Abstract

We use seismographic data from 12 local, shallow earthquakes of magnitude MN 1.0–3.1 that occurred near Sudbury, Ontario, recorded at three stations within 30 km of the source, to examine ground-motion attenuation at close distances. This is an important issue for development of ground-motion prediction equations in eastern North America and for the inference of earthquake source parameters from regional earthquake observations. We show that high-frequency (3–10 Hz) horizontal-component ground motions decay at a geometric spreading rate of approximately R-1.3 in the first 25–30 km from the earthquake source (where R is the hypocentral distance). This is in agreement with the geometric spreading rate determined by Atkinson (2004) and used in the ground-motion prediction equations of Atkinson and Boore (2006). Vertical-component ground-motions in this distance range appear to decay at a slightly slower rate of R-1.1.

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