Characteristics of Swarms of Small Earthquakes in the Stable Craton of Northeastern North America

Session: Seismicity and Tectonics of Stable Continental Interiors
Type: Oral
Date: 4/30/2020
Time: 11:45 AM
Room: 240
Description: 

Earthquake swarms are well known in tectonically active areas, especially those areas with volcanic or geothermal activity. Earthquake swarms associated with fluid or gas injection into the earth also have been well studied in places like Oklahoma. Less well known and well characterized are earthquake swarms in stable cratons, where seismicity rates are generally low and large earthquakes are infrequent. In this study, the spatial and temporal histories of several swarms of small earthquakes in the northeastern U.S. are summarized. The swarms took place at Moodus, CT in the 1980s, at Bar Harbor, ME in 2006-2007, near Albany, NY from 2007 to 2011, at Searsport, ME in 2011, at McAdam, NB from 2012 to 2017 and at Wauregan, CT in 2015. Each swarm lasted from a few weeks to several months, with the largest event sometimes occurring early and sometimes later in the swarm. All of the swarms were comprised of tens to hundreds of events, with most near the lowest detectable magnitude for the source area. All of the swarms came from confined source volumes that were no more than about 2 km in lateral extent. In some of the swarms, the individual event locations migrated bilaterally from the focus of the first event in the swarm, whereas other swarms showed primarily unilateral migration of the event locations. In all of the cases studied, the swarm events aligned on or parallel to mapped geologic structures, suggesting that the structures controlled the spatial patterns of the swarms. The Albany swarms probably took place at focal depths of about 20 km, but all of the other swarms had foci with depths less than 2 km. Although their specific triggering mechanism is unclear, swarms of small earthquakes are one way that the stable craton of northeastern North America responds to the modern stress field.

Presenting Author: John E. Ebel

Authors