Seismic Techniques at www.japanese-home-gardens.com

Research associated with defense and Security also has contributed; the goal of detecting remote nuclear explosions has required the development of new seismic techniques, techniques that are equally applicable to study of the earth's interior, earthquakes, and volcanic eruptions. Combined with the recent surge in computer technology and the development of lasers, the availability of these satellite and seismic data has led to a far more comprehensive view of the earth, its atmosphere, and its oceans.

Earthquakes can also occur when rock folds that can no longer support the elastic strain break to form a fault. Seismic (earthquake) waves spread outwards in all directions from the focus - much as sound waves do when a gun is fired [Key, 4]. There are two main types of seismic wave: the compressional wave and the shear wave [2]. Compressional waves cause the rock particles through which they pass to shake back and forth in the direction of the wave. Shear waves make the particles vibrate at right-angles to the direction of their passage. Neither type of seismic wave physically moves the particles: instead it merely travels through them.

One spectacular seismic field instrument that has recently been used in a test station in Montana is the large aperture seismic array (LASA). This array of instruments, consisting of more than 600 seismographs buried in shallow holes, is dispersed over an area half the size of the state of Massachusetts. A similar giant array of this nature is under construction in Norway. These arrays record vibrations that reach them from the earth's interior.