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 Tibe...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 geo-physical 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 Pla-teau 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 oro-gen 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 considered as resulted from partially melted rocks.However the low normal vP/vS ratio and the Moho stepwise rise fail to support significant partial melting in the middle-lower crust of the central-northern Tibetan plateau.Furthermore,the lower-velocity of crust occasionally disappears,and/or local thinned exhibits their non-stationary spatial distribution.展开更多
Along the western Kunlun-Tarim-Tianshan geoscience transect in the northwestern China,an integrated geophysical investigation was carried out. Owing to the abominable natural conditions there,the sounding profile coul...Along the western Kunlun-Tarim-Tianshan geoscience transect in the northwestern China,an integrated geophysical investigation was carried out. Owing to the abominable natural conditions there,the sounding profile could not cross the whole transect,consequentially,a variety of velocity structures in the transverse and vertical orientations beneath the whole transect were not obtained,such as the case within the western Kunlun orogenic belt. To supply a gap of deep seismic soundings within the western Kunlun orogenic belt,we used the Bouguer gravity anomaly data and the relationship between the compressive wave and the density to obtain the density structure of the crust beneath the western Kunlun and the southern Tarim basin by a forward fitting of gravity anomalies within the two-dimensional polygonal model of uniform medium. The crust of the Tarim basin with a rigid basement was like an asymmetrical arc,whose surface feature was the Bachu uplift in the middle of the Tarim basin. Beneath the conjoint area between the Tarim basin and the western Kunlun belt,there was a V-shape structure located just up to the top of the uplifted Moho. The multi-seismological structures jointly revealed that the face-to-face continent-continent collision beneath the western Kunlun is a new structural style within the continent-continent collision zone,which is a real model proved by the numerical modeling.展开更多
Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface struc...Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface structures.For the development and utilization of urban underground space,two parameters in the shallow surface are important,namely,the shear wave velocity(V_(S))and the predominant period of the site,which determine the elevation and aseismic grade of the building design.The traditional method is mainly to obtain the two above-mentioned parameters through testing and measuring drilling samples.However,this method is extremely expensive and time consuming.Therefore,in this research,we used the multichannel surface wave acquisition method to extract the fundamental dispersion curve of single-shot data by using the phase shift method and obtain the V_(S) characteristics in the uppermost 40 m by inversion.We arrived at the following two conclusions based on the V_(S) profile.First,the study area can be roughly divided into five layers,among which the layers 0−8 m,14−20 m,and 20−30 m are low-velocity layers,corresponding to miscellaneous fill,a water-bearing sand layer,and a sand layer;therefore,the V_(S) is relatively low.In contrast,the layers at 8−14 m and 30−40 m are high-velocity layers that are mainly composed of clay,with a relatively better compactness and relatively high V_(S) values.In addition,a low-speed anomaly appears abruptly in the high-speed area at 20−40 m.This anomaly,when combined with geological data,suggests that it is an ancient river channel.Second,from the V_(S) value,the V_(Se)(equivalent shear wave velocity)was calculated.The construction site soil was categorized as class III,with good conditions for engineering geology.In addition,we calculated the predominant period of the site to be 0.56-0.77 s based on the V_(S).Therefore,in the overall structural design of the foundation engineering,the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.展开更多
Fine structures of the crust and upper mantle of the basin-and-range juncture on the northwestern margin of the Qinghai-Tibetan Plateau are first delineated by the deep seismic reflection profile across the juncture z...Fine structures of the crust and upper mantle of the basin-and-range juncture on the northwestern margin of the Qinghai-Tibetan Plateau are first delineated by the deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains. Evidence is found for the northward subduction of the northwest marginal lithosphere of the Qinghai-Tibetan Plateau and its collision with Tarim lithosphere beneath the West Kunlun Mountains. The lithosphere image of the face-to-face subduction and collision determines the coupling relationship between the Tarim Basin and the West Kunlun Mountains at the lithosphere scale and reflects the process of continent- continent collision.展开更多
