The surface rupture zone and paleoseismic evidence on the seismogenic fault of the 1976 Ms 7.8 Tangshan earthquake, China

Abstract

The Ms 7.8 Tangshan earthquake of 1976 was the largest earthquake that occurred in the northern North China Plain over the last 300 years. Most of the earthquake scarps had been disturbed or had disappeared, except for some seismic ruins and relics that were protected or had remained. Aerial photos taken after the earthquake also indicate the locations of some of these scarps. In this study, we reinvestigated the surface rupture zone of this earthquake and conducted composite borehole profiling and trenching across the new-found surface rupture to obtain the paleo-earthquake events of the seismogenic fault. The following major conclusions regarding the Ms 7.8 Tangshan earthquake have been reached. 1) The length of the rupture zone of the Tangshan earthquake was >47 km. In addition, to the east and west sides of the main surface rupture, there was a prominent secondary fissure zone. 2) The Tangshan Fault experienced nine paleoearthquake events since 115 ka. The timing of the four faulting events prior to the 1976 earthquake was 7.76–8.13 ka, around 16.2 ka, around 24.3 ka, and >32.41 ka. Considering the earthquake of 1976, the recurrence interval of the five strong earthquake events is about 8.1 ka. 3) The magnitudes of these paleoearthquakes E2 to E5, which happened before the Tangshan earthquake, were about Ms 7.6–7.7, Ms 7.5–7.9, Ms 7.7–7.8, and Ms 7.5, respectively. Research on the 1976 Tangshan earthquake is important for improving earthquake predictions in the North China Plain.