Earthquake collapse mechanisms and periodic, migrating seismicity during the 2018 summit collapse at Kīlauea caldera

Abstract

The 2018 Lower East Rift Zone eruption of Kīlauea volcano was accompanied by a remarkable and periodic succession of collapses in the summit region. Between May-August the eruption and collapse sequence included 54 earthquakes (M∼5; M5s) observed worldwide, and over 45,000 intervening earthquakes (M≥0). We estimated seismic full moment tensors for the M5s and analyzed the spatiotemporal evolution of the intervening seismicity. The hypocenters were concentrated between 0-3 km depths and reveal arcuate bands that migrated outward by ∼300 m (map view) and downward by ∼200 m. The temporal evolution reveals almost daily successions of escalating earthquake swarms, followed by an M5, followed by a quiescent period. The moment tensors reveal consistent collapse mechanisms with vertical P-axis orientations. Poisson's ratios estimated from the moment tensors were variable at first (ν=0.1−0.3) and from June 26 onward converged to ν∼0.28, similar to loading cycles observed in lab experiments. The shallower collapses approximately follow the expanding contour of the crater, while deeper collapses aggregate first to the north of the previous crater and later to the east and south. We interpret that the magma storage complex beneath the summit region comprises a distributed plexus of cracks that progressively evacuated and underwent collapse as magma drained from the summit region to feed the eruption.