ALBERT

Description: On 1 June 2014 (03:35 UTC), an M w  3.2 earthquake occurred in Weld County, Colorado, a historically aseismic area of the Denver–Julesburg basin. Weld County is a prominent area of oil and gas development, including many high-rate class II wastewater injection wells. In the days following the earthquake, the University of Colorado, with support from the U.S. Geological Survey and Incorporated Research Institutions for Seismology–Portable Array Seismic Studies of the Continental Lithosphere, rapidly deployed six seismic stations to characterize the seismicity associated with the 1 June earthquake (the Greeley sequence) and to investigate its possible connection to wastewater disposal. The spatial and temporal proximity of earthquakes to a high-rate wastewater disposal well strongly suggests these earthquakes were induced. Scientific communication between the university, state agencies, and the energy industry led to rapid mitigation strategies to reduce the occurrence of further earthquakes. Mitigation efforts included implementing a temporary moratorium on injection at the well, cementing the bottom portion of the disposal well to minimize hydrologic connectivity between the disposal formation and the underlying crystalline basement, and subsequently allowing injection to resume at lower rates. Following the resumption of wastewater disposal, microseismicity was closely monitored for both increases in earthquake rate and magnitude. Following mitigation efforts, between 13 August 2014 and 29 December 2015, no earthquakes larger than M  1.5 occurred near the Greeley sequence. This study demonstrates that a detailed and rapid characterization of a seismic sequence in space and time relative to disposal, combined with collaboration and communication between scientists, regulators, and industry, can lead to objective and actionable mitigation efforts that potentially reduced the rate of earthquakes and the possible generation of larger earthquakes.