PS09, Yellowknife, Northwest Territories, Canada
Thumbnail Profile: Yellowknife
Yellowknife, the capital of Canada's Northwest Territories since 1967, is located on the north shore of Great Slave Lake on the west side of Yellowknife Bay. The area was named after the local Yellowknives Dene First Nation indigenous Indian tribe.
Gold was first reported in the area of Yellowknife Bay in the late 19th century and in the Dogrib language spoken by the indigenous population, the city is still known as Somba K'e ("where the money is").
Climate and Geography
Weather conditions can be arduous in Yellowknife’s semi-arid subarctic climate with temperatures ranging from lows of -50ºC to highs of +20ºC.
The terrain is rugged, consisting mainly of large rock outcroppings separated by muskeg, a soil type (also a peatland or wetland type called a bog) common in arctic and boreal areas and lakes.
Primary seismic station PS29 in Yellowknife is one of four primary seismic stations covering the far north of the American continent, with the next seismic station thousands of kilometres away. Access to the station is challenging: in summer it is sometimes possible only by helicopter and in winter only with four-wheel drive, all-terrain vehicles or snow-mobiles.
All array sites are located on Precambrian granite rocks that form part of the Canadian shield and are more than 2,400 million years old. Because the nearest ocean is over 1,000 km away, micro-seismic ‘noise’ (background signals) from oceanic sources is quite low. The chief source of natural noise in winter is “icequakes” and in summer wave action on the Great Slave Lake. The predominant background noise in this environment comes from human activity - heavy equipment in the nearby gold mines, diesel generators and rock-crushing plants. As the city of Yellowknife has grown, there has been a corresponding increase in background noise from human activity, causing the abandonment of one seismometer site too close to the city.
Yellowknife is an historic seismic station. It was one of the first three stations in the International Monitoring System (IMS) to be certified in the year 2000, along with Hamar, Norway, and Mina, North Virginia, USA.
The initial seismic array station was established near Yellowknife in 1962 as one of the United Kingdom’s Atomic Energy Agency’s international teleseismic medium-aperture arrays.
Links to the 18 array sites were upgraded in 1976, between 1986 and 1989, and again in 1999-2000 when there was a complete upgrade of the array station.
Thus, over the intervening years, the station has recorded literally thousands of seismic events worldwide, including nearly all underground nuclear explosions detonated by the nuclear weapon States before the Comprehensive Nuclear-Test-Ban Treaty (CTBT) opened for signature in 1996 and a defacto moratorium on nuclear testing came into effect.
The Yellowknife array is one of the largest seismic arrays by IMS standards and has a remarkable detection record, particularly for the French nuclear explosions that took place in the South Pacific from 1966 to 1996. It also detected the announced North Korean nuclear test on 9 October 2006. In addition, the station complex houses radionuclide station RN16, which also played an important role in detecting the DPRK announced nuclear test.
Canada hosts IMS facilities representing each of the four technologies making up the International Monitoring System (IMS): two other primary seismic stations, six auxiliary seismic stations, one hydroacoustic station, one infrasound station, four radionuclide stations and one radionuclide laboratory.
Testing, Evaluation and Certification
A seismic station has three basic parts, all of which have to be tested: a seismometer to measure the ground motion; a recording system which registers the data digitally with an accurate time stamp; and a communication system interface.
Yellowknife’s station performance has been excellent. Average failure rates have been minimal (i.e. one per two years for the satellite link; one per three years for the seismometer and better than one per ten years for the digitizer and power supply). Spare equipment is stored on site.
Today a total of three full-time technicians maintain the array network, as well as a geomagnetic observatory.
After a thorough evaluation, PS09 at Yellowknife in Canada’s Northwest Territories was formally certified on 28 July 2000 as the first of 50 planned primary seismic stations of the IMS.