Faulting in the South Flank of Kilauea Volcano, Hawaiʹi

Models developed to explain the deformation of Kilauea volcano largely rely on seismic and geodetic data that cover only a short period of activity. Kilaueaʹs active South Flank contains two normal fault systems — the Koaʹe and Hilina systems — that must reflect longer-term deformation of the edifice. The scale and origin of these faults is poorly understood. Both fault systems consist of en echelon fault segments that have significant interaction and linkage. The presence of relay ramps between fault segments, systematic stepping senses, and slip and displacement data all suggest that the fault systems link down to individual larger faults. The Hilina Fault System (HFS) is ≥42 km long and ∼9 km deep, while the Koaʹe Fault System (KFS) is underlain by two to three smaller faults, the largest of which is at least 14 km long and 4 km deep (and possibly extends down to the basal thrust at 9 km depth). We suggest that the HFS has developed as a result of ‘differential slip’ on the thrust at the base of the edifice and that footwall uplift on the HFS causes antithetic faulting in the South Flank, which provides a new explanation of the origin of the KFS.