DILATION-CREEP MODEL OF EARTHQUAKE SOURCE DEVELOPMENT AND THE TANGSHAN EARTHQUAKE

摘要:

The article has made a simple exposition of the dilation-creep model of earthquake source development(abbreviated DC).Inelastic volumetric dilation of rock masses and fault creep are considered as two basic phys-ical processes in the DC model. The physical mechanism of precursors of the M=7.8 Tangshan earthquake has also been analysed and discussed in this paper. The results show that the precursors of the Tangshan earth-quake were not caused by only one factor and the precursors observed in-and around the epicentral area prior to this earthquake can be grouped in to three types. TypeⅠ precursors may be causally related to rock dilata-ncy. Type Ⅱ precursors result from fault creep. Type Ⅲ precursors may be associated with some sort of upward migration of mass in the crust or the upper mantle, and/or may be attributed to large scale stressing process accommodated by some combination of stable slippage and discontinuous brittle rupture (namely small earthquake) along the faults. It was sug-gested that repeated dilation and discontinuous creep occurred during the process of source development of the Tangshan earthquake and the prepa-ratory process of the Tangshan earthquake can be divided into the follo-wing six phases: elastic stress accumulation(from 1954 to 1967);earlyinelastic dilation(from 1968 to 1969);early fault creep(from 1970 to 1973);the second dilation(from the end of 1973 to the first half of 1975);the second evident fault creep(from the second half of 1975 to the end of Apr.1976);and fault creep just before the main shock(from the end of Apr.1976 to the occurrence of the Tangshan earthquake).It is regarded hat the preparatory process of the Tangshan earthquake,as one of the intraplate events,may be controlled jointly by the upward migration of deep mass and large scale intraplate stress field.This characteristic prob-ably is different from that of earthquake along plate boundary.

Abstract:

The article has made a simple exposition of the dilation-creep model of earthquake source development(abbreviated DC).Inelastic volumetric dilation of rock masses and fault creep are considered as two basic phys-ical processes in the DC model. The physical mechanism of precursors of the M=7.8 Tangshan earthquake has also been analysed and discussed in this paper. The results show that the precursors of the Tangshan earth-quake were not caused by only one factor and the precursors observed in-and around the epicentral area prior to this earthquake can be grouped in to three types. TypeⅠ precursors may be causally related to rock dilata-ncy. Type Ⅱ precursors result from fault creep. Type Ⅲ precursors may be associated with some sort of upward migration of mass in the crust or the upper mantle, and/or may be attributed to large scale stressing process accommodated by some combination of stable slippage and discontinuous brittle rupture (namely small earthquake) along the faults. It was sug-gested that repeated dilation and discontinuous creep occurred during the process of source development of the Tangshan earthquake and the prepa-ratory process of the Tangshan earthquake can be divided into the follo-wing six phases: elastic stress accumulation(from 1954 to 1967);earlyinelastic dilation(from 1968 to 1969);early fault creep(from 1970 to 1973);the second dilation(from the end of 1973 to the first half of 1975);the second evident fault creep(from the second half of 1975 to the end of Apr.1976);and fault creep just before the main shock(from the end of Apr.1976 to the occurrence of the Tangshan earthquake).It is regarded hat the preparatory process of the Tangshan earthquake,as one of the intraplate events,may be controlled jointly by the upward migration of deep mass and large scale intraplate stress field.This characteristic prob-ably is different from that of earthquake along plate boundary.