conference & convention
enabling the next generation of networks & services
Dense Ocean floor Network System for Mega Thrust
Earthquakes & Tsunamis（DONET）
-Towards Understanding Mega Thrust Earthquakes,
the Geohazard & Disaster MitigationYoshiyuki KANEDA, Katsuyoshi KAWAGUCHI, Eiichiro ARAKI, Hiroyuki
MATSUMOTO, Takeshi NAKAMURA, Shinichiro KAMIYA, Keisuke ARIYOSHI, Takane
HORI
Earthquake and Tsunami research project for Disaster Prevention
Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Email: [email protected]
Japan Agency for Marine-Earth Science and Technology (JAMSTEC),
2-15 Natsushima-cho, Yokosuka 237-0061 JAPAN
Abstract: The Nankai Trough is well known as the mega thrust earthquake generating
tsunamis, with the interval of 100-200 years. To understand and elucidate the recurrences of
the mega thrust earthquakes, ocean floor network systems for the real time monitoring of
seismogenic zone are quite useful and important. We are developing the ocean floor network
system (DONET), funded by Japanese government MEXT project. The data from DONET
will be applied to the early warning earthquakes and tsunamis. Furthermore, the precise data
of crustal activities from DONET will improve the recurrence cycle simulation model using
data assimilations.
1. INTRODUCTION
The Nankai Trough is well known as the
mega thrust earthquake generating
tsunamis, with the interval of 100-200
years. There are three mega thrust
earthquake seismogenic zones in the
Nankai trough. Especially, the 1944 /1946
earthquakes in Showa Nankai trough
earthquakes and the 1854 Ansei Nankai
trough earthquakes, first ruptures were
starting from the Tonankai seismogenic
zone. However, according to Prof.
Okamura of KOCHI University, super
mega thrust earthquakes with large
tsunamis such as the 1707 Hoei
earthquake, the 1361 Shohei earthquake
and the 684 Hakuho earthquakes are
estimated to be occurring with intervals of
300-400 years or 700 years by historical
tsunami research. These facts are very
severe problems for Japan. Based on recent
Copyright © 2010 SubOptic
structural
researches,
observational
researches and advanced simulation
researches, we recognize that the Tonankai
seismogenic is very important area to
understand the recurrence system of mega
thrust earthquakes around the Nankai
trough. Therefore, we have been starting to
developing and deploying the dense ocean
floor observatory network system around
the Tonankai seismogenic zone to monitor
crustal
activities
using
broadband
seismometer, accelerometer and precise
pressure gauges. The probability of next
Tonankai earthquake recurrence is estimate
as 60-70%. So, to monitor the crustal
activities for the early warning and
improvement
of
recurrence
cycle
simulation of mega thrust earthquakes, the
ocean floor network is significant and
important. In this paper, we explain the
recent and detailed developing of this
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ocean floor network system (DONET).
Furthermore, the new project including
observation simulation and mitigation
researches of mega thrust earthquakes
around the Nankai trough is starting as 5
years project (2008-20012). Especially, the
Ocean floor network data is very important
and powerful to progress the new project.
enabling the next generation of networks & services
There are imaged key structures such as
subducting seamount in the Nankai
seismogenic zone, cyclic ridge subducting
system in the Tokai seismogenic zone and
splay faults and the irregular structure
around the Tonankai seismogenic zone
(Figure2). Moreover, results of mega thrust
The Nankai trough is well known as mega
thrust earthquake seismogenic zone.
There are 3mega thrust rupture zones such
as the Tokai, Tonankai and Nankai
seismogenic zone (Figure1). In these
rupture area, mega thrust earthquakes over
M8 are occurring with a interval of 100200years (Table1).
In seismogenic zone researches such as
structural researches using seismic
refractions and reflections, we have
succeeded to image the key structures to
understand recurrences of mega thrust
earthquakes around the Nankai trough.
Copyright © 2010 SubOptic
earthquake recurrence cycle simulation
show that the first ruptures are occurring
around the Tonankai earthquake rupture
zone in each recurrence cycle.
