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Slip rate along the Lijiang-Ninglang fault zone estimated from repeating microearthquakes

December 22, 2008

The China Digital Seismic Network (CDSN) provides excellent opportunities to quantify the kinematics and characterize the dynamics of the active fault systems in China. By carefully examining waveforms microearthquakes occurring in South China (Yunnan Province) in the period of 1999-2006, we found that approximately 40% of the earthquakes are similar or repeating events. Along the Lijiang-Ninglang fault, we used 2 well-organized clusters that occurred in the brittle-ductile transition zone to estimate the deep slip rate. The estimated slip rate of 5 mm/yr at 23 km depth roughly agrees with the tectonic loading rate inferred from geologic and geodetic data. The discovery of repeating microearthquakes in China (see Li et al., 2007) provides a new means for inferring the slip rate at depth along active faults, the nests of large devastating earthquakes.

The study was mainly conducted by Dr. CHEN Qifu and Dr. LI Le from the Institute of Earthquake Science, China Earthquake Administration in collaboration with Dr. NIU Fenglin from Rice University, and has been published in Volume 53 Issue 23 (December 15, 2008) of Chinese Science Bulletin in Chinese, and published online on November 4, 2008 in English.

Fault slip rate is a key parameter to infer the recurrence of earthquakes. It has been widely investigated with mainly geologic and geodetic methods. Most of the geologic and geodetic observations are, however, surficial measurements, which are frequently not even close to those occurring at seismogenic depth, as demonstrated by the devastating Wenchuan earthquake occurring at the east edge of the Tibetan Plateau in May, 2008. According to most of the geodetic observations, little deformation was identified across the Longmenshan fault that hosted the earthquake. As such, in-situ measurement of slip rates at seismogenic depths from the recurrence of repeating microearthquakes could be crucial. Meanwhile studying the spatial distribution of these repeating microearthquakes could provide another perspective of earthquakes, the size of the large asperities that may directly link to the future large earthquakes.

Science in China Press