The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation
By using the network observation of subionospheric VLF/LF signals in Japan and in Russia, we have found a significant ionospheric perturbation prior to the recent 2011 March 11 Japan earthquake (EQ) in the off-sea of the Tohoku area, which was an exceptionally huge plate-type EQ. A remarkable anomal...
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| Опубліковано в: : | Радіофізика та електроніка |
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| Дата: | 2012 |
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Інститут радіофізики і електроніки ім. А.Я. Усикова НАН України
2012
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| Цитувати: | The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation / M. Hayakawa, Y. Hobara, A. Rozhnoi, M. Solovieva, K. Ohta, J. Izutsu, T. Nakamura, Y. Yasuda, H. Yama-guchi, Y. Kasahara // Радіофізика та електроніка. — 2012. — Т. 3(17), № 4. — С. 64-69. — Бібліогр.: 27 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-105922 |
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Hayakawa, M. Hobara, Y. Rozhnoi, A. Solovieva, M. Ohta, K. Izutsu, J. Nakamura, T. Yasuda, Y. Yama-guchi, H. Kasahara, Y. 2016-09-13T15:40:08Z 2016-09-13T15:40:08Z 2012 The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation / M. Hayakawa, Y. Hobara, A. Rozhnoi, M. Solovieva, K. Ohta, J. Izutsu, T. Nakamura, Y. Yasuda, H. Yama-guchi, Y. Kasahara // Радіофізика та електроніка. — 2012. — Т. 3(17), № 4. — С. 64-69. — Бібліогр.: 27 назв. — англ. 1028-821X https://nasplib.isofts.kiev.ua/handle/123456789/105922 537.877 By using the network observation of subionospheric VLF/LF signals in Japan and in Russia, we have found a significant ionospheric perturbation prior to the recent 2011 March 11 Japan earthquake (EQ) in the off-sea of the Tohoku area, which was an exceptionally huge plate-type EQ. A remarkable anomaly (with decrease in the nighttime amplitude and also with enhancement in dispersion) has been detected on March 5 and 6 on the propagation path from the NLK transmitter (Seattle, USA) to Chofu (together with Kochi and Kasugai), and also we have observed the corresponding VLF anomaly during a prolonged period of March 1–6, with minima in the nighttime amplitude on March 3 and 4 on the path from JJI transmitter (Miyazaki, Kyushu) to Kamchatka, Russia. Используя наблюдения распространения СДВ/ДВ-радиоволн над Тихим океаном на японской и российской сети станций, удалось обнаружить значительное возмущение ионосферы, предшествовавшее последнему мощному землетрясению в Японии 11.03.2011 г. Эпицентр землетрясения находился в море, в области Тохоку, а само событие относится к исключительно мощным землетрясениям, связанным с перемещением тектонических плит. Явно выраженная аномалия (уменьшение ночной амплитуды сигнала при увеличении ее дисперсии) была обнаружена 5 и 6 марта на трассе распространения от передатчика NLK (Сиэтл, США) к наблюдателю в Чофу, Япония (аналогичные явления – на трассах распространения в Кочи и Кацугаи). Аналогичная длительная аномалия в СДВ-распространении регистрировалась с 1 по 6 марта с минимальной ночной амплитудой 3 и 4 марта на трассе от передатчика JJI (Миязаки, Кюсю) до Камчатки, Россия. Використовуючи спостереження поширення СДВ/ДВ-радіохвиль над Тихим океаном на японській і російській мережі станцій, вдалося виявити значне збурення іоносфери, що сталося перед останнім потужним землетрусом у Японії 11.03.2011 р. Епіцентр землетрусу знаходився в морі, в області Тохоку, а сама подія відноситься до виключно потужних землетрусів, пов’язаних з переміщенням тектонічних плит. Явно виражена аномалія (зменшення нічної амплітуди сигналу при збільшенні її дисперсії) було виявлено 5 та 6 березня на трасі від передавача NLK (Сіетл, США) до спостерігача в Чофу, Японія (аналогічні явища – на трасах поширення до Кочі й Кацугаї). Аналогічну тривалу аномалію в СДВ-поширенні реєстрували з 1 по 6 березня з мінімальною нічною амплітудою 3 і 4 березня на трасі від передавача JJI (Міязакі, Кюсю) до Камчатки, Росія. en Інститут радіофізики і електроніки ім. А.