It is difficult to acquire deep seismic reflection profiles on land using the standard oil-industry acquisition parameters. This is especially true over much of Tibetan plateau not only because of severe topography and rapid variation of both velocity and thickness of near-surface layer, but also strong attenuation of seismic wave through the thickest crust of the Earth. Large explosive sources had been successfully detonated in US, but its application in Tibetan plateau rarely has an example of good quality. Presented herein is the data of a 200-kg single shot we recorded in west Qinling, northeastern Tibetan plateau. The shot gather data with phenomenal signal-to-noise ratios illustrate the energy of the Prop phase. Although the observations are only limited to the northeastern Tibetan plateau and thus cannot comprise an exhaustive study, they nevertheless suggest that large explosions may be a useful exploration tool in Tibetan Plateau where standard seismic sources and profiling methods fail to produce adequate data of low crust.
Qiusheng LiRui GaoHaiyan WangJisheng ZhangZhanwu LuPengwu LiYe GuanRizheng He
This paper applies the convolutional differentiator method, based on generalized Forsyte orthogonal polynomial （CFPD）, to simulate the seismic wave propagation in two-phase media. From the numerical results we can see that three types of waves, fast P-waves, S-waves and slow P-waves, can be observed in the seismic wave field. The experiments on anisotropic models demonstrate that the wavefront is elliptic instead of circular and S-wave splitting occurs in anisotropic two-phase media. The research has confirmed that the rules of elastic wave propagation in fluid-saturated porous media are controlled by Biot＇s theory. Experiment on a layered fault model shows the wavefield generated by the interface and the fault very well, indicating the effectiveness of CFPD method on the wavefield modeling for real layered media in the Earth. This research has potential applications to the investigation of Earth＇s deep structure and oil/gas exploration.
A test of deep seismic reflection profiling across the central uplift or metamorphic belt of the Qiangtang （羌塘） terrane, Tibet plateau, provides a first image of the crustal structure. Complex reflection patterns in the upper crust are interpreted as a series of folds and thrusts, and bivergent reflections in the lower crust may represent a convergence between the Indian and the Eurasian plates.
The Qinghai （青海）-Tibet plateau is the newest and biggest orogenic belt in the world and a natural laboratory for researching continental geodynamics, such as continent-continent collision, convergence, subduction, and plateau uplift. From the 1950s to the present, there have been many active-source （deep seismic sounding and deep seismic reflection profiling） and passive-source seismic probing （broadband seismic observations） implemented to reveal the crust-mantle structure. In this article, the authors mainly summarize the three seismic probings to discuss the Moho depth of the Qinghai-Tibet plateau based on the previous summaries. The result shows that the Moho of the Qinghai-Tibet plateau is very complex and its depth is very different; the whole outline of it is that the Moho depth is deeper beneath the south than the north and deeper in the west than in the east. In the Qiangtang （羌塘） terrane, the hinterland of the Qinghai-Tibet plateau, the Moho is shallower than both the southern and the northern sides. The deepest Moho is 40 km deeper than the shallowest Moho. This trend records the crustal thickening and thinning caused by the mutual response between the India plate and the Eurasia plate, and the eastward mass flow in the Qinghai-Tibet plateau.
The Tibetan plateau as one of the youngest orogen on the Earth was considered as the result of continent-continent collision between the Eurasian and Indian plates. The thickness and structure of the crust beneath Tibetan plateau is essential to understand deformation behavior of the plateau. Active-source seismic profiling is most available geophysical method for imaging the structure of the continental crust. The results from more than 25 active-sources seismic profiles carried out in the past twenty years were reviewed in this article. A preliminary cross crustal pattern of the Tibetan Plateau was presented and discussed. The Moho discontinuity buries at the range of 60-80 km on average and have steep ramps located roughly beneath the sutures that are compatible with the successive stacking/accretion of the former Cenozoic blocks northeastward. The deepest Moho （near 80 km） appears closely near IYS and the crustal scale thrust system beneath southern margin of Tibetan plateau suggests strong dependence on collision and non-distributed deformation there. However, the -20 km order of Moho offsets hardly reappears in the inline section across northern Tibetan plateau. Without a universally accepted, convincing dynamic explanation model accommodated the all of the facts seen in controlled seismic sections, but vertical thickening and northeastern shorten of the crust is quite evident and interpretable to a certain extent as the result of continent-continent collision. Simultaneously, weak geophysical signature of the BNS suggests that convergence has been accommodated perhaps partially through pure-shear thickening accompanied by removal of lower crustal material by lateral escape. Recent years the result of Moho with -7 km offset and long extend in south-dip angle beneath the east Kunlun orogen and a grand thrust fault at the northern margin of Qilian orogen has attract more attention to action from the northern blocks. The broad lower-velocity area in the upper-middle crust of the Lhasa block was once consid
