2.11 Center for Geophysical Observation and Instrumentation

Professors: IWASAKI Takaya, KATO Teruyuki(concurrent), Koketsu Kazuki(concurrent),

MORITA Yuichi(concurrent), NAKAI Shun’ichi(concurrent), OBARA Kazusige,

SHINOHARA Masanao, UTADA Hisashi(concurrent).

Associate Professors: ARAYA Akito,　MOCHIZUKI Kimihiro，OHMINATO Takao,

TSURUOKA Hiroshi(concurrent), URABE Taku.

Assistant Professors: AOKI Yosuke(concurrent), KURASHIMO Eiji(concurrent), MAEDA

Takuto, NAKAGAWA Shigeki(concurrent), OGAWA Tsutomu, TAKAMORI

Akiteru(concurrent), YAMADA Tomoaki(concurrent)

Project Researchers: ISHIHARA Takemi, MACHIDA Yuya.

Techinical Assistants; ABE Keiko, HARADA Yasuko, FUJITA Sonomi, OOKAWA Rie.

Adjunct Research Fellows?: OHASHI Masatake, TAKAHASHI Hirotaka.

Graduate Students: DEGUCHI Takehiro, SAKAI Hirotaka, ARARAGI Kotaro ANNOURA

Satoshi.

Foreign Research Fellows: Chao Tzukai Kevin

Center for Geophysical Observation and Instrumentation was established in 2010 under the

reorganization of ERI. This center is responsible for management and maintenance of

observational facilities including seismic, volcanic and geo-electromagnetic observatories and

permanent/temporal observing stations, technical and analytical instruments. We are also

responsible for maintaining and developing our effective data acquisition and transfer system,

which contribute to the basic and inevitably important part of observational researches for

earthquake, volcano, crustal deformation and electromagnetic phenomena. Furthermore, our

center is intensively carrying out marine geophysical observation. Therefore, designing and

developing new and high tech observational systems is a very important activity of our center.

We undertake big national scientific projects of MEXT under cooperation of other divisions

of ERI including Earthquake Prediction Research Center and Coordination Center for Prediction

Research of Earthquakes and Volcanic Eruptions, in which our contribution covers a wider

research range including basic observation, data processing and interpretation.

2.11.1 Onshore observational research for earthquakes and crustal deformations

(1)Seismic observations on land(1-1) Regional seismic observation network

We are carrying out observation by the seismic observation network in Kanto, Koshinetsu

(Northern part of central Japan), Kii Peninsula, and Western Seto (SW Japan). And, two cables of

ocean bottom seismometer are maintained at the offshore of Izu Peninsula and Sanriku (NE Japan).

Those data were unified and processed with other seismic network data by the other universities and

the research institutions. Additionally, these data were combined with data by urgent/temporal

seismic observations to provide more detailed and reliable information on seismic activity.

(1-2) Urgent seismic observationWe have carried out some urgent seismic observations in collaboration with the other universities

and research institutions, in order to solve some seismic activities. After the Tohoku Earthquake

occurred, the seismic activity of Japan significantly increased. For example, the seismic swarms

occurred frequently in northern Nagano prefecture. In such a case, seismic observation just above the

hypocenters is inevitably important for the precise distribution of events to avoid significant effect

by heterogeneity structure. The precise distribution in northern Nagano prefecture was consistent

with one of the plain estimated from a focal mechanism solution. The focal mechanism solutions

were of a thrust type in northeast area and of a strike slip type in southwest area. This feature cannot

be explained simply by stress field after the Tohoku Earthquake. In the areas with the higher crustal

seismic activity, dense seismic observations by telemetry system have been undertaken to elucidate

the features of seismic activity and their temporal change [[Fig.1]]．

Fig.1. Map of temporal seismic stations operating in seismically active areas.

(2) In-situ crustal deformation measurementsWe have been conducting in-situ measurements of crustal deformation using

various sensors of strain and tilt, and compares the data with other sensors like GNSS to investigate the relation of crustal deformation with earthquake generation. The observational system comprises large-scale horizontal tunnels, and vertical boreholes and small- scale horizontal tunnels; the former systems are located in Aburatsubo, Nokogiriyama, Yahiko and Fujigawa, and the latter in Izu peninsula, Tokai, and Tonankai-Nankai areas. The large-scale horizontal tunnels employs mainly water-tube tilt meters and quartz tube strain meters, while borehole measurements uses recently developed multi-component borehole instruments. The obtained data have been regularly reported to the Coordinating Committee of Earthquake Prediction and printed in the Report of the Committee. [Figure 1] shows recent examples of observed records at Fujigawa observatory. A consortium of crustal deformation researchers are cooperating each other to promote dissemination of data publicly, for which ERI

has delivered data of Nokogiriyama, Fujigawa, Ito and Muroto. Facilities at Aburatsubo and Nokogiriyama Observatories are used for collaborative researches with other research institutes.

