STT51-01

Japan Geoscience Union Meeting 2016

Seismic Monitoring System using Optical Fiber and DAS (Distributed Acoustic Sensing)Technology*Tsunehisa KIMURA1, Gareth LEES1, Arthur HARTOG1
1.Schlumberger Fiber-Optic Technology Center
DAS (Distributed Acoustic Sensing) technology has been introduced more than 5 years ago for thedemands of pipeline monitoring and intrusion detection in Oil & Gas business. The latest opticalfiber sensing technology using ‘Phase’ data now allows DAS to record Seismic signal including VSP(Vertical Seismic Profiling). The system is called ‘hDVS’ (heterodyne Distributed VibrationSensing) in order to distinguish from pipeline monitoring system.
Unlike conventional seismic recording system, which usually use electro-magnetic sensor orGeophone, hDVS/DAS uses optical fiber as vibration sensor. It measures dynamic strain of the
optical fiber, either SMF (Single-Mode Fiber) or MMF (Multi-Mode Fiber) for entire length or thesection defined by the system. In case of SMF, the maximum length of the optical fiber is around50km with current system, while the maximum length is reduced to around 10km for MMF, depending on
the level of optical signal loss and optical sampling frequency. We are currently developing newsystem, which would be able to record over 50km length of SMF (100km is theoretical maximum lengthfor hDVS/DAS).
There are several advantages of hDVS/DAS system compare with current seismic monitoring system suchas:a) Able to use existing optical fiber installations as seismic sensor instantly.
b) One system can measure line sensor as long as 50km rather than dot sensor.
c) Easier to expand as monitoring network by using existing optical fiber network.
d) Spatial resolution and gauge length can be set as parameters.
e) Core part of optical fiber is made of high-silica glass which can be installed at harshenvironment over 200 degC where conventional sensors cannot be used.
f) Optical fiber is a passive component and no high risk of failure.
There would be more benefits can be identified.
During the presentation, mechanism of hDVS/DAS system will be explained followed by examples ofseismic data recorded during Field trials last few years.
Keywords: DAS, hDVS, Optical Fiber, Laser, Seismic Monitoring©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Seismic velocity change in Tokai region detected by Morimachi ACROSS*Shuhei Tsuji1, Koshun Yamaoka2, Ryoya Ikuta1, Toshiki Watanabe3, Akio Katsumata4, Takahiro Kunitomo2
1.Faculty of Science, Sizuoka University, 2.Graduate school of Environmental Studies, Nagoya
University, 3.ERI, University of Tokyo, 4.Meteorological Research Institute, JMA
In this study, we monitored seismic waves generated by Morimachi ACROSS using High sensitivity
seismograph network Japan (Hi-net) stations in Tokai region, and detected two types of temporal
travel time changes, secular change and co-seismic change at the time of the 2011 Tohoku-oki
Earthquake. We associated the secular and co-seismic changes to closing and opening of the cracks
beneath the region due to tectonic strain and strong shaking of the ground, respectively.
ACROSS (Accurately Controlled Routinely Operated Signal System) is a kind of artificial seismic
source system for monitoring the temporal variation in propagation properties of seismic waves in
the crust. We measured temporal variation in the travel time of S-wave during a period from 2007 to2014 at five Hi-net stations within 35km away from the ACROSS source. The temporal variation ofeach component was fit by secular, annual, half-annual and offset at the time of the 2011
Tohoku-Oki earthquake (Fig.1).
In all stations, the secular changes were advance in contrast that the co-seismic changes weredelay. The secular advances ranged from 0 to 1 ms/yr and the co-seismic delays ranged from 0 to 5ms. Both the secular and co-seismic changes showed significant polarization anisotropy. The secularadvances were larger in NW component in the five stations. On the other hand, the co-seismic delays
were larger also in the same NW component (Fig.2).
If we assume travel time was changed by closing or opening of cracks, the anisotropic changes
suggest the selective closing and opening of the cracks in the NE direction. We analyzed thecrustal strain during the observation period using GNSS earth observation network system (GEONET).
This region showed NW-SE compression and NE-SW extension as the inter-seismic and co-seismicstrain, respectively. For the secular changes, inter-seismic strain is well-matched to suggestedcrack closing. Thus the secular changes may reflect the stress changes in the crust due to tectonic
stress buildup. In the co-seismic changes, the co-seismic strain don't match to suggested crack
opening. Thus we give the following interpretation. In this region, the crack density in the strikeof NE is larger than that in other directions. The strong shaking of 2011 Tohoku-Oki earthquake
caused spontaneous opening of all cracks due to increase of pore pressure. So the observed
anisotropy should reflects persistently existing preferred orientation of cracks. Considering thegeological structure of Tokai region, the interpretation may possible.
Acknowledgments.
We used the data by Hi-net, provided by National Research Institute for Earth Science and DisasterPrevention.
Reference
Ryoya Ikuta et al., 2014, Monitoring of seismic velocity change in Tokai region underground byusing ACROSS, Seismological Society of Japan Fall meeting, S19-P07
Takahiro Kunitomo, 2014, An improvement in the Precision of Measuring Seismic Travel Time Changes
with the Use of the Hi-net Data, ZISIN, SECOND SERIES, Vol.66, No.4 97-112
Yasuhiro Yoshida, 2011, Crustal activity monitoring by using Accurately Controlled Routinely
Operated Signal System (ACROSS), Technical Reports of the Meteorological Research Institute,
Vol.63, 88-114
Figure Caption
Fig1. Travel time advance at Kakegawa Hi-net station©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Blue and red open circles show observed and predicted travel time advance with reference to Feb 28,
2007.
Predicted one is expressed by linear combination of secular, annual, half-annual variations andoffset at the time of the 2011 Tohoku-Oki earthquake (red vertical line).
Fig2. Co-seismic (top) and Secular (bottom) travel time changes
Star shows the location of Morimachi ACROSS source. Ellipses show travel time variations withuncertainty expressed by their width of the arc colored by red (advance) and blue (delay). The axesof each ellipse correspond to the travel time variation of Tt and Rr components.
Keywords: seismic ACROSS, seismic velocity change, travel time change, Hi-net, Tokai region©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

