Ocean Networks Canada - Haida Gwaii

ONC detects M6.1 earthquake near Haida Gwaii

vkeast@uvic.ca — Fri, 24 Apr 2015 22:41:22 +0000

Seismic sensors on Ocean Networks Canada’s seafloor observatory installed offshore Vancouver Island detected an earthquake in the Northeast Pacific Ocean on the morning of 24 April 13:56:16 UTC (7:00 a.m. PDT)

The magnitude 6.1 earthquake struck offshore the Haida Gwaii Region, with its epicentre about 280 kilometres south west of Prince Rupert, British Columbia.

Figure1: ONC Earthquake Sensors and 24 April earthquake epicentre

The Haida Gwaii event was preceded by a magnitude 5.5 earthquake off the coast of Northern California twelve and a half hours earlier. It is unclear whether these earthquakes, occurring about 1300 km away from each other, are in some way related. It is, however, intriguing that the events were located at the southern and northern reaches of the Cascadia subduction zone and that the ONC seismometer at Endeavour detected numerous small local events during the same period of time.

Figure2. Seismic activity recorded by Endeavour seismometer on 24 April. Each horizontal line represents one hour of vertical ground motion (even hour black; odd hour blue). Bigger earthquakes show as large excursions crossing several rows. Small events right after each fourth hour are caused by electrical interference from the camera that observes hot vent fauna at the Endeavour location.

For more information: Martin Heesemann, ONC staff scientist

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Haida Gwaii Rumbles Picked Up on ONC's Hydrophone

rlat@uvic.ca — Fri, 02 Nov 2012 07:00:00 +0000

From Alaska to Vancouver, residents along the west coast felt the powerful magnitude 7.7 earthquake that struck the Haida Gwaii archipelago at 8:04PM PDT, on October 27th, 2012.

ONC seafloor hydrophones also registered the low-frequency rumbles from this earthquake, along with the calls of humpback whales in the area. This recording is from a hydrophone on Barkley Upper Slope, positioned at a depth of 396 m. In this clip, sound has been sped up 250% to make the earthquake noise audible to the human ear. The squeaking noises prior to the main quake are the sped-up whale calls.

With thanks to John Dorocicz, Acoustics Systems Developer, Ocean Networks Canada

Haida Gwaii Quake Monitored by NEPTUNE Canada

rlat@uvic.ca — Sun, 28 Oct 2012 07:00:00 +0000

Just after 8 pm on October 27, a magnitude 7.7 earthquake struck off the coast of BC, at a depth of 17 kilometres and centred 139 km south of Masset in the Haida Gwaii region.

Residents along the west coast—from Alaska to the lower mainland—also felt numerous aftershocks up to magnitude 5.8. No major damage or injuries have been reported.

Although similar in size to the earthquakes in Japan (2011) and Chile (2010) this event represents the first regional tsunami tracked by the NEPTUNE observatory.

"Ocean Networks Canada sensors at various locations and depths are designed to register and monitor these events, that are caused by a buildup of stresses in the earth’s crust," said Dr. Martin Heeseman, earthquake dynamics specialist with the Ocean Networks Canada Observatory. "Seismographs monitored the ground motion caused by these quakes, while bottom pressure recorders and the CORK pressure sensor measured the long (tsunami) waves that crossed over the 800 km cabled seafloor network."

These highly specialized, ultra-sensitive instruments provide real-time data that may provide vital information for emergency organizations and coastal residents.

The data from this earthquake, a sample of which is given above, is unique for the study of near-field tsunamis. “This is the first time we have data from our offshore stations to test the models and response of the coast to these near-field waves,” said Dr Steve Milhaly, Ocean Networks Canada's specialist in ocean/climate dynamics. “It’s these locally generated tsunami waves that will be the devastating ones for our coastal regions.”

This was the largest tremblor to hit Canada since 1949, when an 8.1-magnitude quake hit west of the Queen Charlotte Islands, in the same area. In January 1700, a 9.0-magnitude earthquake struck offshore of Vancouver Island.

