Focal Mechanism Solutions of the 2003 Delingha, Qinghai M6.7 Earthquake Sequence and Their Tectonic Implications

• Published in: Chinese journal of geophysics 2012-11, Vol.55 (6), p.680-688
• Main Authors: SUN, Chang‐Hong, XU, Feng, YANG, Yu‐Bo, QIAN, Rong‐Yi, MENG, Xiao‐Hong
• Format: Article
• Language: English
• Subjects: Delingha earthquake sequence; Faulting style; Northeastern Tibetan plateau; Snoke's algorithm of focal mechanism determination
• ISSN: 0898-9591; 2326-0440
• DOI: 10.1002/cjg2.1762

Using digital seismic records from 8 portable stations and from stations of the National Digital Seismic Network, we have measured the polarities and amplitude ratios of direct P, SH and SV waves of the 2003 Delingha, Qinghai M6.7 earthquake and its aftershocks. Applying the Snoke's (2003) grid search algorithm we determined focal mechanism solutions of 48 M≥2.4 earthquakes. We also analyzed Harvard focal mechanism solutions of the Delingha mainshock and its 6 aftershocks in 2004. Our study results show that the mainshock and most aftershocks have a reverse faulting mechanism with fault strike in NWW‐SEE and the northern hanging wall moving upward and southward. Two normal faulting aftershocks may result from possible tensile fractures in front part of the compressive thrust arc. During the second phase of earthquake activity in 2004 the motion of main thrust fault might have induced rupture of some strike‐slip faults in eastern part of the source region. The Delingha earthquakes are located in a wide NWW‐SEE trend compression zone in the northeastern Tibetan plateau, and the present‐day uplift of this compression zone serves as the seismogenic origin of the Delingha earthquake sequence.