The breakdown of minerals, and significant seismic consequences, has been shown to occur at shallower depths in these seismic hotspots, including parts of the Pacific Northwest. The Cascadia Subduction Zone, where plates meet under the Pacific Ocean. Pacific Geoscience Centre, provides firm support for a recent theory that explains how intraslab earthquakes work and confirms the hazard posed to certain geographic areas. The study appears in today's issue of the journal Science. Many of the largest earthquakes occur at subduction zones.
Depth is shown in kilometers.
Great thrust earthquakes occur at shallow depths of 0 to 50 kilometers along the sloping boundary between the descending plate and the continental margin. In contrast, intraslab earthquakes occur within the descending oceanic crust at depths of 50 to 300 kilometers beneath the surface and are caused by different processes. In many cases, such as the Pacific Northwest, these less easily understood earthquakes occur closer to major population centers than the larger offshore earthquakes. The historic record bears this out. In 1996, Stephen H. Kirby and colleagues at the U.S. Geological Survey proposed a mechanism for intraslab earthquakes which is supported by the current study.