Lateral Lithospheric Strength Variations: A Deeper Explanation for the Abundance of Induced Seismicity in Oklahoma
Abstract
Induced seismicity in the central U.S. is understood to be related to wastewater injection associated with unconventional oil production. However, the rise in seismicity has not been uniform across the different regions where this activity is taking place, with Oklahoma exhibiting an unparalleled number of events. Variations in induced seismicity rates are generally thought of in relation to operational parameters (depth of injection, flow rates, cumulative flow volumes) or crustal geology (aquifer permeability and connection to the bedrock, orientation of basement faults). Although all these parameters have an effect, the role of the mantle lithosphere and its lateral strength variations have been overlooked and may be significant. It has long been hypothesized that lateral variations in lithospheric strength can concentrate the regional stresses and focus seismicity in continental interiors. To test whether this is a contributing factor in Oklahoma seismicity, we explore the effects of a relatively weak Ouachita embayment on the local stress field. This is a zone where a rift-transform-rift system broke off a fragment of Laurentia, resulting in an area of thinned lithosphere with a peculiar geometry that includes a 90-degree angle. Our preliminary models load the lithosphere with the regional stress and find the Ouachita cusp produces a stress concentration on its obtuse side, where the Oklahoma seismicity occurs. We suggest these elevated deviatoric stresses are responsible for the increased rate of seismicity. Molchan error diagram analysis shows that the modeled deviatoric stresses are successful at predicting where induced seismicity occurs. We conclude that subcrustal structure may be playing an important and thus far underappreciated role in determining a region's susceptibility to induced seismicity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S11B..05B
- Keywords:
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- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8164 Stresses: crust and lithosphere;
- TECTONOPHYSICS