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We examine the spatiotemporal variations in seismic parameters corresponding to the 2018 Kīlauea eruption. We find that the summit area had mainly strike‐slip focal solutions prior to the eruption, whereas normal‐faulting was the predominant feature during the eruption, partially due to the collapse events. In contrast, the majority of the earthquakes in the central south flank had normal‐faulting solutions before December 2017, in agreement with the normal‐faulting of the Hilina Fault System, while there are more reverse solutions during the eruption. We also observe temporal variations in the estimated in situ Vp/Vs ratios corresponding to the eruption, with increases in the summit and decreases in the East Rift Zone. The sustained low Vp/Vs ratios below 4 km depth under the summit caldera may suggest persistent ascent of volatiles from the mantle. The low Vp/Vs values in the East Rift Zone are probably associated with increased degassing. Plain Language Summary: In this study, we investigate changes in earthquake faulting geometry and the ratio of compressional (P) wave speed to shear (S) wave speed in space and time that might be related to the 2018 Kīlauea volcano eruption. We find that the earthquake fault orientations changed in both the summit area and the central south flank as early as in December 2017, indicating that the internal forces within the volcano had changed months before the eruption. We also detect changes in the ratios of P to S wave speed corresponding to the eruption. Very low ratios are observed beneath the summit and the Lower East Rift Zone, which can be explained by the movement of volatiles. Our results suggest that seismic parameters can be very sensitive to volcanic activities and their detailed analyses have considerable potential for addressing key issues regarding the evolution of volcanic and tectonic activity. Key Points: Temporal changes in focal mechanisms are observed in December 2017Temporal variations in Vp/Vs ratios are resolved beneath the summit caldera and in the East Rift Zone [ABSTRACT FROM AUTHOR]

Abundant seismicity beneath the Island of Hawai'i from mantle depths to the surface plays a central role in understanding how volcanoes work, grow, and evolve at this intraplate oceanic hotspot. We perform systematic waveform cross‐correlation, cluster analysis, and relative relocation of 347,445 events representing 32 years of seismicity on and around the island from 1986 to 2018. We successfully relocate 275,009 (79%) events using ∼1.7 billion differential times (P and S) from ∼128 million similar‐event pairs. The results reveal a dramatic sharpening of seismicity along faults, streaks, rings, rift zones, magma pathways, and mantle fault zones; seismicity delineating crustal detachments on the flanks of Kīlauea and Mauna Loa is particularly well‐resolved. The resulting high‐precision spatio‐temporal image of seismicity captures almost the entire 1983–2018 Pu'u 'Ō'ō‐Kūpaianaha eruption of Kīlauea with its numerous distinct episodes and wide‐ranging activity, culminating in the 2018 lower East Rift Zone eruption and summit collapse. Plain Language Summary: We present a new catalog of high‐precision relocated seismicity across the Island of Hawai'i from 1986 to 2018, a location that has long served as a natural laboratory for studying magmatic and tectonic processes. Key Points: We present a new catalog of high‐precision relocated seismicity across the Island of Hawai'i from 1986 to 2018Dramatic sharpening of seismicity along faults, streaks, rings, rift zones, magma pathways, and mantle fault zonesRelocated catalog captures almost the entire 1983–2018 Pu'u 'Ō'ō‐Kūpaianaha eruption of Kīlauea [ABSTRACT FROM AUTHOR]

Relocations and focal mechanism analyses of deep earthquakes (≥ 13 kilometers) at Kilauea volcano demonstrate that seismicity is focused on an active fault zone at 30-kilometer depth, with seaward slip on a low-angle plane, and other smaller, distinct fault zones. The earthquakes we have analyzed predominantly reflect tectonic faulting in the brittle lithosphere rather than magma movement associated with volcanic activity. The tectonic earthquakes may be induced on preexisting faults by stresses of magmatic origin, although background stresses from volcano loading and lithospheric flexure may also contribute. [ABSTRACT FROM AUTHOR]