Global Omori law decay of triggered earthquakes: large aftershocks outside the classical aftershock zone

Journal of Geophysical Research



Triggered earthquakes can be large, damaging, and lethal as evidenced by the 1999 shocks in Turkey and the 2001 earthquakes in El Salvador. In this study, earthquakes with Ms ≥ 7.0 from the Harvard centroid moment tensor (CMT) catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected. About 61% of earthquakes that occurred near (defined as having shear stress change ∣Δτ∣ ≥ 0.01 MPa) the Ms ≥ 7.0 shocks are associated with calculated shear stress increases, while ∼39% are associated with shear stress decreases. If earthquakes associated with calculated shear stress increases are interpreted as triggered, then such events make up at least 8% of the CMT catalog. Globally, these triggered earthquakes obey an Omori law rate decay that lasts between ∼7–11 years after the main shock. Earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid. Omori's law is one of the few time-predictable patterns evident in the global occurrence of earthquakes. If large triggered earthquakes habitually obey Omori's law, then their hazard can be more readily assessed. The characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of Ms ≥ 7.0. I show an example application to the M = 7.7 13 January 2001 El Salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than Coulomb stress change calculations.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Global Omori law decay of triggered earthquakes: large aftershocks outside the classical aftershock zone
Series title Journal of Geophysical Research
DOI 10.1029/2001JB000646
Volume 107
Issue B9
Year Published 2002
Language English
Publisher Wiley
Contributing office(s) Coastal and Marine Geology Program
Description 20 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Geophysical Research
First page ESE 9-1
Last page ESE 9-20
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