Discriminating Characteristics of Tectonic and Human-Induced Seismicity

We analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human‐induced and natural seismicity. Analysis of end‐member areas known to be dominated by human‐induced earthquakes (The Geyser geothermal field in northern California and TauTona gold mine in South Africa) and regular tectonic activity (the San Jacinto fault zone in southern California and the Coso region, excluding the Coso geothermal field in eastern central California) reveals several distinguishing characteristics. Induced seismicity is shown to have (1) higher rate of background events (both absolute and relative to the total rate), (2) faster temporal offspring decay, (3) higher rate of repeating events, (4) larger proportion of small clusters, and (5) larger spatial separation between parent and offspring, compared to regular tectonic activity. These differences also successfully discriminate seismicity within the Coso and Salton Sea geothermal fields in California before and after the expansion of geothermal production during the 1980s. Online Material: Figures of examined regions, earthquake epicenters, and joint distributions of the time and space components of the nearest‐neighbor distance.