Ocean Networks Canada - Chile

Tsunami alert follows 8.2 quake off Chile

dwowens@uvic.ca — Wed, 02 Apr 2014 04:25:42 +0000

On April 1 at 4:46:45 PM Pacific Daylight Time (23:46:45 UTC), a magnitude 8.2 earthquake occurred off Chile's Pacific coastline, according to the US Geological Survey. Ocean Networks Canada instrumenatation captured both ground shaking and a very small tsunami as they crossed the northeast Pacific.

Map of the epicentre and 16 aftershocks along the subduction zone between the Nazsca and South American plates, 1 April 2014. Data provided by USGS and plotted using Google Earth. (Click to enlarge.)

At a depth of 20.0 km below the seabed, the shallow near-field quake struck 86 km northwest of the mining area of Iquique, hitting a region that has been rocked by numerous quakes over the past two weeks. According to the USGS, this earthquake occurred as the result of thrust faulting at shallow depths near the Chilean coast. The location and mechanism of the earthquake are consistent with slip on the primary plate boundary interface, or megathrust, between the Nazca and South America plates. In this area, the Nazca plate subducts eastward beneath the South America plate at a rate of 65 mm/yr. Subduction along the Peru-Chile Trench to the west of Chile has generated the uplift of the Andes mountain range.

Ocean Networks Canada's seismometer in Cascadia Basin recorded the tremors as they crossed the North Pacific. Seismic data clearly indicate arrival of the initial P waves approximately 750 seconds (12.5 minutes) after the earthquake, and following S waves about 1375 seconds (23 minutes) after the earthquake struck. Bottom Pressure Recorders on the NEPTUNE Observatory also detected passage of the tsunami in real time, as it crosses our observing stations in the northeast Pacific.

Data from the Cascadia Basin ocean-bottom seismometer indicating arrival of P and S waves. The top trace shows East-West motions, the centre trace shows North-South motions, and the lower trace shows vertical motions. (Click to enlarge.)

A 1.9-metre tsunami was recorded at a northern Chilean port Tuesday evening. The Pacific Tsunami Warning Center issued an alert for all of Latin America's Pacific coast. There was no threat issued to the Pacific coast along North America.

NOAA issued a forecast of tsunami heights as the energy propagated away from the source region, indicating heights up to 100 cm close to the epicenter, with rays of 2-10 cm wave heights extending across portions of the South Pacific Ocean toward New Zealand and archipelegos in the South-Central Pacific.

Tsunami wave energy propagation forecast issued by the Pacific Tsunami Warning Center, showing contours of maximum wave amplitudes (in cm) associated with the 1 April 2014 earthquake.

Travel times for tsunami propagation were also modeled by the National Tsunami Warning Center, with expected arrival of a small (2-4 cm) tsunami in coastal British Columbia beginning 15 hours after the event, around 7:00 AM Pacific Daylight Time.

Predicted travel times for tsunami waves generated by the 1 April 2014 earthquake. Three-hour intervals are marked by the heavy white lines, intermediary hours are marked by blue shades and dashed white lines indicate half-hour boundaries. Arrival in both New Zealand and British Columbia was predicted to begin approximately 15 hours after the initial earthquake.

Seafloor pressure traces from the CORK pressure instrument at Cascadia Basin, 1-2 April 2014. The upper plot shows initial passage of the earthquake just past 00 UTC (indicated by the blue lines), followed by passage of the small tsunami beginning at 14 UTC. The lower plot focuses on the tsunami onset period, 11-15:20 UTC. Wave amplitudes at this deep-water site (2660 m) were approximately 8 mm.

No stranger to seismic activity, Chile is one of the world¹s most earthquake-pronecountries. In 2010, a magnitude-8.8 quake and ensuing tsunami in central Chile killed more than 500 people and destroyed several hundred thousand homes along the coast.

Tale of Two Tsunamis

rlat@uvic.ca — Wed, 05 Sep 2012 07:00:00 +0000

A magnitude 8.8 earthquake struck Chile in February 2010, generating a tsunami that crossed the Pacific, with measurable waves recorded throughout coastal British Columbia.

A recent paper, published in Pure and Applied Geophysics, describes this tsunami in detail and compares it to the Great Chilean earthquake and tsunami of May 1960.

After the devastating 2004 Sumatra tsunami, monitoring instrumentation was increased and upgraded by countries around the Pacific, which resulted in an unprecedented amount of data gathered for the 2010 Chilean tsunami. In the northeast Pacific, it was recorded by over 200 high-precision coastal tide gauges, two DART bottom pressure stations and four Ocean Networks Canada bottom pressure recorders. Seismic waves from the earthquake were also recorded by the three NEPTUNE bottom pressure recorders and ocean bottom seismometers. This wealth of data allowed the Canadian researchers at the Fisheries and Oceans Canada to provide a comprehensive analysis of the event.

