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Masayuki FUJITA Hydrographic and Oceanographic Department
Japan Coast Guard
(JCG)
Seafloor Geodesy A New Challenge
for Approaching Great Earthquakes around Japan
18th International Workshop on Laser Ranging
Fujiyoshida, Japan
11 November 2013
By Japan Coast Guard
The Great East Japan Earthquake (M9.0)
Property damages (doors)
Total Collapse : 126,583
Half Collapse : 272,315
Partially Damaged : 742,867
Personnel damages (persons)
Killed : 15,883
Missing : 2,652
Injured : 6,149
(ref. National Police Agency of Japan, Oct. 10, 2013)
14:46
11 March 2011
The Great East Japan Earthquake (M9.0)
Sendai
Fukushima Nuclear PP
Tokyo
Osaka
Pacific Ocean
source region
M7.4
M9.0
M7.7
Japan Sea
M7.5
100 km
14:46
March 11, 2011
Mt. Fuji
Tectonic Overview around Japan
North
American Plate
Eurasian Plate
Philippine Sea plate
Pacific Plate
Rupture area
Earthquake! Earthquake!
141°E 142°E 143°E 144°E
37°N
38°N
39°N
MYGW MYGI
FUKU
Oshika
Peninsula
KAMS
KAMN
24m
15m
23m
5m
15m
Miyagi
Pref.
141°E 142°E 143°E 144°E
37°N
38°N
39°N
0 50 100
km
MYGW
MYGI
FUKU
Oshika
Peninsula
KAMS
KAMN
+3m
-0.8m
+0.9m
+1.5m
+1.6m
Miyagi
Pref.
Horizontal Vertical
Seafloor Geodesy has found
huge offshore displacements !!
Sato et al. (2011) reported in Science Magazine
Earthquake!
Masayuki FUJITA Hydrographic and Oceanographic Department
Japan Coast Guard
(JCG)
Seafloor Geodesy A New Challenge
for Approaching Great Earthquakes around Japan
18th International Workshop on Laser Ranging
Fujiyoshida, Japan
11 November 2013
JCG operating SLR at Simosato - Operated more than 30 years since 1982 - Core site of the Marine Geodetic Control project in Japan
Simosato
Marine Geodetic Control Network
Poster Presentation Po35: “Satellite Laser Ranging at Shimosato Hydrographic Observatory”
(7838)
Role of Space Geodesy
for earthquake research
Role of Space Geodesy for earthquake research
• Verifying and understanding plate tectonics
– Measurement of present-day long-range movement
~Success in SLR & VLBI
Early VLBI results by Heki et al. (1987)
Early SLR results by Sasaki (1990)
(ITRF Website)
Role of Space Geodesy for earthquake research
• Verifying and understanding plate tectonics
– Measurement of present-day long-range movement
~Success in SLR & VLBI
• Monitoring crustal deformation
– Real-time measurement
– Contribution to modeling
~Development of high-density GPS network
(Modification to the figure produced by the Geodetic Society of Japan)
Intraplate movement for interseismic period
Dense GPS network in Japan
GEONET by Geospatial Information Authority of Japan
- 1200 reference points
- Real time operation
Role of Space Geodesy for earthquake research
• Verifying and understanding plate tectonics
– Measurement of present-day long-range movement
~Success in SLR & VLBI
• Monitoring crustal deformation
– Real-time measurement
– Contribution to modeling
~Development of high-density GPS network
Seafloor Geodesy ~ Open a new window in this field
How it works?
In the coseismic case for the 2011 event (M9.0)
Seafloor Geodesy ~ Open a new window in this field
Coseismic movement (onland+seafloor) associated with the 2011 event
on land (by GSI)
on seafloor (by JHOD)
M9.0
M9.0
on land (by GSI)
on seafloor (by JHOD) Horizontal Vertical
Without Seafloor data
Maximum 27m
With seafloor data
Maximum 56m
from GSI web page
Slip distribution model with and without seafloor data
Mechanism of Tsunami Excitation
Continental Plate Oceanic Plate
???
Without Seafloor data
Maximum 27m
With seafloor data
Maximum 56m
from GSI web page
Slip distribution model with and without seafloor data
How & what to measure ?
General aspects
Seafloor Geodesy
GPS/Acoustic combination technique
How to measure ?
Earthquake
What is a target?
Interseismic movement
Coseismic movement
at centimeters level !!
could be at meters level
Earthquake
8cm/y? 4cm/y? 6cm/y?
coupled area (asperity)
where landward plate is dragged down together
oceanic plate ~10cm/y
landward plate
Seafloor movement at centimeters level
What is a target?
