Ocean Networks Canada - seismometer

Sharing Ocean Data

vkeast@uvic.ca — Tue, 26 Aug 2014 19:55:30 +0000

- Dr. Kim Juniper, Director of User Engagement

Ocean Networks Canada (ONC) operates the world’s largest civilian observatory network for monitoring the oceans. Maintaining ONC’s nearly 900 kilometres of networked underwater sensors requires the cooperation of other major ocean stakeholders in the northeast Pacific, Salish Sea and western Arctic. The fishing industry and the Canadian Coast Guard are kept up to date on locations of infrastructure to minimize the risk of strikes by trawl gear or interference with safe navigation.

In addition to the physical infrastructure, ONC has agreements with other ocean stakeholders related to protection of sensitive data. All data from sensors on the network are normally freely available over the Internet, to anyone. Some of these data have been identified as commercially sensitive, because they record the functioning of new instruments undergoing field-testing on the network by ONC’s commercial partners. Such data are not released until the manufacturer is satisfied with the performance of the new instrument.

Deployment of a test hydrophone array, October 2013

Other data are sensitive from a national security point of view. A cooperation agreement with the Royal Canadian Navy addresses the issue of acoustic signatures of naval ships and submarines that can be recorded by ONC’s hydrophones and broadband seismometers. This agreement allows the military to divert data streams from hydrophones and broadband seismometers before data are directed to ONC’s data acquisition and archiving system, Oceans 2.0. These ‘data diverts’ normally occur during the transit of military vessels through the area being monitored by ONC sensors. Diverted data are examined by military technicians, and most are returned directly to ONC within a few days. Data deemed “sensitive” are stored and could eventually become available to researchers upon request.

Diverted data are examined by military technicians, and most are returned directly to ONC within a few days. Data deemed “sensitive” are stored and could eventually become available to researchers upon request.

The conditions of the agreement with military stakeholders and the latest statistics on data diversion are reviewed twice each year in meetings attended by ONC, and the Canadian and US navies. These meetings are held in a spirit of cooperation, and reasonable and justifiable requests from both sides for modifications to the working arrangement are usually accepted.

Ocean Networks Canada Data Policy Statement

Magnitude 6.6 Earthquake

dwowens@uvic.ca — Thu, 24 Apr 2014 20:06:29 +0000

Multiple Ocean Networks Canada instruments recorded a magnitude 6.6 earthquake that struck beneath the seafloor off northern Vancouver Island at 8:10 PM (Pacific Daylight Time), 23 April 2014. Shaking from the earthquake was felt throughout Vancouver Island and by many people on the lower mainland in southwestern British Columbia.

Maps showing earthquake epicentre and aftershock locations (above, detail map shown above-right) and moderate to light shaking felt across northern Vancouver Island (lower map). The epicentre was 94 km south of Port Hardy, British Columbia and approximately 250 km north of NEPTUNE installations at Cascadia Basin. (Click to enlarge.)

Seismic Data

The main shock and numerous subsequent aftershocks were clearly recorded by seismometers at Cascadia Basin and Endeavour, as shown in data below. (Some of the smaller aftershocks shown in the seismic data from Endeavour may be associated with unrelated small local earthquakes that are frequently observed in this seismically active region.)

Earthquake initial shock and subsequent aftershocks recorded by the Cascadia Basin and Endeavour seismometers between 3:10-5:30AM, 24 April 2014 (UTC time) or 8:10-10:30 PM, 23 April 2014 (Pacific Daylight Time).

Bottom Pressure Recordings

Seafloor shaking was recorded by bottom pressure recorders at Cascadia Basin, Clayoquot Slope and Barkley Canyon shortly after the earthquake struck. However, there was no indication of a tsunami in the pressure data.

Seafloor pressure measured by bottom pressure recorders at three sites on the NEPTUNE Observatory. These recorders are situated at depths of 1285 m, 2706 m and 411 m. Pressure disturbances indicate seafloor shaking beginning approximately 3:11 AM, 24 April 2014 (UTC time) or 8:11 PM, 23 April 2014 Pacific Daylight Time).

