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Magma supply rates from the mantle to Hawaiian volcanoes serve as an important control on eruptive behavior at the surface. The Pa ̄hala Sill Complex, a collection of magma-bearing, seismogenic structures at 40 km depth beneath Hawai‘i, presents an opportunity to elucidate interactions between stress and magma transport processes in the mantle. We invert for full moment tensors of sill earthquakes and identify predominantly shear mechanisms with persistent tensile faulting components. Slip occurs in-plane with the sill structures. Pressure axes are radially oriented about a point near Mauna Loa, consistent with a stress field generated by a flexural load. Together, these observations suggest that magma flux through the sill structures generates seismicity by increasing pore pressure and promoting slip. Our results suggest that stress changes in mantle structures may enable fluctuations in magma supply rates to the surface over short timescales. 

Abstract Gas extraction from the Groningen gas reservoir, located in the northeastern Netherlands, has led to a drop in pressure and drove compaction and induced seismicity. Stress-based models have shown success in forecasting induced seismicity in this particular context and elsewhere, but they generally assume that earthquake clustering is negligible. To assess earthquake clustering at Groningen, we generate an enhanced seismicity catalog using a deep-learning-based workflow. We identify and locate 1369 events between 2015 and 2022, including 660 newly detected events not previously identified by the standard catalog from the Royal Netherlands Meteorological Institute. Using the nearest-neighbor distance approach, we find that 72% of events are background independent events, whereas the remaining 28% belong to clusters. The 55% of the clustered events are swarm-like, whereas the rest are aftershock-like. Among the swarms include five newly identified sequences propagating at high velocities between 3 and 50 km/day along directions that do not follow mapped faults or existing structures and frequently exhibit a sharp turn in the middle of the sequence. The swarms occurred around the time of the maximum compaction rate between November 2016 and May 2017 in the Zechstein layer, above the anhydrite caprock, and well-above the directly induced earthquakes that occur within the reservoir and caprock. We suggest that these swarms are related to the aseismic deformation within the salt formation rather than fluids. This study suggests that the propagating swarms do not always signify fluid migration. 

Interacting magmatic sills at about 40-kilometer depth under the island of Hawai‘i feed into multiple different volcanoes.