Я. Усикова НАН України Радіофізика та електроніка Распространение радиоволн, радиолокация и дистанционное зондирование The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation Ионосферный предвестник землетрясения 11 марта 2011 г. по наблюдениям транстихоокеанского распространения СДВ/ДВ-радиоволн на сети станций Іоносферний провісник землетрусу 11 березня 2011 р. за спостереженням транстихоокеанського поширення СДВ/ДВ-радіохвиль на мережі станцій Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation |
| spellingShingle |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation Hayakawa, M. Hobara, Y. Rozhnoi, A. Solovieva, M. Ohta, K. Izutsu, J. Nakamura, T. Yasuda, Y. Yama-guchi, H. Kasahara, Y. Распространение радиоволн, радиолокация и дистанционное зондирование |
| title_short |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation |
| title_full |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation |
| title_fullStr |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation |
| title_full_unstemmed |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation |
| title_sort |
ionospheric precursor to the 2011 march 11 earthquake as based on the japan-pacific subionospheric vlf/lf network observation |
| author |
Hayakawa, M. Hobara, Y. Rozhnoi, A. Solovieva, M. Ohta, K. Izutsu, J. Nakamura, T. Yasuda, Y. Yama-guchi, H. Kasahara, Y. |
| author_facet |
Hayakawa, M. Hobara, Y. Rozhnoi, A. Solovieva, M. Ohta, K. Izutsu, J. Nakamura, T. Yasuda, Y. Yama-guchi, H. Kasahara, Y. |
| topic |
Распространение радиоволн, радиолокация и дистанционное зондирование |
| topic_facet |
Распространение радиоволн, радиолокация и дистанционное зондирование |
| publishDate |
2012 |
| language |
English |
| container_title |
Радіофізика та електроніка |
| publisher |
Інститут радіофізики і електроніки ім. А.Я. Усикова НАН України |
| format |
Article |
| title_alt |
Ионосферный предвестник землетрясения 11 марта 2011 г. по наблюдениям транстихоокеанского распространения СДВ/ДВ-радиоволн на сети станций Іоносферний провісник землетрусу 11 березня 2011 р. за спостереженням транстихоокеанського поширення СДВ/ДВ-радіохвиль на мережі станцій |
| description |
By using the network observation of subionospheric VLF/LF signals in Japan and in Russia, we have found a significant ionospheric perturbation prior to the recent 2011 March 11 Japan earthquake (EQ) in the off-sea of the Tohoku area, which was an exceptionally huge plate-type EQ. A remarkable anomaly (with decrease in the nighttime amplitude and also with enhancement in dispersion) has been detected on March 5 and 6 on the propagation path from the NLK transmitter (Seattle, USA) to Chofu (together with Kochi and Kasugai), and also we have observed the corresponding VLF anomaly during a prolonged period of March 1–6, with minima in the nighttime amplitude on March 3 and 4 on the path from JJI transmitter (Miyazaki, Kyushu) to Kamchatka, Russia.
Используя наблюдения распространения СДВ/ДВ-радиоволн над Тихим океаном на японской и российской сети станций, удалось обнаружить значительное возмущение ионосферы, предшествовавшее последнему мощному землетрясению в Японии 11.03.2011 г. Эпицентр землетрясения находился в море, в области Тохоку, а само событие относится к исключительно мощным землетрясениям, связанным с перемещением тектонических плит. Явно выраженная аномалия (уменьшение ночной амплитуды сигнала при увеличении ее дисперсии) была обнаружена 5 и 6 марта на трассе распространения от передатчика NLK (Сиэтл, США) к наблюдателю в Чофу, Япония (аналогичные явления – на трассах распространения в Кочи и Кацугаи). Аналогичная длительная аномалия в СДВ-распространении регистрировалась с 1 по 6 марта с минимальной ночной амплитудой 3 и 4 марта на трассе от передатчика JJI (Миязаки, Кюсю) до Камчатки, Россия.