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Japan Geoscience Union Meeting 2016

Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net) Construction of subsea part of the S-net *Masashi Mochizuki1, Toshihiko Kanazawa1, Kenji Uehira1, Hiromi Fujimoto1, Shin-ichi Noguchi1,Takashi Shimbo1, Katsuhiko Shiomi1, Takashi Kunugi1, Shin Aoi1, Takumi Matsumoto1, Shoji Sekiguchi1,Yoshimitsu Okada1, Masanao Shinohara2, Tomoaki Yamada2
1.National Research Institute for Earth Science and Disaster Prevention, 2.Earthquake ResearchInstitute, University of Tokyo
NIED ( National Research Institute for Earth Science and Disaster Prevention ) has launched theproject of constructing an observatory network for tsunami and earthquake on the seafloor, after
the occurrence of the 2011 off the Pacific coast of Tohoku earthquake by the reflection that wecould not monitor the expanse of the earthquake and the tsunami outbreak on site and in real time
due to poor coverage of observation in ocean area. The project has been financially supported by
MEXT ( Ministry of Education, Culture, Sports, Science and Technology - Japan ).
The observatory network was named “S-net”. S-net consists of 150 seafloor observatories which areconnected in line with optical cables. The total length of submarine optical cable is about
5,700km. S-net system extends along Kuril and Japan trenches around Japan islands from north tosouth covering the area between southeast off island of Hokkaido and off the Boso Peninsula, Chiba
Prefecture. Each observatory equips two sets of quartz type pressure gauge and four sets ofthree-component seismometers. Digitized data from those sensors are transmitted to land and used
for early warning and precise measurement for earthquakes and tsunamis.
Two Japanese cable layer ships, which are specially designed for installation and repairing ofsubmarine telecommunication cables, have been used for installation of the S-net submarine cablesystem. The S-net submarine cable system including the observatories is buried 1m beneath theseafloor to prevent from interference with fishing industry in the area shallower than 1,500m water
depth. Those cable layer ships have capabilities of burying submarine cables. The S-net submarine
cable system was originally designed to be deployed with the cable layer ships.
Three of authors are now board on C/S SUBARU, which is one of two cable layer ships describedabove, and in charge of installation of a subset of the S-net submarine observatory network which
covers the area between east off Aomori Prefecture and south off island of Hokkaido. Installationsof 23 observatories and about 800km length optical cable on the seafloor will be completed shortlyafter.
We will report the progress of the construction of S-net submarine cable system in thispresentation.
Keywords: Seafloor Observatory Network, Tsunami, Submarine Earthquake©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net) System of landing station part *Kenji Uehira1, Toshihiko Kanazawa1, Masashi Mochizuki1, Hiromi Fujimoto1, Shin-ichi Noguchi1,Takashi Shimbo1, Katsuhiko Shiomi1, Takashi Kunugi1, Shin Aoi1, Takumi Matsumoto1, Shoji Sekiguchi1,Masanao Shinohara2, Tomoaki Yamada2
1.National Research Institute for Earth Science and Disaster Prevention, 2.Earthquake ResearchInstitute, University of Tokyo
Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net) project toconstruct a large-scale seafloor network of cable-linked observatories is in progress around Japan
Trench and Kuril Trench in Japan. The S-net consists of 150 ocean bottom earthquake and tsunami
observation stations, ocean bottom fiber optic cables which are about 5,700 km in total length,
landing stations, IP-VPN network which delivers data to data centers, and data centers. The ocean
bottom fiber optic cables connect the observation stations to land, and they are drawn inside
landing stations.
We have constructed five landing stations; Minamiboso station in Minamiboso City, Chiba Pref.,Kashima station in Kashima City, Ibaraki Pref., Watari station in Watari Town, Miyagi Pref., Miyako
station in Miyako City, Iwate Pref., and Hachinohe station in Hachinohe City, Aomori Pref.. TheWatari station is located on the third floor of reinforced concrete building, and other stations
are container-type data centers.
In the landing station, there are a high voltage receiving transformer equipment, an emergency
diesel generator with a tank which can store fuel for one week, uninterruptible power supplies(UPSs), a power feed equipment (PFE) that supplies constant DC current (1.1 A) to a submarine cableand observation units, optical receiver transmission equipment, optical wavelength divisionmultiplexing equipment (WDM), GPS clocks, data conversion servers, data transmission servers,
supervisory equipment, and so on.
In each earthquake and tsunami observatory under sea water, there installed two sets of threecomponent servo accelerometers, a set of three component velocity seismometers (analog outputs),
and two quartz type depth sensors and a set of three-component quartz type accelerometers(frequency outputs). These data are transmitted to the landing stations as the digital data which
synchronized to a GPS clock signal supplied from the landing station. The data of frequency outputs
are frequency count values at sampling frequency of 8 kHz, and these of analog outputs aredigitized values by 24 bits AD converter at sampling frequency of 1 kHz. Data conversion servers at
the landing station receive these data. The 8 kHz frequency count data are converted into physicalvalue data of 100 Hz (acceleration) or 10 Hz (water pressure and temperature), and these physicaldata are delivered to data transmission servers. The 1 kHz digitized analog data are converted into
100 Hz data by decimation filter, and delivered to data transmission servers.
The data received by data transmission servers will be transmit to Tsukuba data center, Tokyo
backup data center, Japan Metrological Agency (JMA), and related institutions via two control
center using an IP-VPN network.
Keywords: Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net)©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

