Reevaluation of the offset of the Great Wall associated with the 1739 M 8.0 Pingluo earthquake, Yinchuan Graben, China (Invited)

The study of large-magnitude earthquakes that occurred prior to the availability of routine instrumental measurements relies mainly on the analysis of historical documents and field observations. Significant uncertainties often exist in relation to the location of the epicenter, the magnitude, and the actual extent of damage, including the number of fatalities, caused by individual historical earthquakes, because records are generally focused on the effects in the restricted regions that were settled. In these cases, field observations of the geologic effects of large historical and paleo-earthquakes provide direct evidence of the co-seismic ground deformation and macro-seismic intensity of these large-magnitude events, and can therefore help to improve our ability to assess seismic hazards in densely populated epicentral regions. The ruins of ancient civilizations that experienced and were damaged by earthquakes are often used as surface indicators in the study of past seismic events in regions with long historical records, such as China, Japan, and Turkey. China is located in one of the most active seismic regions of the world and has experienced numerous destructive earthquakes over its long history. The damage caused by previous large-magnitude earthquakes has been recorded in historical documents, and co-seismic ground deformation is locally preserved in ruined ancient buildings such as temples, tombs, and other constructions erected over the past several thousand years. Previous studies have shown that the Great Wall of China was damaged and offset by the ca. M 8 Pingluo earthquake of 1739 along an active fault zone in the Yinchuan graben, on the western margin of the Ordos Block in northern central China (e.g., Deng and Liao, 1996, JGR; Zhang et al., 1986, BSSA). In this study, we reevaluate, on the basis of our investigation, the ground deformation caused around the area of the Great Wall by the ca. M 8 Pingluo earthquake of 1739 along an active fault zone in the Yinchuan Graben, on the western margin of the Ordos Block in northern central China. Previous studies have shown that the Great Wall of China was damaged and right-laterally offset by the 1739 M 8 Pingluo earthquake up to ~1.6-2 m, with a 0.1-1.9 m vertical component, at three locations. However, our recent fieldwork and in-situ measurements have shown that the Great Wall was not affected by the ca. M 8 Pingluo earthquake of 1739, as reported previously, but was actually built on preexisting active fault scarps. This study reinterprets the offset of the Great Wall on the basis of these new field observations, and attempts to identify the seismogenic source fault that triggered the 1739 Pingluo earthquake. More work is required if we are to better understand the deformation characteristics of the seismogenic source fault, and also improve our ongoing assessments of the seismic hazard within the densely populated area of the Yinchuan Graben, central China. Reference: Lin, A., Rao, G., Hu, J. and Gong, W., 2013. Reevaluation of the offset of the Great Wall associated with the ca. M 8.0 Pingluo earthquake of 1739, Yinchuan graben, China. Journal of Seismology, in press.