The deep seismic sounding profile across the Tianshan Mountains revealed a two-layer crustal structure in the Tianshan region, namely the lower and upper crusts. Lateral variations of layer velocity and thickness are ...The deep seismic sounding profile across the Tianshan Mountains revealed a two-layer crustal structure in the Tianshan region, namely the lower and upper crusts. Lateral variations of layer velocity and thickness are evidently shown. Low-velocity layers spread discontinuously at the bottom of the upper crust. The Mono depth is 47 km in the Kuytun area and 50 km in the Xayar area. In the Tianshan Mountains, the Moho becomes deeper with the maximum depth of 62 km around the boundary between the southern and northern Tianshan Mountains. The average velocity ranges from 6.1 to 6.3 km/s in the crust and 8.15 km/s at the top of the upper mantle. Two groups of reliable reflective seismic phases of the Moho (Pm1 and Pm2) are recognized on the shot record section of the Kuytun area. A staked and offset region, 20-30 km long, is displayed within a shot-geophone distance of 190-210 km in Pm1 and Pm2. Calculation shows that the Moho is offset by 10 km in the northern Tianshan region, 62 km deep in the south while展开更多
Among the numerous GGT projects in China, the GGT from Yadong to Golmud crossing the whole Tibetan Plateau stands out for its peculiar tectonic environment of continentcontinent collision orogeny and characteristic ge...Among the numerous GGT projects in China, the GGT from Yadong to Golmud crossing the whole Tibetan Plateau stands out for its peculiar tectonic environment of continentcontinent collision orogeny and characteristic geophysical fields of a co-existing thick yet warm crust. The terrestrial heat flow measurements have resulted in setting up a heat flow profile at the highest elevations on a global scale running through the 'Roof of the World'. It extends from south to north for about 1300 km, consisting of 22 heat flow values from 13 individual studied regions: Puma Lake (91 mW/m^2, average value, the same below),展开更多
基金financed by the Ministry of Land and Resources of China (2004DKA20280-2-5)International Sciences and Technology cooperation (2006DFA21340)+5 种基金the special funds for Sciences and technology research of public welfare trades (200811021)the key innovation project for sciences and technology of Ministry of Land and Resources (1212010711813)the China Geology survey Bureau and resources land investigation project(1212010611809)the Basic outlay of scientific research work from Ministry of Science and Technology of the People's Republic of China (J0803)the National Natural Science Foundation of China (40830316 and 40874045)SINOPPROBE-Ⅱ and Open Fund (NO.GDL0603_) of Key Laboratory of Geo-detection (China University of Geosciences,Beijing),Ministry of Education"
文摘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 geo-physical 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 Pla-teau 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 oro-gen 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 considered as resulted from partially melted rocks.However the low normal vP/vS ratio and the Moho stepwise rise fail to support significant partial melting in the middle-lower crust of the central-northern Tibetan plateau.Furthermore,the lower-velocity of crust occasionally disappears,and/or local thinned exhibits their non-stationary spatial distribution.
基金supported by the National Natural Science Foundation of China (40404011, 40774051, 49734230)the basic outlay of scientific research work from Ministry of Science and Technology of the People’s Republic of China in 2007 and 2008 (J0707, J0803)+2 种基金Sino-American collaboration project from Ministry of Science and Technology of the People’s Republic of China (2006DFA21340)China National Probing Project (SinoProbe-02)Open Fund of Geo-detection Laboratory, Ministry of Education of China, and China University of Geosciences (No. GDL0602)
文摘Along the western Kunlun-Tarim-Tianshan geoscience transect in the northwestern China,an integrated geophysical investigation was carried out. Owing to the abominable natural conditions there,the sounding profile could not cross the whole transect,consequentially,a variety of velocity structures in the transverse and vertical orientations beneath the whole transect were not obtained,such as the case within the western Kunlun orogenic belt. To supply a gap of deep seismic soundings within the western Kunlun orogenic belt,we used the Bouguer gravity anomaly data and the relationship between the compressive wave and the density to obtain the density structure of the crust beneath the western Kunlun and the southern Tarim basin by a forward fitting of gravity anomalies within the two-dimensional polygonal model of uniform medium. The crust of the Tarim basin with a rigid basement was like an asymmetrical arc,whose surface feature was the Bachu uplift in the middle of the Tarim basin. Beneath the conjoint area between the Tarim basin and the western Kunlun belt,there was a V-shape structure located just up to the top of the uplifted Moho. The multi-seismological structures jointly revealed that the face-to-face continent-continent collision beneath the western Kunlun is a new structural style within the continent-continent collision zone,which is a real model proved by the numerical modeling.
