The Accommodation of the South Flank's Motion by the Koa‘e Fault System, Kīlauea, Hawai‘i: Insights From the June 2012 Earthquake Sequence

The Koa‘e fault system is a prominent and complex structural element of Kīlauea Volcano, Hawai‘i. On 5 June 2012, a sequence of shallow earthquakes occurred in the central part of the Koa‘e fault system. The Interferometric Synthetic Aperture Radar (InSAR) data from multiple satellites spanning the time of the earthquake occurrence indicate a maximum of ~10-cm surface displacement above the seismic events in the Koa‘e. The Global Positioning System (GPS) data from multiple stations show that there was a slow slip event in the south flank in late May 2012. Field visits to the fault after the earthquakes revealed ground cracks. In this study, we combine the seismic, InSAR, GPS data, and field observations to investigate the characteristics of the Koa‘e fault system. We relocate the seismic events in the central part of the Koa‘e fault system, compute the focal mechanisms for the events in the June 2012 earthquake sequence, invert for a two-fault model based on the surface deformation, and discuss their relationships with the 2012 slow slip event. Based on our Coulomb stress-change calculation, we infer that the 2012 slow slip event may have triggered both the seismic events and the surface deformation and played a major role in the evolution of the Koa‘e fault system and the accommodation of the south flank's motion. Our integrated analyses are helpful to constrain the fault geometry in the Koa‘e system and to shed light on the role of Koa‘e in the structural evolution of Kīlauea.