THE POTSDAM SEISMIC NETWORK AND EARTHQUAKES IN NORTHERN NEW YORK

The Potsdam Seismic Network consists of seven short period vertical seismic stations located in the St. Lawrence Valley and Adirondack Region of Northern New York. It is part of the Lamont-Doherty Cooperative Seismographic Network (LCSN) used to study the seismicity and earthquake hazard of northeastern United States. Recently two stations have been upgraded with two broadband three component systems that use AC as an energy source. This network is located in the Northern New York-Western Quebec seismic zone a region of moderate seismicity.

The Northern New York-Western Quebec Seismic Zone extends from the Adirondack Mountains Northwesterly into Western Quebec. Most of the earthquakes in this zone have small magnitudes ranging from 1 to 4 and shallow focal depths of less than 10 km. Fault plane solutions indicate the earthquakes are due to reverse faulting on northwest striking fault planes. The strike of the fault planes is the same as the trend of earthquakes but not the trend of the mapped faults in the area. Even though most of the earthquakes are small, damaging earthquakes of magnitude greater than 5 occur such as the 5.9 magnitude Massena-Cornwall (1944), the 5.2 magnitude Goodnow earthquake (1983) and the 5.3 magnitude Au Sable Forks earthquake (2002).

Several explanations have been presented to explain these earthquakes in the region. They include reactivation of faults by a high stress field, reactivation of fractures formed by the North American plate moving over a hot spot, glacial isostatic rebound, and stress concentrations around mafic plutons and an extension of the New England seamount chain into northern New York. Detailed gravity measurements in the area indicate most epicenters are located along steep gravity gradients suggesting the earthquakes occur along zones of weakness marked by contacts of rock types of varying density.