AGU: Geophysical Research Letters

 

Editors' Highlight

Loading by Hawaii's volcanoes: An explanation for the 15 October 2006 earthquakes

On 15 October 2006, two earthquakes shook the northwest coast of the island of Hawaii 6 minutes apart—the Kiholo Bay event (M_w = 6.7) and the shallower but still unexpectedly deep Mahukona event (M_w = 6.0). Their close proximity in space and time suggests a common origin, but sharp contrasts in mechanism and depth present an unusual fault-aftershock relationship. McGovern (2007) hypothesized that these "fraternal twin" earthquakes are the divergent outcomes of a single process: downward flexing of the lithosphere in response to loading by the massive Hawaiian volcanoes. The initial Kiholo Bay event is readily explained through models of lithospheric flexure as brittle failure in a high-stress zone in the lower lithosphere. However, an explanation for the depth (also within the mantle) of the Mahukona event requires models that incorporate a strong stiffness contrast between crust and mantle in order to produce peak upper lithosphere stresses at the stiffer mantle's top. This compressional high-stress zone also traps magma near the base of the crust, thereby explaining the seismically observed thickening from below (underplating) of Hawaiian volcanoes.

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