Research on Relationship Between Stress Field Variation and Earthquakes in Shanxi Area, China

Abstract

Based on the focal mechanism solution database established by collecting 37 years initial motion of small earthquakes (1970~2006), the space‐time evolution characteristics of small‐earthquake integrated mechanisms in Shanxi fault zone are studied in this paper. The results indicate that small‐earthquake integrated mechanisms in Shanxi fault zone are mainly dominated by strike slip normal faults; those at two ends of the zone are dominated by extension tectonics and those in the central region by shearing. The difference between the stress field of Huabei and the regional stress fields of Xinding and Taiyuan Basins is very large. The relationship between horizontal motions and earthquake activities in Shanxi fault zone is analyzed according to the 12 stages of re‐measuring data of GPS monitoring network along the Shanxi fault zone (1996~2007). The results indicate that the Shanxi fault zone now is mainly controlled by compressional stress field along NWW‐SEE direction and tensile stress along NNE‐SSW. One obvious stress disturbance occurred during the period of 1998~1999, which was stronger in the north and weaker in the south. This was followed by Datong‐Yanggao M5.6 earthquake on 1st Nov.1999.

Three‐Dimensional Crustal Structures of the Shanxi Rift Constructed by Rayleigh Wave Dispersion Curves and Ellipticity: Implication for Sedimentation, Intraplate Volcanism, and Seismicity

“…The Vs maps are plotted as perturbations relative to the average Vs at individual depths, which are indicated at the upper left corner of each panel. The white dots in (a) represent the epicenters of earthquakes with M L > 3.5 from Song et al (2012). (i) Map of sediment thickness.…”

“…The black bold lines indicate the Moho depths obtained from our joint inversion. The white dots represent the focuses of earthquakes with M L > 3.0 from 1981 to 2014 (Song et al, 2012). The red triangle denotes the location of the Datong Volcanoes (DTV).…”

“…The Shanxi Rift is an earthquake prone area, and the earthquakes there mostly take place in the upper/middle crust. Song et al (2012) found that focal depths of deep earthquakes become shallower from south to north in the Shanxi Rift (white dots shown in Figure 12). However, the mechanism responsible for such seismicity pattern is still under debate.…”

“…A high-resolution model of crustal structures is key to understanding the magma plumbing system in the Shanxi Rift. Most earthquakes in the Shanxi Rift took place in the upper/middle crust, and the focal depths of earthquakes become shallower from south to north in the Shanxi Rift (Song et al, 2012). The factor controlling the shallowing of deep earthquakes from south to north still remains enigmatic.…”

Late Cenozoic faulting deformation of the Fanshi Basin (northern Shanxi rift, China), inferred from palaeostress analysis of mesoscale fault-slip data

“…In contrast, graben floor elevations increase northward from 380 to 1010 m (Li et al 2018) and are associated with low Bouguer gravity anomalies, which rise from east (−80 mGal) to west (−130 mGal) as shown by geophysical data (Xu & Ma, 1992). The underlying crust is 32-39 km thick, thinner than the underlying crust of the surrounding mountains (Tang et al 2010), and the Moho depth laterally varies from 36 to 45 km beneath the axial zone (Shi et al 2014).…”