Fig.1. The earth’s strain, tilt (solid: float type water tube tiltmeter, dots: reading type w.t.t.),

atmospheric pressure (daily mean) and daily precipitation at the Fujigawa Observatory (2012 and

2013).

(3)Integrated observational research for strain and stress accumulation processes in inland earthquake regions

Under the national program for earthquake and volcanic eruption prediction, our center has been performing observational research to elucidate strain and stress accumulation and rupture style associated with inland earthquakes under the cooperation with Earthquake Prediction Research Center and Coordination Center for

Prediction Research of Earthquakes and Volcanic Eruptions. Since 2009, we have undertaken

an integrated observational research project in the area of 1891 Nobi earthquake, the largest

inland earthquake in Japan. This project covers a wide range of observations by regional seismic

network, dense seismic array near the fault and seismic expeditions with use of controlled

seismic sources, from which important results on crustal heterogeneity related with the inland

earthquake occurrence has being clarified (see details in Sec.2.5.1(1)).

(4) Development and maintenance of the crustal activity monitoring system

We developed new computer infrastructure, being named as the "Crustal Activity Monitoring

System" (CrAMS), which monitors the present status of the crustal activity in whole Japan through

seismicity and seismic waveforms. By providing efficient ways on accessing raw seismic data and

automatically analyzed results, it also assists researchers in ERI to do new geophysical discovery

and explore new research subjects, for activating the research in ERI.

The CrAMS stores continuous seismic waveforms transmitted in real-time in an integrated

fashion. We keep the computer infrastructure so that researchers in ERI can access those data very

easily. In addition, either of real-time or event-trigged seismic data is automatically analyzed and/or

visualized. They can be accessed from a web-based interface. This automatic data-viewing system

currently involves the following contents: Continuous seismic waveform traces of each station,

broadband multi-traces, envelopes for deep low-frequency tremor, and event-triggered waveforms of

near-field/far-field earthquakes.

2.11.2 Observational research in marine area

(1) Seafloor observation for the 2011 off the Pacific coast of Tohoku earthquake

In the source region, approximately 50 Ocean Bottom Seismometers (OBSs) were deployed at

the mainshock. Four days after the mainshock, we had started to deploy seventy-two OBSs, and

we initiated observation of the aftershocks at more than 120 sites [[Fig.1]]. A part of the

deployed OBSs were recovered in April and early May. We deployed OBSs at the same site

during the recovery and other OBSs were deployed at additional site to enlarge the observation

area [[Fig.1]]. In June, we installed spatially high-density OBS networks in the off-Miyagi and

off-Ibaraki, off-Chiba regions, and the observation continued to September, 2011[[Fig.1]]. From

September 2011 to October 2012, we performed long-term observation by using 40 long-term

OBSs in the whole source area [[Fig.2]]. During the long-term observation, we constructed

high-density OBS network in the southern source region from April 2012 to November 2012.

Long-term observation was performed in the off-Fukushima region and the southern region off

Miyagi from August 2012 to November 2013 [[Fig.2]]. From October 2013, we are carrying out

long-term observation in the region off Miyagi and Iwate.

Fig.1. Aftershock observations of the 2011 off the Pacific coast of Tohoku earthquake using OBSs

(part1).

Fig.2. Aftershock observations of the 2011 off the Pacific coast of Tohoku earthquake using OBSs

(part2).

(2) Research projects based on marine observations(2-1) Special project for the earthquakes off Miyagi prefecture

In a region off Miyagi, large earthquakes occurred repeatedly. We performed seismic monitoring

using long-term OBSs from 2005 to 2009 to obtain long-term records and detect temporal variation

of seismic activity. Long-term OBSs were deployed at the same site repeatedly. We can compare

seismic structure by marine surveys with hypocenter distribution. In the plate boundary zone, there is

a high seismicity. The subduction Pacific plate bends rapidly at depths of 20-30 km. The seismicity

in the plate boundary zone is high in region deeper than this bending [[Fig.1]]. In addition, long-term

temporal variation of seismic activity was recognized using long-term records.

Fig.1. Comparison of seismic activity with velocity structure off Miyagi, Tohoku Japan..

