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The GEAT department welcomes Dr. Hiroko Kitajima from Texas A & M University as our next seminar speaker.

Title: In-situ stress and pore pressure in the Nankai Trough subduction zone

When: Tuesday, November 7 @ 4:10 pm
Where: 2050 Agronomy Hall

Abstract: Understanding the mechanics of plate boundary earthquakes requires a sound investigation of in-situ stress condition and deformation processes. Strength and slip behaviors of subduction megathrusts are controlled by the physical properties and stress state of not only the fault zones themselves but also the adjacent wall rocks in overriding and subducting plates. Despite the importance, stress and pore pressure are particularly difficult to measure directly, and quantitative constraints are rare.

The Nankai Trough is located off the southwest coast of Japan, where devastating earthquakes and tsunamis recur every 150-300 years. The Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) has carried out since 2007 to drill, sample, and instrument the seismogenic plate boundary fault. To date, multiple non-riser boreholes have drilled into the shallow portion of accretionary prism and an incoming plate, and a deep riser borehole at Site C0002 has drilled into the Kumano forearc basin and the underlying accretionary prisms down to 3 km and will be extended to reach the plate boundary fault at ~5 km in 2018-2019. In this seminar, I present my collaborative research on quantification of in-situ stress, pore pressure, and rock strength at Site C0002. We quantify them by integrating drilling data, geophysical logging, downhole measurements, and laboratory experiments, and using empirical relations that describe sediment compaction behavior as a function of loading path. We find that the Kumano Basin is loaded in uniaxial vertical strain conditions in a normal faulting regime, whereas the prism below is loaded with greater differential stress due to tectonic loading, has a modestly elevated pore pressure, and lies in a strike-slip faulting regime. This can be reconciled with slip on the megathrust fault if the horizontal stresses vary with time or depth, and/or if shear stress along the megathrust is low.

Bio: Dr. Hiroko Kitajima studies deformation processes and mechanisms of rocks through experimental rock deformation that can simulate in situ pressure, temperature, and strain rate conditions. Her research focuses on understanding the physics of earthquakes; the micromechanics of compaction and shear deformation and on granular materials at high strain rates and high pressures; and interaction between deformation and fluid flow. She combines lab experimental work with numerical modeling, geophysical data, and fieldwork. She and her research group members have been involved in fault zone drilling projects in both Integrated Ocean Drilling Program (IODP) and International Continental Scientific Drilling Program (ICDP).