1:30 PM - 1:45 PM
[S01-07] Constraining Lithospheric Transverse Isotropy Using the Non-double Couple Components of the Moment Tensors
The seismic moment tensor, which represents the equivalent body-force system of the seismic source (Backus and Mulcahy, 1973), may exhibit non-double couple components (NDCs) when the earthquake occurs on a planer fault if the source medium is anisotropic (Kawasaki and Tanimoto, 1981; Aki and Richards, 1981). Kawakatsu (1991, GRL) reported that the NDCs of the moment tensors for shallow earthquakes from the Harvard CMT catalog (Dziewonski et al.,1981; predecessor of GCMT) exhibit a systematic characteristic dependent on faulting types. Specifically, the sign of NDC on average systematically switches between normal-faulting and reverse-faulting. The average NDC parameter ε (Giardini, 1983) is negative for thrust faulting and positive for normal faulting. This behavior can be explained if the source region is transversely isotropic with a vertical symmetry axis (radially anisotropic). In fact, the transverse isotropy model of PREM at a depth of 24.4 km predicts the observed systematic NDC pattern, although the magnitude is underestimated, indicating the potential to enhance our understanding of the lithospheric transverse isotropy using the NDC of the moment tensors.
To investigate the lithospheric transverse isotropy structure utilizing the NDCs of the moment tensors, we propose a novel inversion scheme, building upon the approaches employed by Vavrycuk (2004) and Li, Zheng, et al. (2018) for deep and intermediate-depth earthquakes, but with necessary modifications to address shallow sources (Kawakatsu, 1996, GJI). Synthetic tests indicate the possibility of constraining the S-wave anisotropy (ξ) and the fifth parameter (ηκ; Kawakatsu, 2016, GJI), although these parameters exhibit substantial correlation. We plan to extend this method to real data from the GCMT catalog (e.g., aftershocks of the 2011 Tohoku earthquake to study the transverse isotropy structure of the old Pacific plate) and will discuss the applications and findings of this analysis.
To investigate the lithospheric transverse isotropy structure utilizing the NDCs of the moment tensors, we propose a novel inversion scheme, building upon the approaches employed by Vavrycuk (2004) and Li, Zheng, et al. (2018) for deep and intermediate-depth earthquakes, but with necessary modifications to address shallow sources (Kawakatsu, 1996, GJI). Synthetic tests indicate the possibility of constraining the S-wave anisotropy (ξ) and the fifth parameter (ηκ; Kawakatsu, 2016, GJI), although these parameters exhibit substantial correlation. We plan to extend this method to real data from the GCMT catalog (e.g., aftershocks of the 2011 Tohoku earthquake to study the transverse isotropy structure of the old Pacific plate) and will discuss the applications and findings of this analysis.