Inversion of the Earthquake Rupture Process: Methods, Case Studies and Applications to Emergency Response

Abstract

To understand the seismogenesis and the earthquake mechanism, and to find a way helping reduction of seismic disaster, in the last two and more decades, we have been devoting to the study of earthquake rupture process, developing new methods and applying the methods to earthquake case studies as well as earthquake emergency response. In this article, we briefly review the methods developed, present three representative examples to illustrate the methods and their applications and summarize the events for which the earthquake rupture processes were processed and were reported to the authorities and released to the public immediately for the rapid emergency response. In the three examples, the 2008 M_W7.9 Wenchuan earthquake, the 2010 M_W6.9 Yushu earthquake and the 2016 M_W7.8 Kaikoura, New Zealand, earthquake are included. The 2008 M_W7.9 Wenchuan earthquake ruptured an area 350 km × 50 km along the 470-km-long NE-SW striking Longmenshan Fault, released seismic moment of about 9.4 × 10²⁰ Nm and resulted in the average stress drop of about 18 MPa and the maximum stress drop of about 65 MPa, respectively. There were two substantial concentrated-slip patches on the fault plane with slips of up to 8.9 and 6.7 m, just beneath the elongated area extending from Yingxiu-Dujiangyan to Wenchuan and the meizoseismal area near Beichuan, respectively. During the rupture process, irregular high rupture velocities of 3.6, 4.0, 4.4, 3.5 km/s in the four stages, respectively, were found. The spatiotemporal rupture process exhibited a complex asymmetric bilateral rupture, with overall direction of northeast azimuth. The 2010 M_W6.9 Yushu earthquake ruptured unilaterally and released the scalar seismic moment of about 2.7 × 10¹⁹ Nm, resulting in the average slip of about 0.6 m and the average stress drop of 15 MPa. The rupture process lasted about 16 s, including two clearly distinguishable sub-events. The first one was between 0 and 5 s, corresponding to the asperity with a maximum slip of 0.8 m. The second was between 5 and 16 s, corresponding to the asperity 17–54 km southeastern from the epicenter. The 2016 M_W7.8 Kaikoura earthquake had a very complex source process. It lasted for about 100 s, producing a rupture area about 160 km long along strike direction and about 50 km wide in down-dip direction and resulting in a release of scalar moment 1.01 × 10²¹ Nm. Spatially, the rupture area consisted of two asperities, with one close to the rupture initiation point having a maximal slip value of about 6.9 m while the other far away in north having a maximal slip value of about 9.3 m. Temporally, the first asperity slipped for about 65 s and the second initiated 40 s later and lasted for 40 s, with both of them slipping about 25 s simultaneously. As to focal mechanism, the first asperity had a nearly thrust slip while the second had both thrust and strike-slip components. The methods have been applied to over 70 significant earthquakes across the world for rapid emergency response since 2008. The applications show that the methods prove to be effective in the earthquake emergency response, and the results may be used to reduce the losses caused by the earthquakes.