Strain-geoelectric resistivity precursor and the virtual dislocation model to the Tangshan earthquake
Tóm tắt
The complete records of geoelectric resistivity before two earthquakes were analyzed, including 16 stations within 240 km around the Tangshan earthquake and 2 stations within 50–60 km from theM6.1 Datong earthquake. By eliminating various disturbances in the records and realizing the precursory anomalies to be reliable, the authors studied the distribution of the geoelectric precursor field, which proves to be physically related to the earthquake source stress field. Comparision of the sign distribution of coseismic resistivity changes with the solution of earthquake source mechanism indicates that, the coseismic resistivity changes are of opposite sign but similar spatial distribution with respect to the corresponding resistivity precursor changes. Therefore, from the resistivity observations we are of the opinion that the Tangshan earthquake is an elastic rebound process. A virtual dislocation model of geoelectric precursor for the Tangshan earthquake is proposed, in which the geoelectric precursors are supposed to be caused by the strain accumulation due to a virtual dislocation, which is opposite in sign to the actual slip taking place at the earthquake occurrence. Taking into account of the non-linear characteristics of the amplification factorK=(Δρ/ρ)/ɛ in a range of 10−7–10−5 strain changes, the theoretical distribution of geoelectric precursors for the Tangshan earthquake was calculated based on the theory of fracture mechanics and reasonably selected dislocation parameters. The results show that the semi-quantitative theoretical values are in good agreement with the observed, suggesting that the virtual dislocation model of the geoelectric precursor is appropriate to the Tangshan earthquake.
Tài liệu tham khảo
Brace, W. F. and Orange, A. S., 1968. Electrical resistivity change in saturated rocks during fracture and frictional sliding.J Geophys Res,73: 1433–1445.
Fitch, T. J. and Scholz, C. H., 1971. Mechanism of underthrusting in southwest Japan: a model of convergent plate interactions.J Geophys Res,76: 7260–7292.
Nur, A., 1974. Tectonophysics. In:Prc. 3-rd Conference of Int. Soc. Rock Mech., 253–273.
Qian, F. Y. and Zhao, Y. L.et al., 1983. Geoelectric resistivity anomalies before earthquakes.Scientia Sinica (Series B),26(3): 326–336.
Wang, X. H., Qi, G. Z. and Zhao, Y. L., 1985. Resistivity precursors and spreading of fualt prior to its instability.Scientia Sinica (Series B),28: 420–436.
Wideman, C. J. and Major, M. W., 1967. Strain steps associated with earthquakes.Bull. Seism Soc Am,57: 1429–1444.
Zhao, Y. L., Li, Z. N. and Qian, F. Y.et al., 1995. Comprehensive study for geoelectric precursors from intermediate-term to short-term or impending earthquake.Earthquake, (4): 308–314 (in Chinese).
Zhao, Y. L. and Qian, F. Y., 1994. Geoelectric precursors to strong earthquake in China.Tectonophysics,233: 99–113.
Zhao, Y. L. and Qian, F. Y.et al., 1983. Experiments in situ of electrical resistivity changes.Acta Seismologica Sinica,5(2): 217–225 (in Chinese).
Zhao, Y. L., Qian, F. Y. and Xu, T. C., 1991. The relationship between resistivity variation and strain in a loadbearing rock-soil layer.Acta Seismologica Sinica,4(1): 127–137.