Maturity of nearby faults influences seismic hazard from hydraulic fracturing

Proceedings of the National Academy of Sciences of the United States of America
By: , and 

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Abstract

Understanding the causes of human-induced earthquakes is paramount to reducing societal risk. We investigated five cases of seismicity associated with hydraulic fracturing (HF) in Ohio since 2013 that, because of their isolation from other injection activities, provide an ideal setting for studying the relations between high-pressure injection and earthquakes. Our analysis revealed two distinct groups: (i) deeper earthquakes in the Precambrian basement, with larger magnitudes (M > 2), b-values < 1, and many post–shut-in earthquakes, versus (ii) shallower earthquakes in Paleozoic rocks ∼400 m below HF, with smaller magnitudes (M < 1), b-values > 1.5, and few post–shut-in earthquakes. Based on geologic history, laboratory experiments, and fault modeling, we interpret the deep seismicity as slip on more mature faults in older crystalline rocks and the shallow seismicity as slip on immature faults in younger sedimentary rocks. This suggests that HF inducing deeper seismicity may pose higher seismic hazards. Wells inducing deeper seismicity produced more water than wells with shallow seismicity, indicating more extensive hydrologic connections outside the target formation, consistent with pore pressure diffusion influencing seismicity. However, for both groups, the 2 to 3 h between onset of HF and seismicity is too short for typical fluid pressure diffusion rates across distances of ∼1 km and argues for poroelastic stress transfer also having a primary influence on seismicity.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Maturity of nearby faults influences seismic hazard from hydraulic fracturing
Series title Proceedings of the National Academy of Sciences of the United States of America
DOI 10.1073/pnas.1715284115
Volume 115
Issue 8
Year Published 2018
Language English
Publisher PNAS
Contributing office(s) Earthquake Science Center
Description 10 p.
First page E1720
Last page E1729
Country United States
State Ohio