Source spectral properties of small to moderate earthquakes in southern Kansas

Trugman, DT, Dougherty SL, Cochran ES, Shearer PM.  2017.  Source spectral properties of small to moderate earthquakes in southern Kansas. Journal of Geophysical Research: Solid Earth. :n/a-n/a.

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7212 Earthquake ground motions and engineering seismology, 7215 Earthquake source observations, 7223 Earthquake interaction, forecasting, and prediction, 7230 Seismicity and tectonics, ground motion, induced seismicity, source parameters, source spectra, stress drop, wastewater injection


The source spectral properties of injection-induced earthquakes give insight into their nucleation, rupture processes, and influence on ground motion. Here we apply a spectral decomposition approach to analyze P wave spectra and estimate Brune-type stress drop for more than 2,000 ML1.5–5.2 earthquakes occurring in southern Kansas from 2014 to 2016. We find that these earthquakes are characterized by low stress drop values (median ∼0.4 MPa) compared to natural seismicity in California. We observe a significant increase in stress drop as a function of depth, but the shallow depth distribution of these events is not by itself sufficient to explain their lower stress drop. Stress drop increases with magnitude from M1.5 to M3.5, but this scaling trend may weaken above M4 and also depends on the assumed source model. Although we observe a nonstationary, sequence-specific temporal evolution in stress drop, we find no clear systematic relation with the activity of nearby injection wells.