A seismic survey is used to investigate the earth’s subterranean structure. The technique of seismic surveying is generally used for oil and gas exploration. During 2010 Survey Gisborne Limited were engage to undertake survey work to set out six seismic lines totalling approximately 50 kilometres using GPS and conventional survey equipment in an area just north of Wairoa.
The photographs below show staff from Survey Gisborne Limited setting out positions along a line at predetermined distances to mark the locations for drilling and blasting. Once a bore hole has been drilled specialised personnel then place a blasting cap into the hole. During a seismic survey, seismic waves are generated by dynamite when detonated. The seismic waves will pass through the earth encountering different materials. Some of the energy is reflected off the boundaries between the different strata while other waves will pass through. The reflected energy returns to the surface and the speed and strength is measured by special detectors, known as geophones.
Seismic surveying for gas and oil exploration can show areas of materials of various densities and positions. This doesn't necessarily mean that these areas actually contain oil or gas, as it could indicate any number of materials, such as water.
The reliability of the vast amount data collected is analysed by specialists in the oil and gas exploration industry. Data obtained will include different soil compositions and solidity, measurements to bedrock and water tables, rock structure and more. This information is invaluable given the significant commercial value of this commodity.