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Rupture process and dynamic implications of the July 29, 2008 Mw 5.4 Chino Hills, California Earthquake

Chen Ji

Published 2012, SCEC Contribution #1262

The source model of the 2008 Mw 5.4 Chino Hills, California, earthquake is
constrained using near-field seismic body waves recorded by the California Integrated Seismic Network (CISN). Finite fault inversions are preformed for the two fault models
based on the nodal planes derived from the CISN moment tensor solution. The northeast
dipping plane (strike = 289; dip = 62), which has a similar strike as the nearby
Whittier fault, is chosen as the causative fault because it fits the data significantly better.
Our inversion result indicates that the majority of the Chino Hills earthquake rupture
occurred in a compact area. In particular, 48% of the total seismic moment (1.6 1017 Nm)
was released by the failure of a 1.8 km2 asperity located east of the hypocenter in a
short time window from 0.4 to 0.8 s after the rupture initiation. The average slip is
approximately 0.5 m but the maximum slip is 1.8 m. The average rupture velocity is
1.9 km/s. The static stress drop calculated using the slip model is up to 80 MPa and the
average stress drop changes from 19 to 38 MPa, depending on the average schemes.
The weighted average slip velocity is 6.5 m/s for entire rupture and is 11 m/s for the east
asperity. The inferred available energy and radiated energy are 8 1013 J and 2.5 1013 J,
respectively. Radiation efficiency is then 0.31, which is moderately low compared with
previous earthquakes but consistent with the inferred high average fracture energy density,
ranging from 6.5 to 14.8 MJ/m2.

Ji, C. (2012). Rupture process and dynamic implications of the July 29, 2008 Mw 5.4 Chino Hills, California Earthquake. Journal of Geophysical Research,. doi: 10.1029/2011JB008856..