An Improved Earthquake Catalog During the 2018 Kı̄lauea Eruption From Combined Onshore and Offshore Seismic Arrays

The Island of Hawai’i was formed by repeated eruptions of basalts at an oceanic hotspot. Kı̄lauea, the youngest among the subaerial volcanoes of the island, erupted intensely in 2018. The eruption provided an opportunity to look into the mechanisms that operate at the volcano and associated earthquake activities, as it was recorded simultaneously, for the first time, by onshore and offshore seismometers. We used most of the publicly available seismic data during the eruption period, including temporary arrays, to build a more complete earthquake catalog during the eruption than that provided by the Hawaiian Volcano Observatory. We used a short-time-average/long-time-average method to identify potential earthquakes. The detections were associated with events and automatically picked with P-wave and S-wave arrivals, which were used to locate the events in a three-dimensional velocity model. After re-examining these earthquake events, their coda/duration magnitudes were determined. The resulting half-year catalog contains 375,736 events with one of the highest daily earthquake numbers ever reported (6,128 on 21 June 2018). A great number of events were recorded during the caldera collapses, from its beginning until its rapid ending. The catalog also contains abundant events near the Pu’u‘ō‘ō vent and in the lower East Rift Zone, where an increase of seismicity in mid-July and August indicated a step-up in magma intrusion after the eruption.