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Influence of geological setting on stress released by hydraulic fracture-induced earthquakes
- Source: First Break, Volume 36, Issue 4, Apr 2018, p. 77 - 81
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- 01 Apr 2018
Abstract
Recent studies of injection-induced seismicity suggest that induced events have lower stress drops than tectonic earthquakes, suggesting stress drop can potentially be used as a discriminant parameter between natural and anthropogenic earthquakes. The main physical mechanisms responsible for low stress drop earthquakes, that is earthquakes that release less stress during failure than the average natural earthquake in a similar tectonic setting, are related to the increase in pore pressure and fault lubrication that result from the presence of fluids on the fault surface. Fluids reduce the effective normal stress applied on a fault allowing it to slip under lower stress conditions. Hough (2014) found that induced earthquakes have a factor of 2 to 10 lower stress drops relative to natural earthquakes, for 11 injection-induced moderate earthquakes in central and eastern United States based on their intensity reports. Sumy et al. (2016) also found a factor of 10 difference between the stress drops of natural and induced earthquakes when studying 87 Mw1.8 to Mw3.5 induced earthquakes in Oklahoma. A few other studies found opposing results. Huang et al. (2016) found the stress drops of 25 small earthquakes in central Arkansas to be comparable to Californian tectonic earthquake stress drops, and Viegas and Abercrombie (2011) also found the stress drops of a sequence of moderate earthquakes in Colorado to be comparable to the stress drops of Californian earthquakes. However, Viegas and Abercrombie (2011) noted that Central and North America intraplate earthquakes are expected to have higher stress drops than plate boundary California earthquakes (Viegas et al., 2010) making the comparison a false equivalency.