Surface ruptures from the 1556 Huaxian earthquake, North China, measured using high-resolution topography: Implications for large magnitude normal-faulting earthquakes in continental interiors

Abstract

On January 23, 1556, a large normal-faulting earthquake struck Huaxian county, in the eastern part of the Weihe Graben, North China. The direct effects of the great shock and the following famine, exposure to coldness, and disease together killed more than 830,000 people, making the Huaxian earthquake the deadliest in history. Estimates of its magnitude vary widely, with intensity data leading to estimates of 8¼ to 8½, whereas geological estimates of slip and fault length suggest a range of 7.5–8.0, but with remaining uncertainty due to the lack of detailed measurements along the entire rupture zone. In this study, we use high-resolution digital elevation models (DEMs) derived from Pléiades stereo satellite imagery to map the surface ruptures and measure the fault scarps associated with the 1556 earthquake. We use the vertical offset measurements and the cumulative offset probability density (COPD) method to constrain the surface slip distribution of the 1556 event and to examine evidence for prior rupture. We find an average vertical displacement of 6.3 ± 0.7 m, consistent with a moment-magnitude (M_w) of 7.3–7.9 that, although large, is much smaller than earlier estimates derived from seismic intensity data. Although the Huaxian earthquake is likely the largest known well-defined normal-faulting event in history, it aligns with the global pattern that normal-faulting earthquakes in continental interiors rarely exceed M_w 8. We suggest that the magnitudes of other large historical earthquakes in North China need to be reexamined by direct fault parameters, rather than by shaking intensity and death toll.