Aftershock deficiency of induced earthquake sequences during rapid mitigation efforts in Oklahoma

Journal Article · Tue Jul 09 00:00:00 EDT 2019 · Earth and Planetary Science Letters

DOI:https://doi.org/10.1016/j.epsl.2019.06.036· OSTI ID:1564385

Goebel, T. H. W.; Rosson, Z.; Brodsky, E. E.; Walter, J. I.

Induced seismicity provides a rare opportunity to study earthquake triggering and underlying stress perturbations. Triggering can be a direct result of induced stress changes or indirect due to elastic stress transfer from preceding events leading to aftershocks. Both of these processes are observable in areas with larger magnitude induced events, such as Oklahoma. We study aftershock sequences of M2.5 to M5.8 earthquakes and examine the impact of targeted injection rate reductions. In comparing aftershock productivity between California and Oklahoma, we find similar exponential scaling statistics between mainshock magnitude and average number of aftershocks. For events with M≥4.5 Oklahoma exhibits several mainshocks with total number of aftershocks significantly below the average scaling behavior. The sequences with deficient aftershock numbers also experienced rapid, strong mitigation and reduced injection rates, whereas two events with M4.8 and M5.0 with weak mitigation exhibit normal aftershock productivity. The timing of when aftershock activity is reduced correlates with drops in injection rates with a lag time of several days. Large mainshocks with significantly reduced aftershocks may explain decreasing seismicity rates while seismic moment release was still increasing in Oklahoma in 2016. We investigate the expected poroelastic stress perturbations due to injection rate changes within a layered axisymmetric model and find that stresses are lowered by 10s to 100s kPa within the injection-affected zone. For earthquakes induced by poroelastic stress-increase at several kilometers from wells, the rapid shut-in of wells may lead to elastic stress reductions sufficiently high to arrest unfolding aftershock sequences within days after mitigation starts.

• Research Organization: Univ. of California, Santa Cruz, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0015539
• OSTI ID: 1564385
• Alternate ID(s): OSTI ID: 1612296
• Journal Information: Earth and Planetary Science Letters, Journal Name: Earth and Planetary Science Letters Journal Issue: C Vol. 522; ISSN 0012-821X
• Publisher: Elsevier
• Country of Publication: Netherlands
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
aftershock deficiency
geochemistry & geophysics
induced seismicity mitigation
poroelastic stress coupling