A study on the association of ionospheric perturbations with the earthquakes in Japan, as based on t

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A study on the association of ionospheric
perturbations with the earthquakes in Japan, as
based on the JG2AS signal observation at
Moshiri(Hokkaido) and at Kamchatka(Russia)
The University of Electro-Communications
Shinko Maekawa, Masashi Hayakawa
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Introduction
VLF/LF subionospheric radio wave monitoring is
widely used in recent years for analysis of
earthquake preparatory process. There are two
possible methods for such an analysis.
?Terminator time method
(Hayakawa et al, J.Comm.Res.Lab,43,160-180,1996)
?Analysis of nighttime fluctuation of VLF signal
amplitude and/or phase.
(Shvets et al, J.Atmos.Electr,22,2,87-99,2002)
VLF signal (Amplitude)
Night time
Terminator time
In this work, we present LF signal anomalies
associated with Tokachi-oki earthquake(25
Sep,2003, M8.3), focusing our attention to
nighttime LF signals.
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Description of measurements
Path
JG2AS- KAM(Kamchatka)
Distance 780km
JG2AS-HOK(Hokkaido)
Distance 2300km
JG2ASJapan time standard transmitter(40kHz)
Sampling rate
20s
Tokachi-Oki EQ
Sep 25, 2003 at 1950 UT
Period
Magnitude 8.3
Aug. 2003- Oct 2003
Depth 27 km
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Example of daily original data(Sep.2003)
HOK
KAM
KAM and HOK amplitudes fluctuated before the
earthquake.
We applied signal processing to above LF signals
to estimate signal fluctuation quantitatively.
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Data Processing
(Focus our attention to night time fluctuation)
?Remove stationary trend(Ex. Seasonal)
Ak(t) Original amplitude data
ltAk(t)gtrunning mean of 5 days
Night time fluctuation is emphasized.
?Estimate signal fluctuation by dA(t)
Signal fluctuation defined as
We compared the time series of Signal fluctuation
with Tokachi EQ.
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Results?
Signal fluctuation around Tokachi EQ
Aug.
Oct.
Maxima in signal fluctuation take place 5-8 days
before EQ.
Signal fluctuation increased for both signals at
HOK and at KAM 5-8 days before EQ.
We checked details of KAM and HOK night time data
5-8 days before EQ.
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Results?
Original data and spectral intensity around
Tokachi EQ
HOK
KAM
KAM and HOK spectral intensity increased with
period of 0.5h-3h (in the frequency range of
gravity wave) 5-8 days before EQ.
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Results?
Cross-correlation between KAM and HOK original
data
Example of Cross-correlation
Cross-correlation around EQ
Sep.16
date
Sep.
EQ
Stronger correlation between HOK and KAM data.
Cross-correlation analysis indicates stronger
correlation between HOK and KAM data before EQ
with a time difference about 1 hour, KAM path
leads.
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Conclusion
About 5-8 days before Tokachi-oki earthquake, we
found interesting phenomena mentioned below.
Signal deviation increased in the signals
observed at HOK and KAM 5-8 days before EQ.
KAM and HOK spectral intensity increased with
period of 0.5h-3h (in the frequency range of
gravity wave) 5-8 days before EQ.
Cross-correlation analysis indicates stronger
correlation between HOK and KAM data before EQ
with a time difference about 1 h, KAM path
leads.
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Thank you for your attention.
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Terminator time analysis
(Relation between TT variation and Tokachi-oki
earthquake )
Seasonal variation
Short-period variation
Terminator time variation increase in winter
season.
Tokachi-Oki EQ
Terminator time seems to fluctuate around EQ,
however
We cannot separate seasonal variation and TT
anomaly caused by EQs
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Statistic study of Terminator time
on East-West propagation path
Constituent element of TT
Annual variation
Annual variation
Seasonal variation
Short period variation
(associated with EQ?)
Short period variation
Seasonal variation
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East-West and North-South propagation?
East-West
North-South
Daily variation
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East-West and North-South propagation?
North-South
East-West
Short period variation
Terminator time distribution
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Signal fluctuation
period from Jan-Oct. 2003 at KAM
Signal response depend on season.
(associated with AGW seasonal trend?)
(A.V.Shvets et al,2004)
EQ Mgt5 occurred during 2003
(Depthlt50km,3rd Fresnel zonecircle of 150 km
around Tx and Rx)
This graph shows stronger correlation between
signal fluctuation at KAM and EQ event.
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Intensification of 16-days oscillations before
Tokachi EQ
Tokachi EQ
16-days oscillations increased before EQ.
Frequency range of planetary wave
The stronger fluctuation was caused by seasonal
variations of the planetary wave influence onto
the ionosphere response on AGW.
AGW can be generated by seismic process.
(A.V.Shvets et al,2004)