In response to the COVID-19 global pandemic, many populated and active regions have become deserted and show significant reductions in their background seismicity, especially campuses across the United States (U.S.). Seismic sensors located in the vicinity of or within U.S. campuses show that anthropogenic seismic noise remains elevated during the ordinary, nonpandemic, academic year, only subduing during periods of recess (e.g., winter break). Here, we use power spectral density (PSD) data computed by the Incorporated Research Institutions for Seismology Data Management Center for quality assessment to calculate root mean square (rms) amplitude and analyze the effects of the COVID-19 school closures. We processed and analyzed PSD data for 46 seismic stations located within 50 m of a U.S. university or college. Results show that 42 campus stations show an overall rms drop following a statewide school closure.

To explore the ability to indirectly detect and attribute various operations conducted at a nuclear reactor using waveform data, we investigated the seismic signals recorded near the High Flux Isotope Reactor (HFIR) located at Oak Ridge National Laboratory in Oak Ridge, Tennessee. Specifically, we processed seismic data collected from a single seismoacoustic station, WACO, near the HFIR facility, and employed a power spectral density misfit detector to identify signals of interest and associate the detections with operational events. Initial results suggest that this method provides a promising means of regularly detecting at least 19 unique operations. With additional station deployment and more comprehensive data logs, we anticipate that future analysis will offer an additional means to seismically monitor nuclear reactors (such as HFIR) health and performance more accurately.

In the last decade, induced seismicity (earthquakes incited by anthropogenic activity) has drastically increased resulting from subsurface waste-water fluid injection and CO2 sequestration. In addition, seismologists have observed large (M ≥ 7) earthquakes that can trigger other earthquakes via (1) changes in static stress and (2) imposed transient dynamic stressing related to seismic waves generated by a mainshock. Although the exact mechanism for dynamic triggering remains uncertain, observations of earthquake triggering may reveal mechanisms that lead to earthquake failure. Given well-documented instances of induced earthquakes and fluid injection in Oklahoma, we investigate the occurrence of dynamic triggering and mechanisms of failure in the region. We analyze 124 M ≥ 7 remote earthquakes across a seven-year period (2010–2016), utilizing seismic data retrieved from EarthScope’s USArray Transportable Array, the Oklahoma Seismic Network, and a template matched earthquake catalog for Oklahoma to identify dynamically triggered earthquakes. We also identify previously uncataloged events through a short-term to long-term average ratio energy detector and analyst inspection of waveforms. We quantify the results using several statistical approaches to identify significant increases in local seismicity rates following the P-wave arrival of each remote mainshock. We identify 26 mainshocks that dynamically trigger either instantaneous or delayed earthquakes in Oklahoma. We conclude that mainshock transient stresses appear to contribute to natural and induced stress states in Oklahoma and can advance the earthquake cycle in the region. Our results emphasize the identification of instantaneous dynamic triggering; however, we also capture delayed triggering (i.e., past the first few hours following a mainshocks wavetrain passes). We find triggered earthquakes correlate well with regions of sustained fluid injection in Oklahoma, suggesting that increased pore fluid pressure may be lowering the effective normal stress across faults in the region and, thus, increasing susceptibility to transient stressing especially by Rayleigh waves.

Summary The state of Utah, USA, experiences around 3,800 cataloged earthquakes per year, highlighting that the region is seismically active and susceptible to earthquakes. Following the 2002 Denali Fault (M7.9) earthquake in Alaska, the region showed an elevated seismicity rate for three weeks following the passage of high amplitude surface waves, suggesting that the region may be particularly susceptible to dynamic triggering. With over 23,396 faults and each fault presenting a potential fault for triggering, we systematically search for dynamic triggering throughout the state of Utah caused by large, global earthquakes with M≥7. Specifically, we analyze earthquake catalogs and all available waveform data to determine statistical increases of seismicity rate following the passage of seismic arrivals. While we find instances of dynamic triggering, our results show that these events occur sparsely in the region. In total, less than 20% of the 273 mainshocks that occur from 2000 to the end of 2017 show a statistical indication of dynamic triggering throughout the Utah region, highlighting that dynamic triggering is limited for stresses created by transient signals from global M≥7 earthquakes, with the exception being the Denali Fault (M7.9), Alaska earthquake (i.e., an instance of significant triggering).