Використовуючи спостереження поширення СДВ/ДВ-радіохвиль над Тихим океаном на японській і російській мережі станцій, вдалося виявити значне збурення іоносфери, що сталося перед останнім потужним землетрусом у Японії 11.03.2011 р. Епіцентр землетрусу знаходився в морі, в області Тохоку, а сама подія відноситься до виключно потужних землетрусів, пов’язаних з переміщенням тектонічних плит. Явно виражена аномалія (зменшення нічної амплітуди сигналу при збільшенні її дисперсії) було виявлено 5 та 6 березня на трасі від передавача NLK (Сіетл, США) до спостерігача в Чофу, Японія (аналогічні явища – на трасах поширення до Кочі й Кацугаї). Аналогічну тривалу аномалію в СДВ-поширенні реєстрували з 1 по 6 березня з мінімальною нічною амплітудою 3 і 4 березня на трасі від передавача JJI (Міязакі, Кюсю) до Камчатки, Росія.
|
| issn |
1028-821X |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/105922 |
| citation_txt |
The ionospheric precursor to the 2011 march 11 earthquake as based on the Japan-pacific subionospheric VLF/LF network observation / M. Hayakawa, Y. Hobara, A. Rozhnoi, M. Solovieva, K. Ohta, J. Izutsu, T. Nakamura, Y. Yasuda, H. Yama-guchi, Y. Kasahara // Радіофізика та електроніка. — 2012. — Т. 3(17), № 4. — С. 64-69. — Бібліогр.: 27 назв. — англ. |
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РРААССППРРООССТТРРААННЕЕННИИЕЕ РРААДДИИООВВООЛЛНН,, РРААДДИИООЛЛООККААЦЦИИЯЯ ИИ ДДИИССТТААННЦЦИИООННННООЕЕ ЗЗООННДДИИРРООВВААННИИЕЕ
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ISSN 1028−821X Радиофизика и электроника. 2012. Т. 3(17). № 4 © ИРЭ НАН Украины, 2012
UDC 537.877
M. Hayakawa1,2,3,4, Y. Hobara2,5, A. Rozhnoi6, M. Solovieva6, K. Ohta7, J. Izutsu7, T. Nakamura8,
Y. Yasuda3, H. Yamaguchi4, Y. Kasahara5
1The University of Electro-Communications (UEC), Advanced Wireless Communications Research Center,
1-5-1 Chofugaoka, Chofu Tokyo 182-8585, Japan
2UEC, Research Station on Seismo Electromagnetics, Chofu Tokyo, Japan
3Hayakawa Institute of Seismo-Electromagnetics, Co. Ltd., UEC Incubation Center, Chofu Tokyo, Japan
4Earthquake Analysis Laboratory, Information Systems Inc., Kita-aoyama 2-12-42- 305, Minato-ku Tokyo 107-0061,
Japan
5UEC, Graduate School of Informatics and Engineering, Chofu Tokyo, Japan
6Institute of Physics of the Earth, Russian Academy of Sciences, 10 Gruzinskaya, Moscow, 123810, Russia
7Chubu University, 1200 Matsumoto-cho, Kasugai Aichi 487-8501, Japan
8Kochi University, Akebono-cho, Kochi, Japan
THE IONOSPHERIC PRECURSOR TO THE 2011 MARCH 11 EARTHQUAKE AS BASED
ON THE JAPAN-PACIFIC SUBIONOSPHERIC VLF/LF NETWORK OBSERVATION
By using the network observation of subionospheric VLF/LF signals in Japan and in Russia, we have found a significant
ionospheric perturbation prior to the recent 2011 March 11 Japan earthquake (EQ) in the off-sea of the Tohoku area, which was an
exceptionally huge plate-type EQ. A remarkable anomaly (with decrease in the nighttime amplitude and also with enhancement in
dispersion) has been detected on March 5 and 6 on the propagation path from the NLK transmitter (Seattle, USA) to Chofu (together with
Kochi and Kasugai), and also we have observed the corresponding VLF anomaly during a prolonged period of March 1–6, with minima in
the nighttime amplitude on March 3 and 4 on the path from JJI transmitter (Miyazaki, Kyushu) to Kamchatka, Russia. Fig. 4. Bibliogr.: 27 ref.
Key words: ionospheric precursor, VLF/LF subionospheric propagation, 2011 March 11 Japan earthquake.
It is recently agreed that there exist
electromagnetic precursors to earthquakes (EQs) [1–6].
