S33B-2770
Observation of Magnetic Signals from Earthquake Faulting Using High-resolution HTS-SQUID Magnetometer: Feasibility of Super-early Warning of Earthquakes

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Yuta Katori1, Kan Okubo1, Tsunehiro Hato2, Akira Tsukamoto2, Keiichi Tanabe2, Nobuhito Onishi3, Chikara Furukawa3, Shinji Isogami4 and Nobunao Takeuchi5, (1)Tokyo Metropolitan University, Tokyo, Japan, (2)International Superconductivity Technology Center, Kanagawa, Japan, (3)Tierra Tecnica, Tokyo, Japan, (4)Fukushima National College of Technology, Fukushima, Japan, (5)Tohoku University, Sendai, Japan
Abstract:
Electromagnetic changes associated with earthquakes have been investigated previously. Our research group has also employed the magnetometers for seismomagnetic observations since March 2004.

Our observation site happened to be situated at an epicentral distance of 26 km from the 2008 Iwate-Miyagi Nairiku earthquake ofM7.2, NE Japan. In this earthquake, we have reported successful observation of “co-faulting" Earth’s magnetic field changes (Okubo et al., 2011 EPSL). Magnetic fields began to change almost simultaneously with the onset of the earthquake rupture and grew before the first P wave arrival. Such magnetic signals are most probably generated by the changing stress field due to earthquake rupturing, i.e. the piezomagnetic effect.

On the other hand, this observation result suggested that the geomagnetic variation signal accompanying fault movement, whose sources are the piezomagnetic effects, is very small. The observed change of geomagnetic field might be approximately less than several hundred pico-tesla.

Therefore, to obtain more observation data of “co-faulting" magnetic field change, development of a higher-sensitive magnetometer system is very important. Then, our research group tried to develop the HTS-SQUID (high-temperature-superconductor based superconducting-quantum-interference-device) magnetometer systems for high-resolution observation of Earth’s magnetic field. Since March 2012 we have introduced long-term precise geomagnetic observations using the HTS-SQUID magnetometer system Unit No.1 (mark I) at Iwaki observation site (IWK) in Fukushima, Japan. Additionally, since October 2014, we have also introduced the new HTS- SQUID magnetometer system Unit No.2 (mark II). The sampling interval of the magnetometers is 0.02 sec (50Hz). The system clock has been synchronized by use of GPS signals. A high-resolution accelerometer is also installed at observation point.

In this study, we show the observation results of geomagnetic field changes associated with the earthquake using our high-resolution HTS-SQUID magnetometer systems. Further efforts in the future would support a feasibility of a new system for a super-early warning of destructive earthquakes with the combined seismic-magnetic measurements.

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