For more information, visit the extended news release: Haida Gwaii Earthquake and Tsunami

Haida Gwaii Earthquake and Tsunami

rlat@uvic.ca — Sat, 27 Oct 2012 07:00:00 +0000

A powerful magnitude 7.7 earthquake struck central Moresby Island in the Haida Gwaii archipelago at 8:04PM PDT, 27 October 2012. Residents along the west coast—from Alaska to Vancouver—also felt several aftershocks up to magnitude 5.8. However, no major damage or injuries were reported. This was the largest temblor to hit Canada since 1949, when an 8.1-magnitude quake hit west of the Queen Charlotte Islands, in the same area.

The following plots show both seismic and bottom pressure data collected by Ocean Networks Canada instrumentation, located approximately 600 km south of the earthquake epicenter. The light-blue plots at upper-left illustrate changes in pressure, as measured by bottom pressure recorders at four node locations. In the top three plots, initial strong blue signatures, beginning at 3:04 UTC, indicate shaking of the seafloor as seismic energy passed through the region. As this energy dispersed, the recordings indicate changes in sea level above each bottom pressure recorder as waves emanating from the disturbance traveled across the ocean's surface. The fourth plot shows bottom pressure anomalies at Folger Passage, a shallow (100 m) near-shore station where surface swell typically conceals tsunami waves from easy detection by the casual viewer.

The lower five plots, in dark blue above, illustrate seismic energy as measured by four Ocean Networks Canada seafloor seismometers and one land-based seismometer located in Bella Bella on British Columbia's central coast. Earthquake onset is clearly indicated in all five plots, with Bella Bella recording the earliest onset, because it is located much closer to the earthquake epicenter, 265 km to the southeast. The Bella Bella seismometer is part of the Canadian National Seismograph Network, maintained by National Resources Canada's Pacific Geoscience Centre.

Numerous aftershocks were also detected following the initial earthquake, with over 50 magnitude 4+ aftershocks recorded in the initial 16 hours. Most of these aftershocks occurred beneath the seafloor, as indicated in the following USGS map.

Tsunami warnings originally issued for a large stretch of the North and Central coast, as well as the Haida Gwaii region and eastward to Hawaii, were later cancelled or downgraded. One wave that hit Langara Island, northern-most island in the Haida Gwaii archipelago, measured 69 cm. Tsunami wave heights as high as 76 cm were recorded in Kahului, Maui, HI, and harbour oscillations up to 1.2 m were measured in Hilo, HI.

The tsunami generated by this earthquake was not nearly as large and devastating as those struck Sri Lanka, Indonesia and Japan in recent years, because it occurred on a strike-slip (lateral) fault. Vertical displacement for strike-slip earthquakes is typically much less than may be expected from a major subduction earthquake. The following short video illustrates the distinction between strike-slip and subduction earthquakes.

For scientists like those at the Pacific Geoscience Centre and other institutions studying tsunami propagation in the northeast Pacific, this event will provide valuable insights. The tsunami generated by this earthquake was similar in size to other tsunamis, such as last year's Japan tsunami and the Chilean tsunami of February 2010, when they reached the northeast Pacific. Although tremendously large in their source regions, these tsunamis diminished significantly after crossing large ocean basins to reach coastal British Columbia. The Haida Gwaii tsunami is the first regional tsunami tracked by Ocean Networks Canada's sensor network; its local source region is expected to result in different wave responses in BC's coastal embayments. By comparing these two types of tsunamis (distant vs. local), scientists can begin to piece together a picture of how BC coastal zones may react to large tsunamis originating in this region.

Ocean Networks Canada - Haida Gwaii

ONC detects M6.1 earthquake near Haida Gwaii

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Haida Gwaii Rumbles Picked Up on ONC's Hydrophone

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Haida Gwaii Quake Monitored by NEPTUNE Canada

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Haida Gwaii Earthquake and Tsunami

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