Abstract
We investigate earthquake distribution and focal mechanisms associated with the 2018 Kīlauea volcano eruption in Hawaii. Our high‐precision earthquake relocations delineate an aseismic zone bounded by two subhorizontal bands of seismicity at 3.5 and 7 km depths beneath the eastern south flank, both of which are dominated by the shallow‐dipping reverse faulting during the 2018 activity. We interpret the deeper seismicity as related to the basal décollement that separates the volcanic edifice from the oceanic crust. The shallower seismicity is a feature exhibited in the recent activity and, which we propose, reveals a detachment that either represents the contact between Mauna Loa and Kīlauea volcanoes or coincides with the onland extension of the base of the Hilina slump. We suggest that large earthquakes, such as the 1975 Mw 7.7 and the 2018 Mw 6.9 mainshocks, are capable of triggering failures of both the basal décollement and the shallower surface.
Plain Language Summary
In 2018, Kīlauea volcano in Hawaii experienced an eruption that changed the magmatic behavior in the past few decades. In this study, we use the earthquake data recorded by Hawaiian Volcano Observatory to study the seismic activity during the 2018 Kīlauea volcano eruption. We improve earthquake location accuracies using high‐precision seismic data and velocity model and find the earthquake distribution shows different characteristics from the background seismicity in the southern portion of the volcano. A planar seismicity layer at about 7 km depth, also observed in previous location catalogs, is positioned along the interface between the volcanic edifice and the oceanic crust. A shallower layer at 3.5 km depth is a new feature of the recent activity, which we propose represents the boundary between Mauna Loa and Kīlauea volcanoes or the onland extension of a large submarine landslide. We suggest that large earthquakes are strong enough to trigger displacements at both surfaces. The discovery of the new shallower plane will also impact our understanding of slow earthquakes in the volcano.
Key Points
A high‐precision relocation catalog is available for the earthquakes during the 2018 Kīlauea eruption
A new band of shallow microearthquakes at 3.5 km depth is revealed beneath the south flank of Kīlauea volcano
This shallow layer may coincide with either the contact between Mauna Loa and Kīlauea volcanoes or the base of the Hilina slump
