STUDY ON THE CHARACTERISTICS OF FORESHOCK AND ID IDENTIFICATION
ZHU CHUAN-ZHEN; WANG LIN-YING (Institute of Geophysics,SSB,Beijing 100081,China)
In the paper,the multifractal features of foreshock in broad sense have beenanalysed before and after the strong and moderate earthquaks occurred in ChineseContinent during past 2l years. Generalized fractal dimension Dq and correspondingsingularity spectrum f),as well as its variations with time for the spatialtemporal distributions of seismicity are calculated by using Fixed-mass and Fixed-radius methods.The results show,1) The spatial and temporal distributionsof foreshock in broad sense in the regions under study have illustrated amultifractal pattern,despite of whether the strong earthquakes with M≥7.0occurred or not in the regions.( 2) Dq ( q→ ∞) both in space and time showsdecreasing prior to the occurrence of strong earthquakes about half a year to oneyear. The phenomenon of decreasing dimensions of acoustic emissions beforefractures of rocks has also been observed in rockfailure experiment with large scalespecimens( 0. 5m× 0. 5m×1. 0m).( 3) The tectonic environment for preparingstrong earthquakes(M ≥ 7. 0) is quite different compared with that for moderateearthquakes.The high degree of heterogeneity of crustal stress distribution mayplay an important role in preparing large intra-plate earthquakes.
【CateGory Index】： P315