Development of a geophone-based ocean bottom seismometer in Taiwan

Taiwan is located near the edge of the continental Eurasia plate and the Philippine Sea plate, a quake-prone zone. Averagely speaking, out of 1000 sensible quakes detected per year, more than 50% of the epicenters are located in the surrounding waters. Therefore, there is a great need from our seismology community to deploy ocean bottom seismometer (OBS) to have high fidelity data, and widen the aperture of the observation as well. In this paper, we report the development of a “midweight” OBS called Yardbird which has one year deployment duration. We utilized the newly available ultra-low power MCU (micro control unit) and SD card to design a compact data logger. The response of 4.5-Hz geophones was extended to 3 s and used as the seismic sensors. With the compactness of the sensor module, it enables us to design a compact dual-axis motor-driven stage to level the vertical component to be less than 0.1 degree with respect to the gravity. Currently, the total power consumption of Yardbird OBS is less than 0.2 mW for three channels. A pilot experiment and was conducted in the south western Okinawa trough in 2010. During the three months experiment, an array of five Yardbirds captured and deep quakes from the subducting oceanic plate. The results prove that the performance of Yardbird OBS suffices the basic needs of seismic research.