Seafloor Geodesy
Observation by JCG
GPS/A Observation system with S/V (Hull-mounted system)
Acoustic transducer
GPS antenna
Motion sensor
Seafloor stations (Mirror-type transponders)
Seafloor
Photo by JAMSTEC
CTD XBT
XCTD
Onsite operation
≒水深
Water depth
The vessel runs at a speed of 5-8 knots.
Ranging data of about 5200 shots
測量船
1300shots
(5 hours) ×4 times
Transmitted signal Received signal
round-trip travel time
Seafloor Stations
(Mirror Transponders)
Seafloor Reference
Point
Data analysis
Seafloor Geodesy
Flow of data analysis
Round-trip travel time
b/w vessel and transponder
(1) Acoustic wave analysis
Antenna position
(2) Kinematic GPS analysis
Acoustic Wave Data
GPS Data
Attitude Data
Transducer position
Correction
Sound Speed Data
Seafloor station
position
(3) Underwater positioning
Seafloor Reference
Point
(1) Acoustic wave analysis
Received Transmitted (M-sequence signal)
Correlogram
Cross-correlation method
1λ= 100μsec ~15cm
Original M-seq signal
Flow of data analysis
Round-trip travel time
b/w vessel and transponder
(1) Acoustic wave analysis
Antenna position
(2) Kinematic GPS analysis
Transducer position
Attitude Data
Correction
Seafloor station
position
Sound Speed Data
(3) Underwater positioning
Seafloor Reference
Point
Acoustic Wave Data
GPS Data
Ranging error Sound speed error
(3) Underwater positioning
Seafloor station
Acoustic Ranging
- Station position - Sound speed
Linear Inversion
E
E
E
E
nE
E
E
z
y
x
G
t
t
t
2
1
• Errors included in the sound speed
Major error source
●Sound speed in water ~1.5km/s
●Temporal & Spatial variation
●0.1% ~ 15cm/s
D=2000m ~20cm difference
0
500
1000
1500
2000
2500
1470 1480 1490 1500 1510 1520
sound velocity [m/s]
dept
h [
m]
1.5km/s
10m/s
A.Vel
Depth
500m
Error reduction through estimation of sound speed
Sound speed estimation
1478.0
1478.5
1479.0
0 1 2 3 4 5 6 7
SV0
SV1
SV2
HOURS OF DAY
So
un
d V
elo
cit
y (
m/s
)
Observed
estimated
(Fujita et al., 2006)
temperature, salinity
CTD,XCTD,XBT
Estimation condition - horizontally layered - 2nd polynomial approximation in time
Precision of seafloor positioning ~Example of time series at TOKW~
RMS=1.7cm
East-West
RMS=1.3cm
North-South
2006 2008 2007 2009 2010 2011 2012
Seafloor Geodesy
Major Results
for the interseismic period
130 Eー
130 Eー
140 Eー
140 Eー
30 Nー 30 Nー
40 Nー 40 Nー
JCG
Tohoku Univ.
Nagoya Univ.
Distribution of Seafloor Reference Points (before the 2011 Great East Japan Earthquake)
●Landward slope of the Major trench ・Japan Coast Guard:18 about 100km interval ・Tohoku Univ. : 6 mainly off Miyagi Pref. ・Nagoya Univ. : 8 Suruga bay, Kumano basin
●Water depth mostly 1500 - 2500m (JCG)
Pacific Plate
Philippine Sea Plate
Eurasian Plate
North American
Plate
Focal regions
Tohoku
region
Nankai
region
Tohoku region
where the huge earthquake has just occurred
Seafloor Geodesy ~ Major Results
Time series of the estimated positions before the 2011 earthquake
(2002-2011.2, vs EU) Pacific
Plate
↑ 8/16/2005
(M7.2)
↑ 3/11/2011
(M9.0)
MYGI MYGW FUKU
Eastward
Northward
↑ 8/16/2005
(M7.2)
↑ 3/11/2011
(M9.0)
↑ 3/11/2011
(M9.0)
Interseismic crustal velocities (before the 2011 earthquake)
138°E 140°E 142°E 144°E 146°E
36°N
38°N
40°N
0 50 100
km
5cm /y
5.5cm/y
1.9cm/y
Pacific Plate
8cm/y
Postseismic movements (Mar.2011-Jul.2013)
KAMN
KAMS
MYGI MYGW
FUKU
CHOS
E-W
U-D
N-E
Example of time series at FUKU
2011 event
Expansion of
Seafloor Network
140° 141° 142° 143° 144° 145°
35°
36°
37°
38°
39°
40°
41°
−7000
−7000
−7000
−7000
−7000
−7000
−7000
−6000
−6000
−6000
−6000
−6000
−6000
−6000
−6000
−6000
−5000
−5000
−5000
−5000
−5000
−5000
−4000
−4000
−4000
−3000
−3000
−3000
−3000
−2000
−2000
−2000
−2000
−1000
−1000
−1000
0
0
0
0
0
#01
#02
#03
#04
#05 #06
#07
#08
#09
#10 #11
#12#13#14
#15
#16
#17
#18
#19
#20
GJT1GJT3
GJT4
GFK
釜石沖1
釜石沖2
宮城沖2
宮城沖1
福島沖
銚子沖
2011/3/11(M9.0)
By Tohoku University
20 more sites in 2012
・1000~2000m ・・・ 1
・2000~3000m ・・・ 4
・3000~4000m ・・・ 2
・4000~5000m ・・・ 7
・5000m以深 ・・・ 6
1-D to 2-D
Nankai region
where huge earthquakes were repeated and are expected in the future
Seafloor Geodesy ~ Major Results
Nankai Megathrust earthquakes
Mt.Fuji
Earthquake!
