Our research group reported successful observation of "co-faulting" Earth's magnetic field changes due to piezomagnetic effects caused by earthquake rupturing in 2008 Iwate-Miyagi Nairiku earthquake of M7.2 using geomagnetic observation system with fluxgate magnetometers. This is an important finding; the electromagnetic fields propagate from the sources to the observation site at speed of ca. 3.0 × 10 8 m/s in the crustal materials. Further efforts could lead us to a new system for super-early

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... warning of earthquake detection with the geomagnetic signal. On the other hand, the observed result with the earthquake was suggested that the geomagnetic field change accompanying fault movement, whose sources are the piezomagnetic effects, is very small and short term; therefore development of a high-resolution magnetometer system is very important. To solve this problem, we first developed long-term precise geomagnetic observations using high-temperature-superconductor based superconductingquantum-interference-device (HTS-SQUID) magnetometer system. The HTS-SQUID magnetometer system had never achieved for high-resolution geomagnetic observations in outdoor field. Since March 2012, we have observed the geomagnetic field using a first HTS-SQUID magnetometer at Iwaki observation site (IWK) in Fukushima, Japan. In this study, comparison between the introduced HTS-SQUID magnetometer and conventional flux-gate clarified that the HTS-SQUID magnetometer in our system has higher resolution of magnetic field observation.