ANOMALOUS VLF SUBSURFACE ELECTRIC FIELD CHANGES PRECEDING EARTHQUAKES

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概要

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• The vertical component of the subsurface electric field have been observed at seven stations in central Japan in order to find precursory phenomena effective for the prediction of earthquake and volcanic eruptions. Electric fields were measured by an antenna made by using the casing pipe in boreholes ranging from about 100 to about 800 m deep. Two horizontal components of electric field changes were also measured for reference. Fields were measured in three frequency bands : 0〜0.7 Hz, 0.01〜0.7 Hz (ULF), 1kHz〜9kHz (VLF). The amplitude of VLF signals and the waveform of ULF signals were recorded by analog recorders at speeds of 2〜20 cm/h at the observation site, and by sending data over commercial telephone lines with a personal computer at Tsukuba. During observations over several years signals of VLF and ULF bands of the vertical component revealed changes that were of interest for earthquake prediction. These signals had rarely been observed simultaneously at different observation sites. Here analysis is focused to characteristics of the particular pattern of intermittent signals in the VLF band observed at Tsukuba. Anomalous changes in the pattern of intermittent signals in the VLF band had been found to occur during the period of the swarm activity off east Izu peninsula in 1989. The same kind of anomalous changes occurred within about 2 weeks before earthquakes with magnitude M≳5.0, focal depth H≲80 km and epicentral distance Δ≲200 km occurring mainly in land areas. Although the relationship between the changes and the swarm activities was inferred only from the point of view of the sequental occurrence of the two phenomera without any direction-finding measurements, the relationship was confirmed by the reoccurrence of the same particular electric field changes at the times of repeated swarm activities.

• 独立行政法人防災科学技術研究所の論文
• 1995-03-31

著者

• FUJINAWA Yukio

  National Research Institute for Earth Science and Disaster Prevention

• Takahashi K

  Communications Res. Lab.

• TAKAHASHI Kozo

  Communications Research Laboratory (CRL)

• Fujinawa Y

  National Research Institute For Earth Science And Disaster Prevention

• TAKAHASHI Kozo

  Communications Research Laboratory

関連論文

• Electric Field Variations Related to Seismic Swarms
• Studies of the Georesistivity Structure in the Central Part of the Northeastern Japan Arc
• Some Features of the ULF Band Electromagnetic Field Changes Related with Earthquake Swarms(2) (〔2000年 CONDUCTIVITY ANOMALY研究会〕) -- (電磁気的手法による地殻活動監視と予測)
• ULF-bands Electric Field Changes Related to the Seismic Swarm
• Conductivity distribution and seismicity in the northeastern Japan Arc
• 2-D georesistivity structure in the central part of the northeastern Japan arc
• Local Galvanic Distortions in the Central Part of North-Eastern Japan(Part1)
• An evaluation of VLF band electromagnetic field phenomena using a neural network
• Modeling of Non-Stationary Electrokinetic Effect in a Conductive Crust
• Experiments to Locate Sources of Earthquake-related VLF Electromagnetic Signals
• ANOMALOUS VLF SUBSURFACE ELECTRIC FIELD CHANGES PRECEDING EARTHQUAKES

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