Abstract

The M 5.0 23 June 2010 Val-des-Bois, Quebec, earthquake produced a rich instrumental and felt ground-motion database. We use instrument-corrected response spectra and Fourier amplitude data from 120 stations, at distances from 60 to 1,000 km, to examine the attenuation and source characteristics of this important event. The Val-des-Bois earthquake produced relatively large response spectral amplitudes at distances less than 200 km, greater than predicted by most recent ground-motion prediction equations (GMPEs) (including the Atkinson and Boore 2006 equations). By contrast, reported intensities at regional distances tended to be smaller than predicted by intensity GMPEs (Atkinson and Wald 2007), although they were high in the epicentral area. From recent moderate earthquakes in eastern North America (ENA) (2010 Val-des-Bois and the 2005 Riviere du Loup event), we have learned that amplitudes at near distances are not well-predicted by average attenuation shapes drawn to pass through regional observations. To infer the source spectrum or near-source motions, we suggest the use of seismic moment as a constraint on the level of the source spectrum. Using Q-corrected observations to deduce the source-spectral shape, and the known seismic moment to fix its absolute amplitude level, we obtain an apparent source spectrum for the Val-des-Bois earthquake. The Val-des-Bois source spectrum is well described by a Brune model with a stress drop of 250 bars. Future work will focus on resolving near-source attenuation issues to provide better GMPEs for ENA for all magnitudes.

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