The observation of seismo-electromagnetic and
related phenomena can be customarily classified into
the two categories: (1) direct effects emitted from the
lithosphere and received on the Earth’s surface, and
(2) the indirect effects of EQs which are the
perturbations (or disturbances) taking place either in
the atmosphere or in the ionosphere due to pre-EQ
lithospheric activities. As for the first category, there
are observed lithospheric emissions in a wide
frequency range from DC/ULF to VHF (very high
frequencies) or even higher. The first example is the
DC (direct current) geoelectric signals [7], and the
second example is ULF (ultra low frequency)
electromagnetic emissions which seems to be very
promising for EQ prediction (e.g., see [8–10]). As for
the second category, there are several techniques to
reveal atmospheric and ionospheric precursors,
including satellite infrared sensors, vertical sounding
of the ionosphere from the ground, GPS observations,
in-situ plasma observations, etc. [11]. Probing by
anomalous propagation of radio waves is one of the
methods. The further reviews on the second category
have been published on the atmospheric
perturbations [12] and on the ionospheric
perturbations [13–15].
Among different kinds of electromagnetic
precursors mentioned above, the ionospheric
perturbations belonging to the second category seem
to be the most reliable because there have been
accumulated a substantial number of VLF/LF (very
low frequency/low frequency) works including both
case and statistical studies summarized in [13].
Recently the lower ionospheric perturbation as
detected by sub-ionospheric VLF/LF propagation is
shown to be statistically significantly correlated with
the EQs, which take place within the wave sensitive
area around the propagation path and with
magnitudes tentatively greater than 6.0 and shallower
depth (< 40 km) [16, 17]. These papers were based
on an abundant number of the inland EQs during
seven years, which lend a further support to our
previous similar statistical studies though based on
the less number of events and during smaller time
periods [18–20]. The similar statistical correlation
has also been obtained by Liu [14] between the upper
ionosphere and EQs on the basis of vertical sounding
from the ground and GPS TEC (total electron
contents) observation. These together suggest that the
ionosphere is extremely sensitive to the pre-seismic
activity not only in the lower region, but also in the
F2 layer. A few possible mechanisms for seismo-
ionospheric perturbations have already been
proposed (e.g., [2, 3, 21]), but it is not well
understood at the moment which mechanism is
dominant.
Concurrently with the above-mentioned
statistical studies, we are interested in the case
studies of huge EQs, because these are of vital
importance in investigating the detailed
temporal/spatial characteristics of such seismo-
ionospheric perturbations, and also their relationship
is significant with the corresponding lithospheric and
atmospheric phenomena. Our former case studies
included, (1) Kobe EQ (17 January, 1995)
М. Хаякава и др. / Ионосферный предвестник землетрясения…
_______________________________________________________________________________________________________________
65
(2) Tokachi-oki EQ (25 September, 2003)
(3) Niigata-chuetsu EQ (23 October 2004) (4) the
1999 Chi-chi EQ in Taiwan (5) the 2004 Sumatra
EQ. Details of impact of these EQs are summarized
in review [13]. All these EQs except the Tokachi-oki
and Sumatra EQs were of the land-type due to fault
activity, so we know characteristics of ionospheric
perturbations from the inland EQs having in mind the
above-mentioned statistical studies [16, 17].
The 2011 Japan EQ was extremely huge, of
9.0 magnitude, and it belongs to oceanic EQs taken
place in the Pacific Ocean due to the plate
movement. It is interesting to search for the
ionospheric perturbation preceding this oceanic EQ,
and, if so, to compare characteristics of oonospheric
perturbations from this sea EQ with the former
properties of many inland EQs.
1. The 2011 Tohoku EQ. There happened
an extremely huge EQ (with magnitude of 9.0) under
the seabed in the Pacific Ocean off the Tohoku area
of Japan, which is formally named the EQ of the
2011 off the Pacific coast of Tohoku. This EQ took
place at 14:46:18 LT on March 11, 2011 with its
epicenter at the geographic coordinates (36°6.2′N,
142°51.6′E) as shown in Fig. 1 by a red star with its
date and its depth of ~20 km. This event was a
typical oceanic EQ of the plate type just around
Japan, which is completely different from the
extensively-studied fault-type EQs such as Kobe EQ,
Niigata-chuetsu EQ, etc.
