Identification of Paleoearthquakes and Coseismic Slips on a Normal Fault Using High-Precision Quantitative Morphology: Application to the Jiaocheng Fault in the Shanxi Rift, China

Junjie Zou,Adam D Sproson,Yongsheng Zhou,Shuang Geng,Zhanyu Wei,Feng Shi,Yoshiki Shirahama,Yusuke Yokoyama,Honglin He,Marie-Luce Chevalier

doi:10.2113/2021/2550879

Abstract

AbstractThe quantitative morphology of bedrock fault surfaces combined with aerial surveys and field identification is a useful approach to identify paleoearthquakes, obtain coseismic slips, and evaluate the seismogenic capacity of active faults in bedrock areas where traditional trenching methods are not applicable. Here, we report a case study of the Jiaocheng Fault (JCF) in the Shanxi Rift, China. Although several studies have been conducted on the JCF, its coseismic slip history and seismogenic capacity are still unclear. To address these problems, we investigated two bedrock fault surfaces, Sixicun (SXC) and Shanglanzhen (SLZ), on the JCF’s northern segment using quantitative morphological analysis together with aerial and field surveys. Quantitative fractal analysis based on the isotropic empirical variogram and moving window shows that both bedrock fault surfaces have the characteristics of vertical segmentation, which is likely due to periodic earthquakes, the coseismic slip of which can be determined by the height of the segments. Three seismic events at SXC, with a coseismic vertical slip of 1.74, 1.65, and 1.99 m, and three seismic events at SLZ, with a coseismic vertical slip of 1.32, 2.35, and 1.88 m, are identified. Compared with the previous studies, these three seismic events may occur in the Holocene, but it requires absolute dating ages to support, which is also the focus of our future work. Considering the seismologic capability (M&gt;7.5) and the relationship between the recurrence interval of ~2.6 kyr and elapsed time of more than 3 kyr, the seismic hazard of the northern and middle segments of the JCF requires immediate attention.

Highlights

Full understanding of the behavior and history of an active fault is the key to assessing seismic hazards and reducing the impacts from earthquake disasters [1]
Since the main purpose in this study was to reconstruct the seismic slip history of bedrock fault scarps, we focused on vertical changes in morphology and presented the data as scatter plots (right panels of Figures 6(a)–6(c) and 7(a)–7(c))
The study of bedrock fault surfaces using a combination of aerial survey, field identification of weathering bands, and quantitative high-resolution morphology analysis can provide theoretical and methodological support for the research of active faults in bedrock areas

Summary

Introduction

Full understanding of the behavior and history of an active fault is the key to assessing seismic hazards and reducing the impacts from earthquake disasters [1]. Considering the relative shortness and general absence of historical earthquake records, paleoearthquake research is the most effective way to extend the history of earthquakes and produce more complete seismic records [3]. The main aim of paleoearthquake research is to obtain the information relating to the activity of prehistoric earthquakes, especially the number, timing, and size [4]. The traditional method to study an active fault is based on the analysis of displaced Quaternary sediment through the trenching technique [5, 6], which has been widely applied to paleoseismology, becoming a major contributor to paleoseismic studies in continental deformation zones [7,8,9].

Methods

Results

Conclusion