October 28, 2012 Earthquake: Queen Charlotte Islands, Canada

Felt ReportFelt (V) in the Masset-Queen Charlotte area and (IV) at Houston, Kitimat, Prince Rupert and Terrace. Felt (III) in much of western British Columbia and in Southeastern Alaska. Felt from Seattle, Washington to

Juneau, Alaska and to Calgary, Alberta. Thermal springs on Hotspring Island in Gwaii Haanas Natl Park Preserve, Haida Gwaii, stopped flowing after the earthquake, but were starting to show signs of recovery in mid-January 2013. A generally-small, but nearly Pacific-wide tsunami was recorded, with much higher wave heights in Hawaii than in the rest of the Pacific. Also, the West Coast and Alaska Tsunami Warning Center observed that a small tsunami was

recorded at Sitka, Alaska after having been reflected

off the Hawaiian Islands.

Tectonic Summary

The October 28th, 2012 (October 27 at the location of the epicenter) M 7.7 earthquake south of Masset, Canada, occurred as a result of oblique-thrust faulting near the plate boundary between the Pacific and North America plates. At the location of this event, the Pacific plate moves approximately north-northwest with respect to the North America plate at a rate of approximately 50 mm/yr.

This earthquake is likely associated with relative motion across the Queen Charlotte fault system offshore of British Columbia, Canada. Studies of tectonics in this region suggest plate motions are taken up by strike slip faulting parallel to the plate boundary, accompanied by lesser amounts of thrust motion to accommodate the oblique nature of the plate motion vector between the two plates with respect to the orientation of the main plate boundary fault structure. This oblique component of plate motion may involve either underthrusting of the western edge of the Pacific Plate beneath North America, or be taken up on crustal faults within the North America plate. The October 28th earthquake is consistent with either scenario. Its rupture extended approximately 100-150 km along strike, along the shallow extent of the source fault. Slip amounts reached approximately 5m, in a patch to the south of the epicenter. Aftershocks delineate the rupture well, as shown here.

This region of the Pacific:North America plate boundary has hosted 7 earthquakes of magnitude 6 or greater over the past 40 years - the largest of which was a M 6.6 earthquake in 2009, 80 km to the south east of the 2012 earthquake. In 1949, a M 8.1 earthquake occurred closer to the Pacific:North America plate boundary, likely as a result of strike-slip faulting, approximately 100 km northwest of the October 28th earthquake, near the northern extent of Haida Gwaii region (formerly Queen Charlotte Islands).

(above from reference #1053)

Haida Gwaii earthquake yields new data. A team of federal government scientists that descended on Haida Gwaii following last month's 7.7 magnitude earthquake is getting new insights into the fault that caused it - and the fear it generated. Seismologist Alison Bird is one of about a dozen experts from Natural Resources Canada who were dispatched to the archipelago when the shaking started.

"My heart was in my throat until I started reading the reports, and started realizing that everyone's fine," Bird said. There were no physical injuries from the most severe Canadian quake in more than 60 years, and Bird says the worst building damage may have been a cracked foundation and a crumbled chimney. (reference #10023)

A small number of failed chimneys from October's event were documented as far away as Tlell (115 km from fault rupture). (reference #10829)