Are Narrow Spatial Aftershock Zones Specific To Fluid-induced Earthquakes?

Abstract:

Aftershock cascades play an important role in forecasting seismicity in natural and human-made situations. While their behavior including the spatial aftershock zone has been the focus of many studies in tectonic settings, this is not the case when fluid flows are involved. Using high-quality seismic catalogs, we probe earthquake-earthquake triggering in five settings influenced by fluids: i) induced seismicity in Oklahoma and Kansas, ii) natural swarms in Long Valley Caldera (California), Fillmore (California), Mogul (Nevada), and iii) suspected swarms in the Yuha Desert (California). All settings exhibit significant aftershock behavior highlighting the importance of secondary processes. The spatial aftershock zones scale with mainshock magnitude as expected based on the rupture length. While i) and ii) show a rapid decay beyond their rupture length, iii) exhibits long-range behavior suggesting that fluid migration might not be the dominant mechanism. We also find that aftershock productivity might allow to distinguish between natural swarms and induced seismicity.