Figure 1.

Recently, due to environmental concerns and improved technology, it is often no longer necessary to use explosive charges to generate the needed seismic waves. Instead, most seismic crews use non-explosive seismic technology to generate the required data. This non-explosive technology usually consists of large heavy wheeled or tracked vehicle carrying special equipment designed to create a large impact or series of vibrations. These impacts or vibrations create seismic waves similar to those created by dynamite. In the seismic truck shown, the large piston in the middle is used to create vibrations on the surface of the earth, sending seismic waves that are used to generate useful data.

The same sort of process is used in offshore seismic exploration.

Instead of trucks and geophones, a ship is used to pick up the seismic data. Instead of geophones, offshore exploration uses hydrophones, which are designed to pick up seismic waves underwater. These hydrophones are towed behind the ship in various configurations depending on the needs of the geophysicist. Instead of using dynamite or impacts on the seabed floor, the seismic ship uses a large air gun, which releases bursts of compressed air under the water, creating seismic waves that can travel through the Earth's crust and generate the seismic reflections that are necessary.

Figure 2.

Ex.2 What processes are shown at Figure 1 and Figure 2?

Describe them.

Text 9 Magnetometers and Gravimeters

Ex.1 Read the text below and decide which answer A, B, C, D or E best fits each space.

In addition to using seismology to gather data concerning the (1) _______ of the Earth's crust, the magnetic (2) ________ of underground formations can be measured to generate geological and geophysical data. This is accomplished through the use of magnetometers, (3) ______ are devices that can measure the small differences in the Earth's magnetic field. In the early days of magnetometers, the devices were large and bulky, and only able to (4) ________ a small area at a time. However, in 1981, NASA launched a satellite, (5) _______ with magnetometer technology, capable of taking magnetic measurements on a continental scale. This satellite, called Magsat, allows for the study of underground rock formations and the Earth's mantle on a larger scale, and provides clues as to tectonic plate (6) _______ and the (7)_______ of deposits of petroleum, natural gas, and other valuable minerals.

In addition to using variances in the Earth's magnetic field, geophysicists can also measure and (8) _______ the difference in the Earth's gravitational field to gain a better understanding of what is underground. Different underground formations and rock types all have a slightly different effect on the gravitational field that surrounds the Earth. By measuring these minute differences with very (9) _______ equipment, geophysicists are able analyze underground formations and have a clearer insight into exactly what types of formations lie below ground; and, whether or not they have the potential for containing (10) _________ .

1	A. system	B.composition	C. substance	D. state	E. mixture
2	A. abilities	B. features	C. signals	D. properties	E. conditions
3	A. which	B. who	C. there	D. those	E. such
4	A. conduct	B. watch	C. analyze	D. search	E. survey
5	A. installed	B. connected	C. equipped	D. made	E. sent
6	A. change	B. migration	C. removal	D. movement	E. operation
7	A. location	B. weight	C. quality	D.distribution	E. lay out
8	A. sharp	B. sensible	C. fragile	D. important	E. sensitive
9	A. point out	B. calculate	C. record	D. feel	E. fix
10	A. water	B.hydrocarbons	C. deposits	D. chemicals	E. bacteria

Text 10