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TitleThe McAdam, New Brunswick earthquake swarms of 2012 and 2015-2016: extremely shallow, natural events
AuthorBent, A L; Halchuk, S; Peci, V; Butler, K; Burke, K B S; Adams, J; Dahal, N; Hayek, S
SourceSeismological Research Letters vol. 88, no. 6, 2017 p. 1586-1600, https://doi.org/10.1785/0220170071
Year2017
Alt SeriesNatural Resources Canada, Contribution Series 20170001
PublisherSeismological Society of America
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNew Brunswick
NTS21F; 21G; 21H; 21I; 21J; 21K; 21N; 21O; 21P
AreaMaine; McAdam; United States
Lat/Long WENS -70.0000 -64.0000 48.0000 45.0000
Subjectsgeophysics; earthquakes; seismicity; earthquake studies; seismographs; seismological network; seismology
Illustrationslocation maps; satellite images; plots; graphs
ProgramCanadian Hazard Information Service, Canadian Hazard Information Service
Released2017 08 23
AbstractBeginning in March 2012 inhabitants of McAdam, New Brunswick reported feeling and/or hearing many earthquakes within a 1-2 km2 area of the village. The largest events (MN < 2.6) were recorded by regional seismographs, the closest at that time being 65 km away. Public concern combined with the large number of events and their localization led the Geological Survey of Canada (GSC) to deploy three temporary instruments in McAdam. The University of New Brunswick (UNB) provided a fourth. The instruments remained in place for several months and were then removed as activity had largely died off by June 2012. There was a short resurgence in activity late in 2015 with seven felt events occurring 7-9 December. In February 2016, the swarm activity picked up considerably. In light of the increased activity, which included the largest earthquake of the sequence (MN 3.3 on 9 February 2016) the GSC redeployed four instruments which remained in place for several months until the activity subsided. As of 1 November 2016, 164 earthquakes were located, some by enough stations to allow precise depth determination by one or more methods. All the earthquakes were extremely shallow, 0.0-1.2 km. The majority of epicenters lie in a WNW-ESE trending ellipse. Focal mechanisms determined for a small number of events are largely consistent with northeast-southwest compression and with earthquakes in neighboring regions. Sixty-eight of the events were reported as felt, with several of the felt events being of magnitude (MN or ML) less than 1.0. A strong motion recorder recorded a PGA of 9%g from an MN 1.7 earthquake at about 0.8 km hypocentral distance. There was no human activity that could have induced or triggered the swarm, and the cause remains unexplained. McAdam sits on Silurian metasediments intruded by the granitic Pokiok Batholith exposed just to the NW. No faults are mapped close to McAdam, but the events might have occurred on a NW-SE splay of the Fredericton Fault.
Summary(Plain Language Summary, not published)
In the spring of 2012 and again during the winter of 2016, residents of McAdam, New Brunswick reported feeling many earthquakes. This activity has been identified as a seismic swarm. While mostly very small, the earthquakes occurred directly beneath the community. Temporary seismograph stations were installed in McAdam to better record the earthquakes. Research using data from these stations as well as permanent stations at greater distances allowed us to determine precise locations and depths for many of the earthquakes, focal mechanisms (fault orientation and style) and place the earthquakes in a regional context. The earthquakes were all extremely shallow occurring at depths of less than 1.5 km. We have not been able to determine what triggered the swarm activity but we have ruled out human activities, such as mining and fracking.
GEOSCAN ID300253