Earthquake Engineering

The objective of earthquake engineering is to prevent or mitigate disasters, especially damages to structures, caused by earthquakes. Academic and practical methods of simulating or evaluating 1) design earthquake motion, 2) response, 3) seismic performance, 4) damage, or 5) risk, are developed and improved for application to seismic design, repair and strengthening of structures and soils. The methods of the research includes post-earthquake damage survey, strong motion observation, shaking table test, static collapse test (Fig.1), analysis and theory.

Seismic performance test of reinforced concrete wall at ERI, November 2004

Applied Seismology Laboratory and Strong Motion Observation Office

We are working for various problems related to seismic ground motion. Our recent research subjects are 1) Modeling earthquake faults as sources of seismic ground motions (Rupture process of the Miyagi-ken Hokubu earthquake). 2) Exploring underground structures that influence seismic ground motions (Tomographic analysis of explosion and gravity data). 3) Simulation of seismic ground motions by the source model in the structure model (Computation of long-period ground motions from the Tokachi-oki earthquake. 4) Monitoring of seismic ground motions by seismometer arrays and temporary observations after large earthquakes (Discovery of complex surface wave propagation in the Kanto basin).

Slip distribution on the curved fault surface of the 2003 Miyagi-ken Hokubu earthquake

Numerical simulation of long-period ground motions from the 2003 Tokachi-oki earthquake

Strong Motion Seismology

Our recent subjects for preventing and reducing earthquake damage are 1) to assess site characteristics during earthquakes and 2) to establish the strong motion database. The method of array analysis for microtremors is especially superior in determining S-wave velocity model with low cost.

Structure model determined by microtremors (right) compared with the results by reflection survey (left) and sonic log　(center)

An example of data retrieval from the strong-motion database using map image

Historical Earthquakes

There are some descriptions in the old documents that an earthquake occurred with damage. For example, the distributions of the seismic intensities of the 1751 and the 1828 Echigo earthquake can be given by these descriptions, and we can recognize the source area of the 2004 Mid Niigata earthquake occupies the area between the source areas of those two historical earthquakes.

Distribution of the detailed seismic intensity of the 1828 Echigo-Sanjo earthquake and source regions of the 1751, 1828, and 2004 earthquake.

Computer Simulation of Strong Ground Motion

In order for predicting strong motions expecting for future large earthquakes, computer simulation of seismic wave propagation has been conducted using the Earth Simulator. Simulation result demonstrating that large shaking starts at Osaka and Nagoya after 40 s from the earthquake occurs, and at 90 s in Tokyo. Significant amplification in ground motion arises in the cities, resulting in relatively longer period shaking around 6 to 12 s in the center of Tokyo.

Computer simulation of strong ground motion during a Tokai hypothesis earthquake. Source and structural model (top) and snapshot of wave

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