中科大地球与行星物理学术报告通知-Hitoshi Kawakatsu

报告人简介：

Prof. Hitoshi Kawakatsu is an Emeritus Professor at the Earthquake Research Institute, University of Tokyo. A leading seismologist, he has made pioneering contributions to understanding Earth’s deep interior, subduction dynamics, and the lithosphere–asthenosphere system. He received his Ph.D. in geophysics from Stanford University in 1985. A Fellow of AGU and AAAS and recipient of the EGU’s Beno Gutenberg Medal and the AGU’s Inge Lehmann Medal, Prof. Kawakatsu has authored over 130 papers, including in Nature and Science, and leads global initiatives such as the Pacific Array Project.

报告摘要：

The seismic moment tensor (MT), which represents the equivalent body-force system of the seismic source, may exhibit non-double-couple components (NDCs) even for faulting on a planar surface if the source medium is anisotropic. We demonstrate that the systematic source-type dependence of the non-double couple components of the GCMT solutions for shallow sources (Kawakatsu, 1991, GRL) can be attributed to the presence of vertical transverse isotropy (VTI), characterized by an anisotropy parameter ξ>1. In fact, the VTI model of the PREM at a sub-Moho depth predicts the observed systematic NDC pattern quite well. It is important to recognize that this is an intrinsic property of the moment tensor in anisotropic media within the Burridge-Knopoff-type framework (Aki and Richards, 1980), rather than an artefact of unmodelled propagation effects. Given that most published moment tensor solutions (e.g., GCMT, W-phase, USGS, F-net, etc.) adopt this framework, direct interpretations assuming isotropic source structures—such as inferred slip directions—may be systematically biased. To evaluate the significance of this effect, it is crucial to quantify how realistic anisotropic structures can generate NDC components in MT solutions. We address this issue by incorporating lithospheric anisotropy derived from surface-wave tomography into moment-tensor modelling. Our approach accounts for both radial and azimuthal anisotropy in simulating MTs, including NDC components, under the assumption of planar faulting, following the framework of Kawakatsu (2024, BSSA). Regional analyses for areas exhibiting strong lithospheric anisotropy (e.g., Tibet) or distinctive tectonic settings (e.g., outer-rise regions of the Tonga subduction zone) reveal that anisotropy can exert a substantial and systematic influence on MT characteristics. Finally, we discuss prospects for an emerging research framework of “Anisotropic Earthquake Seismology,” which aims to integrate seismic anisotropy and MT analysis.