Takao Aizawa

Monitoring a Building Using Deconvolution Interferometry. I: Earthquake‐Data Analysis

Abstract For health monitoring of a building, we need to separate the response of the building to an earthquake from the imprint of soil‐structure coupling and from wave propagation below the base of the building. Seismic interferometry based on deconvolution, where we deconvolve the wave fields recorded at different floors, is a technique to extract this building response and thus estimate velocity of the wave that propagates inside the building. Deconvolution interferometry also allows us to estimate the damping factor of the building. Compared with other interferometry techniques, such as cross‐correlation and cross‐coherence interferometry, deconvolution interferometry is the most suitable technique to monitor a building using earthquake records. For deconvolution interferometry, we deconvolve the wave fields recorded at all levels with the waves recorded at a target receiver inside the building. This receiver behaves as a virtual source, and we retrieve the response of a cut‐off building, a short building that is cut off at the virtual source. Because the cut‐off building is independent from the structure below the virtual source, the technique might be useful for estimating local structure and local damage. We apply deconvolution interferometry to 17 earthquakes recorded during two weeks at a building in Fukushima, Japan, and estimate time‐lapse changes in velocity and normal‐mode frequency. As shown in a previous study, the change in velocity correlates with the change in normal‐mode frequency. We compute the velocities from both traveling waves and the fundamental mode using coda‐wave interferometry. These velocities have a negative correlation with the maximum acceleration of the observed earthquake records.

The Evaluation Ahead of Tunnel Face Using Seismic while Drilling

The seismic refraction method from the ground surface has routinely been applied to planning of tunneling as a preliminary survey. A tunnel support pattern is designed based on elastic wave velocity of the mountain obtained by seismic refraction survey. Where overburden on a tunnel is thick, the resolution in velocity structure obtained by this technique becomes poor. A survey ahead of the tunnel from the tunnel face while boring is considered to be effective compared with a ground seismic survey. Two methods are generally used in the survey ahead of the tunnel from tunnel face: one by seismic reflection such as the Tunnel Seismic Prediction (TSP) and Horizontal Seismic Profiling (HSP) methods and the other by drilling data called the Drilling Survey System (DRISS). The authors applied a new exploration method by the use of drilling vibration data called TSPD (Tunnel Seismic Probe Drilling) to estimate elastic wave velocity distribution ahead of the tunnel face. Unlike Seismic While Drilling (SWD) commonly used for ahead of drilling in the petroleum exploration, this method investigates the nature of the rocks between the bit of pilot drilling and the cutting edge of the tunnel. The field tests of TSPD were carried out at a road tunnel. The first test helped to identify and correct the problems in data acquisition. The second field test confirmed improvement of S/N ratio of the waveform, and evaluated the elastic wave velocity structure ahead of the tunnel face.

Experimental study of quartz crystal gravity sensor by MEMS technology

Quartz sensor is promising as a gravity sensor. This paper describes an improved technique of gravity sensor, based on the VCXO and crystal properties from the principle of the quartz motion sensor. The size of prototype sensor is around 27.0×12.0×1.0 mm. The sensor is used in the experiment, which give the gravity change. The experimental results show the relationship between gravity change and load resonant frequency. Then, from these results, we show that the load resonant frequency changes in direct proportion to gravity change.

Seismic Tomography Investigation in 140m Gallery in the Horonobe URL Project

The Japan Atomic Energy Agency (JAEA) is conducting the Horonobe Underground Research Laboratory (URL) Project to enhance reliability of disposal technologies through investigations of the deep sedimentary environment at Horonobe, Hokkaido, Japan. An excavation disturbed zone (EDZ) is expected to occur around an underground gallery when it is excavated for disposal of radioactive waste. A number of in-situ experiments for rock properties and extent of the EDZ were carried out at the “140m Gallery” at a depth of 140m below the surface of the Horonobe URL. One of the experiments is seismic tomography survey using a hammer seismic source. Its observation area was 3m square on the horizontal plane along the sidewall of the 140m Gallery. The measurement was repeated with the progress of excavation of a tunnel. In this experiment, a decrease of seismic velocity in the rock around the new tunnel and its distribution were observed. It is considered that seismic tomography investigation captured the EDZ developed around the tunnel.

Detecting Abandoned Air-Raid Shelter Using The S-Wave Seismic Reflection Method

A high-resolution S-wave survey was conducted over a known air-raid shelter to evaluate its effectiveness in detecting an underground void. It is a part of a government project of prevention of accidents of caving shelters. The survey used a mechanical impactor powered by an air compressor as the source and a purpose-built S-wave land streamer. The good quality of the data acquired warranted a focused processing to the depth of the target, and migrated stack and instantaneous amplitude sections show the target clearly.