Fig. 1. Location of Japanese VLF/LF transmitters JJY (Fukushima)
and JJI (Miyazaki) (blue diamonds) and the VLF/LF receiving
stations (by red stars). Ellipse outlines the wave sensitive area of
propagation path NLK–CHF. Epicenters of the main shock and its
foreshock are indicated with the red stars marked by corresponding
dates
2. VLF/LF subionospheric network. We
established the Japanese and the Pacific network for
sub-ionospheric VLF/LF propagation just after the
1995 Kobe EQ within the framework of the former
NASDA's frontier project [21]. This network
observation has been continued for over 15 years
until now. The main observatories within Japan at the
moment are (1) Moshiri in Hokkaido (abbreviated as
MSR), (2) Chofu in Tokyo (CHF), (3) Kasugai near
Nagoya (KSG), (4) Kochi in Shikoku island (KCH),
and (5) Tsuyama, Okayama (TYM). These are shown
by red stars in Fig. 1, although TYM is not illustrated
in the figure. Some additional observatories are
planned to be built shortly. At each receiving station,
we normally detect simultaneously the signals from
two Japanese transmitters with call signs of JJY (in
Fukushima, 40 kHz) and JJI (in Miyazaki, Kyusyu,
22.2 kHz) as shown by blue diamonds in Fig.1 and
also a few foreign transmitters, i.e., NWC (North-
West Cape, Australia), NPM (Hawaii), and NLK
(Seattle, USA)). The details of this VLF/LF network
and corresponding VLF receiving system can be
found in [13, 16, 17, 21].
This sub-ionospheric VLF/LF network was
extended to cover a wider area of the Pacific ocean
by including a station in Taiwan [22] and in
collaboration with Russian colleagues a station in
Russia, Petropavlovsk-Kamchatsky (PTK) shown by
green dot in Fig. 2 [3]. Observations at PTK were
performed very regularly resulting in significant
scientific merits [23–25]. The Russian group has
recently established one more station at Yuzhno-
Sakhalinsk (YSH) also show by a green dot in Fig. 2.
These two stations are equipped with the same type
of VLF/LF receiving system as used at Japanese
stations.
Fig. 2. Position of Japanese VLF/LF transmitters JJY and JJI
(triangles) and observatories PTK and YSH (green dots). Elliptic
wave sensitive areas are plotted for the paths JJY–YSH, JJY–PTK,
JJI–YSH, and JJI–PTK. The main shocks and aftershocks are show
by circles of size being proportional to the EQ magnitude
45°
40°
35°
30°
130° 135° 140° 145°
Geographic Longitude [deg]
G
eo
gr
ap
hi
c
La
tit
ud
e
[d
eg
]
45°
40°
35°
30°
km
120°E 140°E 160°E
45°N
35°N
М. Хаякава и др. / Ионосферный предвестник землетрясения…
_______________________________________________________________________________________________________________
66
3. Observational results and analysis
method. Fig. 1 illustrates three paths from NLK
transmitter (Seattle, USA) to Japanese VLF/LF
observatories CHF, KSG and KCH. The fifth Fresnel
zone is plotted by thin ellipse for the propagation
path NLK–CHF being the wave sensitive area for
this path. This means that any EQ taking place within
sensitive area results in a significant changes in VLF
radio signal received at the observatory (either in
amplitude or in phase, or both).
Concerning the analysis, we do not follow
the terminator-time method initially developed for
the Kobe EQ [26], but apply an alternative «the
nighttime fluctuation method» [16–20], in which we
investigate only the nighttime amplitude data. The
nighttime fluctuation method is much simpler in
application than the terminator-time method. We first
read the amplitude A(t) as a function of current time t
during the local night of a particular day and estimate
the average amplitude <A(t)> as the function of the
same time, but averaged during the period from one
day to 30 days prior to the current date. Thus, we can
find deviation dA(t) = A(t) − <A(t)>. By using this
residue, we estimate trend of the nighttime average
amplitude being the mean value of )(tdA against the
local time. The second parameter is the dispersion,
which characterizes the rate of amplitude fluctuations
around the average. These two parameters are
independent random variables, and we normalize
them by their standard deviations (σ) in the interval
30 to 1 day before the current day. Further details of
this nighttime fluctuation method might be found in
[16, 17, 20].
