EVALUATING MCADAM, NEW BRUNSWICK EARTHQUAKE SWARMS: AN ANALYSIS USING DOUBLE DIFFERENCE RELATIVE LOCATIONS

An evaluation of four McAdam New Brunswick earthquake swarms between March of 2012 and February of 2016 is being carried out using P and S arrival times of earthquakes in the swarms input into a double difference relative location method. Since March of 2012 four earthquake swarms have occurred beneath the town of McAdam New Brunswick. Due to the close proximity of the absolute earthquake locations and the short time period over which the events took place in each swarm, we are attempting to obtain a more precise spatial pattern for the earthquakes using the relative location method. In this study, we looked at 34 McAdam earthquakes the first of which took place on November 11, 2015 and the last of which took place on February 9, 2016. The best strategy for locating these earthquakes using the double difference relative location method was to use 3 earthquakes as master earthquakes because there appears to be three distinct sequences of well-correlated waveforms. We chose to use a magnitude 1.6 occurring on December 9^th at 00:59, a magnitude 2.4 on February 5^th and a magnitude 2.6 at 00:24 on February 9^th as master earthquakes. The December swarm had 10 earthquakes from November 30^th to December 9^th and ranged from magnitude 1 to magnitude 2.1. The early February swarm had 10 earthquakes from February 5^th to February 8^th ranging from magnitude 1.6 to magnitude 2.9. The later February swarm had 14 earthquakes from February 8^th to February 9^th. Due to a high cross correlation value between the December swarm and the late February swarm to the early February swarm, we chose to locate all the earthquakes relative to the master earthquake of February 5^th at 00:24. The resulting spatial configuration showed that with 2 exceptions, all the earthquakes studied occurred within 1 km² of the master earthquake on 5 February. The December swarm and the late February swarm show a NE-SW strike and the early February swarm shows a NW-SE strike. The December swarm and the late February swarm are to the southeast of the early February swarm. The late February swarm was consistently deeper than the early February and December swarms which were relatively similar in depth. The 34 earthquakes evaluated so far suggest that the swarms in McAdam, New Brunswick occurred within 1 km of each other, at a shallow depth and on multiple fault planes.