What is Geophysics ?
Geophysics is the study of the earth and its environment using techniques and knowledge from physics. Because it utilizes methods from physics, mathematics, geology and chemistry, it is considered a multidisciplinary field. Geophysics for the purpose of engineering includes using geophysics to search for groundwater, metals, and hydrocarbons. There are two main types of geophysics. The first is exploration geophysics, which is done on a small scale, and global geophysics, which is geophysics pertaining to the world as a whole.
Exploration Geophysics: Exploration geophysics is the application of geophysics to find natural resources such as metals and hydrocarbons. In a team to extract oil, first a geologist will find clues that oil exist. Afterward, a geophysicist will study the physical properties of the soil. They utilize gravimetric and magnetometry to find the distribution of crystalline terrains. Then, data compiled and studied by geologist, geophysicists and petroleum engineers.
Global Geophysics: Global geophysics includes the study of earthquakes, the Earth's magnetic field, oceanography and heat flow. While exploration geophysics deals mainly with the Earth's crust, global geophysics focuses on global structure and its history. To do this, geophysicist study the Earths' shape, density, pressure, temperature and gravitation field.
Geophysics and Engineering: Geophysicist and engineers may use the geophysics field to better study and understand things such as the construction of highways and bridges. It is also used to check groundwater and items buried underground such as archaeological artifacts and unexploded ordnance. Geophysics studies geohazards such as earthquakes and structures, and is useful in the construction of dams.
Subsurface formations are mapped by measuring the times required for a seismic wave (or pulse), generated in the earth by a near-surface explosion of dynamite, mechanical impact, or vibration, to return to the surface after reflection from interfaces between formations having different physical properties. The reflections are recorded by detecting instruments responsive to ground motion. They are laid along the ground at distances from the shot point which are generally small compared with the depth of the reflector.Variations in the reflection times from place to place on the surface usually indicate structural features in the strata below. Depths to reflecting interfaces can be determined from the times using velocity information that can be be obtained either from the reflected signals themselves or from surveys in wells. Reflections from depths as great as 20,000 ft can normally be observed from a single explosion, so that in most areas geologic structure can be determined throughout the sedimentary section.
What is Seismic Exploration ?
Seismic exploration is the search for commercially economic subsurface deposits of crude oil, natural gas, and minerals by the recording, processing, and interpretation of artificially
induced shock waves in the earth. Artificial seismic energy is generated on land by shallow borehole explosives such as dynamite, or surficial vibratory mechanisms mounted on specialized trucks; in marine environments, air guns fire highly compressed air bubbles into the water that transmit seismic wave energy into the subsurface rock layers. Seismic waves reflect and refract off subsurface rock formations and travel back to acoustic receivers called geophones (on land) or hydrophones (in water). The travel times (measured in milliseconds) of the returned seismic energy, integrated with existing borehole well information, aid geoscientists in estimating the structure (folding and faulting) and stratigraphy ( rock type, depositional environment, and fluid content ) of subsurface formations, and facilitate the location of prospective drilling targets. The first known seismic exploration trials were conducted by John C. Karcher and colleagues, who performed a primitive seismic survey and mapped a shallow limestone bed at Belle Isle, Oklahoma in the summer of 1921. Since then, seismic technologies have evolved into ever more sophisticated techniques through the use of digital computer processing, improved energy sources, advanced acoustic receivers (multi-component), three-dimensional, and four-dimensional (time-lapse) seismic surveys. Seismic exploration is now the most prevalent geophysical technique used in the search for hydrocarbons. Because of potential damage to environmentally sensitive areas such as offshore and arctic regions, seismic exploration activities are strictly regulated by state and federal governments.
Department of Physical Science and Engineering 4700 King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia.
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