Frequency-Dependent Attenuation Characteristics of Coda and Body Waves in the Kumaun Himalaya: Implications for Regional Geology and Seismic Hazards

被引:8
作者
Sivaram, K. [1 ]
Gupta, Sandeep [1 ]
机构
[1] CSIR, Natl Geophys Res Inst, Uppal Rd, Hyderabad 500007, India
关键词
Seismic coda waves; body waves; attenuation; Kumaun Himalaya; NEW-YORK-STATE; S-WAVES; MULTIPLE-SCATTERING; INTRINSIC ATTENUATION; COLLISION ZONE; SOUTH-AFRICA; SHEAR-WAVES; CRUST; SEPARATION; MANTLE;
D O I
10.1007/s00024-022-02963-8
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
We investigate the frequency-dependent seismic attenuation characteristics of the crust beneath Kumaun Himalaya, India, using seismic coda waves (Q(c)(-1)) and high-frequency body waves (Q(alpha)(-1) and Q(beta)(-1)). We used about 300 local earthquakes, well-recorded by 32 three-component broadband stations, for characterizing the seismic attenuation. The corresponding geodynamic implications are analyzed for the entire study region and for major tectonic segments such as the Lesser Himalaya (LH) and the Higher Himalaya (HH). The coda quality factor, Q(c), computed from the single backscattering model, shows a dependence on both frequency (1-20 Hz) and lapse times (20-50 s). Expressed as power laws (Q(c) = Q(0)f(n)), Q(0) (Q at 1 Hz) and n (frequency-dependence exponent) vary as 320 and 0.78 for lapse time window (LTW) 20 s to 656 and 0.55 at LTW 50 s. Similarly, the Q factor of body waves (Q(alpha) and Q(beta)), computed using the coda normalization and extended coda normalization methods (Yoshimoto et al. Geophys J Int 114: 165-174, 1993), also show strong frequency dependence. They are expressed as Q(alpha )= (36.28 +/- 0.05)f((0.85 +/- 0.01)) and Q(beta) = (50.58 +/- 0.15)f((0.94 +/- 0.01)). The ratio Q(beta)/Q(alpha) is found to be larger than unity in the whole frequency range for the entire study region. This observation is interpreted as an effect from seismically active regions and heterogeneous crustal regimes. Additionally, to characterize the dominant attenuation mechanism, we separate the quality factors for intrinsic attenuation (Q(i)(-1)) and scattering attenuation (Q(s)(-1)), using the Wennerberg (Bull Seismol Soc Am 83:279-290, 1993) formulation. Our study shows that the seismic attenuations are different for the LH and the HH segments. This possibly is due to the mechanism of underthrusting and deformation in the LH segments, leading to a dominant scattering attenuation and the multitude of fractures and pores in the crust. Our study shows that (1) Q(c)(-1) is less than Q(beta)(-1), which seems to adhere to Zeng's (J Geophys Res 96:607-619, 1991) theory; (2) Q(c)(-1) is closer to Q(i)(-1); (3) the ratio (Q(alpha)(-1)/Q(beta)(-1)) lies between 1.7 and 2.25. The results are in agreement with several theoretical and laboratory experiments and suggest heterogenous crustal media. The varying attenuation characteristics, seismic energy budget and radiating efficiency have a significant role in seismic hazard analysis in Kumaun Himalaya.
引用
收藏
页码:949 / 972
页数:24
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