基金This study was supported by the National Natural Science Foundation of China(grant nos.42074115,41574094)the National Key R&D Program of China(grant no.2017YFC0601301)+1 种基金the Geological Survey Project of the China Geological Survey(grant no.DD20189132)the Key Laboratory of Deep-Earth Dynamics,Ministry of Natural Resources(grant no.J1901-3).
文摘Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface structures.For the development and utilization of urban underground space,two parameters in the shallow surface are important,namely,the shear wave velocity(V_(S))and the predominant period of the site,which determine the elevation and aseismic grade of the building design.The traditional method is mainly to obtain the two above-mentioned parameters through testing and measuring drilling samples.However,this method is extremely expensive and time consuming.Therefore,in this research,we used the multichannel surface wave acquisition method to extract the fundamental dispersion curve of single-shot data by using the phase shift method and obtain the V_(S) characteristics in the uppermost 40 m by inversion.We arrived at the following two conclusions based on the V_(S) profile.First,the study area can be roughly divided into five layers,among which the layers 0−8 m,14−20 m,and 20−30 m are low-velocity layers,corresponding to miscellaneous fill,a water-bearing sand layer,and a sand layer;therefore,the V_(S) is relatively low.In contrast,the layers at 8−14 m and 30−40 m are high-velocity layers that are mainly composed of clay,with a relatively better compactness and relatively high V_(S) values.In addition,a low-speed anomaly appears abruptly in the high-speed area at 20−40 m.This anomaly,when combined with geological data,suggests that it is an ancient river channel.Second,from the V_(S) value,the V_(Se)(equivalent shear wave velocity)was calculated.The construction site soil was categorized as class III,with good conditions for engineering geology.In addition,we calculated the predominant period of the site to be 0.56-0.77 s based on the V_(S).Therefore,in the overall structural design of the foundation engineering,the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.
文摘Fine structures of the crust and upper mantle of the basin-and-range juncture on the northwestern margin of the Qinghai-Tibetan Plateau are first delineated by the deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains. Evidence is found for the northward subduction of the northwest marginal lithosphere of the Qinghai-Tibetan Plateau and its collision with Tarim lithosphere beneath the West Kunlun Mountains. The lithosphere image of the face-to-face subduction and collision determines the coupling relationship between the Tarim Basin and the West Kunlun Mountains at the lithosphere scale and reflects the process of continent- continent collision.
文摘The deep seismic sounding profile across the Tianshan Mountains revealed a two-layer crustal structure in the Tianshan region, namely the lower and upper crusts. Lateral variations of layer velocity and thickness are evidently shown. Low-velocity layers spread discontinuously at the bottom of the upper crust. The Mono depth is 47 km in the Kuytun area and 50 km in the Xayar area. In the Tianshan Mountains, the Moho becomes deeper with the maximum depth of 62 km around the boundary between the southern and northern Tianshan Mountains. The average velocity ranges from 6.1 to 6.3 km/s in the crust and 8.15 km/s at the top of the upper mantle. Two groups of reliable reflective seismic phases of the Moho (Pm1 and Pm2) are recognized on the shot record section of the Kuytun area. A staked and offset region, 20-30 km long, is displayed within a shot-geophone distance of 190-210 km in Pm1 and Pm2. Calculation shows that the Moho is offset by 10 km in the northern Tianshan region, 62 km deep in the south while
基金Project supported by the National Natural Science Foundation of China
文摘Among the numerous GGT projects in China, the GGT from Yadong to Golmud crossing the whole Tibetan Plateau stands out for its peculiar tectonic environment of continentcontinent collision orogeny and characteristic geophysical fields of a co-existing thick yet warm crust. The terrestrial heat flow measurements have resulted in setting up a heat flow profile at the highest elevations on a global scale running through the 'Roof of the World'. It extends from south to north for about 1300 km, consisting of 22 heat flow values from 13 individual studied regions: Puma Lake (91 mW/m^2, average value, the same below),