2.2　Symbols

M——seismic magnitude；

Muz——upper limit magnitude of a seismic zone or belt；

b——correlation coefficient of magnitude and frequency；

M0——lower limit magnitude of a seismic zone or belt；

——annual average occurrence rate of earthquake of magnitude M0 and above in a seismic zone or belt；

Mu——upper limit magnitude of a potential seismic source zone；

——space distribution function of earthquakes in a potential seismic source zone，the space distribution function of earthquakes in the ith potential seismic source zone and at the jth magnitude step；

f（θ）——directional probabilistic distribution function of potential seismic source zone.