简介:Beforeastrongearthquake,thereisoftenaprocessofquiescenceor2absence2ofregionalseismicactivity,whichisaphenomenonthathasattractedtheattentionofmanyscholarsinChinaandothercountries(LU,etal,1985;Wesson,1973).Inthepastten-oddyears,someChineseseismologistsmade,earlierorlater,specialstudiesonthequiescenceanomalyofseismicityinsomespecifiedareasfromdifferentangles.TakingtheconvertedannualfrequencyofM=5.0earthquakesinNorthChinaregionasacharacteristicquantity,JIANGandFENG(1989)analyzedthequiescenceanomalyofseismicactivitybyfuzzyrecognition.