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!