Publication Date:
2000
Description:
Nagao et al. monitor the geoelectric potential difference between pairs of
electrodes (or dipoles) buried at about 2 m depth at several stations in Japan for the
purpose of observing co-seismic signals. Studying several recent earthquakes, they
report that the signals commence not with the origin time of the earthquakes but with
the arrival time of seismic waves. They find two types of co-seismic changes:
offset/decay type, which last long after the seismic vibrations cease, and oscillatory
type, which decay with the seismic vibrations. They also find that the amplitude of the
co-seismic signals does not scale with the dipole length. Also in this issue, Hayakawa
et al. [1531] investigate ultra low frequency (ULF) electromagnetic emissions associated
with a large earthquake that occurred at Biak Island, Indonesia, in February 1996.
Examining data from Biak and Darwin, they find that the ULF emissions observed about 1.5
months before the quake serve as a precursory signature of the earthquake.
Keywords:
Earthquake
;
Electromagnetic methods/phenomena
;
0699
;
Electromagnetics
;
General
;
or
;
miscellaneous
;
7223
;
Seismology
;
Seismic
;
hazard
;
assessment
;
and
;
prediction
;
9320
;
Information
;
related
;
to
;
geographic
;
region
;
Asia
;
9810
;
General
;
or
;
miscellaneous
;
New
;
fields
;
(not
;
classifiable
;
under
;
other
;
headings)
;
GRL
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