(2-2) Study on Tonankai, Nankai earthquakes and earthquakes occurring in trench regions

We conducted observations across the boundary using long-term OBSs above the estimated

source region of Nankai and Tonakai earthquakes From 2003 to 2008. The purpose of this

observation is to recognize seismic activity around the source region. We applied a tomographic

analysis using arrival times of earthquakes, and identified three segments about the Vp/Vs ratio

around the subducting plate interface [[Fig.1]]. Dense seafloor earthquake observation using long-

term OBSs in Japan trench and Kuril trench regions were also performed to obtain exact seismicity

from 2004 to 2009. We divided target area into five regions, and one-year observation was carried

out in each region. From these data, we estimated the geometry of the subducing Pacific plate.

Seismicity and plate geometry relate to source regions of past large earthquakes [[Fig.2]].

Fig.1. Fig.2.11.2.(4-2)-1. Average Vp/Vs distribution in Nankai trough region, SW Japan．Three segments of Vp/Vs ratio are found. Red stars indicate low frequency events by JMA.Fig.2. Fig.2.11.2.(4-2)-2. Hypocenter distribution off the Pacific coast of NE Japan using long-term ocean bottom seismometer (LT-OBS) network.

(2-3) Study on the interrelation between the Tokai, Tonankai, and Nankai earthquakes

We carried out monitoring of earthquakes, low-frequency events, tremors and vertical movement

of seafloor by spatially dense network of long-term OBSs and broadband OBSs with precise

pressure gauge from 2008 to 2013 to contribute evaluation of the interrelation between the Tokai,

Tonankai, and Nankai earthquakes. The observation area was off-Kii peninsula and a trough region

of Kii-channel. The obtained records include low-frequency events (LFEs) which differ from

ordinary earthquakes, and characteristics of low-frequency events were revealed [[Fig.1]]. Precise

pressure gauges recorded pressure changes by tsunami and ground motion due to the 2011 off the

Pacific coast of Tohoku earthquake.

Fig.1. Detection of low frequency event (LFE) and its temporal variation by long-term ocean bottom seismometers and broadband ocean bottom seismometers with pressure gauge.

(2-4) Special project on the highly strained area along western part of Tohoku arc

Seafloor seismic observation was carried out from 2008 to 2012 in the highly strained area along

western part of Tohoku arc and eastern edge of Japan Sea to evaluate a size and probability of

occurrence of a large earthquake. In the first year, seafloor observation using pop-up long-term

OBSs in the off-Joetsu region was performed. Seismic activity is concentrated in upper crust and

compressional stress with east-west direction is dominant in the region. In 2010, we deployed newly

developed Ocean Bottom Cabled Seismometers (OBCS) in the southeastern region of Awashima

island, Niigata [[Fig.1]]. The OBCS uses TCP/IP for data transmission and control of the system.

Microearthquakes occur in depths of 5-20 km below the Awashima region. We continue observation

by OBCS.

Fig.1. New compact Ocean Bottom Cabled Seismometer (OBCS) system operating in the Japan Sea.

(2-5) Geophysical and geological studies of earthquakes and tsunamis for off-Tohoku district, Japan

The 2011 off the Pacific coast of Tohoku earthquake on March 11th 2011 has the largest

magnitude in Japan and aftershock activity is high at the present. We carried out monitoring of

earthquakes, low-frequency events, tremors and vertical movement of seafloor by spatially dense

network of long-term OBSs and broadband OBSs with precise pressure gauge from 2012 to 2014 to

evaluate a size and probability of occurrence of a large earthquake and tsunami. We deployed 40

long-term OBSs in the off-Boso and off-Ibaraki regions in April. The observation period is an half

year [[Fig. 1]]. As a result, temporal changes of aftershock activity are revealed. From fall of 2012,

we performed one-year observation in the off-Ibaraki, off-Fukushima and the southern region off

Miyagi.

Fig.1. Hypocenter distribution in the southern source region of the 2011 Tohoku

earthquake with use of long-term pop-up type ocean bottom seismometers (October 2011 - November 2012).

(2-6) Research project for prevention of seismic and tsunami disaster in Nankai trough and Nansei

Syoto trench regions

Necessity for estimation of maximum size of large earthquakes in Nankai trough arises from the

occurrence of the 2011 Tohoku earthquake and consideration of interrelation of earthquake

occurrence and spatiotemporal extension of source region of earthquake and tsunami is needed. To

contribute the consideration, seafloor broadband seismic observation will be conducted from 2014 to

2022. The purpose of the observation is to obtain detailed seismic activity and low-frequency events

near trench, and to estimate characteristic of slip on plate interface. These results are expected to

contribute precise estimation of source region of huge earthquakes. In March 2014, broadband OBSs

will be deployed in Bungo-channel and the region off Miyazaki.

