Analysis of Radon Gas Variation as a Precursor of Earthquake Prediction Using RAD7.

An earthquake is a natural disaster caused by an unexpected release of seismic energy due to extreme stress within the earth’s crust. Such energy is released because of aggressive movements of the tectonic plates in active fault zones. The accumulated energy, containing immense pressure, is transferred from the earth’s crust to its surface in the form of seismic waves. An earthquake occurs because the accumulated stresses exceed a certain frictional resistance limit. If for a particular point an accumulation of stresses at the fault is detected, it can be inferred that there is a possibility of earthquake occurrence. Earthquake prediction research aims to detect those variations in a number of physical parameters in a region under study, which may show some anomalous changes prior to an earthquake. These are termed as earthquake precursors. Precursors of various geophysical and geochemical natures are used in earthquake prediction. The most promising precursor is the variation in the rate of upward gas migration. Changes in the rate are most significant in the vicinity of existing faults and fractures. The changes in stresses preceding a major earthquake may either increase or decrease the permeability of faults and fractured zones. Thus, pronounced changes in the rate of migration of gases to the earth’s surface in the vicinity of faults and fractured zones can be used as short term precursors of seismic events. During seismic activities, radon gas seeps upward and enters the atmosphere. This radon gas is collected and measured and can be used to predict the arrival of an earthquake. The DURRIDGE RAD7 uses a solid state alpha detector. A solid state detector is a semiconductor material (usually silicon) that converts alpha radiation directly to an electrical signal. It has the ability to electronically determine the energy of each alpha particle. This makes it possible to tell exactly which isotope (polonium-218, polonium-214, etc.) produced the radiation, so that we can immediately distinguish old radon from new radon, radon from thoron and signal from noise. The RAD7 measures radon gas concentration. Radon daughters do not have any effect on the measurement. The RAD7 pulls samples of air through a fine inlet filter, which excludes the progeny, into a chamber for analysis. The radon in the RAD7 chamber decays, producing detectable alpha emitting progeny, particularly the polonium isotopes. Even though the RAD7 detects progeny radiation internally, the only measurement it makes is of radon gas concentration. In other words we can say, the RAD7 does not measure radon daughter concentrations but measures only radon gas concentrations.