Abstract

Magnitude (M)–log area (A) relations have been the focus of considerable research in the past two decades because of their importance in estimating moment magnitude M for earthquake probability calculations and seismic‐hazard analysis. For M<6.5 earthquakes, with source dimensions less than the seismogenic width W, there is a strong consensus for constant stress‐drop scaling. For the larger earthquakes (M>7) that dominate the moment balancing in continental crust, the L‐model scaling employed by Hanks and Bakun (2002, 2008) involves fault slip growing with fault length L when L>W∼15  km or so, requiring that static stress drops increase with increasing fault slip. Constant stress‐drop representations of the same larger‐earthquake data, such as Shaw (2009, 2013), require slip at depths significantly greater than W∼15  km. Available evidence supports neither of these requirements leaving us perplexed as to how large‐earthquake ruptures initiate and propagate in continental crust. Deep slip M–logA models that involve an unknown amount of seismic moment/earthquake slip at unknown depths>W are not appropriate for use in earthquake probability studies governed by shallow‐slip (depths≤W) seismic moment/earthquake slip balancing, such as those in California during the twenty‐first century.

You do not currently have access to this article.