The 2015 Plainfield, CT Earthquake Swarm: Induced Earthquakes Due to an Abandoned Quarry?
Date: 4/26/2019
Room: Grand Ballroom
From January until July 2015 an active earthquake swarm took place in the town of Plainfield, CT. The swarm was preceded by three small earthquakes in October and November of 2014 (MLg 0.9, 0.6 and 0.9), and it started in earnest on 8 January 2015 with an earthquake of MLg 2.0. The largest event of MLg 3.1 took place on 12 January 2015, and it was felt throughout eastern Connecticut and all of Rhode Island. Many of the earthquakes of the swarm were felt or heard by local residents. On 13 January 2015 Weston Observatory, in conjunction with the Connecticut Geological Survey, installed four portable seismographs in the epicentral area to record the swarm events, and those instruments recorded earthquakes to July 2015. Using data from the regional and local seismic stations, at least 180 earthquakes have been confirmed, and the portable instruments contain signals from another 200 detections that may also be very small events. Absolute event locations computed using data from the portable seismic stations trend along the eastern and southwestern sides of a dry abandoned rock quarry at focal depths ranging from about 1.6 km depth to just below the earth’s surface. The seismicity along the eastern side of the quarry parallels the 45° west-dipping nodal plane of the pure thrust focal mechanism of the MLg 3.1 event. The events east of the quarry follow the mylonitic Lake Char Fault zone, a structure that runs from southern Connecticut into Massachusetts. The events southwest of the quarry trend toward the northwest and are on-strike with a northwest-striking fault that is mapped about 3 km northwest of the quarry. The locations of the events in the Plainfield swarm along with the focal mechanism of the largest event suggest that the removal of the rock load from the 20-m deep quarry may have induced this earthquake swarm. Why no earthquakes were detected from this locality until several years after the quarry was abandoned is not known.
Presenting Author: John E. Ebel
Authors
John E Ebel ebel@bc.edu Weston Observatory, Boston College, Weston, Massachusetts, United States Presenting Author
Corresponding Author
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Justin Starr jcstarr45@gmail.com Weston Observatory, Boston College, Weston, Massachusetts, United States |
Parker W Aubin paubin@geiconsultants.com GEI Consultants, Inc., Chicago, Illinois, United States |
Margaret A Thomas margaret.thomas@ct.gov Department of Energy and Environmental Protection, Hartford, Connecticut, United States |
The 2015 Plainfield, CT Earthquake Swarm: Induced Earthquakes Due to an Abandoned Quarry?
Session
State of Stress and Strain in the Crust and Implications for Fault Slip Based on Observational, Numerical and Experimental Analysis