High-precision relocation of long-period events beneath the summit region of Kı̄lauea Volcano, Hawai‘i, from 1986 to 2009

Long-period (0.5–5 Hz, LP) seismicity has been recorded for decades in the summit region of Kı̄lauea Volcano, Hawai‘i, and is postulated as linked with the magma transport and shallow hydrothermal systems. To better characterize its spatiotemporal occurrence, we perform a systematic analysis of 49,030 seismic events occurring in the Kı̄lauea summit region from January 1986 to March 2009 recorded by the ∼50-station Hawaiian Volcano Observatory permanent network. We estimate 215,437 P wave spectra, considering all events on all stations, and use a station-averaged spectral metric to consistently classify LP and non-LP seismicity. We compute high-precision relative relocations for 5327 LP events (43% of all classified LP events) using waveform cross correlation and cluster analysis with 6.4 million event pairs, combined with the source-specific station term method. The majority of intermediate-depth (5–15 km) LPs collapse to a compact volume, with remarkable source location stability over 23 years indicating a source process controlled by geological or conduit structure.