The SEG Virtual Geoscience Center is the online museum representing the former SEG Geoscience Center. In 2008 and 2009 under the direction of Susan Henley, Director SEG's now defunct Geoscience Center, Mariaisabel Johnston Romandini and Nicole Paizis spent many hours scanning biographies from GEOPHYSICS and from SEG Awards Citation documents for the addition to an updated "Virtual Museum of Geophysics". The SEG Virtual Geoscience Center was created to serve the interests of the SEG membership in the following ways:
- The SEG membership - To preserve our geophysical heritage. This is accomplished by
- providing a pictorial archive of all the instruments and displays within the Geoscience Center, and providing documentation about the manufacture and historical uses of these instruments
- providing an archive of biographies of important geophysicists who have helped paved the way in geophysical exploration
- listing and honoring distinguished geophysicists who have received special recognition by the Society of Exploration Geophysicists
- listing and honoring (through archived pictures, speeches, and writings) those who have served the Society as its President
- special exhibits that display emerging or past technologies that have or will shape geophysical exploration for minerals and fossil fuels
- The general public - To provide an introduction to geophysics and the role it has played in acquiring natural resources necessary for the betterment of humankind and to familiarize the general public with technological issues and the people important to formulating public policy related to the exploration and development of natural resources.
- Students of all ages, especially K-12 level - To provide an introduction to science, specifically geophysics, and to encourage young students to consider a career in geophysics.
The Virtual Geoscience Center displays pictures of geophysical items that are on display or archived at the SEG Geoscience Center in Tulsa. Currently, the online collection has 144 on display. All of these instruments are loaned to the SEG Geoscience Center or have been donated by companies and individuals.
At the top-level, there are four basic types of items: magnetic, electrical, seismic and gravity instruments. You will find a description of these types of instruments in their appropriate section. We also have collected a gallery of "interesting" instruments or objects that do not fit into one of the four major categories as well as some historical information and photographs - you can check these out in the Gallery category.
We need your help
There are many pieces of information we store about each instrument besides the basic name-description couplet; for instance, its manufacturer and date, item number, and donor, if applicable. In many cases, you will find little or no information, just a picture or two. We appreciate any assistance you can offer to identify some of these instruments. If you know any information about any instrument in our collection, have pictures showing the instrument being used in the field, have a question, would like to make a correction, do not hesitate to contact us. On each item page, you will find a "Do You Know More" button. Click this button to open up a form so that you can conveniently provide us with what you know. There are a few instruments that are total unknowns. We collected these "unknowns" into a separate page which you may access if you follow this link.
Categories of items
Computational devices, aids, and tables
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.
In gravity prospecting, geophysicists measure minute variations in the force of gravity from rocks up to a few miles beneath the earth's surface. Different types of rocks have different densities, and the denser rocks have the greater gravitational attraction.
If the higher-density rock formations are arched upward in a structural high, such as an anticline, the Earth's gravitational field will be greater over the axis of the structure than along its flanks. A salt dome, on the other hand, which is generally less dense than the rocks into which it is intruded, can be detected from the low value of gravity recorded above it compared with that measured on either side.
The anomalous variations in gravity that reveal the geologic structures sought in oil exploration may represent only one-millionth or even one-ten millionth of the Earth's total field!
Magnetic prospecting looks for variations in the magnetic field of the earth that are caused by changes in the subsurface geologic structure or by differences in the magnetic properties of near-surface rocks. The inherent magnetism of rocks is called the magnetic susceptibility.
Sedimentary rocks generally have a very small magnetic susceptibility compared with igneous or metamorphic rocks, which tend to have a much higher magnetite (a common magnetic mineral) content. Most magnetic surveys are designed to map the geologic structure on or inside the basement rocks (the crystalline rocks the lie beneath the sedimentary layers) or to detect magnetic minerals directly.
The magnetic method was initially used for petroleum exploration in areas where the structure in oil-bearing sedimentary layers appeared to be controlled by topographic features, such as ridges or faults, on the underlying basement surface. Since the development of aeromagnetic methods, most magnetic surveys undertaken for oil exploration are carried out to ascertain the thickness of the sedimentary section in areas where such information is not otherwise available.
Electrical and electro-magnetic methods measure either natural or man-made electric and/or magnetic fields. These measurements can be taken on land, in the air, at sea, or in a borehole. From these measurements, some parameter of the subsurface is derived. The most used parameter is resistivity (or its inverse, conductivity).
All rocks conduct electricity to varying degrees. The resistance to electrical current flow is called 'resistivity' and is measured with a direct-current (DC) resistivity instrument using electrodes that are implanted in the earth. DC resistitivity surveys commonly probe to depths of several hundred meters, and are often used for groundwater and engineering studies. (Fresh groundwater is resistive, whereas brackish water is conductive). The Megger earth tester shown below is an example of a hand-held resistivity instrument developed for measurement of the the earth grounding resistance for power supplies.
Conductivity (how well a rock conducts electricity) is the reciprocal of resistivity, and can be measured inductively without physical contact with the ground. Such instruments are called 'electromagnetic' and are based on measurement of the time-varying magnetic field in the frequency range 10 hertz to several hundred kilohertz. The early airborne electromagnetic system shown below was developed for searching for highly-conductive metallic ore bodies. Such systems discovered over $10 billion worth of ore deposits in Canada in the 1960s and 1970s. Hand-held metal detectors or 'treasure hunters' are examples of electromagnetic devices.
Examples of EM methods include: Magnetotellurics (MT), Audio MT (AMT), Controlled-Source AMT (CSAMT), Induced Polarization (IP), Direct-Current Resistivity (DC), Electromagnetics (EM). Often no distinction is made between EM and electrical methods and they are referred to as either EM or electrical.
What are EM methods used for? EM geophysics are used to look for almost any resource, whether it's minerals, oil, gas, groundwater, or geothermal energy. They are used for environmental and engineering applications, such as mapping brine contamination in the subsurface, or for finding things, such as archaeological sites or spent ordinance on bombing ranges. Some applications involve more academic topics, like mapping plate boundaries and deep-seated structures.
Displays and graphics