Crustal structure beneath Beijing and its surrounding regions derived from gravity data

Abstract

In this paper we use gravity data to study fine crustal structure and seismogenic environment beneath Beijing and its surrounding regions. Multi-scale wavelet analysis method is applied to separating gravity fields. Logarithmic power spectrum method is also used to calculate depth of gravity field source. The results show that the crustal structure is very complicated beneath Beijing and its surrounding areas. The crustal density exhibits laterally inhomogeneous. There are three large scale tectonic zones in North China, i.e., WNW-striking Zhangjiakou-Bohai tectonic zone (ZBTZ), NE-striking Taihang piedmont tectonic zone (TPTZ) and Cangxian tectonic zone (CTZ). ZBTZ and TPTZ intersect with each other beneath Beijing area and both of them cut through the lithosphere. The upper and middle crusts consist of many small-scale faults, uplifts and depressions. In the lower crust, these small-scale tectonic units disappear gradually, and they are replaced by large-scale tectonic units. In surrounding regions of Beijing, ZBTZ intersects with several other NE-striking tectonic units, such as Cangxian uplift, Jizhong depression and Shanxi Graben System (SGS). In west of Taihangshan uplift, gravity anomalies in upper and middle crusts are correlated with geological and topographic features on the surface. Compared with the crust, the structure is comparatively simple in uppermost mantle. Earthquakes mainly occurred in upper and middle crusts, especially in transitional regions between high gravity anomaly and low gravity anomaly. Occurrence of large earthquakes may be related to the upwelling of upper mantle and asthenosphere heat flow materials, such as Sanhe earthquake (MS8.0) and Tangshan earthquake (MS7.8).

Land subsidence in Beijing and its relationship with geological faults revealed by Sentinel-1 InSAR observations

“…Previous studies have analyzed the mechanisms of the subsidence and mentioned that the spatial subsidence pattern in Beijing is different from those in other places, e.g. the subsidence bowl pattern in Tianjin and Shanghai (Liang et al, 2013), indicating there might be some connections with these faults. Therefore, it is crucial to perform long-term, wide-coverage subsidence monitoring in Beijing to investigate the relationship between subsidence and these tectonic faults to enable a comprehensive understanding of potential geological hazards forecasting, subsidence mitigation strategies and fast emergency response.…”

“…In order to investigate whether the subsidence rate was stable or not, continuous monitoring using InSAR with wide spatial coverage is ideal (e.g. Berger et al 2012) (C-band) (Gong et al, 2009), (Ng et al, 2012), (Li et al, 2013), (Hu et al, 2014), (Zhu et al, 2015), (Chen et al, 2015) (Chen et al, 2016), (Chen et al, 2017), (Gao et al, 2018), (Zhou et al, 2018) ( (L-band) (Ng et al, 2012), (Liang et al, 2013), (Du et al, 2018)…”

Characterization of Aquifer System and Groundwater Storage Change Due to South-to-North Water Diversion Project at Huairou Groundwater Reserve Site, Beijing, China, Using Geodetic and Hydrological Data

“…This method has been applied to many places, such as California [11], Colorado [12], and Utah [13] in the United States, to characterize the aquifer storativity property and monitor the water storage change. Over the NCP, InSAR and GPS studies detected rapid land subsidence caused by groundwater extraction in many cities, including Beijing [14,15], Tianjin [16], Dezhou [17], and Cangzhou [18]. Due to the SNWD Project, water storage has been recovering in recent years, and the HGRS in Beijing has experienced the most dramatic change due to the SNWD Project, providing a unique opportunity to probe into the aquifer storage recovery process in the HGRS region.…”