Showing papers by "Geophysical Survey published in 2004"

Crustal structure of the southern Dabie ultrahigh‐pressure orogen and Yangtze foreland from deep seismic reflection profiling

Abstract: A new 140-km-long seismic reflection profile provides a high-resolution crustal-scale image of the southern Dabieshan high-pressure (HP) metamorphic belt and the Yangtze foreland fold-and-thrust belt. The seismic image of the stacked section shows that the southern Dabieshan metamorphic terrane and Yangtze foreland belt are separated by a large north-dipping fault. In the foreland the upper crust is dominated by a series of folds and thrusts formed during the collisional stage in the mid-Triassic; it was reworked by crustal extension resulting in the formation of a late Jurassic and Cretaceous red-bed basin. The southern Dabieshan profile shows stacked crustal slabs developed along the margin of the collisional orogenic belt. The Moho reflectors at 10–11 s (∼30–33 km) are seismically prominent and segmented by a number of south-verging thrusts that were probably developed by foreland-directed thrusting of the deeply subducted continental crust during exhumation. The seismic reflection profile suggests that structures related to the Triassic–Jurassic subduction and exhumation of the Yangtze plate are preserved despite the severe crustal extension superimposed during the late Mesozoic and Cenozoic.

RS+GCPs select basic information of landslide

Abstract: Based on practice over 20y's landslide RS investigation, this paper introduces the main RS+GCPs information resources, what's the basic information of landslide and the relation among RS resolution and possible recognized minimum landslide(PRML) and different scale landslide RS investigation. RS data can be divided into three types of panchromatic, Multi-spectral, SAR, based on spectral characteristics, and two types of arero and satellite based on sensors, that is the main and most important information resources. GCPs mainly comes from topographic map, GPS measurement and DEM made of stereo pair of aero or satellite image or by means of InSAR.Only ortho-mage processed by means of geometric correction and geographic coordinate register is the base for investigating landslide.The basic landslide information consists of elements of landslide and its developing environment. There are about 16 elements for an entire landslide,which are:sliding mass, boundary, scarp, terrace, tongue, sliding axle, bulge, tension fracture, shear fracture, fan type fracture, bulge fracture, fracture edge, depression on the back, sliding surface, sliding zone, sliding bed. Not every landslide has above 16 elements but sliding mass and scarp is at least the basic elements for any landslide. There are 3 basic geological environment factors for producing a landslide,that are ① material which can be evolved sliding surface, ② frail surface or zone making parts of slope separate from original slope, ③space for landslide moving ahead. Otherwise, induced environment factors including human beings' activities data should be investigated and collected as well.Up till now most of landslide RS investigation uses aero-photos. The space resolution of aero-photo is depends on the film's quality for distinguishing maximum line pairs/mm, the lens' properties and the contrast of objects and environment.Apart from the image quality and space resolution, the possible recognized minimum landslide-PRML is related to kinds, typicality and contrasts of landslide.Generally speaking each single element of landslide which should at least cover 10×10 pixels can then be recognized clearly and the entire landslide can be recognized at least cover 10×20×2 pixels according to practices. Different regions and landslides have different PRML. Through statistics the landslide at least covering (1?000) pixels can then be primarily analyzed qualitatively and quantitatively, and at least coving (2?000) pixels can then be analyzed qualitatively and quantitatively in detail, so that different scale landslide RS investigation needs different space resolution of image.