Recent relocation and focal mechanism analyses of deep earthquakes beneath Kilauea volcano, Hawaii indicate that seismicity is concentrated on a horizontal fault zone at a depth of 30 km, with seaward slip of the upper block on a low-angle plane. We discuss whether the observed localization of the earthquakes can be explained primarily by stresses induced by flexure of the Pacific Plate beneath the Hawaiian load. We find that flexural stresses are consistent with the observed fault plane orientation, and the direction and rate of slip. The mechanisms of mantle earthquakes in other regions of Hawaii are also consistent with the flexural calculation. However, the model has four shortcomings: (1) the fault zone is displaced 15-20 km to the NW of the region of predicted maximum shear stress; (2) the maximum shear stress on preferred fault planes in the vicinity of the fault zone seems too low to overcome Coulomb friction (by about a factor of 2, assuming hydrostatic pore pressure); (3) the fault zone is much more localized laterally than is the region of large flexural stresses and stressing rates and (4) the fault zone is more localized vertically than might be inferred from the calculation as well. Simple and plausible extensions of the plate flexure model that account for spatial variations in the location of pore fluids, and/or the possible existence of a passive low shear stress magma transport system can overcome most of these shortcomings. Several magma pipes would be necessary to explain the observed earthquake locations, and simple thermal arguments indicate that such pipes could be conduits for porous flow if they are a few kilometres in radius.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- Flexure of the lithosphere
- Magma flow