A catastrophic, buried fault-generating earthquake: The 1937 M7.0 Heze earthquake in the south-central North China Plain

Abstract

The North China Plain (NCP) is a region with a high level of seismic hazards. Since 1830, eight historical M7.0–7.9 earthquakes have been recorded in the NPC, seven of which have occurred on the boundary of the subblocks, and only the 1937 Heze earthquake has occurred in the interior of the Ji-Lu Subblock. Why did this intraplate earthquake occur there? What are its seismogenic conditions and seismogenic mechanisms? The Liaocheng-Lankao Fault (LLF) is an important buried active fault in the south-central NCP, and the 1937 Heze earthquake occurred 10 km east of it. What role did the LLF play in this earthquake? Using shallow seismic reflection detection and drilling combined with Quaternary dating methods reveals that the southern segment of the LLF is a Holocene active fault, and the northern segment is a late Pleistocene active fault. The BCS drilling profile reveals four paleoseismic events in the southern LLF since the late Pleistocene, and the average vertical slip rate of the southern LLF since 21 ka is approximately 0.35 ± 0.04 mm/a. The analysis of the intensity lines, surface rupture distribution, and focal mechanism solution of the 1937 Heze M7.0 earthquake implies that the NNE-striking Xiaoliu-Xieyuanji Fault and the WNW-striking Dongming-Chengwu Fault are the seismogenic faults of the 1937 Heze M7.0 earthquake. The LLF, as the deep major fault in the region, controlled the accumulation of stress, stimulated the earthquake with its deep movement, and reduced the effect of the seismic energy westward, acting as the regional seismic controlling fault of the 1937 Heze M7.0 earthquake. Another branch fault near Yangji, approximately 50 km north of Heze, is a new stress concentration area and may be at risk of a large earthquake. In addition, the northern segment of the LLF may also be reactivated in the future and produce an M ≥ 7.0 earthquake.