Triggering of the Mw 7.2 Hawaii Earthquake of 4 May 2018 by a Dike Intrusion

A Mw 7.2 earthquake struck the south flank of Kilauea, Hawaii, on 4 May 2018, following a period of volcanic unrest. To investigate its relationship with the stress changes induced by prior tectonic and magmatic activity, we model the coseismic slip distribution, preintrusion deformation, and dike intrusion using geodetic, seismic, and tsunami observations. The decollement beneath the south flank was creeping seaward by similar to 25cm/year. Diking started on 20 April and led to fissure eruption on 3 May. The magmatic activity and creep resulted in an onshore U-shaped zone of stress unloading, fringed by an off-shore zone of stress buildup that apparently guided the 2018 rupture. It takes only 20 to 35 years at the preintrusion rate to accumulate a moment deficit equivalent to the moment that was released in 2018. This event falls short of balancing the moment budget since the 1975 Mw 7.7 earthquake. Plain Language Summary As one of the most active volcanoes on Earth, Kilauea volcanos in Hawaii are responsible for various deformation sources including summit reservoirs, rift zones, decollement faults, and slumps, which result in thousands of earthquakes each year. While most of the minor earthquakes (M < 4) there are related to magma movement through conduits and cracks, the causes and mechanisms for less frequent but large and devastating events, such as the 1975 Ms 7.2 Kalapana earthquake and the 1868 similar to M 8 Great Kau earthquake, are still not fully understood, and only conceptual models were proposed partially due to poor observations at that time. We act to further the prior analysis to combine seismological and geodetic data sets to constrain the relationships of magmatic processes with large-scale triggered earthquakes, using the April 2018 Hawaiian eruption and the corresponding 4 May 2018 Mw 7.2 as a case study. Our results show the creep on the decollement constantly alter the stress accumulation, while dike intrusion trigger the occurrence of the large earthquakes. Besides, it will take about 20 to 35 years for such a damaging earthquake to reoccur on the decollement beneath the south flank of Kilauea.