地震先行現象と地震予知の4段階

抄録

Relationship between precursor time and earthquake magnitude is examined for tilt and strain precursors amounting 112 in number. No dependence of precursor time on magnitude is found for precursors as observed with horizontal pendulum type tiltmeters and strainmeters. However, logarithmic precursor time seems to be linearly correlated to magnitude for precursors observed with water-tube tiltmeters. On the basis of the logarithmic precursor time vs. magnitude plot for precursors excluding tilt, strain and foreshock, two types of precursors are pointed out. The type-I precursors occur several hours prior to the main shock, their precursor time being ap proximately constant regardless of the magnitude of the main shock. The precursor time (T) of the type-II precursor are correlated to the magnitude (M) in a linear fashion aslog₁₀ T=0.76M-1.83in which T is measured in units of days. The nature of these two types of precursors suggests a practicable strategy of earth quake prediction along with the earthquake statistics and monitoring of crustal strain.