The definition of the ambient night is
considerably complicated for the east-west long-
range propagation from NLK to Japanese stations
(such as CHF), the distance D = 7~8 Mm. By
considering the sunrise and sunset at the transmitter
and the observatory (the terminator times [26]) and
by checking the real diurnal variations at the NLK–CHF
path, we have chosen the universal time (UT) interval
from 10 hr to 12 hr as the nighttime at particular
path. That is, only during this period the propagation
path is completely in the dark.
Fig. 2 illustrates relative location of two
Russian observatories, PTK and YSH and the
Japanese VLF/LF transmitters (JJY in Fukushima
and JJI in Miyazaki). These latter might be seen in
Fig. 1 as well. The wave sensitive areas for all
propagation paths are also shown (i.e., JJY–YSH,
JJY–PTK, JJI–YSH, and JJI–PTK) together with the
locations of the main shock and aftershocks.
Next, we have to discuss the nighttime
interval for the Russian data because we use the same
nighttime fluctuation method. The February night
lasts from UT 10 hr 30 min to 18 hr 40 min, an the
interval is UT = 11:00–16:30 during May.
Correspondingly, the nighttime for March and April
is within this interval, as UT = 10:30–11:00 for
sunset and it is 16:30–18:40 for sunrise. The data
analysis from Russian records is exactly the same as
the above mentioned analysis of Japanese data.
The analysis period covered the interval
from February 1 to May 22, 2011, including our target
EQ on March 11.
3.1. Significant propagation anomalies
associated with the propagation paths from
American transmitter NLK. Fig. 1 suggests that the
propagation paths from the American transmitter
NLK (at Seattle, USA) to Japanese receiving stations
(CHF, KSG, KCH) are favorably located with respect
to the epicenter of this oceanic EQ. Especially, the
NLK–CHF path is just above the EQ epicenter, and
the corresponding wave sensitive area of this path is
plotted by a thin elliptic line in Fig. 1. Two other
propagation paths from NLK to KSG and from NLK
to KCH (only the corresponding great-circle paths
are shown) are also favorable for noticing
corresponding ionospheric perturbations, although
the sensitive areas were not shown for simplicity.
In accordance to theoretical expectations,
Fig. 3 illustrates the experimentally observed
evolution of propagation characteristics for the above
paths. Fig. 3, a refers to the NLK–CHF path,
Fig. 3, b, – to NLK–KCH path, and Fig. 3, c, – to the
NLK–KSG path. We depict in Fig. 3 (from top to
bottom) the trend and dispersion, normalized by their
standard deviations (σ).
Let us look at the top panel (trend) of
Fig. 3, a presenting the most important propagation
path NLK–CHF during the period from January 1.
We see that trend does not fall down to –2σ level
during the whole period, except the January 29 date
and an exclusively significant propagation anomaly
during two days of March 5 and 6. The anomaly of
March 5 has a remarkable trend decrease exceeding
–3σ and approaching –4σ. Almost simultaneously,
the second parameter (dispersion) increases
approaching +2σ. The anomaly is also recognized in
Fig. 3, b for the propagation path from NLK to KCH.
The anomaly for this path is rather evident in such a
way that the most important parameter, trend
exhibited a significant decrease reaching –2σ level.
On the other hand, the anomaly for the NLK–KSG
path (Fig. 3, c) is less pronounced during the same
days of March 5 and 6. However, the overall VLF
response to the EQ is very evident.
We must comment on other propagation
anomalies seen in Fig. 3. In paper [16], we have
tentatively chosen an EQ magnitude threshold of
M = 6 (this means rather strong Eqs only), and we
have obtained a significant correlation exceeding the
2σ criterion. However, even if we reduce the
magnitude threshold to M = 5.5, the correlation
М. Хаякава и др. / Ионосферный предвестник землетрясения…
_______________________________________________________________________________________________________________
67
between VLF/LF anomalies and the EQs will be still
significant: just around 2σ level [18, 19]. Therefore
we must try to associate other depletions in trend of
Fig. 3 to EQs in the relevant region. First of all, we
comment on the anomaly on January 29 in Fig. 3, a.
a)
b)
c)
Fig. 3. Evolutions of the propagation anomalies observed at three
propagation paths: (a) NLK–CHF, (b) NLK–KCH and (c) NLK–KSG.
