An elastic wedge model for the development of coeval normal and thrust faulting in the Mauna Loa-Kilauea rift system in Hawaii

A long-standing enigma of the Mauna Loa-Kilauea rift system in Hawaii is th e coeval development of normal and thrust faults that are vertically partit ioned. To address this question, we developed a simple elastic wedge model that explores plausible boundary conditions in terms of tractions for gener ating such a fault pattern. Analytical solutions that best simulate the obs erved faulting style and geodetically determined strain at the surface requ ire that (1) the pore fluid pressure ratio within the wedge (lambda) and al ong the basal decollement (lambda (b)) must be exceedingly high (i.e., lamb da = lambda (b) = 0.90-0.95) and (2) a tensile stress of the order of 10-30 MPa must have existed in the very top part of the rift zone at the back si de of the wedge-shaped rift flank. The high pore fluid pressure within the rift flank may be induced by pumping of fluids during emplacement of magma, whereas the high pore fluid pressure along the basal decollement may be ca used by compaction of water-saturated sediments between the volcanic pile a bove and the oceanic floor below. Although the predicted tensile stress in the rift zone could be related to the presence of a relatively steep topogr aphic slope, our results show that this is not a prerequisite. Therefore we attribute occurrence of tensile stress to either upward bending of the Haw aiian volcanic pile due to emplacement of magma, or inflation of a shallow magma chamber several kilometers beneath the surface. In any case, the resu lts of our model indicate that magma emplacement in the shallow part of the rift zone may be a passive process, while the deep rift zone experiences f orceful emplacement (i.e., active rifting via magma push).