Major earthquakes seem to appear from nowhere without warning and may cause untold devastation, particularly in poorer countries that are ill-prepared for disaster. It is no wonder, then, that people around the world have attempted to find ways to predict when and where an earthquake might occur.
There is a great deal of ancient folklore, particularly in China and Japan, about the warning signs of impending earthquakes. These signs, known as precursors, are said to include unusually hot and humid weather, fogs, strange cloud formations, and lights in the sky. In addition, there are tales about bizarre animal behavior, changes in well water levels, and plants flowering out of season. In 2008, three weeks before a major earthquake in China’s Sichuan province, an area particularly prone to earthquakes, animals in a local zoo began to exhibit strange behavior, and thousands of toads appeared on a street after water disappeared from a pond 350 miles east of the epicentre. Modern folklore has also added electronic phenomena such as disturbances to lamps, radios, and telecommunications equipment to the list.
While a connection between these events and earthquakes cannot be proven scientifically, there is an overwhelming amount of anecdotal evidence, particularly with regard to animal behavior. It has therefore been suggested that animals may be able to sense super-and sub-sonic audio frequencies or perhaps changes in electromagnetism and atmospheric ionization that precede earthquakes.
It is also believed that animals can hear P Waves or primary waves. These are extremely fast seismic wave that move through solid rock, creating vibrations in the same way that sound waves create vibrations in the air. P Waves are usually the first indicators of earthquakes received at seismic stations. In fact, a network of P-wave sensors was installed in the Coachella Valley, California in 2002 as the first phase in the development of a California-wide earthquake early warning system.
In 2004, scientists analyzing data from an earthquake in Parkfield, California identified another possible precursor: weak signals indicating movements in underground water which occurred in the 24 hour pre-quake period. However, the signals were so faint that they could also have been caused by background interference, and no definitive conclusions were drawn.
There does, however, appear to be stronger evidence for electromagnetic precursors. The emission of an electromagnetic signal began two weeks prior to and peaked immediately before a 7.1-magnitude earthquake in Loma Prieta, California in 1989. Subsequently, scientists detected an eight-minute series of electromagnetic pulses 19 hours before a 5.6 magnitude earthquake near San Jose, California in 2007.
While skeptics believe there may be other possible explanations for these signals, mineralogist T. Freund has demonstrated in laboratory modeling of pre-earthquake conditions that rocks can develop electrical currents under pressure.
Members of the scientific community continue to debate whether precursors exist, and if so what they might be. In the meantime, earthquake prediction remains a fuzzy exercise in statistical probability based on an area’s proximity to fault lines and the amount of time which has elapsed since its last major quake.