Seafloor pressure anomalies (dBar) measured by bottom pressure recorders at three sites on the NEPTUNE Observatory. These recorders are situated at depths of 1285 m, 2706 m and 411 m. Blue lines show unfiltered wave height anomalies, while red lines are filtered to highlight longer-period waves such as tsunamis. Pressure disturbances indicate seafloor shaking (in blue) as the seismic waves passed, but there was no subsequent indication of a tsunami in the pressure data.

Ocean Networks Canada instruments on (and in) the seabed of the Fraser River Delta also registered the shaking, providing scientists at Natural Resources Canada information on how the delta sediments, and pressures within, respond to large earthquakes. An unproven, but commonplace, perception is that earthquakes could cause failure on the delta; Natural Resources Canada scientists are testing this hypothesis.

Rumbles and Crackles

The sound of the earthquake was recorded by Ocean Networks Canada's low-frequency hydrophone in Cascadia Basin, approximately 250 km away from the epicentre. The noise generated was so loud it saturated the hydrophone input. The spectrogram and audio recording of the earthquake are shown below. This recording has been sped up 400% to make the earthquake audible. The crackling sounds were caused when the hydrophone sensor was saturated.

Strike-slip Earthquakes

Seismologist analyses and the absence of a tsunami suggest that this earthquake likely occured 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.

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.

Northern California Earthquake Strikes Southern Cascadia Subduction Zone

dwowens@uvic.ca — Mon, 10 Mar 2014 16:26:38 +0000

This map shows the location of the main shock and aftershocks at the Mendocino Triple Junction between the North America, Pacific and Gorda tectonic plates.

Ocean Networks Canada's NEPTUNE observatory is about 900 km to the north, and its seismometers in Cascadia Basin, Barkley Canyon and Clayoquot Slope recorded the powerful main shock as well as some of the larger (up to magnitude 4.6) aftershocks about 2 minutes after the event (see seismic recordings below).

NEPTUNE seismic recordings of the 10 March 2014 earthquake. Three components, North (HHN), East (HHE) and Vertical(HHZ) of 3 seismometers show the various earthquake signals arriving at different times. The top 3 traces were recorded by the ocean bottom seismometer in Cascadia Basin; the second set of 3 traces are from the Barkley Canyon seismometer and the lowest 3 traces are from the seismometer at Clayoquot Slope The green bar indicates the origin time of the main shock; about 2 minutes later the fast travelling P-waves (indicated by the red bars) arrive at the NEPTUNE stations, and almost 2 minutes later the S-waves arrive (indicated by the yellow bars), immediately followed by low-frequency surface wave shaking. About 10 minutes after the main shock, high frequency water sound arrives, as clearly visible in the top two panels. (Click to enlarge.)

The southern end of the Cascadia subduction zone terminates at the northern end of the San Andreas fault, meeting at the Mendocino triple junction between three tectonic plates, the North American plate in the east, the Pacific plate in the south, and the Gorda plate to the north. The San Andreas fault zone compensates mostly the lateral motion between the North American and the Pacific plate, whereas the Cascadia subduction thrust fault takes up the motion of the Juan de Fuca plate going down (subducting) below North America.

The 10 March earthquake occurred at a depth of around 16.6 km, and its fault mechanism was taking up mostly lateral motion from the interplay between the Pacific and the Gorda plate. It was not a subduction thrust earthquake and therefore did not generate any tsunami. However, as every earthquake redistributes tectonic stresses in the area (hence the many aftershocks), we will keep an extra eye out for any other seismicity in that region.

Northern California Earthquake Detected by NEPTUNE Seismometers

dwowens@uvic.ca — Mon, 10 Mar 2014 07:00:00 +0000

10 March 2014, 05:18 UTC (10:18 pm local time) a magnitude 6.8 earthquake struck the southern end of Cascadia subduction zone. The epicentre location of the earthquake was about 50 km west of the California coast. During the subsequent few hours many aftershocks followed in the same area. Ocean Networks Canada seismometers in Cascadia Basin (NV.NC27), Barkley Canyon (NV.NCBC) and Clayoquot Slope (NV.NC89) recorded the powerful main shock as well as some of the larger (up to magnitude 4.6) aftershocks about 2 minutes after the event.

