北京平原区地面沉降分布特征及影响因素

地面沉降是北京平原区主要地质灾害之一。文中采用永久散射体差分干涉测量(PS-InSAR)技术获取平原区地面沉降空间分布特征,基于GIS空间分析平台,将多种地面沉降影响因素分别与PS-InSAR获取的地面沉降场形变信息进行耦合研究,查明地面沉降与多种影响因素之间的响应关系。研究发现:(1)北京市地面沉降发育较为严重的地区主要出现在平原区东部、北部以及南部等地,存在多个沉降中心,最大沉降速率达到152mm/a,区域不均匀沉降现象明显,并且有连成一片的趋势。(2)地面沉降分布具有明显的构造控制特性,沉降区多位于几大活动断裂交接部位的沉积凹陷地区,与第四纪沉积凹陷十分吻合。地面沉降的发展趋势与活动断裂的走向具有明显的对应关系,在有活动断裂通过的区域,地面沉降剖面线上表现出明显的转折或突变,断裂两侧区域不均匀沉降十分明显。(3)地面沉降分层沉降量与对应层位上黏性土占比呈正比例关系,其空间分布特征及变化趋势与平原区的地层结构及可压缩黏性土层厚度具有很好的一致性,沉降范围整体由北西向的单一结构区向南东方向的多层结构区扩张。沉降速率大于50 mm/a的沉降区大多分布在黏性土层厚度大于100 m的地区,几大沉降中心与黏性土层厚度较大地区吻合较好。(4)第二承压含水层(顶底板埋深100~180 m)地下水开采对地面沉降影响最大,沉降中心与该层位地下水位降落漏斗区高度吻合,是地面沉降的主要贡献层位。

Distribution characteristics and influence factors of land subsidence in Beijing area

Land subsidence is one of the main geological disasters in Beijing area. In this study, the authors investigated the spatial distribution characteristics of land subsidence in Beijing area by using the permanent scatter interferometric synthetic aperture radar (PS-InSAR) technique and studied the relationship between the multiple factors of land subsidence and the deformation obtained by PS-InSAR on the GIS spatial analysis platform,. Some conclusions have been reached:(1) The land subsidence in Beijing area mainly occurs in the east, north and south of the plain, where there are multiple settlement centers, with the maximum settlement rate reaching 152mm/a. The regional uneven subsidence areas are obvious, and there is a trend that these areas are connected with each other to form a complete subsidence region. (2) The distribution of land subsidence areas is controlled by structures; the subsidence area is mainly located in the area of the sedimentary depression formed by several major active faults, which is in agreement with features of the Quaternary deposit. There is an obvious corresponding relationship between the development trend of the land subsidence and the strike of active faults. In the area of active faults, the land subsidence section line shows obvious turning or abrupt change, and the uneven subsidence on the two sides of the fault is very obvious. The layered settlement is directly proportional to the cohesive soil in the corresponding layer. The spatial distribution of the land subsidence has a good agreement with the stratigraphic structure and the thickness of the compressible cohesive soil layers in Beijing area. The range of the land subsidence area expands from the northwest characterized by the single structural zones to the southeast characterized by the multistructure zones. The areas where the settlement rate is more than 50 mm/a are mostly distributed in the area whose thickness of the compressible cohesive soil layers is more than 100 m. The settlement centers are in good agreement with the large thickness of the cohesive soil layers. (4) The second confined groundwater (top and bottom depth being 100~180 m) exploitation is the most influential factor responsible for the land subsidence, and the settlement centers are in agreement with the groundwater funnel.