the 2011 Tohoku Earthquake detected by GPSacoustic geodetic observation Tadashi Ishikawa Hydrographic and Oceanographic Department Japan Coast GuardJCG UNAVCO 2012 Science Workshop Mar 1 2012 ID: 806358
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Slide1
Seafloor movements associated with the 2011 Tohoku Earthquake detected by GPS/acoustic geodetic observation
Tadashi IshikawaHydrographic and Oceanographic DepartmentJapan Coast Guard(JCG)
UNAVCO 2012 Science WorkshopMar. 1, 2012
Mariko Sato, Naoto
Ujihara
, Shun-
ichi
Watanabe(JCG)
Akira Asada, Masashi Mochizuki (Univ. of Tokyo)
Hiromi Fujimoto,
Motoyuki
Kido (Tohoku Univ.)
Keiichi Tadokoro (Nagoya Univ.)
Slide2OutlineJCG has been a developing a system for precise seafloor geodetic observation with the GPS/Acoustic combination technique.The primary purpose is to detect the seafloor crustral movement caused by the subduction of the oceanic plate.JCG have succeeded in detecting seafloor movements caused by the 2011 Tohoku earthquake.
Slide3Outline
Objective ~ What to measure ~
Observation System ~ How to measure ~
Observation Results
~
Seafloor movements associated with the Tohoku EQ
~
Slide4Earthquake distribution around JAPAN
Eurasian platePacific
platePhilippine Sea
plate
North American
plate
depth of hypocenter
Hypocenter distribution
(1998-2007, M>4)
Japan has historically suffered damage from huge
earthquakes.
The focal regions of such huge earthquakes usually lie beneath the seafloor, especially on the side of the Pacific Ocean.
Japan Trench
Nankai
Trough
1 Objective
Slide5Mechanism of plate boundary type earthquakeMechanism of Earthquakes
1 Objective
Eurasian plate
Pacific
plate
Philippine Sea
plate
North American
plate
8-9cm/yr
3-5cm/yr
C
rustal deformation data is the one of the most important information to investigate the
interplate
coupling
Slide6Ground station for monitoring Crustal deformaition (GPS,SLR,VLBI)
・MEXT・Universities・NIED・GSI・
JCG・AISTGEONET
Dense GPS network over
1200
sites
GEONET was established for the monitoring the crustal deformation
by GSI (Geospatial Information Authority of Japan)
1 Objective
Slide7Crustal deformation detected by GEONET (1996-1999)
GEONET GPS station
reference point
GEONET revealed many interesting geodynamic phenomena relating to the plate motion, mechanism of
earthquakes and volcanic activity.
1 Objective
Slide8A lot of geodetic data on the ground
However1 Objective
Slide9・MEXT
・Universities・NIED・GSI・JCG・AIST
TOHOKU
TOKAI
TONANKAI
NANKAI
Focal regions of Huge Earthquake lie beneath the seafloor
Lack of data in the sea area limits the investigation of geodynamic phenomena
1 Objective
Slide10Our Seafloor Reference Points1 Objective
Nankai
TroughJapan Trench
TOHOKU
TOKYO
Since 2000, The JCG has installed seafloor reference points to monitor the crustal deformation in the
sea area
Terrestrial
Seafloor
GEONET
Seafloor
Reference Point
technique
GPS
GPG/Acoustic
organization
GSI
JCG
# of sites
~1200
27
Depth:1000-3000m
Slide11Outline
Objective ~ What to measure ~
Observation System ~ How to measure ~
Observation Results
~
Seafloor movements associated with the Tohoku EQ
~
Slide12Terrestrial
Precise measurements using Electromagnetic waves (GPS, SLR, VLBI, ....)Undersea
Cannot use Electromagnetic wave due to absorption in seawater
Measurements using Acoustic Wave
How to measure the seafloor movement ?
The
idea is based on early works by SIO (e.g.
Spiess
, 1985)
GPS/Acoustic Combination Technique
2
Observation System
Slide13GPS/Acoustic Combination Geodetic Observation2 Observation System
Kinematic GPS Positioning
Oceanic Plate
Plate boundary
Terrestrial
GPS stations
Acoustic Ranging
Seafloor
stations
(acoustic transponder)
Survey vessel
Continental Plate
The combination of GPS Positioning and Acoustic
Ranging
enables seafloor positioning
Slide14System Configuration2
Observation SystemKinematic GPS Positioning
Acoustic Ranging
Seafloor Positioning
To determine the position of the on-board GPS antenna
To measure the travel time b/w the on-board transducer and seafloor transponder
To determine the position of the seafloor transponders with cm-level accuracy
Slide15On-board Unit
GPS Antenna
(Trimble Zephyr Geodetic)
Acoustic Transducer
(Link-Quest custom)
Fiber Optic Gyroscope
(IXSEA PHINS)
Survey vessel "MEIYO"
2
Observation System
Slide16Seafloor Unit
Depth
（（（）））
（（（）））
（（（）））
（（（）））
Transponders are installed at seafloor by a free fall
Photo by JAMSTEC
One reference point consists of four acoustic transponder
2
Observation System
Slide17Flow of data analysis
Seafloor Transponder position
Round-trip travel
time
b/w transducer and transponder
Acoustic signal analysis
Acoustic Wave Data
Sound Speed Data
Underwater
positioning
Antenna position
Kinematic
GPS analysis
Transducer position
GPS Data
Attitude Data
Convert
Fujita et al., EPS 2006
2
Observation System
Slide18KGPS analysis
GEONET(GSI)
Terrestrial Reference
Station
Mast-top GPS antenna
RINEX; 2Hz data sampling
Ephemeris; IGS Final orbit
Offshore observation ; very long base line (over 100km)
Using IT(
Interferometric
Translocation) software developed by O.L. Colombo(NASA)
Ephemeris
2
Observation System
Determination of the mast-top antenna position
Slide19Acoustic Ranging
10kHz acoustic pulse (ID +
Mesurement)Coded with M-sequence codeUsing Cross-Correlation method
ID
ID
Mirror-type Transponder at Seafloor
Return the signal if ID number is identified
ID
ID
Hull-mounted Acoustic Transducer
Receive
Transmit
Measurement
of the round-trip travel time b/w vessel and transponder
2
Observation System
102ms
204ms
Slide20Underwater positioning
Transducer position determined by KGPS analysisAcoustic travel timedetermined by signal analysis
Sound Speedobtained by CTD and XBT
Determine Transponder Position
with cm precision
Distance b/w
Transducer and Transponder
2
Observation System
Slide21Outline
Objective ~ What to measure ~
Observation System ~ How to measure ~
Observation Results
~
Seafloor movements associated with the Tohoku EQ
~
Slide22Our result obtained at Tohoku regionCrustal deformation (interseismic period) caused by subduction of the Pacific plateCoseismic movement caused by the 2011 Tohoku earthquake
Postseismic movement after the 2011 Tohoku earthquakebefore the earthquake
after the earthquakeat the earthquake
3
Observation Result
Slide233 Observation Result
Fukushima
Miyagi
5.5cm/yr
1.9cm/yr
Pacific plate
8~9cm/year
The
seafloor stations
moved toward west
2-6
cm per year.
