Anatomy of a Caldera Collapse: Kilauea 2018 Summit Seismicity Sequence in High Resolution

Date: 4/26/2019

Time: 09:00 AM

Room: Puget Sound

The Kilauea eruption and caldera collapse of 2018 was an incredibly dynamic sequence, observed at close distances by a dense, modern, multi-faceted network. The seismic sequence associated with summit caldera collapse was especially rich, with cycles of seismicity closely tracking cycles of large (typically M_w 5.2-5.4) collapse events associated with magma withdrawal from the summit area. To gain further insight into the summit sequence, we applied waveform-based earthquake detection, double-difference relocation, and correlation-based focal mechanism analyses. Using ~2800 earthquakes cataloged by the Hawaiian Volcano Observatory from April 29 to August 6, 2018, we detected and relocated ~44,000 events. Event hypocenters form complex structures in space and time. The vast majority of seismicity concentrated just east of Halema’uma’u crater, at shallow depths of 2.5 km or less below Kilauea summit, and roughly outlined the eastern extent of caldera collapse. We note changes in event distributions at different stages of the repeated collapse cycles, with events early in each cycle concentrating near the center of the seismic zone, with activity moving to the perimeter later in the cycle. Using cross-correlations to measure relative P and S polarities, we cluster events by similarity of polarity patterns observed across the network. Some mechanism clusters are formed by earthquakes with primarily double-couple slip, while others are composed of distinctly non-double-couple events dominated by dilatational first motions. In total, these events illuminate complex kinematics and dynamics associated with the 2018 Kilauea caldera collapse. The double-couple mechanisms likely reflect slip on faults accommodating caldera subsidence; the implosive events may reflect sudden closure of cracks or dikes.

Presenting Author: David R. Shelly

Authors