(3) Development of seafloor seismic and geodesy observation system

(3-1) Development of seafloor seismic and tsunami observation system with optical fiber using

Information Communication Technology

Earthquake Research Institute deployed seafloor seismic and tsunami observation system using

optical fibers off Sanriku in 1996. The Sanriku system is based on tele-commucation technology and

has high reliability, however has disadvantages for cost and operation. Therefore we develop new

system using ICT for data transmission and system control, and deployed the system off Awashima

island, Niigata in 2010. The new system has redundancy for communication and advantages of low

cost, small size and light weight. In 2011, the Sanriku system was damaged by the 2011 Tohoku

earthquake. We are restoring the Sanriku system and a new system using ICT will be deployed in

addition [[Fig.1]].

Fig.1. Fig.2.11.2.(5-1)-1. Development of the third generation OBCS system using Information and Communication Technology (ICT).

(3-2) Technology development of survey of sub-seafloor hydrothermal ore deposits

We are developing an underwater gravimeter for exploration of a seafloor hydrothermal deposit

using Autonomous Underwater Vehicle (AUV) or Remotely Operated vehicle (ROV) from 2009.

The gravity sensor is mounted on a gimbal mechanism with a fiber gyroscope. The first system was

produced in 2011 [[Fig.1]] and we evaluated the system on land. From September 6th to 9th 2012,

the first practical measurement in marine area was carried out by using JAMSTEC’s AUV Urashima

during R/V Yokosuka YK12-14 cruise to evaluate performance of the system. From data analyses,

the resolution of the gravity data from the first practical measurement is estimated to reach 0.1 mgal.

Fig.1. Underwater gravity measurement system.

(3-3) Development and application of ultra-deep ocean bottom seismometers

We have been developing compact ultra-deep ocean bottom seismometer (UOBS), and began to

apply the UOBSs to observations. In 2012, we succeeded to obtain data recovered from over 7,500

m depth two month after the settlement. In 2013, we installed 3 UOBSs in the Japan Trench during a

controlled seismic survey by JAMSTEC whose profile transect the trench axis. The UOBSs recorded

not only P but S phases so clearly that the data enabled us estimate Poisson’s ratio in the shallowest

part in and around the trench region.

(3-4) Development of broadband ocean bottom seismometer with precise pressure gauge for

detection of vertical movement of seafloor

We developed broadband ocean bottom seismometer with precise pressure gauge (BBOBSP) for

observation with ultra broadband frequency, and produced the proto-type in 2009. Because pressure

is outputted as frequency, we developed new recorder with Chip Scale Atomic Clock (CSAC) as a

reference of frequency measurement. According to the new recorder, we reduce error of frequency

measurement caused by error of oscillation in the reference. We succeeded to detect a seafloor

vertical movement caused by large aftershock of the 2011 Tohoku earthquake using the BBOBSP. At

the present, the developed BBOBSP is used practically [[Fig.1]].

Fig.1. Newly developed ocean bottom seismometers. Left: Broadband OBS with precise pressure gauge, right: OBS whose sensors are servo-type accelerometers.

(3-5) Basic development for tilt observation on seafloor

The next generation model of broadband ocean bottom seismometer (BBOBS-NX) with

burying seismic sensor in sediment was developed in ERI. We are developing a tilt observation

system on seafloor using the technology of the BBOBS-NX. First we confirmed that mass

position of a broadband sensor observed the Earth tide on land. Then, BBOBS-NX was

modified to record the mass position and deployed the proto-type on seafloor in 2012. We

obtained records for evaluation of possibility of seafloor tilt detection. From 2013, long-term

test observation is being carried out off Boso-peninsula.

3. Multi-discipline observations at active volcanoes

We conduct multi-discipline observations such as volcanic earthquakes, ground deformation,

magnetic changes, infrasound, thermal image, and other observations at 5 active volcanoes in

Japan, Asama volcano, Izu-Oshima volcano, Mt. Fuji, Kirishima volcanoes and Miyakejima

volcano, closely cooperating with VRC (volcano research center). In addition, we are carrying

out various types of observations at volcanoes other than above mentioned 5 volcanoes

cooperating with researchers at other organizations. [Figure.1] shows station distribution for

Asama, Izu-Oshima, Mt. Fuji, and Kirishima volcanoes. Here in this report, we mainly put

stress on the observations themselves. We leave the details on the scientific targets and the

results of the data analyses to the report by VRC.

