Interseismic Quiescence and Triggered Slip of Active Normal Faults of KīLauea Volcano’s South Flank During 2001-2018

Date: 4/26/2019

Time: 10:45 AM

Room: Puget Sound

The mobile south flank of Kīlauea Volcano on the Island of Hawaiʻi has generated a number of large earthquakes on its basal detachment, with the most recent being the May 4, 2018 M6.9 earthquake. The south-dipping Hilina fault system (HFS) appears to represent the headscarp of a large-scale gravitationally driven landslide complex. This series of faults is known to have slipped coseismically by several meters during large detachment earthquakes, including the 1975 quake. The Koaʻe fault system (KFS) consists of north-dipping normal faults bounding the summit region of Kīlauea Volcano to the north. These shallow faults slip slowly during interseismic periods and are triggered by volcano-tectonic episodes. To date, geodetic monitoring has been unsuccessful in conclusively detecting interseismic motion of the HFS, which might in part stem from the lack of sufficient geodetic coverage. We analyze kinematic GPS data collected between 2001 and 2017. Our results indicate that the faults did not significantly slip during this time. The lack of interseismic slip is possibly due to the south flank having been in compression from two major intrusive events in 2007 and 2011. Despite its substantial magnitude, space-based radar interferograms show that the May 4, 2018, M6.9 earthquake only triggered sub-cm level slip along sections of the mapped HFS surface trace. Up to 20 cm of offset occurred on what appears to be a newly formed (or previously unknown) fault near the eastern end of the HFS. During the 3 months following the M6.9 earthquake, up to tens of cm of slip occurred along the KFS, helping accommodate rapid large-scale subsidence of Kīlauea’s summit region as large volumes of summit reservoir magma fed the lower East Rift Zone eruption. The HFS appears to activate only in concert with large earthquakes on the basal detachment, while the KFS displaces by aseismic creep during small seismic events and in response to substantial subsurface magma redistribution, including rift zone intrusions and volume loss of the summit magma chamber.

Presenting Author: Kang Wang

Authors