Geoscience Reference
In-Depth Information
One of the first known instruments for geophysical measurement is a seismoscope invented in
a.d. 132 by the Chinese philosopher, Chang Hêng (Needham, 1959). This seismoscope reportedly
had the capability to not only detect earthquakes, but could also determine the direction from which
the earthquake originated. Many of the geophysical methods employed today originated or were
more fully developed based on the needs of the mining and petroleum industries. In fact, present
levels of worldwide production for minerals, oil, and natural gas could not have been achieved with-
out the use of geophysics as an exploration tool.
The magnetic compass was used to find iron ore as early as 1640 (Dobrin and Savit, 1988).
Robert Fox devised the self-potential method using copper-plated electrodes and a galvanometer to
find copper sulfide ore bodies in Cornwall, England, during 1830 (Reynolds, 1997). Robert Thalén
wrote
On the Examination of Iron Ore Deposits by Magnetic Methods
in 1879 and contributed to
the invention of some of the first magnetometers (Telford et al., 1976). These Thalén-Tiberg and
Thomson-Thalén magnetometers proved very successful for mineral prospecting in Sweden dur-
ing the late 1800s. Initial development of resistivity and electromagnetic induction methods for the
mining industry occurred between 1910 and 1930. Airborne magnetometers refined for submarine
detection during the Second World War were employed shortly afterward to quickly prospect for
minerals over large areas (Dobrin and Savit, 1988). The introduction of airborne electromagnetic
surveys for mineral exploration also occurred shortly after the Second World War ended.
Dobrin and Savit (1988) and Lawyer et al. (2001) detail some of the early history involving ini-
tial applications of geophysical methods for the petroleum industry. A torsion balance field device
for measuring anomalies in the Earth's gravitational field was refined by Baron Roland von Eötvös
of Hungary in the late 1800s. Crude seismic methods were developed by the French, British, Ger-
mans, and Americans during the First World War as a means to locate enemy artillery positions.
Torsion balance gravity measurements and fan-pattern seismic refraction surveys were then used
to find oil fields associated with Texas Gulf Coast salt domes in the 1920s. Conventional seismic
refraction methods introduced in 1928 to the Middle East were soon found to be particularly effec-
tive within Iran for locating limestone structures containing substantial oil reserves. J. C. Karcher
conducted the first seismic reflection experiments from 1919 to 1921 and then demonstrated the
potential of this geophysical method for oil exploration by mapping a shallow rock unit in central
Oklahoma during 1921. The first oil discovery attributed to seismic reflection occurred during 1927
with the Maud Field in Oklahoma. Seismic reflection is the predominant geophysical method used
for petroleum exploration today.
Although radar technologies were introduced during the Second World War, it was not until
the early 1960s that ground-penetrating radar was first employed as a geophysical tool, initially to
investigate the subsurface characteristics of polar ice sheets (Bailey et al., 1964). Archeological,
environmental, geotechnical engineering, and hydrological geophysical surveys became more and
more common in the latter half of the past century. There was some agricultural research activity
in the 1930s and 1940s related to soil moisture measurement with resistivity methods (Edlefsen and
Anderson, 1941; Kirkham and Taylor, 1949; McCorkle, 1931), but for the most part, the application
of geophysical methods to agriculture did not gain momentum until the 1960s, and to a greater
extent in the 1970s, with the use of resistivity methods for soil salinity assessment (Halvorson and
Rhodes, 1974; Rhoades and Ingvalson, 1971; Rhoades et al., 1976; Shea and Luthin, 1961). Greater
historical detail on the application of geophysical methods to agriculture is provided in Chapters 2
and 3 of this topic.
Geophysical surveys conducted for petroleum, mining, hydrological, environmental, geotechni-
cal engineering, archeological, and agricultural applications vary dramatically in scale with respect
to the investigation depth of interest. Petroleum industry oil and gas wells have been drilled to lev-
els 8 km beneath the surface based on information obtained from seismic reflection surveys. Most
geophysical surveys conducted in the mining industry have an investigation depth of interest that is
less than 1 km. There are, however, some deep mining operations extending more than 3 km below
ground, and therefore mining geophysical surveys can occasionally require greater investigation
