Fault scaling relationships depend on the average fault slip rate

John G. Anderson, Glenn P. Biasi, & Steven G. Wesnousky

Awaiting Publication August 10, 2017, SCEC Contribution #7485

This study addresses whether knowing the slip rate on a fault improves estimates of magnitude (M_{W}) of shallow, continental surface-rupturing earthquakes. Based on 43 earthquakes from the database of Wells and Coppersmith (1994), Anderson et al. (1996) previously suggested that estimates of M_{W} from rupture length (L_{E}) are improved by incorporating the slip rate of the fault (S_{F}). We re-evaluate this relationship with an expanded database of 80 events, that includes 56 strike-slip, 13 reverse, and 11 normal faulting events. When the data are subdivided by fault mechanism, magnitude predictions from rupture length are improved for strike-slip faults when slip rate is included, but not for reverse or normal faults. Whether or not the slip rate term is present, a linear model with M_{W}\sim\log L_{E} over all rupture lengths implies that the stress drop depends on rupture length - an observation that is not supported by teleseismic observations. We consider two other models, including one we prefer because it has constant stress drop over the entire range of L_{E} for any constant value of S_{F} and fits the data as well as the linear model. The dependence on slip rate for strike-slip faults is a persistent feature of all considered models. The observed dependence on S_{F} supports the conclusion that for strike-slip faults of a given length, the static stress drop, on average, tends to decrease as the fault slip rate increases.

Key Words
earthquake scaling

Citation
Anderson, J. G., Biasi, G. P., & Wesnousky, S. G. (2017). Fault scaling relationships depend on the average fault slip rate. Bulletin of the Seismological Society of America, (awaiting publication).


Related Projects & Working Groups
Broadband Working Group, Ground Motion Prediction