In 1854, 1944/46, actually, first ruptures
were starting from the Tonankai
earthquake rupture zone ahead of the
Nankai earthquake rupture zone with
intervals of 32 hours in the 1854 Ansei
earthquake and 2years in the Showa
earthquakes. The result of recurrence cycle
simulation indicates the difference patterns
and intervals of mega-thrust earthquake
recurrences in each cycle
(Figure3).
These results of simulation are consisted
with the past two earthquakes in 1854,
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enabling the next generation of networks & services
1944/46 around the Nankai trough. The
new research project for the evaluation of
seismic linkage around the Nankai trough
mega thrust earthquakes is starting as
MEXT project which is as a kind of
Japanese government funded project.
Around the Nankai trough, especially, off
Kii peninsula located around the Tonankai
seismogenic zone, we are deploying the
advanced ocean floor network system
(DONET) and ‘Chikyu’ drilling as IODP
(Integrated Ocean Drilling Program) is
carrying out.
Then, the long term observatory system
using the borehole by Chikyu drilling will
be connected to DONET system. Finally,
we will develop 3 dimensional real time
monitoring system(Figure4).
1. THE DENSE OCEAN FLOOR
NETWORK for EARTHQUAKES
and TSUNAMIS (DONET)
The imaged irregular structure such as a
key structure at the segment boundary
between the Tonankai and Nankai
earthquake rupture zone seems to be the
controller of the Nankai Trough mega
thrust seismogenic zone system (Figure2).
And in each simulation cycles, the first
ruptures are starting from the Tonankai
earthquake rupture zone ahead of the
Nankai earthquake rupture zone (Figure5).
These results are consistent with the past
two earthquakes in 1854, 1944/1946.
(Table2)
Copyright © 2010 SubOptic
Therefore, for real time monitoring of the
mega thrust seismogenic zone, DONET
will be deployed around the Tonankai
seismogenic zone to observe broad band
phenomena (Figure6).
According to previous researches, the
Tonankai seismogenic zone is important to
understand the system of Nankai trough
mega thrust earthquake occurrences.
Therefore, we have developed and been
deploying the dense ocean floor
observatory network system equipped with
multi kinds of sensors such as
seismometers, pressure gauges etc. around
the Tonankai seismogenic zone (Figure7).
Using DONET system, we can detect
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broad band phenomena such as strong
motions, low frequency tremors and very
low frequency earthquakes. Furthermore,
precise multi pressure gauges will be most
useful sensor to not only detect tsunamis
but also monitor ocean floor deformations
with long term observations. These ocean
floor deformation data will be applied to
the data assimilation to improve recurrence
cycle simulation model in the Nankai
trough mega thrust earthquakes.
DONET system will be the one of most
advanced scientific tools to understand the
mega thrust earthquakes around the Nankai
trough.
enabling the next generation of networks & services
This advanced dense ocean floor
observatory network system has useful
functions and purposes as follows,
1) Redundancy, Extension and advanced
maintenance system using the looped
cable system, junction boxes and the
ROV/AUV, etc. (Figure8).
2) Multi kinds of sensors to observe broad
band range phenomena such as long
period
tremors,
low
frequency
earthquakes and strong motion of mega
thrust earthquakes over M8.(Figure9)
3) Speedy evaluation and notification for
earthquakes and tsunamis (Figure10).
This function is most important for disaster
reduction /mitigation.
JMA is starting the early warning system,
therefore, the ocean floor network data will
Copyright © 2010 SubOptic
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contribute to this early warning system for
disaster mitigation.
Especially, for the tsunami early warning,
DONET system is absolutely necessary
and important.
4) Provide observed data such as ocean
floor deformation derived from pressure
gauges to improve the simulation and
modeling researches about the mega thrust
earthquakes
These ocean floor deformation data are
quit necessary for the data assimilation to
improve simulation models (Figure11).
enabling the next generation of networks & services
DONET data will be applied to this new
research project.
2. FUTURE PLAN
We are developing DONET 2 with a high
voltage power system (Figure13).
We will deploy DONET2 around the
Nankai seismogenic zone (Figure14).
We have to apply the data from network to
4) Understanding of the interaction
between the crust and upper mantle
around subduction zone.
