Systematic re-analysis of 23 years of volcanic seismicity on Hawaii Island

Abstract:

The analysis and interpretation of seismicity from mantle depths to the surface plays a key role in understanding how volcanoes work. We are developing and applying methods for the systematic reanalysis of waveforms from volcano-seismic networks, including high-precision earthquake relocation, spectral event classification, and robust focal mechanism and stress drop estimates. Our primary dataset is the ~50-station permanent network of the USGS Hawaiian Volcano Observatory (HVO), but we are extending our methods for application to other volcanic systems. We have converted the entire HVO digital waveform and phase-pick database from 1986 to 2009 (~260,0000 events) to a uniform custom event format, greatly facilitating systematic analyses. A comprehensive multi-year catalog of high-precision relocated seismicity for all of Hawaii Island exhibits a dramatic sharpening of earthquake clustering along faults, streaks, and magmatic features, permitting a more detailed understanding of fault geometries and volcanic and tectonic processes. Automated spectral identification and relocation of long-period (LP, 0.5-5 Hz) seismicity near the summit region of Kilauea Volcano shows that most intermediate depth (5-15 km) LP events occur within a compact volume that has remained at a fixed location for over 23 years. An unanticipated result from our relocation work is the emergence of sharp ring seismicity features. We have so far identified 2 ring features: a full ring of diameter ~2 km on the northwest flank of Mauna Loa, and a half-ring feature of diameter ~0.5 km near Makaopuhi Crater. We are also performing comprehensive spectral analyses to estimate spatial variations in stress drop of shear-failure earthquakes.