The top panel of each frame refers to the normalized average
nighttime amplitude (called trend), and the bottom panel shows the
normalized dispersion. A clear anomaly is seen on March 5 and 6
This anomaly was probably associated with
two EQs that occurred in the off-sea of Iwate
(February 3) and Fukushima (on February 10,
M = 5.3). Further comments are required on other
depletions in trend of Fig. 3, b. The depletion on
January 23 is likely to be related with an EQ in the
off-shore of Chiba on January 25 (M = 5.1). Then,
the depletions in trend on February 1 and 8
(exceeding –2σ level) are likely to be related to
another EQ in Chiba-oki on February 5 (M = 5.2) and
to an EQ in the Miyagi-oki on February 15 (M = 5.5),
respectively. Finally, the depletion on February 5 in
Fig. 3, c is likely to be a precursor to an EQ in
Fukushima-oki (M = 5.3).
3.2. Clear propagation anomaly for the
propagation path from JJI to PTK. Among the three
Russian propagation paths, we have found a possible
effect only at the propagation path from JJI
(Miyazaki, Kyushu) to Kamchatka (PTK). The top
panel of Fig. 4 illustrates temporal evolution of the
nighttime average amplitude (trend), and the second
panel refers to the conventional dispersion. The
bottom plot indicates the EQs occurrence of
magnitude exceeding 5.5. The horizontal dotted lines
indicate the 2σ and –2σ levels.
Fig. 4 shows that a significant and extended
decrease in the nighttime amplitude takes place
during a rather long period from February 28 to
March 6 on the path from JJI to PTK, with a
maximum depletion on March 3 and 4. The
corresponding increases in the dispersion are
simultaneously observed, with the maximum on
March 3 and 4. The dates with VLF/LF propagation
anomaly on the Russian path are a slightly shifted
against that of the NLK–CHF path in Fig. 3. Still,
anomaly on this propagation path is considered to be
the same, owing to some inhomogeneity in time and
in space of the ionospheric perturbation (e.g., [27]).
Fig. 4. Evolution of the propagation characteristics for the
propagation path of JJI–PTK. The top panel shows the normalized
average nighttime amplitude (trend). Horizontal dashed line
indicates the level –2σ. The middle panel depicts the normalized
dispersion with the horizontal dashed line of +2σ. The bottom
panel demonstrates evolution of seismic activity
Finally, we comment on the last Russian
path, JJY–PTK. The wave sensitive area for this
propagation path is seen in Fig. 2. It is completely
within the wave sensitive area of the above-
mentioned JJI–PTK path related to significant
anomalies. Though not shown as a figure, it was
found that trend showed a significant decrease on
March 4, which did not exceed the –2σ level being
approximately –1.5σ. Anyway, an anomaly was
SoftPAL–30 NLK–KCH, 2011/1/1–2011/3/12
D
is
pe
rs
io
n,
σ
T
re
nd
, σ
SoftPAL–30 NLK–KSG, 2011/1/1–2011/3/12
D
is
pe
rs
io
n,
σ
T
re
nd
, σ
SoftPAL–30 NLK–CHF, 2011/1/1–2011/3/12
D
is
pe
rs
io
n,
σ
T
re
nd
, σ
JJI-PTK <dA>
Dispersion
M>5,5
Days from the 1st of February, 2011
M
D
isp
er
sio
n,
σ
T
re
nd
,
М. Хаякава и др. / Ионосферный предвестник землетрясения…
_______________________________________________________________________________________________________________
68
observed at this path as well on March 4, but its
nature indicates on highly non-uniform ionospheric
perturbations.
Summary and discussion. By making full
use of the Japanese-Russian sub-ionospheric VLF/LF
network, the following observational facts have
emerged in possible relation to the 2011 3.11 Japan EQ.
No definite anomaly was detected at the
paths JJY–MSR, JJY–YSH and JJI–YSH.
On the other hand, the clear and significant
anomalies were observed at the two propagation
paths of NLK–Japanese stations (CHF, KSG and
KCH) and JJI–PTK. The anomaly of the path NLK–CHF
took place on March 5 and 6 as a significant decrease
in trend (nighttime average amplitude) exceeding the
–3σ level, accompanied by simultaneous increase in
dispersion. The anomaly on the path JJI–PTK shows
a broad depletion from February 28 to March 6, with
maximum depletions on March 3 and 4, which is also
characterized by a significant decrease in trend and
an increase in dispersion. So, the remarkable
ionospheric perturbation is likely to be persistent, at
least, for 4 days (March 3–6).