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.

Hydrate Growth at Bullseye Vent?

rlat@uvic.ca — Fri, 09 Dec 2011 08:00:00 +0000

Gas hydrates are ice-like solids composed of natural gas, usually methane in marine environments, and water. Hydrates are known to exist in the Cascadia margin, west of Vancouver Island, beneath the seafloor. Sediment stiffness is increased by frozen hydrates, like ice in winter mud. The degree of stiffness is an indicator of the amount of hydrate present per unit volume. Gas hydrate outcrops, venting and topography in the Cascadia margin have been intensively studied and are observed to change over time. Does the volume of hydrates also change with time? University of Toronto researchers Lisa Roach and Nigel Edwards are trying to find out.

An uncommon, specialized exploration technique, known as seafloor compliance is used to probe beneath the seafloor, by examining the deflection of the seafloor caused by waves on the ocean surface. Waves on the surface create pressure changes on the seafloor; as they “push” the seafloor down, it deflects them. The amount of seafloor deflection depends on the stiffness of the sediment, which, in turn, depends on hydrate content. In areas where there are fewer buried hydrates, the seafloor is more compliant (less stiff). The depth at which hydrates are buried beneath the seafloor can be inferred from gravity wave frequency at the seafloor. A compliance value in the higher frequency range describes shallower hydrates, while lower frequencies describe deeper deposits.

Roach and Edwards are using this technique to study changes in buried gas hydrates in a place called Bullseye Vent at our Clayoquot Slope location (depth 1260m). To determine the change in compliance, pressure and velocity data were recorded at 1 second intervals for a total of 228 24-hour long records between 1 October 2010 and 16 May 2011. Pressure was measured with a differential pressure gauge (DPG), capable of recording pressure changes of 1Pa in a background of 1MPa, while very small velocities, associated with seafloor wave deflections as small as the radius of an iron atom, are measured by a broadband ocean-bottom seismometer (OBS). These instruments are part of the NEPTUNE Canada ODP 889 seismic station.

A trend in the compliance over the 228 days was revealed (shown above). The trend represents a -2.88% change in the compliance of the sediments over the study period. This decrease in the compliance corresponds to an increase in the stiffness in sediments (indicating an increase of gas hydrate amount) between 0-600mbsf (metres below seafloor). Hydrates are stable within the top 225m of sediments, so a change in compliance could have been caused by property changes over this depth range. To match the decrease in compliance to the increase in hydrate content, the stiffness of the layer between 0-100mbsf (initial hydrate content of 22%) was varied until the -2.88% change was observed following a model suggested by the IODP drilling. A rather surprising three fold increase in hydrate concentration of the 100m layer, from 22% to 64% is predicted.

Assuming a 100m diameter hydrate mass, the change in hydrate concentration is equivalent to a change in hydrate mass of 600 million kg, which poses the question where does this mass come from? If this decrease is distributed over the entire hydrate zone (~250mbsf) the change in hydrate concentration and mass would be smaller. Maybe the zone of increased stiffness extends to greater depths and is in a layer associated with a hydrate production mechanism?

As more high-resolution data are collected in the future, scientists will gain increased understanding of how fluctuations in compliance relate to the dynamics of the hydrate system and its evolution. There is still much to be learned!

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 - seismometer

Sharing Ocean Data

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Magnitude 6.6 Earthquake

Seismic Data

Bottom Pressure Recordings

Rumbles and Crackles

Strike-slip Earthquakes

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Tsunami alert follows 8.2 quake off Chile

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Northern California Earthquake Strikes Southern Cascadia Subduction Zone

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Northern California Earthquake Detected by NEPTUNE Seismometers

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Haida Gwaii Earthquake and Tsunami

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Hydrate Growth at Bullseye Vent?

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Chilean Earthquake and Tsunami

Major Earthquake

Seismic Monitoring

Tracking the Tsunami

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