LAUSR

In recent years, the Delaware basin of west Texas has seen a sharp rise in earthquake occurrence, driven in large part by increases in unconventional hydrocarbon production. The advent of Texas Seismological Network in 2017 has allowed for the characterization of these events in greater detail. We exploit the recent densification in seismic station coverage to study the spectral properties of earthquakes in this region. We show that the low-frequency moments of S-wave spectra, when corrected for site and distance, can be used to calibrate a consistent moment magnitude scale for small and moderate earthquakes. For a subset of >3000 well-recorded events, we compute earthquake stress drop under the assumption of Brune spectral model. Earthquakes in the Delaware basin show coherent spatial patterns in stress drop across the region. Through a reanalysis of independently collated data from the oil and gas industry, we find that earthquakes that are likely associated with hydraulic-fracturing operations have slightly different spectral characteristics than earthquakes that are likely associated with saltwater disposal. In particular, events associated with hydraulic fracturing show greater variability in the statistical distribution of stress drop and have higher median stress-drop values. Although the differences are subtle, they suggest that there may be important distinctions in the underlying physical mechanisms and resulting hazards of distinct classes of induced events, differences that may be unraveled with more detailed joint analyses of industrial and seismic datasets.