S44A-08
High-speed rupture during the initiation of the 2015 Bonin Islands deep earthquake
Thursday, 17 December 2015: 17:45
305 (Moscone South)
Zhongwen Zhan1, Lingling Ye2, Peter M Shearer3, Thorne Lay4 and Hiroo Kanamori1, (1)California Institute of Technology, Pasadena, CA, United States, (2)Caltech, Pasadena, CA, United States, (3)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (4)University of California Santa Cruz, Santa Cruz, CA, United States
Abstract:
Among the long-standing questions on how deep earthquakes rupture, the nucleation phase of large deep events is one of the most puzzling parts. Resolving the rupture properties of the initiation phase is difficult to achieve with far-field data because of the need for accurate corrections for structural effects on the waveforms (e.g., attenuation, scattering, and site effects) and alignment errors. Here, taking the 2015 Mw 7.9 Bonin Islands earthquake (depth = 678 km) as an example, we jointly invert its far-field P waves at multiple stations for the average rupture speed during the first second of the event. We use waveforms from a closely located aftershock as empirical Green's functions, and correct for possible differences in focal mechanisms and waveform misalignments with an iterative approach. We find that the average initial rupture speed is over 5 km/s, significantly higher than the average rupture speed of 3 km/s later in the event. This contrast suggests that rupture speeds of deep earthquakes can be highly variable during individual events and may define different stages of rupture, potentially with different mechanisms.
