Seismic acquisition is a geophysical prospecting method based on the principle that sound waves travel through the earth depending on the properties of the rock. A seismic wave is initiated by generating an energy wave using seismic vibrators at a known point (the shot point); records are made of the travel times and shape of the seismic waves to arrive at sensitive recorders (geophones).
The Low Impact Activities will comprise Synterra, its employees, agents or contractors carrying out seismic data acquisition and associated activities such as scouting surveying, cultural heritage and environmental clearances and monitoring of the lines on completion of the project.
A Cultural Heritage survey will be undertaken before any works are initiated, 4 personnel will be involved in this survey, 2 cultural representatives, 1 archaeologist and 1 Synterra representative.
This will be done out of one vehicle with the archaeologist and cultural reps walking the lines to inspect for any culturally significant artifacts ( see Figure 1 ). This team can cover approximately 7 kms per day.
Following the cultural survey, the geophone locations are surveyed. A team of 2 surveyors drive the line marking points every 25 meters with a spray paint dot on the ground ( see Figure 2 ).
The paint used is biodegradable and will wash away with rain. The surveyors can cover approximately 8 – 9 kms a day.
Once the Surveyors have completed their positioning the seismic acquisition crew will follow behind, timing would be approximately a week after the surveyors.
The crew will start by augering a 6-inch-deep hole at the receiver location to bury the seismic nodes, this anchors the receiver and assists in keeping wind noise down on the recorded data. This is done with a vehicle-mounted hydraulic auger ( see Figure 3 ).
The data recording crew will follow along to install the nodal receiver. This equipment is cableless and will have minimum impact on daily operations of property owners. A crew of approximately 12 personnel in 6 vehicles will deploy the receiver equipment.
Typically, a receiver will be in its location for approximately 2 days before being retrieved. Two vibrator trucks will then move along the line sending sound wave/vibrations into the ground every 25 meters. They will have a support vehicle that follows them.
The vibrator trucks are controlled by a vehicle that houses the electronics, the recorder and operates the trucks via radio signals. This recording vehicle remains parked in a central location that has good radio communications within the area they are working.
Once the vibrators have completed acquiring the data the field crew will then follow through and retrieve the nodal receivers ( see Figure 4 ), filling the small augered holes as they go. The receivers are then transported to the data harvesting unit which is housed at a laydown area offsite. The entire operation moves along at approximately 7kms per day and typically from when the node is first placed in the ground to when it is retrieved takes approximately a day and a half to two days. All lines are then inspected by the onsite QC person to make sure that all equipment has been removed and all holes have been filled and reinstated to original ground conditions.
Speed limits are placed on vehicles travelling the seismic line to reduce environmental impact and keep dust levels to virtually zero ( see Figure 5 ). Lines can be watered to reduce the effects of dust even further. A vehicle and trailer with a fire unit on it will follow the vibrators as a first response in the event of a fire and the crew has a strict no smoking policy in the field. Typically, the maximum allowable speed limits are 80 km/hr for good unsealed roads, 60 km/hr for farm truck and 40 km/hr along the seismic lines.
Total personnel and equipment in the field at any one time would be a maximum of 11 vehicles and 16 personnel but would average around 6 vehicles and 10 personnel onsite at most times with the crews travelling to and from the data harvesting unit offsite.
For more information regarding Seismic consulting, contact our team today.