrian terranes, they are no longer underlain by high velocity crust and mantle.

show abstract

Section: Figuresupporting

confidence: 83%

Rayleigh Wave Group Velocity Tomography of Siberia, China and the Vicinity

Levshin

Кожевников

1997

Pure and Applied Geophysics

View full text Add to dashboard Cite

show abstract

“…Before the 1991-1992 PASSCAL experiment, many seismic studies measured group and/or phase velocities of surface waves propagating across the plateau and invert for 1-D velocity structure (ROMANOWICZ, 1982;JOBERT et al, 1985;BRANDON and ROMANOWICZ, 1986). Others used Pn and Sn travel times to estimate velocities in the uppermost mantle BARAZANGI and NI, 1982).…”

Section: Tectonic Setting and Previous Resultsmentioning

confidence: 99%

Calibration of the Tibetan Plateau Using Regional Seismic Waveforms

Zhu

Tan

Helmberger

et al. 2006

Pure appl. geophys.

View full text Add to dashboard Cite

We use the recordings from 51 earthquakes produced by a PASSCAL deployment in Tibet to develop a two-layer crustal model for the region. Starting with their ISC locations, we iteratively fit the P-arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters. An average crustal P velocity of 6.2-6.3 km/s is obtained for a crustal thickness of 65 km while the P velocity of the uppermost mantle is 8.1 km/s. The upper layer of the model is further fine-tuned by obtaining the best synthetic SH waveform match to an observed waveform for a well-located event. Green's functions from this model are then used to estimate the source parameters for those events using a grid search procedure. Average event relocation relative to the ISC locations, excluding two poorly located earthquakes, is 16 km. All but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km. This is 15 km shallower, on average, than depths reported by the ISC. The shallow seismicity cut-off depth and low crustal velocities suggest high temperatures in the lower crust. Thrust faulting source mechanisms dominate at the margins of the plateau. Within the plateau, at locations with surface elevations less than 5 km, source mechanisms are a mixture of strike-slip and thrust. Most events occurring in the high plateau where elevations are above 5 km show normal faulting. This indicates that a large portion of the plateau is under EW extension.

show abstract

“…Before the 1990's most seismologic studies of the Tibetan deep structure were aimed at constraining largescale features using stations mostly outside the plateau (Roecker, 1982;Ni and Barazangi, 1983;Jobert et al, 1985;Molnar, 1988). In the last decade, there have been several deployments of seismologic arrays, such as the PASSCAL experiment (McNamara et al, 1994;Owens and Zandt, 1997) and the INDEPTH II/GEODEPTH experiment (Nelson et al, 1996;Kind et al, 1996;Yuan et al, 1997;Fig.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%