A densely distributed high-sensitivity seismograph network in Japan:Hi-net by National Research Institute for Earth Science and DisasterPrevention

Seismic observations to retrieve various information from the Earth are the basis of seismology. A seismic observation system requires various technologies for vibration sensors, analog-and-digital measurement, data transmission, and computing for mass data analysis, for example. New developments in technology are adopted whenever possible in the construction of seismic observation systems. In Japan, after the disastrous Kobe Earthquake in 1995, a high-density and high-sensitivity seismograph network was constructed. The seismic network, called the National Research Institute for Earth Science and Disaster Prevention (NIED) Hi-net, uniformly covers the Japanese Islands with a spacing of 20–30km. As a result, the detection capability for microearthquakes has been greatly improved, and various research using Hi-net data has indicated that this seismic network has a great potential to resolve the underground structure and various geophysical phenomena as a radar-array oriented toward the Earth. Equipped with modern standard techniques, the Hi-net system is designed to be able to be smoothly upgradeable in the future.