Highly sensitive multi-component long period acceleration measurment

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Measurments of long period accerelation are important to detect weak signals generated by deformations in the Earth's core. We performed studies of long period accerelation measurment of 3 components with high sensitivity, by modifying an existing broad band seismoneter STS2, our altimate goal is to develope a 3 component accerelerometer which can detect signals at abount 1000 seconds as small as 1 nanogal. We deployed the modified sensor together with a broadband seismoneter (STS1) in a laboratory within a geodetic measurment tunnel at Esashi, which belongs to National Astronomical Observatory. Mizusawa Observation Center. By 10rgaring outputs from the modified sensor and STS1, and calibrating the modifiod sensor with a remote control techinique, we confirmed that modified sensor has a linearity within a dynamic range as large as 100db, are comporable to the STS1 in a frequency band as high as 5mHZ,bat is inferior to the STS1 in a frequency band longer than 5mHZ.We also performed theoretical considerations on the effects of tenperature and pressure fluctuations on the accerelometer, and summarized methods to surpress such effects to measure long period accerelation as small as 1 nanogal.