Spatial relationships between natural seismicity and faults, southeastern Ontario and north-central New York state

A statistical analysis was carried out to investigate spatial associations between natural seismicity and faults in southeastern Ontario and north-central New York State (between 73degrees18' and 77degrees30'W and 43degrees30' and 45degrees18'N). The study area is situated to the west of the seismically active St. Lawrence fault zone, and to the east of the Lake Ontario basin where recently documented geological and geophysical evidence points to possible neotectonic faulting. The weights of evidence method was used to judge the spatial associations between seismic events and populations of faults in eight arbitrarily defined orientation groups. Spatial analysis of data sets for seismic events in the periods 1930-1970 and post-1970 suggest stronger spatial associations between earthquake epicentres and faults with strikes that lie in the NW-SE quadrants, and weaker spatial associations of epicentres with faults that have strikes in the NE-SW quadrants. The strongest spatial associations were determined for groups of faults with strikes between 101degrees and 146degrees. The results suggest that faults striking broadly NW - SE, at high angles to the regional maximum horizontal compressive stress, are statistically more likely to be spatially associated with seismic events than faults striking broadly NE-SW. If the positive spatial associations can be interpreted as indicating genetic relationships between earthquakes and mapped faults, then the results may suggest that, as a population, NW-SE trending faults are more likely to be seismically active than NE-SW striking faults. Detailed geological studies of faults in the study area would be required to determine possible neotectonic displacements and the kinematics of the displacements. (C) 2002 Elsevier Science B.V. All rights reserved.