Fig.1 Station distribution at Asama, Izu-Oshima, Fuji, and Kirishima volcanoes. Symbol color

indicates quality of telemetry. Blue: good condition. No data loss. Yellow: moderate condition. Slight

data loss. Red: poor condition. Moderate data loss.

(1) Asama volcano

Asama Volcano is located at the central Honshu, Japan. Recent eruptions are moderate scale

vulcanian eruptions in 2004 and small eruptions in 2008 and 2009. We conduct multi-

disciplinary observations involving broadband seismicity, GPS, tilt, infrasound, total

magnetization, thermal image, visual image etc. We perform maintenance and management of

the observation network by making AVO (Asama Volcano Observatory) and KVO (Komoro

Volcano Observatory) as base stations. Observation data are telemetered to AVO by using

wireless LAN and optical fiber networks. These data are then transferred to ERI (Earthquake

Research Institute) in Tokyo by using optical fiber main stream. All the summit stations are

connected with optical fibers. Satellite data transmission using VSAT (Very Small Aperture

Terminal), commercial telephone line, and cellular-phone network are also used according to the

local condition if an observation point. The main results obtained in the last five years from the

2009 to 2013 fiscal year are summarized below.

- In cooperation with the Florence University, we installed an infrasound array on the

western flank of Mt. Asama at the altitude of 2000m.

- We installed an additional MUON station which detects density distribution of the volcanic

edifice using cosmic ray muon.

- We newly installed four borehole tilt-meters, two of which are in the summit area, one is in

the western flank and one is in the eastern flank.

- In the northern flank of Kama-yama, a summit cone of Asama volcano, we installed a

seismic station in order to improve location accuracy of volcanic earthquakes in the summit

area.

- All the broad band seismometers are now 120sec or longer sensors.

- 4 GPS stations were newly installed targeting the magma supply path at the western side of

Asama Volcano.

(2) Izu-Oshima volcanoIzu-Oshima is a volcanic island located 150km south-west of Tokyo. During the volcanic

crisis in 1986-1987, all the residents of the island were evacuated for one month. Since 27 years

has passed since the last eruption, we need to improve the observation network. We have 29

seismic stations, 4 of them are broadband, and 14 GPS stations in the island. In electromagnetic

measurement, both passive and active techniques are applied. The former is the continuous

measurement of total magnetic intensity and the latter is an electric resistivity measurement

called ACTIVE. Infrasound measurements have also started. Near the summit of Mihara-yama,

the highest point in Izu-oshima, observation network is telemetered to OVO (Izu-Oshima

Volcano Observatory) using wireless LAN. These data are then transferred from OVO to ERI in

Tokyo by commercial telephone line. Observation stations on the flank of the volcanic edifice

are telemetered directly from each station to ERI using commercial telephone line. The main

results obtained in the last five years from the 2009 to 2013 fiscal year are summarized below.

- ACTIVE was newly installed and has been operated in the summit crater for monitoring

temporal change in electric resistivity structure.

- Telemetry system has been modernized from FM radio and expensive exclusive telephone

lines to wireless LAN and cast optical-fiber network.

- In order to reduce damages by heavy lightning, arresters and other surge protection devices

has been improved.

- Facilities damaged by salt from sea have been repaired.

(3) Mt. FujiMt. Fuji is located close to the highly populated Tokyo and adjacent area. Once it erupts,

gigantic damages due to ash fall and lava flow are expected. 300 years have passed since the

Hoei eruption in 1707, and magma accumulation in the deep reservoir is expected. We have

operated an observation network consisting of 10 seismic stations, one magnetic measurement

station, and a borehole station measuring strain, tilt and temperature. Among seismic stations 5

of them are broadband sensors. At Mt. Fuji, a similar type of telemetry system has been used.

The main results obtained in the last five years from the 2009 to 2013 fiscal year are

summarized below.

- Telemetry system has been modernized from FM radio and expensive exclusive telephone

lines to wireless LAN and cast optical-fiber network. We removed equipment used for data relay

at two locations.

- We have gradually changed the telemetry protocol from the traditional WIN protocol to

ACT protocol. The latter protocol has a function of automatic supplementation of packet-loss

during the data transmission.

- Some of the solar-powered stations suffered from power shortage due to growth of

vegetation around the station. We have performed various measures to solve the problem.

