Control and Prediction

Monitoring. There is great interest in learning enough about earthquakes to be able to predict their occurrence and possibly even control them. Rock adjacent to a fault in a seismically active area can be monitored for slight changes, such as the development of small cracks, very small tremors called microseisms, and changes in magnetism, electrical properties, and seismic velocity. The formation of cracks in the rock increases the rock's porosity, which can change the local water table—a phenomenon that has been noticed before earthquakes. Similarly, the cracks allow radioactive gases like radon to escape, which can also be detected. Minute changes in the elevation of the earth's surface can also be measured. Asian scientists have documented that various species, including insects, horses, and snakes, are ultrasensitive to seismic activity and can become skittish before an earthquake.

All of these changes are thought to reflect increasing strain that may indicate the onset of an earthquake; however, such changes are not foolproof indicators and may apply to one earthquake and not another. It is also possible that fault zones may actually be quite weak and not require great amounts of strain to create movement.

Using historical data. The probability of an earthquake striking an area can be calculated based on the historical seismic activity in that area. Repeated patterns of earthquakes make it possible to predict when the next one might occur. Seismic gaps are stretches along an active fault zone that have not produced earthquakes for a significant time. Scientists believe that these gaps may be extra‐resistive areas along the fault where strain is being stored in the fault blocks and where earthquakes will likely occur when the strain is finally released.

Reducing built‐up strain. Damage from earthquakes in heavily populated areas could be reduced if the built‐up strain could somehow be released periodically before the rock breaks or moves. It has been accidentally discovered that pumping water under high pressure into the subsurface can trigger earthquakes. The water probably lubricates the fault zones, causing movement, or helps dissipate the strain that was being stored in the rocks. A similar technique might be developed that could release the enormous accumulation of rock strain in quake‐prone areas through a series of nondestructive, low‐magnitude, timed quakes.