Regional characteristics of coda attenuation after the lancang-Gengma earthquake
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In the light of the single scattering model of coda originating from local earthquakes, and based on the aftershock coda registered respectively at the 4 short period stations installed near the foci shortly after theM7.6 Lancang andM7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and theQ c-value of the coda in the Lancang and Gengma areas using a newly-founded synthetic determination method. Result of the study shows the rate of coda amplitude attenuation demonstrates remarkable regional differences respectively in the southern and northern areas. The southern area presents a faster attenuation (Q c=114), whereas the northern area shows a slower attenuation (Q c=231). The paper also discusses the reasons causing such differences. Result of the study also suggests a fairly good linear relation between the coda source factorA o(f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lgM 0=lgA 0(f)+17.6,M D=0.67lgA 0(f)+1.21 and logM 0=1.5M D+15.79. In addition, the rates of amplitude attenuationβ s andβ m are respectively calculated using the single scattering and multiple scattering models, and the ratioβ s/βm=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free pathL of the S-wave scattering in the southern and northern areas are determined to be 54 km and 122 km respectively by the relations which can distinguish between the inherentQ i and scatteringQ s, testify to this areas having lowQ-values correspond to stronger scatterings.
Key wordsSynthetic determination method Rate of coda amplitude attenuation Spatial distribution ofQc Lancang-Gengma earthquake Yunnan region
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- Aki, K., 1969. Analysis of the seismic coda of local earthquakes as scattered waves.J. Geophys. Res.,74, 615–631.Google Scholar
- Aki, K. and Chouet, B., 1975. Origin of coda waves: source, attenuation and scattering effects.J. Geophys. Res.,80, 3322–3342.Google Scholar
- Chen, P. S., Nuttli, O. W., Ye, W. H. and Qin J. Z., 1984. Estimates of short-periodQ values and seismic moments from coda waves for earthquakes of the Beijing and Yunnan regions of China,Bull. Seism. Soc. Amer.,74, 1189–1207.Google Scholar
- Gao, L. S., Hua, Z. X., Li, R. X., 1987. Calculating the mean free path of the S-waves in Beijing region using coda strength and attenuation.Acta Seismologica Sinica,9, 347–363, (in Chinese).Google Scholar
- Hough, S. E. and Anderson, J. G., High-frequency spectra observed at Anza, California: implications forQ structure.Bull. Seism. Soc. Amer.,78, 692–707, 1988.Google Scholar
- Pulli, J. J., 1984. Attenuation of coda waves in New England.Bull. Seism. Soc. Amer.,74, 1149–1166.Google Scholar
- Qin, J. Z., 1989. The relation between the regionalQ-values of the short period waves and seismic intensity attenuation in Yunnan,Collected Papers on Seismic Risks of Yunnan and Guizhou Provinces, Yunnan science and technology Publishing House, 263–260, (in Chinese).Google Scholar
- Qin, J. Z., Kan, R. J., 1986. Calculating theQ-value and seismic moment for Kunming and its neighborhood using coda of near shocks.Acta Geophysica Sinica. 29, 145–156, (in Chinese).Google Scholar
- Qin, J. Z., Li, N., Hu, K. J., 1987. Research of the regionalQ-values of coda waves for the aftershocks in Luquan, Yunnan of 1985.Acta Seismological Sinica,9, 239–252, (in Chinese).Google Scholar
- Sato, H., 1984. Attenuation and envelope formation of three-component inhomogeneous seismograms of small local earthquakes in randomly inhomogeneous lithosphere.J. Geophys. Res.,89, 1221–1241.Google Scholar
- Yan, F. T., Mo, H. J., 1984. Coda of the 1982 Jianchuan earthquake.J. Seism. Res.,7, 505–510, (in Chinese).Google Scholar