Abstract

This study addresses whether knowing the slip rate on a fault improves estimates of magnitude (Mw) of shallow continental surface‐rupturing earthquakes. Based on 43 earthquakes from the database of Wells and Coppersmith (1994), Anderson et al. (1996) suggested previously that the estimates of Mw from rupture length (LE) are improved by incorporating the slip rate of the fault (SF). We re‐evaluate this relationship with an expanded database of 80 events, which 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 MwlogLE 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 LE for any constant value of SF 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 SF 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.

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