- We have restored one observation station which was hit and flown by the slush snow fall.

(4) Kirishima volcanoIn the Kirishima volcanoes located in southern Kyushu, the most remarkable event during

the 5 years interval from fiscal 2009 to fiscal 2013 is the volcanic activity at Shinmoe-dake

crater located at the center of Kirishima Mountains starting from January 2011. Before the

January 2011 eruption, we operated an observation network consists of 5 broadband

seismometers, 3 short period seismometers, and 5 geomagnetic sensors. The observation

network near the summit of Shinmoe-dake is telemetered from summit stations to flank stations

using wireless LAN. The data are then transferred from the flank stations to ERI in Tokyo using

commercial telephone lines and VSAT. Since the volcanic activity increased in 2010, we

concentrated observation resources to Shinmoe-dake. In response to the onset of sub-Plinian and

vulcanian eruptions at Shinmoe-dake in January 2011, we intensively reinforced the observation

network around the Kirishima volcanoes. Followings are part of the network improvement after

the eruption.

- We newly installed infrasound sensors around Shinmoe-dake.

- From the ground deformation observations, the position of the magma chamber which

activated during the 2011 eruption is estimated to be 10km in the northwest of Shinmoe-dake. In

order to clarify seismic structure around the magma chamber, we constructed temporary seismic

network.

- In order to detect ground deformation associated with magma migration from the chamber

to the summit of Shinmoe-dake, we extended GPS network around Kirishima volcanoes.

- All the seismic stations are equipped with broadband seismometer.

- We have repaired near summit stations which were damaged by the volcanic bomb and

corrosive volcanic gas.

- Using unmanned radio-controlled helicopter, we conducted aeromagnetic survey several

times over Shinmoe-dake, and detected the cooling process of lava filling the summit crater of

Shinmoe-dake.

(5) Miyake-jimaMiyake-jima is a volcanic island located 180km south of Tokyo. During the 2000 eruption, a

caldera of 1.6km in diameter was formed at the summit. We have conducted multi-points

electromagnetic survey. Satellite-based telemeter system, Argos, has been used. Typical interval

of volcanic activity at Miyake-jima is around 20 years. Since 13 years has passed since 2000

eruption, it is possible to have next eruption during the following 5 years. We are now preparing

for coming eruption in near future by rearranging the present electromagnetic network and

constructing a new seismic observation station at off-shore rock 10km west of Miyake-jima. At

the time of 2000 Miyake-jima volcanic activity, many OBS (Ocean Bottom Seismometers were

installed in the ocean west of Miyake-jima. Today, all the OBS were removed and thus the

location accuracy of earthquakes in the sea area is low. We are preparing installation of seismic

and GPS station at one of the rocks 10km west of Miyake-jima. We are also preparing

aeromagnetic survey over summit caldera area using unmanned radio-controlled helicopter for

the purpose of detecting temporal change in magnetic field.

(6) Other volcanoes(6-1) Sakurajima

Sakurajima-volcano is one of the most active volcanoes in Japan. Recently, volcanic activity

is increasing and thus we need to put more stress on observation of this volcano. 5 years from

2009 to 2013, we installed seismic sensors and GPS receivers at the summit area of Sakura-jima

using an unmanned radio controlled helicopter. Seismic sensors and GPS are retrieved and re-

installed every year by using the helicopter. We also installed an infrasound sensor in the

southern flank of Sakura-jima. These observations using unmanned helicopter has been carried

out under cooperation with VRC (Volcano Research Center) in ERI. At Sakura-jima, refraction

survey using artificial source is performed every year by cooperation of the universities and

research organizations all over Japan as part of the national project of volcano eruption

prediction. We attend the refraction survey every year.

(6-2)Tarumae volcanoAt Tarumae-volcano in western Hokkaido, we have performed aero-magnetic survey using

unmanned radio controlled helicopter in order to detect thermal change by repeating

observations. Gradual cooling has already been detected by this survey. Aero-magnetic survey at

Tarumae-volcano has been carried out under the cooperation with Hokkaido University, the

Hokkaido Development Bureau, JAMSTEC and VRC.

2.11.4 Observational research on geoelectromagnetism

(1) Standard observation at Yatsugatake geoelectromagnetic observatory

Standard geoelectromagnetic observation has been continued at Yatsugatake Geoelegtromagnetic Observatory as the reference for observations in Tokai and Izu areas. Baseline values of declination, horizontal and vertical components of the geomagnetic data are determined every month with the absolute measurement. Monitoring the geomagnetic total intensity anomaly in the absolute measurement room and temperature measurements have also been continued.

