Nankai Trough Seismogenic Process Research Team
The main objective of Nankai Trough Seismogenic Process Research Team is to advance our knowledge on great earthquake process in the Nankai Trough seismogenic zone, which has caused and will repeatedly cause significant social and economic damages to Japan. For this purpose we focus on acquiring in-situ data through downhole measurements and experiments or core analyses. Through these studies, we firstly estimate how the strain, pore pressures or other critical properties accumulate. More specifically,
- Observation on seafloor deformation with respect to earthquake and tsunami
We collect the data on seafloor deformation (e.g. landslide, BSR, heat flow and seafloor pressure change). Through the analyses, we clarify how accretionary prism grows in geological time scale and interacts with the earthquake generation process.
- Research on earthquake preparation process through in-situ measurements
To understand the earthquake preparation process and to quantify the role of the pore fluid in faulting, we conduct in-situ measurements of stress field, seismic anisotropy, pore pressure and VLF events.
- Long-Term Borehole Monitoring (in collaboration with DONET)
We develop a Long-Term Borehole Monitoring System (LTBMS) and install the system into seafloor borehole. Through the detailed data processing, we evaluate the role of the LTBMS data by the theoretical analysis and numerical simulation for understanding earthquake preparation processes.
- Study for earthquake and crustal deformation predictions
We conduct the modeling of earthquake preparation cycle and the recurrence
by data assimilation with incorporating stress fields, deformation and
hydrological information. Also we determine the physical states and
properties at or near asperities in the seismogenic zone.
Subduction Geodynamics Research Team
Our team aims to demonstrate subduction zone geodynamics by revealing the origin and the evolution of subducting material from subduction input to deeper accretionary prism. We are focusing on Nankai Trough as the most important target, as well as the other subduction zones such as Costa Rica, Southern Kanto, Japan and Northeast (Tohoku) Japan for comparative study. We fully exploit the research expeditions of D/V Chikyu and other R/Vs of JAMSTEC for recovering samples from modern accretionary prisms in corporation with on-land field surveys for ancient analogues.
Below are the four main themes of our current researches:
On-going geological processes and evolution of accretionary prism
- Physical and mechanical properties of materials in accretionary prism
- Core-log-seismic integration in active margin
- Geochemistry and origin of subducting and accreted materials in sucduction zone
We do study SUBDUCTION GEOLOGY & GEOPHYSIS on a basis of Geology employing various interdisciplinary approaches among structural geology, rock physical properties, soil mechanics, rock dynamics, mineralogy, geochemistry, geomagnetism, core-log-seismic integration and so on.
Earth Evolution Modeling Research Team
Earthquakes and volcanoes release thermal and mechanical energies from Earth's interior. Understanding those processes in detail related to activities of deep Earth's interior, we are challenging to construct the 'Numerical Earth Model Suite' (NEMS), which can simulate from birth to present Earth's dynamics across 4.6 billion years. In order to build up the 'NEMS', we are developing 'state-of-the-art' numerical schemes and implementing various complicated physical and chemical processes. Here, with the 'NEMS', we would like to reproduce thermal and chemical evolution scenarios provided from various observational and geological data and ultimately to evaluate surface processes, i.e., earthquakes and volcanoes, coming from activities of deep Earth's interior.
Time variation of thermo-chemical structures in the mantle (Top:
Temperature and bottom: composition; Time goes from left to right).
Snapshots of the core formation simulation with free surface in three dimensions. In order to reproduce a possible scenario after the magma ocean event, we have simulated the sinking instability of iron-rich layer, which is represented by half cropped white iso-surface in the figure. The color on the ortho plane exhibits the mass density.
Snapshots of simulated fluid rope coiling event. We have developed low diffusive advection method and robust Stokes flow solver against viscosity jump. These methods are demonstrated by reproducing the fluid rope coiling event as this figure.
Nonlinear Dynamics and Its Application Research Team
In our team, the earth is thought as one of the large spatial nonequilibrium open system that heating from inner core and cooling from surface, and observation and modeling are made for various nonlinear phenomena of solid-earth. New ideas obtained from the study are applied to not only geoscience but also widely other region of science, and the developed science technologies are actively returned to industrial society. Specifically, we focus on
- constructing a dynamical model for plate subduction and revealing the mechanism of giant earthquakes by numerical simulation and analogue experiment using wide sandbox in various scales, core sample analyses obtained from drilling and at outcrops, and geophysical data analyses. This makes possible to predict maximum size of earthquakes at each subduction zone. A dynamical model for the physical processes prior to failure of rocks is constructed and the physics of preprocesses of earthquakes is revealed. Based on this, observable physical quantities necessary for forecasting these preprocesses are found and new methods to observe the quantities are developed.
- explaining the material dependence on macroscopic friction through a finite element modeling of shear loading experiments on a solid surface with many microscopic asperities. Though the effect of material properties on friction has not been explicitly included in many existing friction laws so far, the application of our numerical simulation to relative plate motions has the potential to provide a new interpretation linking the crustal material and earthquake generation.
- what's happen in actual plate subduction zone? To know this subject, we observe the rock on land and analyze drilled core sample from deepsea floor and experiment the rock-mechanics in laboratory. The rocks in the Boso area (central Japan) and the Shimanto area (southwest Japan) are exhumed from deep paleo-plate subduction zone, and they record the tectonic history and the evolution process from soft sediment to
seismogenic fault-rock. The information of the recurrent history and slip velocities of the submarine active fault are obtained from drilled core sample from deep seafloor. The experiment in laboratory using the clay mineral and calcite crystals give us the information of mechanical behavior of the geologic material. These result based on natural material contributes to the collaboration with the numerical simulation study.
- developing a new visualization system for three-dimensional geographical data obtained from various fields in geoscience by using of existing GIS software packages, API, and new developed standard for 3D programming with the browser, web GL. This system will be useful for researchers to interpret their own research results and provide new way to communicate their knowledge to public people.
- designing the unique algorithms of a discrete element method (DEM) for high performance computing by large-scale parallelization, and developing the software that is available on various platforms such as multi-core CPU, GPU, and supercomputer. Using the simulation technique, effective information on nonlinear dynamics such as physical quantities about pattern formation of powder arisen by multi-body interaction can be obtained. The commercial software of the high performance DEM named as "DEMIGLACE" produced by our research team has performance in introducing to many big private companies. Moreover, a new numerical model which can be described the dynamics of not only viscoelastic deformation but also fracture of individual irregular particles with elasto-viscoplastic constitutive law, and understanding the nonlinear physical phenomena of rocks and powder.