Late-Quaternary strong earthquakes on the seismogenic fault of the 1976 M s7.8 Tangshan earthquake, Hebei, as revealed by drilling and trenching

Abstract

Composite borehole profiling combined with trenching is an effective way to acquire evidence of past ruptures of buried active faults. In this study, three composite borehole profiles and a large-scale trench excavation were carried out across the surface rupture zone of the 1976 M s 7.8 Tangshan earthquake. The following three major conclusions have been reached. (1) The surface rupture zone of the 1976 earthquake extends more than 47 km long to the south of Tangshan city, passing to the west of Sunjialou, to Daodi town in Fengnan County, to Xihe in Fengnan County. (2) The surface rupture zone is divided into south and north branches. The north branch has mainly right-lateral strike-slip motion, and the vertical displacement of the surface is up on the west and down on the east. On the other hand, the vertical displacement of the south branch is up on the east and down on the west, accompanied by some right-lateral slip. Such a faulting style cannot be explained by the movement of a single normal or reverse fault, but is consistent with the vertical displacement field induced by the right-lateral strike-slip of the fault belt. The drilling and trenching data from this study verify that such activity continued through the Late Quaternary on the Tangshan Fault. (3) The fault planes exhumed by trenching and the dislocations of strata revealed by the boreholes indicate that multiple faulting events occurred on the Tangshan Fault in the Late Quaternary. The timing of three ruptures prior to the 1976 earthquake was 7.61-8.13, >14.57, and 24.21-26.57 ka BP. Counting the earthquake of 1976, the recurrence interval of the four strong events is about 6.7 to 10.8 ka. On one of the three borehole profiles, the Niumaku profile, nine faulting events were detected since 75.18 ka BP with an average interval of 8.4 ka. In addition, this paper also discusses the difference between the Late Quaternary sedimentary environments to the north and south of Tangshan city based on stratum dating.Tangshan earthquake, surface rupture zone, multi-stage activity, earthquake recurrence interval, paleoseismic trenching, borehole profile Citation:Guo H, Jiang W L, Xie X S. Late-Quaternary strong earthquakes on the seismogenic fault of the 1976 M s 7.8 Tangshan earthquake, Hebei, as revealed by drilling and trenching.

Contemporary Deformation of the North China Plain From Global Positioning System Data

“…Almost all great historical earthquakes in the NCP occurred along the NNE-trending faults with predominant right-lateral displacements. The surface ruptures of the 1976 Tangshan earthquake, for example, are associated with~2.3 m right-lateral and~0.5 m vertical displacements from geological observations (Guo et al, 1977(Guo et al, , 2011, which corroborate 3.1-3.4 m right-lateral and~0.35 m vertical displacements from geodetic measurements (Huang et al, 1988;Wu et al, 2016). The surface ruptures of the 1976 Tangshan earthquake, for example, are associated with~2.3 m right-lateral and~0.5 m vertical displacements from geological observations (Guo et al, 1977(Guo et al, , 2011, which corroborate 3.1-3.4 m right-lateral and~0.35 m vertical displacements from geodetic measurements (Huang et al, 1988;Wu et al, 2016).…”

“…Fault plane solutions of large historical earthquakes (Figure 1) manifest prominent right-lateral strike-slip displacements (Chen & Nabelek, 1988;Gao et al, 2016). The surface ruptures of the 1976 Tangshan earthquake, for example, are associated with~2.3 m right-lateral and~0.5 m vertical displacements from geological observations (Guo et al, 1977(Guo et al, , 2011, which corroborate 3.1-3.4 m right-lateral and~0.35 m vertical displacements from geodetic measurements (Huang et al, 1988;Wu et al, 2016).…”

“…Two observations, however, contradict the conventional view. Instead, rightlateral strike-slip displacements dominate the coseismic deformations such as the 1787 Sanhe-Pinggu earthquake (Ran et al, 1997), the 1964 Xingtai earthquake (Editorial Group, 1986), and the 1976 Tangshan earthquake (Guo et al, 1977(Guo et al, , 2011. It is unlikely that a region with such frequent great historical earthquakes associated with no present-day deformation.…”

“…Second, surface ruptures associated with great historical earthquakes on the NNE-trending faults do not show prominent normal faulting and extensional component. Instead, rightlateral strike-slip displacements dominate the coseismic deformations such as the 1787 Sanhe-Pinggu earthquake (Ran et al, 1997), the 1964 Xingtai earthquake (Editorial Group, 1986), and the 1976 Tangshan earthquake (Guo et al, 1977(Guo et al, , 2011. Fault plane solutions of recent earthquakes also show overwhelming right-lateral strike-slip motions on almost vertical dipping NNE-trending faults planes (Chen & Nabelek, 1988;Gao et al, 2016).…”

Rn and CO<sub>2</sub> geochemistry of soil gas across the active fault zones in the capital area of China

“…Its seismicity, which is mainly Figure 1. Simplified geological maps of study areas in the capital area of China (modified after Zhu et al, 2006;Seismic Geological Brigade, CEA, 1979;Yin, 2010;Guo et al, 2011). (a) shows the locations of study areas and meteorological observation stations.…”