(2) Continuous geoelectromagnetic observation in Tokai and Izu areasIn Tokai area, the geomagnetic total intensity observation at 9 stations has

been continued. At 5 stations, variation of the geomagnetic field has also been observed. In Izu area, observation of the geomagnetic total intensity at 16 stations, long-span geoelectric field observation and precise resistivity measurement have been continuously undertaken.

5. Research on new observation methods (development of seismic and geodetic instruments using laser interferometry)

A laser interferometer is a highly sensitive and low drift displacement sensor. Its application to seismic and geodetic instruments enables us to make them more precise and compact. Besides, optical detection leads to the highly precise observation in extreme environments, such as deep underground and planetary surface where conventional semiconductor sensors are hard to use.

(1) Broadband strain observation using a long-baseline laser strainmeter

Laser strainmeters can sense a variety of ground motion over the wide time scales, from long-term crustal deformation to seismic waves at tens of hertz. We have developed a highly frequency stabilized laser and applied it to the 100-m laser strainmeter at a 1000-m underground site in Kamioka (ICRR, Univ. of Tokyo), operating with the world's highest sensitivity. We have demonstrated the formulation between the observed and the regional strains using earth tides as a reference, detection of seasonal strain change associated with pore pressure, observation of earth's free oscillation, and geodetic estimation on the seismic-moment of the distant earthquakes by means of far-field strain-step analyses. On March 11, 2011, large seismic waves and strain steps from the Tohoku Earthquake were observed without saturation, showing broadband and wide range performance of the laser interferometer [[Fig.1]]. Along with analyses of various time-scale events extending to seismology and geodesy, a long-baseline strainmeter is being constructed in collaboration with the KAGRA project for a gravitational-wave telescope in Kamioka.

Fig.1. Coseismic strain step associated with the Tohoku Earthquake.

(2) Development of optical-fiber linked instrumentsBy connecting an interferometer sensor and a light source with optical fibers,

the sensor can be made to function without power supply and be used in the extreme environment such as the deep underground and the planetary surface (high/low temperature, strong cosmic radiation, etc.). As an application, a compact broadband seismometer has been developed. The seismometer includes a small long-period pendulum, a laser interferometer as a displacement sensor to detect the pendulum motion, and optical fibers introducing laser light for environmental durability. The prototype was shown to have as good performance as the STS-1 broadband seismometer [[Fig.1]]. The laser interferometer was measured to work within the wide temperature range, -50 deg C to 290 deg C. We consider the seismometer applied to deep underground observation and planetary probe for lunar and Martian exploration.

Fig.1 Prototype broadband seismometer using an optical-fiber-linked interferometer (left) and noise performance (right, blue) as compared with STS-1 broadband seismometer (brown).

(3) Compact absolute gravimeter Absolute gravimeters are useful tools for detecting crustal deformation and

mass distribution associated with magma motion and change of ground water. A compact and mobile absolute gravimeter has been developed for the field use such as the volcanic observation. By applying an accurate fringe detection method and a seismic-noise correction mechanism, we have developed a compact practical model of about 2/3 of the conventional absolute gravimeter in size. Test observation at Kirishima volcano observatory showed its designed precision of 10-8m/s2 [[Fig.1]]. In addition, at Esashi observatory (National Astronomical Observatory, Iwate), a gravity change has been measured regularly over the period before and after the Tohoku Earthquake.

Fig.1. Compact absolute gravimeter (left) and gravity tides (right, blue dots) observed at Kirishima volcano observatory.

(4) Gravity gradiometer for the seafloor explorationA method to detect the gravity anomaly as an exploration technique of the

seafloor ore deposit is being developed. By combining the gravimeter, which detects a large-scale gravity field, with the gravity gradiometer, which measures spatial derivative of the gravity, gravity-anomaly mapping around the

localized ore deposit can be conducted efficiently. A prototype gravity gradiometer comprising an astatic pendulum and an optical sensor was developed and its detectability of 7E (1E=10−9/s2), which is sufficient to detect typical ore deposit, was confirmed from the land observation [[Fig.1]]. In September, 2012, a sea trial observation was conducted in Sagami Bay. Designed operation of the gravity gradiometer onboard the AUV (Autonomous Underwater Vehicle), acoustic communication, and proper data acquisition were confirmed without serious problems.

Fig.1. Gravity gradiometer developed for the seafloor exploration.

