Overlap of Slow and Seismic slip under Kīlauea’s South Flank in the May 4, 2018 Mw6.9 earthquake.

Abstract:

The décollement fault under Kīlauea’s south flank has been the site of regular slow slip events (SSEs). While they have been observed as far back as 1998, since 2005 they have had a regular repeat period of 2.5 years ± 3 months. The last observed SSE was in October, 2015 and the next was expected between February and August, 2018. Instead, on 4 May, 2018, the décollement fault ruptured in a M_w6.9 earthquake. This was one day after lava erupted from the first fissure of Kīlauea’s 2018 lower East Rift Zone eruption and four days after the collapse of Puʻu ʻŌʻō crater and the initiation of downrift magma migration.

A slip model constructed from high-rate (1Hz) GPS solutions shows two subevents separated by 1-2 seconds during the 2018 earthquake. The first occurred near the epicentral region and extended landward towards the rift, and the second proceeded west from the epicenter and was located entirely offshore. The western subevent overlaps substantially with parts of the fault involved in the SSEs, implying that the fault in this area is conditionally stable and can either creep or slip seismically depending on the applied stress rate. We compare slip from kinematic models and seismicity during the earthquake and SSEs to understand the similarities between them. We also investigate the effect of the current deformation regime on the décollement fault and the potential for future SSEs.