The 2010 tsunami claimed 124 lives, but was much smaller and less deadly than 1960 event, which killed 1655 people in Chile and another 235 in Hawaii, Japan and the Philippines. The 1960 Chilean tsunami generated 8 m waves in coastal Japan and 3-4 m waves in California and Alaska. By contrast, the 2010 tsunami, triggered by an earthquake 11 times weaker than the 1960 earthquake, generated estimated maximum wave heights 4.3 m in the Marquesas Islands and up to 2 m in Japan and Hawaii. In coastal British Columbia, maximum wave heights from the 1960 tsunami measured 2.1 m in the Queen Charlotte Islands and 1.26 m in Tofino, while the 2010 tsunami generated maxima of 98 cm in Port Alberni and 68 cm at Winter Harbour on northwestern Vancouver Island.

NEPTUNE Canada and DART bottom pressure recorders captured detailed information about this tsunami as it crossed the northeast Pacific. Deep-sea wave heights ranged from 6.3 – 10.6 cm. The tsunami reached NEPTUNE’s outermost recorders over 50 minutes before striking the west coast of Vancouver Island at Tofino and Bamfield. By comparing these time gaps with those between NEPTUNE Canada recorders and the Washington coast, scientists may be able to improve coastal warnings for arrival of distant tsunamis in coastal Washington and British Columbia.

Researchers also studied the refraction of the tsunami waves as they approached the coast of Vancouver Island. The direction of the incoming wave fronts rotated clockwise significantly (20 degrees to over 40 degrees) as the waves encountered shallower water. There was also a marked clockwise rotation in the direction of propagation of the second train of incoming tsunami waves that arrived 7 hours after the leading tsunami wave train.

Compared with capabilities during earlier devastating tsunamis like the 1960 Chilean event and the 2004 Sumatra tsunami, the Pacific Tsunami Warning System has seen significant improvements. Due to the addition of real-time measurements from seafloor networks like NEPTUNE Canada and the open-ocean DART system, as well as improved coastal networks and advances in tsunami prediction models, it is now possible to provide tsunami warnings with more precise estimated arrival times and specific run-up heights for high-risk regions.

Published research: The 2010 Chilean Tsunami Off the West Coast of Canada and the Northwest Coast of the United States

Chilean Earthquake and Tsunami

rlat@uvic.ca — Thu, 04 Mar 2010 08:00:00 +0000

Major Earthquake

On Saturday, Feb. 27 2010, 0634UTC, a magnitude 8.8 earthquake occurred off the coast of Chile. A tsunami advisory was issued for the BC coast. According to the USGS, "this earthquake occurred at the boundary between the Nazca and South American tectonic plates. The two plates are converging at a rate of 70 mm per year. The earthquake occurred as thrust-faulting on the interface between the two plates, with the Nazca plate moving down and landward below the South American plate."

With a magnitude of 8.8, this recent earthquake was the seventh strongest ever recorded, and 500 times stronger than the magnitude 7.0 earthquake that struck Haiti in January 2010. The most powerful earthquake ever recorded, (magnitude 9.5) also occurred off the coast of Chile in this region, the Valdivia earthquake of May 1960.

Seismic Monitoring

Three Ocean Networks Canada broadband seismometers, which lie buried in seafloor sediments at our Barkley Canyon, Cascadia Basin and Clayoquot Slope locations, recorded the earthquake. The tremor accelerations were also recorded by the gravimeter in our Seafloor Compliance System at Clayoquot Slope.

Tracking the Tsunami

Within an hour of the earthquake, tsunami waves over 5m in height struck coastal Chile, leading to the deaths of hundreds of people. Tsunami waves ranging 1-5m were observed in many locations, including New Zealand, French Polynesia and Hawaii. The tsunami propagated across the Pacific at jet-like speeds and reached coastal British Columbia by 23:00UTC, 16.5 hours after the event. Tsunami wave heights of 50 to 100cm were recorded along the West Coast of Vancouver Island.

Scientists at Canada's DFO Institute of Ocean Science fed data from one of the Ocean Networks Canada bottom pressure recorders into their regional tsunami model for this event, allowing them to simulate wave motions and interactions for coastal British Columbia, including the Strait of Georgia.

Data from events like these are an invaluable aid to scientists, who are working to improve tsunami prediction models for the West Coast. In the future, improved models could greatly benefit emergency response, public safety and disaster-preparedness operations.

Ocean Networks Canada - Chile

Tsunami alert follows 8.2 quake off Chile

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Tale of Two Tsunamis

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Chilean Earthquake and Tsunami

Major Earthquake

Seismic Monitoring

Tracking the Tsunami

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