APPLICATION OF SURFACE AND BOREHOLE HIGH-RESOLUTION SEISMIC TECHNIQUES IN THE EVALUATION OF EARTHQUAKE SITE RESPONSE IN THE OTTAWA VALLEY (EASTERN CANADA)

The Ottawa-St. Lawrence River region is the most active seismic zone in eastern Canada. Although this zone currently has low to moderate seismic activity, there is geological evidence for the occurrence of strong paleoearthquakes. In particular, an area located 90 km east of Ottawa is characterized by severely disturbed terrain and irregular ground surface topography in an otherwise flat erosional plain of Holocene sediments. This deformation has been postulated to be the result of one of the most geologically destructive earthquakes in eastern Canada.

High-resolution seismic techniques have been applied in order to obtain information about the subsurface structure that may have locally influenced the ground motion response causing this deformed terrain. Preliminary results from P-wave seismic reflection profiles reveals that a deep bedrock basin is coincident with the presence of disturbed and deformed sediments at the surface (~175 m max thickness). S-wave reflection and refraction and S-wave seismic borehole techniques have been applied in order to obtain fundamental resonance periods, shear-wave velocity information and attenuation values in the study area. The fundamental site resonance periods estimated throughout the target area suggest a variable soil response to earthquake shaking. Such information is significant for earthquake hazard evaluation at thick soil sites.