Abstract

On 10 October 2012 a moderate, Nuttli magnitude (MN) 4.5, earthquake occurred in the Montreal region. Although it did not cause any damage, it was felt throughout the region and at distances to a few hundred kilometers. The earthquake was very well recorded by seismographs at regional distances, allowing its source parameters (such as focal mechanism and depth) to be determined. Both the regional moment tensor inversion and first‐motion methods indicate predominantly thrust faulting on a northwest‐striking plane, which is typical of the west Quebec seismic zone. A depth of 13–15 km was indicated by the regional moment tensor inversion and by the regional depth phase method. The moment magnitude of 3.7 is slightly smaller than would be expected based on the average MNMw relation but is well within the range of observed values for previous earthquakes. More than 10,000 felt reports were received via an Internet “Did You Feel It?” page. A few weeks later, on 6 November 2012, another moderate (MN 4.2, Mw 3.9) earthquake occurred in the west Quebec seismic zone but in a different location, near the Quebec–Ontario border. This event also had a northwest predominantly thrust mechanism. Depths obtained by regional moment tensor and depth phase methods were both in the 6–8 km range. Over 2500 online felt reports were received. The earthquakes provided a successful test of recent changes made to handle high volumes of Internet traffic that typically occur after a significant earthquake felt in a large, urban area.

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