Tokyo
Nankai Megathrust earthquakes
・Repeated every 100-150 yrs
Hoei Eruption of Mt.Fuji (1707) 49 days after the earthquake
Modified from Seno (2012)
Keicho (1605)
102
107
Nankai(1946) Tonankai(1944)
Hoei (1707)
Recent
Hoei (1707)
Hoei eruption (1707) of Mt.Fuji
Report by the Committee under the Cabinet Office
30cm
3m
8cm
0cm
Tokyo
Spread of Volcanic Ash
1cm
View from SE of Mt.Fuji
Hoei Crater
Aerial photo (Hoei Crater) ※Photos are taken from Wikipedia
Seafloor reference points along the Nankai Trough (before the 2011 Tohoku earthquake)
132 Eー
132 Eー
133 Eー
133 Eー
134 Eー
134 Eー
135 Eー
135 Eー
136 Eー
136 Eー
137 Eー
137 Eー
138 Eー
138 Eー
139 Eー
139 Eー
140 Eー
140 Eー
32 Nー 32 Nー
33 Nー 33 Nー
34 Nー 34 Nー
35 Nー 35 Nー
36 Nー 36 Nー
0 50 100
kmPhilippine Sea Plate
4~5cm/year
JCG Nagoya Univ.
Tohoku Univ.
GPS station by GSI
132 Eー
132 Eー
133 Eー
133 Eー
134 Eー
134 Eー
135 Eー
135 Eー
136 Eー
136 Eー
137 Eー
137 Eー
138 Eー
138 Eー
139 Eー
139 Eー
140 Eー
140 Eー
32 Nー 32 Nー
33 Nー 33 Nー
34 Nー 34 Nー
35 Nー 35 Nー
36 Nー 36 Nー
0 50 100
kmPhilippine Sea Plate 4~5cm/year
Time series of the estimated positions along the Nankai Trough
Eastward Northward TOKE
TOKW
KUMA
SIOE
SIOW
MURO
4.4 years
3.4 years
3.4 years
4.6 years
3.4 years
4.3 years
10cm
March 11, 2011
Tohoku-oki earthquake
(M9.0)
Position reference: EU plate
East
West
Velocity vectors on the seafloor along the Nankai Trough (~2011)
132˚ 133˚ 134˚ 135˚ 136˚ 137˚ 138˚ 139˚32˚
33˚
34˚
35˚
36˚
0 50 100
km5cm /y
TOKE
TOKW
KUMA
SIOE SIOW
MURO
4.1cm/y
4.7cm/y
2.1cm/y
3.1cm/y 4.5cm/y
2.8cm/y
Back slip estimation with and without seafloor data
without seafloor data with seafloor data
Preliminary results by Yokota et al. (2013)
132˚ 133˚ 134˚ 135˚ 136˚ 137˚ 138˚ 139˚32˚
33˚
34˚
35˚
36˚
0 50 100
km5cm /y
Expansion of Seafloor Reference Points along the Nankai Trough (2011~)
EXPANDED
6 pts to 15 pts 1-D to 2-D
Expanded Seafloor Geodetic Network in Japan
0 100 200
km
Japan Coast Guard Japan Coast Guard (2011-) Nagoya University Nagoya University (2013-) Tohoku University Tohoku University (2012-)
Another Seafloor Network in Nankai region
DONET* by JAMSTEC
• Seafloor cable network
– DONET1 : 20 pts, completed in Aug.2011
– DONET2 : 30 pts, started in 2010
• Seismometer, Water-pressure gauge, Hydrophone …
(JAMSTEC homepage)
* DONET = Dense Oceanfloor Network system for Earthquakes and Tsunamis
Thank you for your attention!