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 s tress and seismic energy radiation associated with small patches of a large r fault plane and then applied this method to the slip model of the Northri dge earthquake (Wald et al., 1996). These results must be revised because w e did not take account of the difference between the seismic energy near th e fault and that in the farfield. The fraction f(v(R)) of the near-field en ergy 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 apparen t 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-depe ndent 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 d istributions of apparent stress and radiated energy over the Northridge ear thquake fault zone are about 35 % of those published before.