Though not shown due to the limit of space,
we have tried to demonstrate that anomalous changes
in VLF/LF propagation summarized above, would be
likely relevant to the March 3 EQ. The following
points have been addressed one by one: (1) how
distinct is the VLF/LF propagation anomaly and the
significance using the conventional standard
deviation, (2) what is the temporal evolution of
terminator times (significant changes in terminator-
times), (3) were there any solar-terrestrial effects in
the VLF/LF propagation, especially, the geomagnetic
storms, (4) effects of other EQs and foreshock
activities on the VLF anomaly, (5) correlation of the
present anomaly with other phenomena, and (6) other
examples of VLF/LF propagation anomaly for
oceanic EQs.
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Manuscript received July 13, 2012.
М. Хаякава, Я. Хобара, А. Рожной, М. Соловьева,
К. Ота, Дж. Изуцу, Т. Накамура, Я. Ясуда,
Х. Ямагучи, Я. Касахара
ИОНОСФЕРНЫЙ ПРЕДВЕСТНИК
ЗЕМЛЕТРЯСЕНИЯ 11 МАРТА 2011 г.
ПО НАБЛЮДЕНИЯМ ТРАНСТИХООКЕАНСКОГО
РАСПРОСТРАНЕНИЯ СДВ/ДВ-РАДИОВОЛН
НА СЕТИ СТАНЦИЙ
Используя наблюдения распространения
СДВ/ДВ-радиоволн над Тихим океаном на японской и рос-
сийской сети станций, удалось обнаружить значительное возму-
щение ионосферы, предшествовавшее последнему мощному земле-
трясению в Японии 11.03.2011 г. Эпицентр землетрясения
находился в море, в области Тохоку, а само событие
относится к исключительно мощным землетрясениям, связан-
ным с перемещением тектонических плит. Явно выраженная
аномалия (уменьшение ночной амплитуды сигнала при
увеличении ее дисперсии) была обнаружена 5 и 6 марта на
трассе распространения от передатчика NLK (Сиэтл, США) к
наблюдателю в Чофу, Япония (аналогичные явления – на
трассах распространения в Кочи и Кацугаи). Аналогичная
длительная аномалия в СДВ-распространении регистри-
ровалась с 1 по 6 марта с минимальной ночной амплитудой
3 и 4 марта на трассе от передатчика JJI (Миязаки, Кюсю) до
Камчатки, Россия.
Ключевые слова: ионосферный предвестник, волно-
водное СДВ/ДВ-распространение, японское землетрясение
11 марта 2011 г.
М. Хаякава, Я. Хобара, О. Рожной, М. Соловйова,
К. Ота, Дж. Изуцу, Т. Накамура, Я. Ясуда,
Х. Ямагучі, Я. Касахара
ІОНОСФЕРНИЙ ПРОВІСНИК ЗЕМЛЕТРУСУ
11 БЕРЕЗНЯ 2011 р. ЗА СПОСТЕРЕЖЕННЯМ
ТРАНСТИХООКЕАНСЬКОГО ПОШИРЕННЯ
СДВ/ДВ-РАДІОХВИЛЬ НА МЕРЕЖІ СТАНЦІЙ
Використовуючи спостереження поширення
СДВ/ДВ-радіохвиль над Тихим океаном на японській і
російській мережі станцій, вдалося виявити значне збурення
іоносфери, що сталося перед останнім потужним землетрусом
у Японії 11.03.2011 р. Епіцентр землетрусу знаходився в морі,
в області Тохоку, а сама подія відноситься до виключно
потужних землетрусів, пов’язаних з переміщенням тектоніч-
них плит. Явно виражена аномалія (зменшення нічної
амплітуди сигналу при збільшенні її дисперсії) було виявлено
5 та 6 березня на трасі від передавача NLK (Сіетл, США) до
спостерігача в Чофу, Японія (аналогічні явища – на трасах
поширення до Кочі й Кацугаї). Аналогічну тривалу аномалію
в СДВ-поширенні реєстрували з 1 по 6 березня з мінімальною
нічною амплітудою 3 і 4 березня на трасі від передавача JJI
(Міязакі, Кюсю) до Камчатки, Росія.
Ключові слова: іоносферний провісник, хвиле-
відне СДВ/ДВ-поширення, японський землетрус 11 березня
2011 р.
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