Earthquake-Scaling Relationships from Geodetically Derived Slip Distributions

Empirical earthquake scaling relationships describe expected relationships between moment magnitude and various spatial descriptors of the earthquake rupture (along-strike length, down-dip width, rupture area, and peak and mean slip). These scaling relationships play important roles in many seismological, geological, and hazards-assessment applications. Historically, scaling relationships were defined from various seismological criteria, such as teleseismic finite-fault models or aftershock distributions. The proliferation of earthquake slip distributions from geodetic observations presents an opportunity to reassess earthquake scaling relationships using observations that more directly sample the spatial characteristics of an earthquake than seismological observations. Here, we present a database of 111 earthquake slip distributions from 73 different earthquakes that were derived from geodetic observations. The earthquakes range in magnitude from M-w 5.3 to 9.1. We extract common spatial descriptors from these slip distributions in four different ways to account for biases introduced by inversion regularization, and we regress these spatial descriptors with moment magnitude to derive new empirical scaling relationships. We additionally assess the shape characteristics of the slip distributions and report the average earthquake shape. We find that our scaling relationships differ in important ways from previous studies, and we show that these differences originate from our use of a geodetic slip-distribution database rather than from methods for extracting spatial descriptors. Notably, we find that geodetic slip distributions systematically predict smaller fault areas than seismically derived scaling relationships. Because geodetic source inversions are likely contaminated to some degree by aseismic afterslip, this relationship suggests that seismologically determined scaling relationships systematically overpredict earthquake dimensions. We find that fault length, fault width, peak slip, and mean slip differ from previous studies in ways that are more complex and magnitude dependent. Given the high-model resolution afforded by geodetic observations, our earthquake scaling relationships derived fromgeodetic slip distributions provide improved constraints on empirical scaling relationships. Supplemental Content: Figures for each new earthquake slip distribution presented in this study and tables from text in CSV format, as well as tables of the scaling parameters derived by and used in this study.