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Japan Geoscience Union Meeting 2016

Installation of compact seafloor cabled seismic and tsunami observation system using ICT*Masanao Shinohara1, Tomoaki Yamada1, Shin'ichi Sakai1, Hajime Shiobara1, Toshihiko Kanazawa2
1.Earthquake Research Institute, the University of Tokyo, 2.National Research Institute for Earth
Science and Disaster Prevention
A seismic and tsunami observation system using seafloor optical fiber had been installed offSanriku, northeastern Japan in 1996 to obtain exact seismic activity and to observe tsunami onseafloor. This system is based on the tele-communication technology, and observation was performed
continuously in real-time. In March 2011, the Tohoku-oki earthquake occurred at the plate boundary,and the system recorded seismic waves and tsunamis by the mainshock. These data are useful toobtain accurate position of the source faults and source region of tsunami. However, the landing
station of the system was damaged by huge tsunami, and the observation was suspended. Because thereal-time seafloor observation by cabled system is important in this region, we decide toreconstruct a landing station and install newly developed Ocean Bottom Cabled Seismic and Tsunami(OBCST) observation system for additional observation and/or replacement of the existing system.
From 2005, we have been developed the new compact Ocean Bottom Cabled Seismometer (OBCS) systemusing Information and Communication Technology (ICT). Our system is characterized by securement ofreliability by using TCP/IP technology and down-sizing of an observation node using up-to-date
electronics technology. In 2010, the first OBCS was installed in the Japan Sea. The new OBCSTsystem is placed as the second generation of our system, and uses standard TCP/IP protocol with aspeed of 1 Gbps for data transmission, system control and system monitoring. The Wavelength
Division Multiplexing (WDM) is also introduced to reduce number of optical fibers. There are two
types of observation nodes. Both types have accelerometers as seismic sensors. One type ofobservation nodes equips a crystal oscillator type pressure gauge as tsunami sensor. Another typehas an external port for additional observation sensor by using Power over Ethernet technology.
Clock is delivered to all observation nodes from the GPS receiver on a landing station using simple
dedicated lines. In addition, clock can be synchronized through TCP/IP protocol with an accuracy of
300 ns (IEEE 1588). A simple canister for tele-communication seafloor cable is adopted for theobservation node, and has diameter of 26 cm and length of about 1.3 m.
A route for the new OBCST was selected in consideration of those of the existing cable and plans
for another new cable system, and results form a route survey in 2013. According to the route plan,
the system has a total cable length of 105 km and 3 observation nodes with 30 or 40 km spacing. Two
observation nodes have a built-in tsunami meter, and the furthest observation node has the PoE
port. At the deployment of the cable system, we attached a precise pressure gauge with digital
output to the PoE port.
Deployment of the OBCST system was carried out in September 2015 by using a commercial
telecommunication cable ship. First, the cable ship swept the seafloor along the cable route toremove obstacles on the seafloor. An end of cable was landed to the landing station and the cable
ship started deployment of the cable system offshore. In the region where the water depth is lessthan 1,000 meters, the submarine cable and the observation node closest to the coast weresimultaneously buried with using a plough-type burial machine. Burial depth is 1 meter below theseafloor. Finally, a remote operated vehicle buried the submarine cable around the landing point.
After finishing of the deployment, data recording was immediately started.
From the seismic data from the new system, it is found that the noise levels are comparable tothose at the existing cabled system off Sanriku. In addition, it is confirmed that burial of thesensor package is effective noise reduction. For water pressure data, pressure gauges have a©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

resolution of less than 1 hPa. Data from all the sensors both the new system and the existing
system are consistent.
Keywords: Cabled seafloor observation system, Ocean bottom seismometer and tsunami meter, Real-timeobservation©2016. Japan Geoscience Union. All Right Reserved.

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