2.11.6 Observational research on strong ground motion

(1) Operation of Strong Motion Observation Networks

We are performing observational researches based on the high-density strong motion observation

networks in the Izu-Suruga Bay region, the Ashigara Valley, and others [[Fig.1]], continuing from

the time of “Strong Motion Seismograph Observation Center”. The stations in the Izu-Suruga Bay

region are located on outcrops of the representative rocks, in order to observe the source effects of a

hypothetical Tokai earthquake. Meanwhile, the stations in the Ashigara Valley were installed in 1987

in order to study the effects of surface geology on strong ground motion, and so this region is

considered to be an international test site for studies on the effects. For recent example, strong

ground motions from the 2009 Suruga Bay and 2011 Tohoku earthquakes were observed

successfully.

Fig.1. Strong motion observation networks for observational researches. The red and yellow circles

denote ground and borehole stations, respectively.

(2) Joint strong motion observations with other organizations

To investigate the generation mechanism of strong ground motion and building behavior under

strong ground motions, we are performing joint strong motion observations with other universities

such as the Shinshu and Fukui universities and other institutions.

(3) Provisional observations using mobile strong motion seismometers

We developed mobile strong motion seismometers, and have been used for observing strong

ground motions from aftershocks of such large earthquakes as the 2011 Tohoku earthquake. These

seismometers have amplifiers so that we can observe microtremors as well. They were actually used

for microtremor explorations in City of Kochi and Sanjo area in Niigata Prefecture. They are also

used by other universities under the framework of a joint usage/research center of Japanese

universities

(4) Releasing the strong motion database to the public

We had been developing a database system for archiving and providing public access to observed

strong motion records from 2009, and began releasing the data to the public in 2010, and continue

the release after this at the site (http://smsd.eri.u-tokyo.ac.jp/smad/).

2.11.7 Activities of telemetry office

(1) Operation of telemetry systemTelemetry Office has been operating a telemetry network for observation of earthquakes and

volcanoes. Most of the sensors connected are seismometers and the rest of them include

tiltmeter, extension-meter, GPS, magnetometers etc. The mission of the telemetry system is to

safely collect and store the continuous data from the various sensors which researchers have

installed at remote sites, and sometimes to carry out event processing. The means for

transmission include various IP communication such as satellite VSATs, ISDN, ADSL, optical

fiber, wireless LAN, cellular network. The number of observation sites, which varies according

to the projects underway, is about 200 as of Jan. 2014. As for the satellite telemetry system, we

have two hub stations in Tokyo and Nagano to control upto 140 VSATs which are powerful tool

especially for the studies in remote mountains and islands [[Fig.1]]. In the period from 2012 to

2013, Nanometrics VSATs were replaced by a new generation’s Hakusan and likewise surface

telemetries LT8500 by LF series. Since Feb. 2013, a new disaster-resistive data collection

scheme, in which data from remote stations are sent directly to a JDXnet node, has been

running.

Fig.1 VSAT test site and hub station at Komoro Observatory, Nagano.

(2) Operation of data exchange system between universities and other organizationsIn order to realize the nation-wide distribution of real-time observation data, Telemetry

Office, in cooperation with other universities and EVIC ERI, has built and been maintaining

the JDXnet (Japan Data eXchange network) which utilizes the L2VLAN service of both JGN-

X and SINET4 data highways and connects many research universities and institutions

[[Fig.1]]. Telemetry Office also, representing the universities, is exchanging real-time data

with JMA and NIED at the TDX (Tokyo Data eXchange) site, Otemachi, Tokyo. To realize

the systems above, Telemetry Office is running the proprietary 300km-long optical fiber

network which interconnects JDXnet nodes, TDX, satellite hubs and ERI. Consequently wide

range of researchers in Japan can have access to real-time data from over a thousand

observation stations.

Fig.1 Schematic diagram of JDXnet (Japan Data eXchange network). Only SINET4 part is shown and JGN-X part is omitted for simplicity.

(3) User support for collected dataThe data collected by the telemetry and data exchange systems are offered to the researchers

in and out of ERI through the network. The service includes the distribution of real-time data

via the Internet or JDXnet, as well as on- and off-line use of stored data. The Telemetry Office

is supporting the users both technically and procedurally.

(4) Management of shared-use instrumentsTelemetry Office offers over 1,000 units of observation instruments including VSATs,

surface telemetries, data loggers and seismometers for lending to the researchers of universities

and other institutions, by the rule of the ERIs shared-use. The number of units lent as of Jan.

2014 is about 760.