Off
Fukushima
region is
slower than
off
Miyagi
region.
North American
plate
Crustral
movement caused by the
subduction
of the Pacific plate
before the Tohoku Earthquake
Tokyo
Slide24Observation date after the Tohoku EQ
date
KAMN
KAMS
MYGI
MYGW
FUKU
CHOS
2000-2011
Regular Observation (almost 1-3 times per year)
Mar. 11, 2011
the 2011 Tohoku earthquake
Mar. 27-29
2012
2344
616
Apr. 3-5
1421
1310
Apr. 12-13
2717
2424
Apr. 18
4779
MYGW
MYGI
FUKU
KAMN
KAMS
CHOS
#
of Acoustic ranging shot
Observation error depends on the number of acoustic shot
Ordinary: ~5000 shots
2-5cm
Urgent observation after EQ:
1/8-1/2 of ordinary case
over 10-20cm
3 Observation Result
Slide25Coseismic movements associated with the Tohoku EQ3 Observation Result
The seafloor stations
(near the epicenter) moved4-5 times larger than the terrestrial GPS stations.
The transition uplift to subsidence toward west
may be the key to estimate the area of the source region.
Sato et al., Science 2011
Slide26Result of Tohoku Univ. (GJT3 & GJT4)
GJT4GJT3
Kido et al., GRL 2011
Slide27Estimated coseismic slip from geodetic data by GSI
Estimated by terrestrial GPS data only
Estimated by terrestrial GPS data and seafloor GPS/Acoustic data Maximum 27m
Maximum 56m
from GSI web site
3
Observation Result
Ozawa
et al.,
Nature
2011
Slide28Estimated by Tsunami waveform inversion
>40m
3 Observation ResultFujii
et al., EPS 2011
Estimated by terrestrial GPS data
and
seafloor GPS/Acoustic data
Maximum 56m
Slide29Postseismic movement 3 Observation Result
from GSI web site
Horizontal displacement
after the
mainshock
observed by GPS network (GEONET)
Slide30Postseismic movement 3 Observation Result
Understanding of this result is the subject of future investigation
MYGI
Slide31Future OutlookReinforcement of the seafloor observation networkTohoku regionTohoku Univ. and Nagoya Univ. are planning to install 20 new GPS/A sitesNankai
regionJCG has installed 8 new GPS/A sites in Jan. 2012
Slide32Planned GPS/A sites(~20)
Compatible with JCG systemMain objectives: ・Afterslip distribution
・Coupling near the trench
provisional plan
New site
Existing site
(JCG & Tohoku Univ.)
Tohoku Univ. & Nagoya Univ.
Slide33Repeating Earthquake along Nankai Trough
1605
Keicho EQ
1707
Hoei
EQ
1854
Ansei
Nankai
EQ(M8.4)
Ansei
Tokai
EQ(M8.4)
1944
Tonankai
EQ(M7.9)
1946
Nankai
EQ(M8.0)
????
102
147
92
NANKAI
TONANKAI
TOKAI
Nankai
Trough
Suruga Trough
684
887
1099
1361
1498
Philippine Sea
plate
OSAKA
NAGOYA
Slide34Reinforcement of observation along Nankai Trough
Existing station
New station
Nagoya Univ.
Tohoku Univ.
TOKAI
TONANKAI
NANKAI
Jan. 2012
The JCG installed
eight
new stations
along
Nankai
Trough
Slide35Crustral deformation (2006-2011)
5cm/yr3cm/yr
4cm/yr
2cm/yr
3cm/yr
4cm/yr
5cm/yr
Philippine sea
plate
3-5cm/yr
Eurasian
plate
Slide36SummaryWe have been carrying out GPS/Acoustic seafloor geodetic observations on the landward of the major trenches in the Pacific Ocean.
We detected seafloor movement associated with the Tohoku earthquake. This results will lead to more precise estimation of the fault slip. Seafloor geodetic observation gives fruitful knowledge about
subduction-zone earthquakes.