Hiroshi Iitaka

Remote Detection of the Electric Field Change Induced at the Seismic Wave Front from the Start of Fault Rupturing

Seismic waves are generally observed through the measurement of undulating elastic ground motion. We report the remote detection of the Earths electric field variations almost simultaneously with the start of fault rupturing at about 100 km from the fault region using a special electric measurement. The rare but repeated detection indicates that the phenomenon is real. The characteristic time of diffusion is almost instantaneous, that is, less than 1 second to travel 100 km, more than ten times faster than ordinary seismic P wave propagation. We suggest that the measured electric field changes are produced by the electrokinetic effect through increased pore water pressure of the seismic pulse. It is also suggested that the long range propagation is due to the surface wave mode confined near the interface of the different conductivity. The length scale of the finite strength of the electric field is 16 km, 160 km for electric conductivity of 0.01, 0.001, Sm−1, respectively. This phenomenon suggests a new seismic sensing method and a new earthquake early warning system providing more seconds of lead time.

Vector HTS-SQUID system for ULF magnetic field monitoring

Anomalous magnetic field variations in the ultra low frequency (ULF) band were observed as precursory phenomena of earthquakes. We constructed a portable monitoring system by using HTS-SQUIDs for measuring the ULF environmental vector magnetic field. The operation of the system was verified at Mt. Bandai, an active volcano. The system safely worked over 100 hours on batteries. We have achieved long term monitoring with the system at the National Institute of Advanced Industrial Science and Technology (AIST) from February 7 to March 22 of 2002 using AC power. The measured magnetic field variations were compared with groundwater level, electric field and geo-electric pulse current variations measured at AIST in order to investigate the source of magnetic field radiation found during the long term monitoring.

Development of the HTS-SQUID system for measuring ULF band magnetic field changes related with earthquakes

The electromagnetic field change in the ultra low-frequency (ULF) band was observed in order to investigate the precursory phenomena of crystal activity such as earthquakes, volcanic eruptions and landslides. The measurements are conducted to make clear the generation mechanism of the anomalous electromagnetic field occurring before and during these disastrous phenomena. We have constructed a portable system with a HTS-SQUID magnetometer for the observation of the ULF magnetic field. A dewar that kept liquid nitrogen for about three weeks was developed for a long recording period. The performance of the system was tested at Mt Bandai, an active volcano in Fukushima prefecture, Japan. The system worked for 36 hours. Some anomalous magnetic field changes were recorded before and after the volcanic earthquake which occurred during the field test.