Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

Shemin Ge

Second Advisor

Anne F. Sheehan

Third Advisor

Jonathan W. Godt

Fourth Advisor

Barbara A. Bekins

Fifth Advisor

Paul A. Hsieh

Abstract

Fluid-fault interaction in the subsurface is a critical driver of both natural and induced earthquakes. Fluid-pressure increases inside fault zones lower their frictional resistance to slip and make earthquakes more likely. Inversely, earthquakes also perturb the fluid-pressure field and cause observable changes in groundwater level. This dissertation investigates fluid-fault interaction by studying both groundwater level changes from natural earthquakes and injection-induced earthquakes from fluid injection wells.

Chapter 2 quantifies an extremely sensitive water level to distant earthquakes at Devils Hole in southern Nevada. Examining a 24-year water level record, I find the seismic energy density required to initiate both hydroseismogram and coseismic types of water level response is e ~ 10-6 J/m3, two orders of magnitude smaller than previously documented. This new threshold has implications for the dynamic triggering of earthquakes, as remote earthquakes can lead to pore pressure changes and consequently effective stress changes in fluid-filled fault zones.

Chapters 3 through 5 examine the relationship between fluid injection and the unprecedented seismic rate increase in the U.S. mid-continent beginning in 2009. This rate increase occurred in regions where earthquakes were generally uncommon and not predicted by the laws of natural seismicity. Chapter 3 characterizes seismicity and fluid-pressure changes from injection wells in Jones, Oklahoma, showing that high-rate injection wells are likely responsible for the earthquake swarm. The modeled fluid-pressure perturbation propagates throughout the same depth range and tracks earthquakes to distances of 35 km, with a triggering threshold of ~0.07 MPa. Chapter 4 examines the broad-scale relationship between fluid injection and U.S. mid-continent seismicity using a newly assembled injection well database for the central and eastern U.S. Statistical methods find the entire increase in earthquake rate is associated with fluid injection wells. High injection rate wells (>300,000 barrels/month) are statistically much more likely to be associated with earthquakes than lower rate wells. Finally, in Chapter 5, I quantify a novel case of injection-induced seismicity in the Raton Basin of southern Colorado. Hydrogeologic models show injection can induce earthquakes several kilometers below the reservoir injection interval despite a lack of wellhead pressure needed for injection.

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