A Historical Review of Induced Earthquakes in Texas

In Texas, earthquakes have occurred in close association with activities accompanying petroleum production since 1925. Here we develop a five-question test to categorize individual events as tectonic, possibly induced, probably induced, or almost certainly induced. In Texas, the probably induced and almost certainly induced earthquakes are broadly distributed geographically-in the Fort Worth basin of north Texas, the Haynesville Shale play area of east Texas, along the Gulf Coast in south Texas, and the Permian basin of west Texas. As the technologies applied to manage petroleum fields have evolved, induced earthquakes have been associated with different practices. In fields being driven by primary recovery prior to 1940, earthquakes occurred in fields extracting high volumes of petroleum from shallow strata. Subsequently, as field pressures decreased and secondary recovery technologies became common, earthquakes also occurred in association with water-flooding operations. Since 2008, the rate of earthquakes with magnitudes greater than 3 has increased from about 2 events/yr to 12 events/yr; much of this change is attributable to earthquakes occurring within a few kilometers of wastewater disposal wells injecting at high monthly rates. For three sequences monitored by temporary local seismograph networks, most hypocenters had focal depths at and deeper than the depth of injection and occurred along mapped faults situated within 2 km of injection sites. The record clearly demonstrates that induced earthquakes have been broadly distributed in several different geographic parts of Texas over the last 90 years.