REGIONAL FEATURES OF CODA ATTENUATION OF AFTERSHOCKS OF WUDING, YUNNAN EARTHQUAKE IN NEAR FIELD
Qin Jiazheng
Li Baiji
Qian Xiaodong
Su Youjin
Cai Jingguan
Fu Hong
Abstract：According to dispersion theory of coda of local events, using near-field data aftershocks recorded by two mobile digital stations at the Tianxin and Yunlong after the Wuding, Yunnan MS=6.5 main-shock and sampling at different central frequencies(1.5～20 Hz), spatial distribution features of coda attenuation ratio β(f) are studied. The results show that there exists obvious non-uniformity of coda attenuation ratio β(f) given by the two stations in small region. When f＜6.0 Hz the coda attenuation ratio β(f) observed on both sides of earthquake-generating fault are basically identical. Yunlong station is located on east side and Tianxin station on west side. The corresponding Qc(f) is in the range of 66～120. However, in the range of high freqency(f≥ 6.0 Hz) the coda in near field going through major fault encounters a strong absorption from the fracture zone. The β(f) going through the fault observed at Yunlong station is 30% lower than that in Tianxin station in which the seismic waves do not go through the fault. The reason for the difference in space distribution of coda attenuation is discussed. The results also show that factor A0(f) of waves source is not only related with the source strength, but also with frequence f. The mean free path L of S wave obtained using 1.5～20 Hz is respectively 30 km on east side of the fault and 40 km on west side, from which it is verified that there is a stronger dispersion body when seismic waves go through the fracture zone.
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Publication Date：2001-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：11( 87-97 )