Conventional wisdom in seismology says slip on faults that rupture during the largest continental strike-slip earthquakes is generally limited to the seismogenic layer, the upper 15 km or so of the earth's crust to which aftershocks extend and background seismicity is limited.
That idea when coupled with theory predicts that the amount of slip on faults in large earthquakes should not continue to increase once the dimensions of a rupture have surpassed about 15 km. The prediction is not supported by observation. Slip does continue to increase as the length of earthquake ruptures increase. The contradiction between the prediction and observation has long been recognized to suggest that the physics of large earthquakes is different than small.
This interpretation has been unsettling because it lends uncertainty to the idea that observations from small earthquakes, which are far more abundant, can be scaled upward to make predictions about much less frequent but far more damaging large earthquakes that will occur in the future, a common practice in seismology.
New work by seismologists Geoffrey C. P. King and Steven G. Wesnousky shows how the conundrum may be resolved if slip during the largest earthquakes is allowed to extend modestly below the seismogenic layer and that the base of the seismogenic layer is marked by a transition to stable sliding rather than viscous relaxation.
Geoffrey C. P. King is the Director of the Laboratoire Tectonique at the Centre Nationale de la Recherche Scientifique's Institut de Physique du Globe de Paris. Steven G. Wesnousky is Director of the Center for Neotectonic Studies and Department of Geological Sciences University of Nevada-Reno.
This research was published in the Bulletin of the Seismological Society of America.
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