Induced earthquake magnitudes are as large as (statistically) expected

Nicholas J. van der Elst, Morgan T. Page, Debbie A. Weiser, Thomas H. Goebel, & Seyed M. Hosseini

Submitted September 20, 2016, SCEC Contribution #6366, 2016 SCEC Annual Meeting Talk on 9/13 14:00 (PDF)

Injection-induced seismicity is a major contributor to seismic hazard in the central US. The question now is whether induced seismicity is amenable to statistical forecasting on any useful timescale. One of the major uncertainties affecting such a forecast is how large induced earthquakes can be. Are their maximum magnitudes determined by injection parameters, or by tectonics? Deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected. However, if induced earthquakes occur on tectonic faults oriented favorably with respect to the tectonic stress field, then they may be limited only by the regional tectonics and connectivity of the fault network. In this study, we show that the largest magnitudes observed at fluid injection sites are consistent with the sampling statistics of the Gutenberg-Richter distribution for tectonic earthquakes, assuming no upper magnitude bound. The data pass three specific tests: 1) the largest observed earthquake at each site scales with the log of the total number of induced earthquakes, 2) the order of occurrence of the largest event is random within the induced sequence, and 3) the injected volume controls the total number of earthquakes, rather than the total seismic moment. All three tests point to an injection control on earthquake nucleation, but a tectonic control on earthquake magnitude. The largest observed earthquakes are exactly as large as expected from the sampling statistics. The results imply 1) induced earthquake numbers can be estimated from previous activity and anticipated injection volumes, and 2) induced earthquake magnitudes should be treated with the same maximum magnitude bound that is used to treat seismic hazard from tectonic earthquakes.

Key Words
Induced seismicity, maximum magnitude, operational earthquake forecasting

van der Elst, N. J., Page, M. T., Weiser, D. A., Goebel, T. H., & Hosseini, S. M. (2016, 09). Induced earthquake magnitudes are as large as (statistically) expected. Oral Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)