Debate continues regarding the relative proportion of earthquakes triggered by passing seismic waves versus static stress changes from a main shock. Static stress changes are expected to have long‐term effects on earthquake probabilities, whereas dynamic stress changes due to the passing of seismic waves should not. Both mechanisms are expected to raise seismicity rates in some areas, but only static stress change calculations predict rate decrease shadows. Thus, identification of post‐main‐shock earthquake suppression is diagnostic of a static stress change process. We note that in principle, static stress change theory predicts suppression of particular earthquake mechanisms in a shadow zone rather than an overall rate reduction. A stress shadow can therefore be characterized by a change in the average earthquake focal mechanism before and after a main shock that results from suppression of a given mechanism type. We examined average mechanisms from ±2° radii and 5‐year periods before and after 119 Ms ≥ 7 main shock earthquakes drawn from the Harvard Centroid Moment Tensor (CMT) catalog. Significant average mechanism changes caused by earthquake suppression were found in only two cases. However, by stacking the data, we were able to resolve statistically significant suppression of particular post‐main‐shock focal mechanisms. This indicates that, while static stress shadows are subtle, they are indeed present in the global catalog.
|Publication Subtype||Journal Article|
|Title||A global search for stress shadows|
|Series title||Journal of Geophysical Research Solid Earth|
|Contributing office(s)||Pacific Coastal and Marine Science Center|
|Description||B12304, 16 p.|
|Google Analytic Metrics||Metrics page|