| Title | The McAdam, New Brunswick earthquake swarms of 2012 and 2015-2016: extremely shallow, natural events |
| |
| Author | Bent, A L; Halchuk, S; Peci, V; Butler, K; Burke, K B S; Adams, J ; Dahal, N; Hayek, S |
| Source | Seismological Research Letters vol. 88, no. 6, 2017 p. 1586-1600, https://doi.org/10.1785/0220170071 |
| Image |  |
| Year | 2017 |
| Alt Series | Natural Resources Canada, Contribution Series 20170001 |
| Publisher | Seismological Society of America (SSA) |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | New Brunswick |
| NTS | 21G; 21H; 21I; 21J; 21K; 21N; 21O; 21P |
| Area | Maine; McAdam; United States of America |
| Lat/Long WENS | -70.0000 -64.0000 48.0000 45.0000 |
| Subjects | geophysics; earthquakes; seismicity; earthquake studies; seismographs; seismological network; seismology |
| Illustrations | location maps; satellite images; plots; graphs |
| Program | Canadian Hazard Information Service |
| Released | 2017 08 23 |
| Abstract | Beginning 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 ID | 300253 |
|
|