Earthquake Patterns in Diverse Tectonic Zones of the Globe

Yan Y. Kagan, Peter Bird, & David D. Jackson

Published 2010, SCEC Contribution #1244

We extend existing branching models for earthquake occurrences <br/>by incorporating potentially important estimates of tectonic <br/>deformation and by allowing the parameters in the models to <br/>vary across different tectonic regimes. <br/>We partition the earth's surface into five regimes: Trenches <br/>(including subduction zones and oceanic convergent boundaries <br/>and earthquakes in outer rise or overriding plate); fast <br/>spreading ridges and oceanic transforms; slow spreading ridges <br/>and transforms; active continental zones, and plate interiors <br/>(everything not included in the previous categories). <br/>Our purpose is to specialize the models to give them the <br/>greatest possible prediction power for use in earthquake <br/>forecasts. <br/>We expected the parameters of the branching models to be <br/>significantly different in the various tectonic regimes, <br/>because earlier studies (Bird and Kagan, 2004) found that the <br/>magnitude limits and other parameters differed between similar <br/>categories. <br/>We compiled subsets of the CMT and PDE earthquake catalogs <br/>corresponding to each tectonic regime, and optimized the <br/>parameters for each, and for the whole earth, using a maximum <br/>likelihood procedure. <br/>We also analyzed branching models for California and Nevada <br/>using regional catalogs. <br/> <br/>Our estimates of parameters that can be compared to those of <br/>other models were consistent with published results. <br/>Examples include the proportion of triggered earthquakes and <br/>the exponent describing the temporal decay of triggered <br/>earthquakes. <br/>We also estimate epicentral location uncertainty, as well as a <br/>size of a focal rupture zone of an earthquake and our results <br/>are consistent with independent estimates. <br/>Contrary to our expectation, we found no dramatic differences <br/>in the branching parameters for the various tectonic regimes. <br/>We did find some modest differences between regimes that were <br/>robust under changes in earthquake catalog and lower magnitude <br/>threshold. <br/>Subduction zones have the highest earthquake rates, the <br/>largest upper magnitude limit, and the highest proportion of <br/>triggered events. <br/>Fast spreading ridges have the smallest upper magnitude limit <br/>and the lowest proportion of triggered events. <br/>The statistical significance of these variations cannot be <br/>assessed until methods are developed for estimating confidence <br/>limits reliably. <br/> <br/>Some results apparently depend on arbitrary decisions adopted <br/>in the analysis. <br/>For example, the proportion of triggered events decreases as <br/>the lower magnitude limit is increased, possibly because our <br/>procedure for assigning independence probability favors larger <br/>earthquakes, or possibly because a catalog with fewer events <br/>allows fewer triggering instances to be recognized. <br/>In some tests we censored earthquakes occurring near and just <br/>after a previous event, to account for the fact that most such <br/>earthquakes will be missing from the catalog. <br/>Fortunately the branching model parameters were hardly <br/>affected, suggesting that the inability to measure immediate <br/>aftershocks does not cause a serious estimation bias. <br/>We compare our branching model with the ETAS model and discuss <br/>the differences in the models parametrization and the results <br/>of earthquake catalogs analysis. <br/>

Kagan, Y. Y., Bird, P., & Jackson, D. D. (2010). Earthquake Patterns in Diverse Tectonic Zones of the Globe. Pure and Applied Geophysics, 167(6/7), 721-741. doi: 10.1007/s00024-010-0075-3.