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

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 5.51x10(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 152A degrees/dip 54A degrees/rake 166A degrees, and strike 250A degrees/dip 79A degrees/ rake 37A degrees, respectively. Considering the isoseismals and geological structures in the meizoseismal region, the first nodal plane (strike 152A degrees/ dip 54A degrees/ rake 166A degrees) is preferred to be the seismogenic fault. Thus, the M (s)6.4 earthquake occurred mainly along a right-lateral fault striking 152A degrees. 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.