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Published online: 14 October 2009 | doi:10.1038/nchina.2009.201

Geology: When all hell breaks loose

Felix Cheung

Introduction

© (2009) Nature Geoscience

On 12 May 2008, a magnitude-7.9 earthquake hit the Sichuan province of China, killing more than 80,000 people. The earthquake took many scientists by surprise because the epicentre was located in the Longmenshan fault zone, a zone with relatively low seismic activity. Zhengkang Shen and co-workers at the China Earthquake Administration and Peking University, both in Beijing, and University of California¹ have found that during the 2008 Sichuan earthquake, a major slip at fault junctions triggered the rupture of multiple barriers that ultimately led to the unforeseen disaster.

There are three major faults in the Longmenshan fault zone: the Pengguan, Beichuan and Wenchuan–Maowen faults. The slip rates on these geological faults are low — less than a millimetre per year. Seismological studies indicate that the tremor began on the Beichuan Fault and propagated unilaterally northeastward, breaking surfaces along the Pengguan and Beichuan faults.

The researchers used global positioning system and interferometric synthetic aperture radar data to study the fault geometry and slip distribution associated with the earthquake. They observed that the largest seismic displacement occurred at a site near Beichuan (pictured) and identified three areas of high-slip concentration at the intersections of fault segments close to Yingxiu, Beichuan and Nanba.

The researchers hypothesize that the 2008 Sichuan earthquake broke through several high-slip junctions that connect major fault segments in a cascade rupture. These connecting structures may represent barriers that rarely fail. When they do fail, however, the release of accumulated energy can lead to a major earthquake. The scenario also explains why Yingxiu, Beichuan and Nanba experienced the highest shaking intensity and suffered the greatest damage among all the towns located in the fault zone.

The authors of this work are from:
State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China; Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing, China; Department of Earth and Space Sciences, University of California, Los Angeles, California, USA; College of Disaster Prevention Science and Technology, Sanhe, China; Department of Earth and Planetary Science, University of California, Berkeley, California, USA; Golden Office, US Geological Survey, Colorado, USA; Sichuan Seismological Bureau, Chengdu, China; Second Monitoring Center, China Earthquake Administration, Xi'an, China.

Reference

1. Shen, Z. K. et al. Slip maxima at fault junctions and rupturing of barriers during the 2008 Wenchuan earthquake. Nature Geosci. doi:10.1038/ngeo636 (2009). | Article