Rise time and source duration of the 2008 MW 7.9 Wenchuan (China) earthquake as revealed by Rayleigh waves

• Published in: Earth, planets, and space Vol. 63; no. 5; pp. 427 - 434
• Main Authors: Hwang, Ruey-Der, Chang, Jo-Pan, Wang, Chien-Yin, Wu, Jia-Jhang, Kuo, Ching-Huei, Tsai, Yu-Wei, Chang, Wen-Yen, Lin, Tzu-Wei
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 2011; Terra
• Subjects: Cosmochemistry. Extraterrestrial geology; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Geology; Geophysics/Geodesy; Far East; Asia; China; Rise time; source duration; Rayleigh waves; phase velocity; rupture directivity; seismic energy; exhibits; S-waves; earthquakes; faults; rupture; duration; currents; dynamics; aftershocks; Delay time; direction; models; inverse problem; strike-slip; strike; bars; crust; First order; fault planes; thrust; Phase delay; Wave velocity; stress drops
• ISSN: 1343-8832; 1880-5981
• DOI: 10.5047/eps.2011.01.002

The fault parameters of the 2008 Wenchuan earthquake were studied in a rupture directivity analysis by simultaneously inverting the period of the first Fourier spectral-node and the 100-s phase-delay time of the Rayleigh wave. The results show that the earthquake is a unilateral event with an optimal rupture azimuth of N59°E, consistent with the distribution of aftershocks. They also indicate that the fault plane strike is in the NE-SW direction, corresponding to the fault plane strike of 238° and NW-dipping (reported by the USGS). The inversion shows the source duration (including the rise time and rupture time) and rise time are 70±0.8 s and 9.3±0.6 s, respectively. The rupture velocity estimated only from the rupture time exhibits relatively higher value, 3.45±0.10 km/s, close to or larger than the S-wave velocity in the crust. One possible cause is that the rupture mechanism transferred from the thrust faulting in the southwestern portion of the fault to the strike-slip faulting in the northeastern one. The rise time offers an estimate of the dynamic stress drop (37.8±2.3 bars), from which through a macroscopic view the radiated seismic energy of (5.93±0.4) × 1016 N m is calculated. Although the estimated rupture length (∼210 km) and source duration are shorter than several source rupture models, the current analyses show the first-order rupture feature of the 2008 Wenchuan earthquake rupturing the Longmenshan fault zone.