5) DONET data such as pressure gauges
will be applied to current researches
6) New research project for the estimate
of seismic linkage around the Nankai
trough mega thrust earthquakes is
starting from FY 2008 as 5 years
project (Figure12).
This project is entrusted by MEXT project
which is as a kind of Japanese government
funded project.
Copyright © 2010 SubOptic
understand the detailed crustal activities to
improve simulation model, and to mitigate
disaster damages.
In the second step, we would like to
develop and deploy the advanced ocean
floor network as a regional system and
integrate ocean and land observatory
network data using advanced ocean floor
observatory technologies.
In the next step, we would like to
collaborate with international network
systems such as NEPTUNE(Canada/US),
ESONET(Europe), MACHO(Taiwan) etc.
to progress geosciences and contribute the
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early warning system for huge earthquakes
and tsunamis (Figure15).
In international collaborations, we will
develop ocean floor network technologies
and exchange data of geosciences to
enabling the next generation of networks & services
[5] T. Narumi, S. Kodaira , Y. Tatsumi ,
M.Yamashita , T. Sato , Y. Kaiho , S.
Miura , T. No , K. Takizawa , Y. Kaneda,
Structural variations of arc crusts and rifed
margins in the southern Izu-Ogasawara
arc-backarc system, Geochem. Geophys.
Geosyst,
vol. 10, Q09X08, doi:10.1029/2008GC002146
[6] H. Matsumoto, M. Ohori, Y. Kaneda,
Study on Use of Pressure Gauges in NearField for Tsunami Prediction, Journal of
Coastal Engineering, JSCE, vol.56, p356360
understand the global dynamics such as the
global changes, environmental changes and
natural disaster hazards and mitigations.
Finally, we would like to enhance to the
importance of practical database to
improve structures and simulation using
the data assimilation based on the ocean
floor network data..
4. REFERENCES
[1] Y. Kaneda, M. Ohori, T. Nakamura,
Newly Proposed Disaster Mitigation and
Recovery for the Next Nankai Trough
Megathrust Earthquakes, Journal of
Disaster Research, vol.14 no.2,p151-152, 2009
[2] Y. Kaneda, S. Kodaira, Structural
Research on the Nankai Trough Using
Reflections and Refractions, Journal of
Disaster Research, vol4 no.2, p67-71, 2009.
[3] Y. Kaneda, K. Hirahara, T. Furumura,
New Research Project for Evaluating
Seismic Linkage Around the Nankai
Trough, Journal of Disaster Research, vol4
no.2, p61-66, 2009
[4] K.Ariyoshi,T.Hori, Jean-Pal Ampuero,
Y.Kaneda,T.Matsuzawa,R.Hino,A.
Hasegawa, Influence of interaction
between small asperities on various types
of slow earthquakes in a 3-D simulation for
a subduction plate boundary, Gondwana
Research, vol.16 no.3-4, p534-544
Copyright © 2010 SubOptic
[7] Kodaira, S., T. Iidaka, A. Kato, J.-O.
Park, T. Iwasaki and Y. Kaneda, High pore
fluid pressure may cause silent slip in the
Nankai Trough, Science, 304, 1295-1298,
2004
[8] Park, Jin-Oh, Tetsuro Tsuru, Shuichi
Kodaira, P Phil R. Cummins, and
Yoshiyuki Kaneda, Splay fault branching
along the Nankai subduction zone,
Science,Vol. 297, 1157-1160, 2002.
[9] S.Kodaira, N.Takahashi, A.Nakanishi,
S. Miura, Y.Kaneda, Subducted Seamount
Imaged in the Rupture Zone of the 1946
Nankaido Earthquake, Science, 289 104106,2000
[10] Hori, T., Mechanisms of separation of
rupture area and variation in time interval
and size of great earthquakes along the
Nankai Trough, southwest Japan, J. Earth
Simulator, 5, 8-19, 2006.
[11] Hori, T., N. Kato, K. Hirahara, T.
Baba and Y. K Kaneda, A numerical
simulation of earthquake cycles along the
Nankai trough, southwest Japan: Lateral
variation in frictional property due to the
slab geometry controls the nucleation
position, Earth Planet. Sci. Lett., 228, 215226, 2004.
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