金曜日セミナー：着任セミナー (2019年10月11日) 仲田 理映 氏 (地震予知研究センター 助教)
Seismic waveform inversion and monitoring of Earth’s upper crust
Seismic full waveform inversion and monitoring methods provide subsurface visco-elastic models and their time-lapse changes at an unprecedented level of spatial resolution. The keys for the improvements are to use waveform data (i.e., increased data amount), and to numerically solve the wave equation at finite frequencies (i.e., more rigorous physics) at a cost of acquisition demands, computational costs, and complexities in the inverse problem. The resulting distributions of the Earth elastic properties have been critical for interpreting geological structures, and fluid/stress properties at various scales ranging from near-surface engineering scale (0.01-0.10 km), to exploration of natural resources (0.1 to 10 km), to crustal-scale investigations (10-100 km). For example, a P-wave velocity model obtained from the Ocean Bottom Seismograph dataset in the Nankai subduction zone has delineated extensive low velocity zones and depicted a more complete splay fault system. The model has been critical in deriving a pore-pressure distribution and contributed to a drilling plan. When applied to a near-surface water injection, the waveform invention method successfully has tracked transient velocity changes of less than 1 %. In this talk, I will review theory and current state of seismic waveform inversion and monitoring methods, show the case studies, and envision future research directions.