Research interests

Overview

The basic problem is how we can approach underground as a heterogeneous composite material by using wave phenomena (mainly seismic waves) with a finite frequency band. Under this condition, my research focuses on how we can recognize targets underground through modeling, measurement, data analysis, signal extraction, and interpretation.

Themes

Subsurface imaging using seismic waves

Obtain subsurface structure images and properties using natural earthquakes (aftershocks, swarms, teleseisms) and artificial earthquakes (using active sources)

• Development of seismic data processing
  • Analysis methods applicable to sparse, inhomogeneously distributed stations that are typical to earthquake observations.
  • Application to refined data analysis method using waveform information to earthquake data for higher accuracy and higher resolution.
• Seismic reflection and interferometric imaging, receiver function analysis of earthquake data.
  • Imaging of plate boundary using teleseismic records.
  • Imaging in the crust using local and regional earthquake records.
  • Imaging of basin structure using strong motion records.
• Development of seismic data processing method
  • Wavefield migration/imaging
  • Full-wave inversion/tomography

Accurately-Controlled, Routinely-Operated Signal System (ACROSS) and active monitoring in the Earth

ACROSS sends weak seismic signals that repeat exactly for a long time to monitor the variation of subsurface states using time-lapse measurement

• Tokai Monitoring Experiment
  • Capturing reflection signal from the plate boundary and monitoring its variation.
  • Observation targeted at the next Tokai Slow-Slip Event.
• Monitoring fault healing after the rapture
• Monitoring volcanoes
• Development of borehole-type seismic sources

Sensing subsurface (structure and physical properties, except heterogeneity, discontinuity, and fluid) using wave phenomena.

• Extraction of information useful to monitor subsurface properties contained in observed waveforms
• The Connection between the information with physical structure and state of the target via physical model
  • Wave propagation and fracture models
  • Physical model and wave propagation of plate boundary
• What and how we can see (or can not see) in the Earth using wave phenomena
• wave propagation, imaging, and inversion.
• simulation of the seismic and electromagnetic wavefield.

Students' Thesis

Seminars

• 2023: Ground vibration measurement at Nagoya University Higashiyama Campus.
• 2021: Seismic imaging of subsurface structure: current and future.
• 2019: Passive seismic imaging of crustal structures based on reverse-time migration.
• 2018: An alternative approach of passive seismic imaging based on wavefield extrapolation.
• 2016: Seismic survey of crustal structure, mainly fault structures, in the eastern?central Shizuoka, Japan.

• 2014 (U. Tokyo): Seismic imaging and monitoring of subsurface structure and properties, its current status and future perspective.

• 2013: A guide (as comprehensive as possible) to seismic waveform inversion as a structure estimation problem based on wave theory.
• 2012: An approach from seismic wave propagation to the problem of estimation and monitoring of fault strength and stress accumulation at a plate boundary.
• 2010: A very easy? introduction of seismic interferometry.
• 2009: Imaging subsurface structure by use of earthquakes --- commons and differences between the natural and artificial seismic source ---.
• 2007: Possibility of active monitoring of discontinuity, inhomogeneity and scatterers by use of seismic wave (II) --- wavefield modeling ---.
• 2006: Possibility of active monitoring of discontinuity, inhomogeneity and scatterers by use of seismic wave.
• 2006: Current status of ACROSS research in Nagoya University --- Towards Tokai Monitoring Experiment ---.
• 2005: What should be considered to visualize and monitor underground by use of seismic wave --- Waveform imaging for dummies ---.
• 2004: What should be considered to survey and monitor plate boundaries and faults (and contribution of fluids) by use of seismic wave --- wave propagation, physical properties and physical models---.
• 2003: Waveform inversion of crosswell seismic data and its application to methane hydrate production monitoring.