In 2018, Kīlauea Volcano experienced its largest lower East Rift Zone (LERZ) eruption and caldera collapse in at least 200 years. After collapse of the Pu‘u ‘Ō‘ō vent on 30 April, magma propagated downrift. Eruptive fissures opened in the LERZ on 3 May, eventually extending ~6.8 kilometers. A 4 May earthquake [moment magnitude (Mw) 6.9] produced ~5 meters of fault slip. Lava erupted at rates exceeding 100 cubic meters per second, eventually covering 35.5 square kilometers. The summit magma system partially drained, producing minor explosions and near-daily collapses releasing energy equivalent toMw4.7 to 5.4 earthquakes. Activity declined rapidly on 4 August. Summit collapse and lava flow volume estimates are roughly equivalent—about 0.8 cubic kilometers. Careful historical observation and monitoring of Kīlauea enabled successful forecasting of hazardous events.

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The Pawnee M5.8 earthquake is the largest event in Oklahoma instrument recorded history. It occurred near the edge of active seismic zones, similar to other M5+ earthquakes since 2011. It ruptured a previously unmapped fault and triggered aftershocks along a complex conjugate fault system. With a high-resolution earthquake catalog, we observe propagating foreshocks leading to the mainshock within 0.5 km distance, suggesting existence of precursory aseismic slip. At approximately 100 days before the mainshock, two M ≥ 3.5 earthquakes occurred along a mapped fault that is conjugate to the mainshock fault. At about 40 days before, two earthquakes clusters started, with one M3 earthquake occurred two days before the mainshock. The three M ≥ 3 foreshocks all produced positive Coulomb stress at the mainshock hypocenter. These foreshock activities within the conjugate fault system are near-instantaneously responding to variations in injection rates at 95% confidence. The short time delay between injection and seismicity differs from both the hypothetical expected time scale of diffusion process and the long time delay observed in this region prior to 2016, suggesting a possible role of elastic stress transfer and critical stress state of the fault. Our results suggest that the Pawnee earthquake is a result of interplay among injection, tectonic faults, and foreshocks.

After nucleation, a large earthquake propagates as an expanding rupture front along a fault. This front activates countless fault patches that slip by consuming energy stored in Earth's crust. We simulated the slip of a fault patch by rapidly loading an experimental fault with energy stored in a spinning flywheel. The spontaneous evolution of strength, acceleration, and velocity indicates that our experiments are proxies of fault-patch behavior during earthquakes of moment magnitude (M(w)) = 4 to 8. We show that seismically determined earthquake parameters (e.g., displacement, velocity, magnitude, or fracture energy) can be used to estimate the intensity of the energy release during an earthquake. Our experiments further indicate that high acceleration imposed by the earthquake's rupture front quickens dynamic weakening by intense wear of the fault zone.

The rapidly increased earthquake rate in the central United States has been linked with wastewater injection. While the overall understanding appears clear at large scales, the interaction between injection and faulting at smaller scales within individual sequences is still not clear. For an earthquake sequence in central Oklahoma, we conduct finer‐scale analysis of the spatiotemporal evolution of seismicity and pore pressure modeling. The pore pressure modeling suggests that nearby wells show much stronger correlation with earthquake sequence evolution. Detailed temporal analysis found correlation between earthquake rate, seismic moment, and injection rates from wells in close proximity. However, the observed maximum magnitude (Mmax) is about 1 order of magnitude smaller than expected based on a theoretical relationship between Mmax and cumulative volume. This discrepancy may point toward additional parameters, such as fault size and stress, which influence Mmax. The lower Mmax is consistent with the truncated Gutenberg‐Richter distribution observed from matched filter detected catalog. Overall, the detailed observations suggest that it is possible to resolve relationships between individual disposal wells and induced earthquake sequences.

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The 3 September 2016 M w 5.8 Pawnee earthquake shook a large area of north-central Oklahoma and was the largest instrumentally recorded earthquake in the state. We processed Synthetic Aperture Radar (SAR) from the Copernicus Sentinel-1A and Sentinel-1B and Canadian RADARSAT-2 satellites with interferometric SAR analysis for the area of north-central Oklahoma that surrounds Pawnee. The interferograms do not show phase discontinuities that would indicate surface ruptures during the earthquake. Individual interferograms have substantial atmospheric noise caused by variations in radar propagation delays due to tropospheric water vapor, so we performed a time-series analysis of the Sentinel-1 stack to obtain a more accurate estimate of the ground deformation in the coseismic time interval and the time variation of deformation before and after the earthquake. The time-series fit for a step function at the time of the Pawnee shows about 3 cm peak-to-peak amplitude of the coseismic surface deformation in the radar line of sight with a spatial pattern that is consistent with fault slip on a plane trending east-southeast. This fault, which we call the Sooner Lake fault, is parallel to the west-northwest nodal plane of the U.S. Geological Survey National Earthquake Information Center moment tensor solution. We model the fault plane by fitting hypoDD-relocated aftershocks aligned in the same trend. Our preferred slip model on this assumed fault plane, allowing only strike-slip motion, has no slip shallower than 2.3 km depth, an area of moderate slip extending 7 km along strike between 2.3 and 4.5 km depth (which could be due to aftershocks and afterslip), and larger slip between 4.5 and 14 km depth extending about 12 km along strike. The large slip below the 4.5 km depth of our relocated hypocenter indicates that the coseismic rupture propagated down-dip. The time-series results do not show significant deformation before or after the earthquake above the high atmospheric noise level within about 40 km of the earthquake rupture. Electronic Supplement: Figures showing alternative slip model for the Pawnee mainshock, data fit for the alternative slip model, probability density functions for the smoothing factors of the alternative slip model, and outputs of the Generic Interferometric Synthetic Aperture Radar (InSAR) Analysis Toolbox (GIAnT) time-series analysis.