iPlex Lunch spring-2018

It is now well established that the sharp rise in seismicity in the central United States since 2009 is due to human activity, in particular the deep injection of waste water generated by unconventional fossil fuel production (hydraulic fracturing). It has long been assumed that, in California, so-called induced earthquakes do not contribute significantly to earthquake rates, or hazard. Indeed, it is safe to assume that, overwhelmingly, seismic hazard in California stems from active tectonic processes along the plate boundary that runs through the State. Looking back, however, at some of the moderately large earthquakes that struck the Southland during the early 20th century, there is evidence for an association with primary oil production during the early oil boom years in the Los Angeles Basin and elsewhere. A key factor was production depth; I show that the reach of significant stress change typically extends 2-3 km away from a production horizon, vertically as well as horizontally. Thus, if production wells reach depths of 2-3 km, stress perturbations are potentially significant at the top of the seismogenic crust. While the results suggest that there can be a risk of significant induced earthquakes from conventional oil production, the rate of natural earthquakes within the Los Angeles Basin might actually be lower than previously estimated.