Allison L. Bent

A comparison of eastern North American seismic strain-rates to glacial rebound strain-rates

Glacial rebound strain-rates computed using a simple Laurentide glacial loading model are of the order of 10−9 per year within the region of glaciation and extending several hundred kilometers beyond. The horizontal strain-rates receive approximately equal contributions from horizontal and vertical velocities, a consequence of the spherical geometry adopted for the Earth model. In the eastern United States and southeastern Canada the computed strain-rates are 1–3 orders of magnitude greater than an estimate of the average seismic strain-rate [Anderson, 1986] and ∼1 order of magnitude greater than predicted erosional strain-rates. The predicted glacial rebound strain-rates are not, in general, oriented in such a way as to augment the observed state of deviatoric stress, possibly explaining why the seismic strain-rates are much smaller than the glacial rebound strain-rates. An exception to this may be seismically active regions in the St. Lawrence valley.

Am improved source mechanism for the 1935 Timiskaming, Quebec earthquake from regional waveforms

The Timiskaming earthquake, which occurred near the Quebec-Ontario border at the northwest end of the Western Quebec seismic zone in 1935, is one of the five largest instrumentally recorded southeastern Canadian earthquakes. Previous studies of this earthquake concentrated on modeling teismograms recorded at regional distances, a better constrained focal mechanism is obtained. The waveforms indicate thrust faulting on a moderately dipping northwest striking plane at a depth of 10 km. TheMw of 6.1 determined in this study is in good agreement with previous magnitude estimates (mb 6.1,Ms 6.0, andmbLg 6.2–6.3). The focal mechanism is similar to those of many recent small to moderate earthquakes in the region, and the inferred (from theP axis) acting stress of northeast compression is consistent with the overall eastern North American stress field. The “Lake Timiskaming Rift Valley” in which the earthquake occurred, comprises several northwest striking faults consistent with the strike of the 1935 event. Thus, the 1935 earthquake appears to be a result of faulting on the reactivated Timiskaming graben.

Applications of Moment Tensor Solutions to the Assessment of Earthquake Hazard in Canada

Centroid Moment Tensor solutions (CMT’s) provide valuable information on the physics of an earthquake source, focal depth, and seismic moment. The earthquake rupture is described in terms of nine generalised force couples (a 3 × 3 matrix) that represent shear dislocation and volume change (see Jost and Herrmann 1989).