A method for mapping apparent stress and energy radiation applied to the 1994 Northridge earthquake fault zone - revisited

McGarr and Fletcher (2000) introduced a technique for estimating apparent stress and seismic energy radiation associated with small patches of a larger fault plane and then applied this method to the slip model of the Northridge earthquake (Wald et al., 1996). These results must be revised because we did not take account of the difference between the seismic energy near the fault and that in the farfield. The fraction f(v(R)) of the near-field energy that propagates into the far-field is a monotonic function that ranges from 0.11 to 0.40 as rupture velocity v(R) increases from 0.6 beta to 0.95 beta, where beta is the shear wave speed. The revised equation for apparent stress for subfault ij is tau (ij)(a) = f(v(R))/2 rho beta /D-ij integral (D) over dot (t)(ij)(2)dt, where rho is density, D(t)(ij) is the time-dependent slip, and D-ij is the final slip. The corresponding seismic energy is E-a(ij) = AD(ij)tau (ij)(a), where A is the subfault area. Our corrected distributions of apparent stress and radiated energy over the Northridge earthquake fault zone are about 35 % of those published before.