A broadband seismogram may be represented by a convolution of source time function, the propagation operator and the scattering/attenuation operator. As the propagation operator is frequency independent, and the scat...A broadband seismogram may be represented by a convolution of source time function, the propagation operator and the scattering/attenuation operator. As the propagation operator is frequency independent, and the scattering/attenuation effect may be described by a Q factor depending on frequency via Q -1 =Q -1 1+(Q 2ω) -1 , considering a combination of the displacement spectra, the source spectra may directly be estimated, in which the contribution of the Q value may be eliminated automatically. Using this algorithm, the near source broadband seismograms of five aftershocks of the 1988 Lancang Gengma, Yunnan Province, China earthquake were processed. The results for the M L=3.0 and M L=3.5 aftershocks show that for the same earthquake, similar high frequency fall off may be obtained from different recording stations. The result for the M S=6.7 aftershock shows that consistent source parameters may be gotten from different seismic stations. The parameters estimated also agree with the results obtained by empirical Green′s function approach. The high frequency spectra of the aftershocks exhibit a typical f γ fall off. For the M L =3.0 aftershock, γ ≈3;for the M S=6.7 and M L =4.0 aftershocks, γ ≈2; and for the M L=3.5 and M L=3.0 aftershocks, γ ≈2.5. The corner frequency of the M S=6.7 aftershock indicates that it has a small source dimension, implying that it may come from the rupture of a small but strong barrier.展开更多
On the basis of the assumption that ω^2 model accords with source displacement spectra, we have obtained the mathematical expressions for calculating apparent stresses of moderate-small shocks from low-frequency flat...On the basis of the assumption that ω^2 model accords with source displacement spectra, we have obtained the mathematical expressions for calculating apparent stresses of moderate-small shocks from low-frequency flat level and comer frequency. By using digital seismic records, apparent stress values are calculated for 823 moderate-small shocks of 4 earthquake series in Yunnan area following corrections for instrument response, propagation influence and site effect. The results show that for the 4 earthquake series in Yunnan area, apparent stress hints precursory information, which means that if a moderate-small shock occurs with apparent stress larger than 1 MPa in an earthquake series, a moderate-strong earthquake will occur afterwards; and if there is not moderate-small shock with apparent stress larger than 1 MPa after a moderate-strong event in an earthquake series, strong aftershock will not occur. The research also indicates that the average apparent stress value is 0.8 MPa in Yunnan area, therefore, apparent stress is not obviously related to seismic magnitude.展开更多
Ⅰ. INTRODUCTION The observation of the spectra of the SVC sources is very important in the theory of the slowly varying component (SVC) and for the prediction of solar-terrestrial environment. In order to increase th...Ⅰ. INTRODUCTION The observation of the spectra of the SVC sources is very important in the theory of the slowly varying component (SVC) and for the prediction of solar-terrestrial environment. In order to increase the spatial resolution, solar radio astronomers made used of solar eclipses to observe the SVC sources over a wide range of frequencies to ob-展开更多
文摘A broadband seismogram may be represented by a convolution of source time function, the propagation operator and the scattering/attenuation operator. As the propagation operator is frequency independent, and the scattering/attenuation effect may be described by a Q factor depending on frequency via Q -1 =Q -1 1+(Q 2ω) -1 , considering a combination of the displacement spectra, the source spectra may directly be estimated, in which the contribution of the Q value may be eliminated automatically. Using this algorithm, the near source broadband seismograms of five aftershocks of the 1988 Lancang Gengma, Yunnan Province, China earthquake were processed. The results for the M L=3.0 and M L=3.5 aftershocks show that for the same earthquake, similar high frequency fall off may be obtained from different recording stations. The result for the M S=6.7 aftershock shows that consistent source parameters may be gotten from different seismic stations. The parameters estimated also agree with the results obtained by empirical Green′s function approach. The high frequency spectra of the aftershocks exhibit a typical f γ fall off. For the M L =3.0 aftershock, γ ≈3;for the M S=6.7 and M L =4.0 aftershocks, γ ≈2; and for the M L=3.5 and M L=3.0 aftershocks, γ ≈2.5. The corner frequency of the M S=6.7 aftershock indicates that it has a small source dimension, implying that it may come from the rupture of a small but strong barrier.
基金National Natural Science Foundation of China (40574016), Key Project of State Science and Technology in the Eleventh Five-year Plan (2004BA601B01-04-03), Joint Seismological Science Foundation of China(104047)and Science and Technology Project of Social Development of Jiangsu Province (BS2005069).
文摘On the basis of the assumption that ω^2 model accords with source displacement spectra, we have obtained the mathematical expressions for calculating apparent stresses of moderate-small shocks from low-frequency flat level and comer frequency. By using digital seismic records, apparent stress values are calculated for 823 moderate-small shocks of 4 earthquake series in Yunnan area following corrections for instrument response, propagation influence and site effect. The results show that for the 4 earthquake series in Yunnan area, apparent stress hints precursory information, which means that if a moderate-small shock occurs with apparent stress larger than 1 MPa in an earthquake series, a moderate-strong earthquake will occur afterwards; and if there is not moderate-small shock with apparent stress larger than 1 MPa after a moderate-strong event in an earthquake series, strong aftershock will not occur. The research also indicates that the average apparent stress value is 0.8 MPa in Yunnan area, therefore, apparent stress is not obviously related to seismic magnitude.
文摘Ⅰ. INTRODUCTION The observation of the spectra of the SVC sources is very important in the theory of the slowly varying component (SVC) and for the prediction of solar-terrestrial environment. In order to increase the spatial resolution, solar radio astronomers made used of solar eclipses to observe the SVC sources over a wide range of frequencies to ob-
