Magnitude of the 1920 Haiyuan Earthquake Reestimated Using Seismological and Geomorphological Methods

Abstract

Reported magnitudes ranging between 7.8 and 8.7 highlight a confusion about the true size of the 1920 Haiyuan earthquake, the largest earthquake recorded in the northeast Tibetan Plateau. We compiled a global data set of previously unlooked‐at historical seismograms and performed modern computational analyses on the digitized seismic records. We found the epicenter to be near Haiyuan town and obtained a moment magnitude of MW=7.9±0.2. Following traditional approaches, we obtained mB=7.9±0.3 with data from 21 stations and MS(20)=8.1±0.2 with data from three stations. Geomorphologically, we mapped the surface rupture and horizontal offsets on high‐resolution Pleiades satellite and drone imagery that covered the entire western and middle sections of the 1920 Haiyuan earthquake rupture and compiled offsets reported on the eastern section from field measurements in the 1980s. Careful discrimination between single‐event and cumulative offsets suggests average horizontal slips of 3.0±1.0 m on the western section, 4.5±1.5 m on the middle section, and 3.5±0.5 m on the eastern section, indicating a total moment magnitude of MW=7.8±0.1. Thus, the seismological and geomorphological results agree within the uncertainties, a weighted average giving a moment magnitude of MW=7.9±0.2 for the 1920 Haiyuan earthquake. It is likely that earthquake magnitudes based on the historical M were systematically overestimated.

Large‐Scale Interseismic Strain Mapping of the NE Tibetan Plateau From Sentinel‐1 Interferometry

“…Additional intriguing features include three high shear strain rate fingers and an arcuate‐shaped concentration of contractional strain on the west flank of the Quwu Shan near the eastern termination of the Haiyuan fault (Figure 9a). This feature starts from the east flank of the Hasishan on the Haiyuan Fault and extends from a southern branch (Figure 9b) of the main fault which is commonly believed to be an active fault that did not rupture during the 1920 Haiyuan Earthquake (Cavalié et al., 2008; C. Li et al., 2009; Ren et al., 2016; Matrau et al., 2019; Yao et al., 2019; Ou et al., 2020). Deng et al.…”

“…This feature starts from the east flank of the Hasishan on the Haiyuan Fault and extends from a southern branch ( Figure 9b ) of the main fault which is commonly believed to be an active fault that did not rupture during the 1920 Haiyuan Earthquake ( Cavalié et al, 2008;C. Li et al, 2009;Ren et al, 2016;Matrau et al, 2019;Yao et al, 2019;Ou et al, 2020 ). Deng et al ( 1986 ) and Gaudemer et al ( 1995 ) suggested the branch extends southeastwards and connects with an oblique reverse fault on the southwestern flank of the Quwu Shan ( mapped in Figure 9b ) to form a subordinate fault strand in the Haiyuan Fault Zone.…”

“…We investigate the rapidly deforming NE Tibetan Plateau (Figure 1a), at the leading edge of the northward expansion of the Tibetan Plateau driven by the ongoing collision of India with Eurasia (England & Houseman, 1985; England & Molnar, 1997; Flesch et al., 2001; Molnar & Tapponnier, 1975; Pichon et al., 1992; Tapponnier et al., 2001; Yuan et al., 2013). This area hosted 20 M W > 6.5 earthquakes in the past century, including the M W 7.9 1920 Haiyuan Earthquake (Deng et al., 1986; IGCEA & NBCEA, 1990; Ou et al., 2020; Ren et al., 2016; Xu et al., 2019). Extensive research has been carried out to study the kinematics (P. Zhang et al., 1988; W. Zheng et al., 2013), mechanics (Deng et al., 1984; Gaudemer et al., 1995), and seismic hazard (Liu‐zeng et al., 2015; Xiong et al., 2010) of the major faults in the region, such as the Haiyuan, Kunlun and West Qinling Faults and the Qilianshan thrusts.…”

Geomorphology and Paleoseismology of the Weinan Fault, Shaanxi, Central China, and the Source of the 1556 Huaxian Earthquake

“…This has recently been inferred for some other historical earthquakes within China (e.g., Kulikova & Krüger, 2017; Middleton et al, 2016; Xu et al, 2018). Ou et al (2018) suggest that overestimates in the magnitudes of historical earthquakes in China arise due to the use of Gutenberg and Richter surface wave magnitude ( M ) in the conversion from seismic intensity data. In this case M 8½ will be approximately equivalent to a moment magnitude ( M w ) of ~8.0 ± 0.1.…”

Late Quaternary Slip Rate of the Zihong Shan Branch and Its Implications for Strain Partitioning Along the Haiyuan Fault, Northeastern Tibetan Plateau

“…From south to north, the fault system consists of the Zihong Shan fault, the Hasi Shan frontal fault, the Liushashui fault, and the Shuanglong fault (Figure 2). Previous studies have mainly focused on the Hasi Shan frontal fault, as it is the branch that ruptured during the 1920 Haiyuan M W 7.9 earthquake (IGCEA & NBCEA, 1990; Li et al., 2009; Matrau et al., 2019; Ou et al., 2020; Ren et al., 2015; Zhang et al., 2005). In comparison, little is known about the other three branches.…”