Mechanical models of the 1975 Kalapana, Hawaii earthquake and tsunami

Our objective is to produce a mechanically realistic model for the 1975 Kalapana event that explains the overall deformation and geological evolution of the south flank of Kilauea, and reproduces most known earthquake and tsunami observations. To do this, we present a new structural interpretation of geological data from Kilauea, along with modeling of the tsunami using recent seismic analyses. In so doing, we hypothesize an offshore north-facing normal fault that we call the Kalapana fault, because of its limited onshore expression near Kalapana. We argue that several different interpretations of seismic data are simultaneously true, each coinciding with a specific geological structure. We perform a direct numerical simulation of the 1975 Kalapana tsunami, and we report results for the near field and the far field simultaneously. Our interpretation of geological structures provides sufficient constraints to derive three tsunami sources: the Kalapana fault, a slump, and a thrust fault. These three tsunami sources are mechanically coupled according to our model of Kilauea evolution, although their contributions to tsunami generation remain relatively distinct. Slump displacement predicts a small shear stress beneath Kilauea volcano. We find that our geological interpretation and tsunami sources are sufficiently robust to reproduce almost all tsunami observations. Repeated earthquakes like the 1975 Kalapana event will produce extension and subsidence in the upper flank of Kilauea, as well as compression and uplift of the toe region, accompanied by limited slump movement. These deformations appear to stabilize Kilauea and make catastrophic failure of the volcano flank less likely at this time.