高機能小型オフラインデータロガーを用いた高密度地震観測システム

抄録

We developed a small-size, light weight, and high-performance data logger, that can be used for crustal scale refraction/reflection experiments, in which hundreds of instruments are deployed over several hundred kilometers. Our new data logger has a single-channel 24-bit analog-to-digital converter. The timing is corrected automatically by a built-in GPS receiver, and its accuracy is always within an error of 1 ms. The waveform data are stored in a NAND-type flash memory with capacity of 128MB. Recordings are performed based on a programmable schedule. The maximum continuous recording period is about 96 hours at a sampling rate of 125 Hz. The maximum sampling rate is 1000Hz. The logger has a dimension of 200mm×120mm×75mm, and it weighs 1.5kg including four 1.5V D-size dry cells. The small size and light-weight body enhance portability and manageability. Parameters for recording such as sampling rate and schedule of observation are easily set through a Universal Serial Bus (USB) cable by a laptop computer. In order to easily operate hundreds of loggers, we have developed a special container for transportation, storage, and control of logger. The container stores and controls up to 10 loggers, which are simultaneously operated by the computer. During deployment of the logger, its status including GPS clock, and geophone connection and orientation is automatically checked and displayed by a Light Emitting Diode (LED). After the observation, the loggers are restored to the container and the data are downloaded to the computer. We conducted a seismic reflection experiment on the eastern side of Mt. Fuji, in central Japan. Eight people deployed 148 data loggers in a day and recorded seismic signals from explosive sources using a standard 4.5Hz geophone. We obtained data with well-calibrated time information and high signal-to-noise ratio. The newly developed data logger is confirmed to be useful to obtain spatially dense seismic data with only a small number of crews.