17:15 〜 18:45
[SSS03-P11] High-resolution Tomographic Imaging of the Indo-Australian Plate with Multimode Surface Waves
キーワード：Seismic tomography, Indo-Australian Plate, Surface wave, Multimode phase speed, Indian Ocean
Understanding the Indo-Australian coupled plate dynamics has been an interesting and challenging geophysical phenomenon in geosciences. Since the separation from Antarctica, the Australian plate has been drifting northward (6-7 cm/year), while its counterpart India moves in the northeast direction with a comparatively slower velocity (3.7 cm/year), colliding with the Eurasian continent. Such a differential motion leads to the motivation of further study to better understand the coupled Indo-Australian geodynamics. Seismic surface waves are a powerful tool to achieve enhanced tomography models in oceanic regions, even with limited station coverage. With recent enhanced seismic networks in the southern hemisphere, we can reconstruct the high-resolution tomographic images in the Indian Ocean with enhanced vertical resolution by incorporating higher modes that are more sensitive to the deeper mantle structure.
In this study, we have used many regional seismic networks in and around the Indian Ocean to retrieve multimode phase speed maps of Love and Rayleigh waves for the fundamental mode and up to the 4th higher modes beneath the Indo-Australia plate. We have employed automated multimode phase speed measurements with a fully non-linear waveform inversion by Yoshizawa & Ekström (2010). With an enormous data set of about 22 years, we have compiled a large number of regional surface-wave paths, including 63,000 and 26,000 ray-paths for the fundamental-mode Rayleigh and Love waves, respectively, over a wide period range (30 s - 200 s). Similarly, more than 16,000 paths are achieved for successful analysis of higher modes from both Rayleigh and Love waves. Preliminary high-resolution phase speed maps beneath the Indo-Australia plate indicate some intriguing structural features, such as the relatively slow velocity anomaly along the Ninety East Ridge and the relatively faster anomaly in the shallow upper mantle underneath the Australian Antarctic Discordance. The multimode phase speed maps will be the basis of a 3-D radially anisotropic model under the Indian Ocean, which will be investigated in the future.
In this study, we have used many regional seismic networks in and around the Indian Ocean to retrieve multimode phase speed maps of Love and Rayleigh waves for the fundamental mode and up to the 4th higher modes beneath the Indo-Australia plate. We have employed automated multimode phase speed measurements with a fully non-linear waveform inversion by Yoshizawa & Ekström (2010). With an enormous data set of about 22 years, we have compiled a large number of regional surface-wave paths, including 63,000 and 26,000 ray-paths for the fundamental-mode Rayleigh and Love waves, respectively, over a wide period range (30 s - 200 s). Similarly, more than 16,000 paths are achieved for successful analysis of higher modes from both Rayleigh and Love waves. Preliminary high-resolution phase speed maps beneath the Indo-Australia plate indicate some intriguing structural features, such as the relatively slow velocity anomaly along the Ninety East Ridge and the relatively faster anomaly in the shallow upper mantle underneath the Australian Antarctic Discordance. The multimode phase speed maps will be the basis of a 3-D radially anisotropic model under the Indian Ocean, which will be investigated in the future.