Seismic Refraction Surveys

Ground survey work near the base of Mount Currie was conducted in the summer of 2017 as part of the Mount Currie Landslide Hazard Assessment and Risk Analysis

One aspect of this work was studying the density and volume of previous landslides from Mount Currie as part of assessing the potential for future landslides of a similar or greater volume. Seismic Refraction Surveys are the method used to gather this data.

Frequently Asked Questions

Q. What is the process for conducting Seismic Refraction Surveys?
A. A survey line of cable and sensors is laid, then a corresponding line of small holes are hand dug (3 - 5 m deep) and small explosive charges (roughly the size and strength of a single shotgun shell) are laid in each hole. The charges are barely audible when detonated, produce no flying debris—as the explosions take place underground—and no visible sign on the surface other than a small drill hole. When detonated, the charges create seismic energy that is then measured by the sensors. The process is repeated across the prescribed survey area, building up detailed information that is used to calculate the density of earth and bedrock.

Q. Are these people qualified to be handling explosives?
A. A licensed holder of a WCB Blasters certificate will supervise the handling and detonation of the explosives. 

Q. Will this work have any impact on air traffic in the area / Pemberton Airport operations?
A. No. The charges are small, and the detonations will occur 3 - 5 m underground. Aside from a small drill hole, there will be no disturbance to the ground surface, and no flying debris will be produced. 

Q. What is this doing to the environment?
A. The smallest feasible charge size is used to record the required information, and there is strict observance of setback distances from waterways, as laid out in the Guidelines for the Use of Explosives in or Near Canadian Fisheries Waters. 

Q. So, rock fall from Mt Currie may be increasing, and you are proposing to set off explosives near the base of it. Won't that potentially make the problem worse?!
A. The short answer is that the charges are small and set well away from where the rockfalls have originated. The longer answer: the smallest feasible charge size is used to record the required information, and the seismic energy created by each set of charges is equivalent to an excavator working on a construction site. The survey area is where historical landslides have settled, not on the mountain itself and not anywhere near where rockfalls are originating. 

Q. How long will the be there?
A. It is expected that the process would take a maximum of one week, commencing July 26, 2017.

Q. What about the risk of fire in these current dry conditions?
A. All work will be conducted in compliance with the BC Wildfire Act and corresponding Wildfire Regulation, which regulates high risk activities including the use of spark-producing tools and the preparation or use of explosives. The fire danger rating for the Pemberton Area is currently Level 4 and the survey team is liaising with Pemberton Fire Rescue to ensure all precautions are taken, including maintaining a fire watch for 2 hours following the completion of the work each day, and having adequate fire suppression on site. Should the fire danger rating increase to Level 5 and remain there for three days, all work must cease until the fire risk rating has been downgraded. 

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