Characterizing fault zones at Kilauea & Mauna Loa volcanoes by large-scale mapping of earthquake stress drops and focal mechanisms

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The analysis and interpretation of seismic sources from within Earth's mantle up to the surface plays a key role in understanding how volcanoes work. Hawaii Island is one of the most tectonically, volcanically, and seismically active regions on Earth. The USGS Hawaiian Volcano Observatory (HVO) operates a seismic network that has recorded over 260,000 earthquakes since 1986, but this rich dataset has not been fully exploited. This project supports collaboration between HVO, U.C. Santa Barbara, and U.C. San Diego to apply a number of new large-dataset processing methods to learn more about seismic activity on Hawaii and its relationship to faults and volcanoes. It also supports the educational program at U.C. Santa Barbara by providing funds for graduate student support. The results from this study are expected to yield a sharper and more comprehensive view of fault zone characteristics as well as generate public databases of high-resolution information on seismicity characteristics, suitable for other researchers in their studies of Hawaiian geology, tectonics, and volcanism. This research will lead to improved descriptions of seismicity and tectonics for Hawaii, which will improve our ability to monitor and characterize volcanic and earthquake hazards.By performing systematic and comprehensive analyses of seismicity recorded by HVO, this work will improve earthquake location precision, provide robust estimates of the patterns of earthquake stress drops, and compute more reliable earthquake focal mechanisms on Hawaii. Integrating these results will better characterize crustal and mantle fault zones and magma conduits in and around Kilauea and Mauna Loa volcanoes, and will help to resolve the relationships between seismicity, volcanic activity, and strain transients. Our results will address the following questions: (1) Relocated microearthquakes in Hawaii align along resolvable fault and conduit structures?what do these structures reveal about tectonic and volcanic processes? (2) What is the origin of recently discovered seismicity rings in Hawaii? (3) How do the stress drops of Hawaiian earthquakes compare to other regions? Are there variations in earthquake stress drops that can be used to characterize stress field heterogeneity and identify regions of stress concentration? (4) Can focal mechanisms be improved for small earthquakes in Hawaii and what do they reveal about the faulting process and stress state? (5) Can repeating earthquakes with nearly identical waveforms be used to resolve temporal variations in seismic velocity associated with tectonic and volcanic activity? (6) How do the characteristics of long-period (LP, 0.5-5 Hz) seismicity at Kilauea volcano relate to redistributions of magma and stress within its magma supply system?