Source process of M s6.4 earthquake in Ning’er, Yunnan in 2007

Abstract

The moment tensor solution, source time function and spatial-temporal rupture process of the M S 6.4 earthquake, which occurred in Ning'er, Yunnan Province, are obtained by inverting the broadband waveform data of 20 global stations. The inverted result shows that the scalar seismic moment is 5.51×10 18 Nm, which corresponds to a moment magnitude of M W 6.4. The correspondent best double couple solution results in two nodal planes of strike 152°/dip 54°/rake 166°, and strike 250°/dip 79°/ rake 37°, respectively. Considering the isoseismals and geological structures in the meizoseismal region, the first nodal plane (strike 152°/ dip 54°/ rake 166°) is preferred to be the seismogenic fault. Thus, the M S 6.4 earthquake occurred mainly along a right-lateral fault striking 152°. The source time function shows that the duration time of the earthquake is about 14 s. The most of the energy releases within the first 11 s and in 11-14 s the rupture is weak. The snapshots of the slip-rate indicate that the rupture process has 3 more detailed stages. In the first stage of the first 4 s after rupture initiation, the rupture propagates simultaneously toward both strike and dip directions; in the second stage of the following 3 s, the rupture extends to down-dip direction; and in the third stage, the rupture looks to be scattering on the fault. In general, this earthquake is of bilateral rupture, and the rupture mainly takes place in strike-dip direction. The major ruptured area is in the shape of a diamond with a dimension of 19 km. On the whole fault plane, the maximum slip is about 1.2 m, the average slip is about 0.1 m, the maximum slip-rate is 0.4 m/s and the average slip-rate is 0.1 m/s. The features of the co-seismic theoretical displacement field of the Ning'er earthquake fault, calculated based on the inverted fault parameters, are consistent with those of the observed isoseismals.

Spatio-temporal rupture process of the 2008 great Wenchuan earthquake

“…In all these methods time-histories of the sub-faults were assumed a priori, which, to some extent, affects the objectivity in rupture mode and/or rupture propagation velocity. In this study, we take advantage of the method used in the study of the 2007 Ning'er earthquake [5] . In this method, time-histories of the sub-fault are not given a priori, and the inversion scheme is formulated with data equation, spatially smoothing equation, temporally smoothing equation, and scalar seismic moment minimizing equation as following:…”

“…The moment-rate function (source time function) shown in Figure 6 can be obtained based on the spatio-temporal rupture images as shown in Figure 5 [5] . The source time function indicates that the scalar seismic moment released in the whole earthquake rupture process was about 9.4×10 20 Nm, corresponding to a moment magnitude M w 7.9.…”

“…In this article we present the focal mechanism and dynamic rupture process of the great Wenchuan earthquake obtained by inverting long period seismic data by means of the inversion method based on a finite fault model [5] , and quantitatively analyze the characteristics of co-seismic displacement field of this great earthquake based on the inverted results.…”

The Livelihood Vulnerability of Rural Households in Earthquake-Stricken Areas—A Case Study of Ning’er, Yunnan Province

“…The area affected by the earthquake was up to 3890 km 2 ( Figure 1). This earthquake damaged a large number of buildings; 3 people were killed, more than 300 people injured, and 536,000 people were affected [28]. Since 1884, Ning'er has been a seismically active area, with nine earthquakes with magnitudes larger than 5 near the epicenter of the Ms 6.4 earthquake, six of which had magnitudes larger than 6 and the largest of which was magnitude 6.8, occurring on 1 March 1979.…”

Effect of tidal stress on fault nucleation and failure of the 2007 M s6.4 Ning’er earthquake

“…This zone is located in the Yunnan-Tibet geothermal belt and the seismicity within this area might be particularly sensitive to tidal stresses or far-field seismic surface waves (Lei et al, 2011). Ning'er is a seismically active area where earthquakes M≥5 recur often (Mao et al, 2003;Zhang et al, 2009). Prior to the Ning'er earthquake, six earthquakes M≥6 occurred in this belt (Mao et al, 2003), and a previous study by Wu et al (2005) into tidal triggering revealed that earthquakes in the Pu'er area might be triggered by tidal stresses.…”