Workshop on the Seismogenic Zone at TrenchesSnowbird, Utah March 16-21, 2003

Secular, Transient and Periodic Crustal Movements in Japanese Subduction Zones, and Dynamics Underlying Them

Kosuke Heki

Division of Earth Rotation, National Astronomical Observatory, Japan

Contents

Keyword: Crustal deformation, Japanese Islands, Earthquakes

Secular crustal movementTokai EarthquakeVertical movements, long- and short-term

buying real estates in Japan

Transient crustal movementAfterslip and silent earthquakesWhere do they occur?

a natural creepmeter

Periodic crustal movementSeasonal change of surface loadsSeasonality of seismicity

radio astrometry

What should we do next?

Basic mode of crustal deformation in an island arc(interseismic shortening/coseismic extension)

I was here

In 1994 December,there was an earthquake

House

Front yard

North

!

Surveyed in 1994 Summer

Earthquake in 1994 December (Mw ~ 8 including afterslip)

My case …

Global Positioning System (GPS)

ArrayDense

1998- Mt.Iwatevolcano-seismic crisis

1995 Hyogoken-Nanbucoseismic + postseismic

1995,6,7,8 Seismic Swarm + Dike Injection

time-dependent inversion

Events that occurred 1994-now

1996 Boso Silent Eq.

1994 Sanriku-Haruka-Okiyear-long afterslip

comparable to the main rupture

1994 Hokkaido-Toho-Okicoseismic jump +

northward migration of the postseismic transient

1997 Kagoshima Eqs.1997

Yamaguchi

1996 Hyuganada Eq. sequencetwo earthquakes, afterslip + creep event

Normal/slow earthquakeSilent earthquakeMagma activity

2000 Miyake-Kozu eventsEruption, earthquakes, dike injection

2000- Tokai silent eventStill in progress

2000 Tottori

2001 Geiyo

Hirose et al., GRL, 26, 3237, 1999.

Events to occur (interplate)

Tokai 197XSeismic gap at Suruga Trough

Miyagi-Oki 201XAn asperity at the Japan Trench

Last rupture 1978(80% probability in the next 20 yrs)

Nankai, Tonankai 202XInterplate events at the Nankai Trough

Last rupture 1946,1944

Normal/slow earthquakeSilent earthquake

Boso silent 2008Similar events in 1983, 1990, 1996, 2002

Off-Aomori 20XXLast rupture 1968

1944

1946To

kai

EU

PH

AMNA

Izu microplate

1946 19441854 1854

1707 1707

1605 1605

14981361

1099 1096887

684

Year

(AD

)

A

A

B

B

C

C

D

D

E (Tokai region)

E

20XX 20XX

slower convergence ratelonger recurrence interval

！

Secular movement

Secular

Transient

periodic

Vertical velocities available now

Taneichi

Shizugawa

Reference

Tide Gauge

Combine horizontal and verticalvelocities to estimate slip deficits (backslips)

Slip deficit (backslip)

Savage [1983]

= +

Everywhere is Coupled

Along-strike Difference in Coupling Strength

asperity

Epicenter

(stronger at asperities)

Seis

mo

zone

genic

Yamanaka and Kikuchi, 2001

Subs

iden

ce

Uplift

Neutra

l

Uplif

t

Subsi

dence

Surface projection

of down-dip edge

max. uplift

Interseismic(backslip)

Coseismic(forward slip)

Averaged to zero ??

Slip deficit (backslip) model

Sanriku Coast

North

South

Tanesashi Coast

Kitayamazaki

uplift

subsidence

Transient movement

Transient

secular

periodic

Slow Slips

Silent Earthquake

AfterslipXX

Interseismic(decades to centuries)

Coseismic(seconds to minutes)afterslip

Stable slide

Stable slide

Fast rupture

Postseismic(days to years)

asperity

locked

From Heki et al., 1997

Slip of asperity

Slip of the region surrounding the asperity

?

Heki and Tamura, 1997. GPS

Kuji

Heki and Tamura, 1997. Strainmeter

Large asperity(large interplate earthquake)

Small asperity(characteristic small-earthquake sequences)

= Natural Creepmeter

Matsuzawa et al. (2002)

Characteristic small-earthquake sequence (= a small isolated asperity)

Afterslip of 1994 Sanriku Eq.

1993.0 1995.0 1997.0 1999.0

Cum

ula

tive s

lip (

cm)

0

10

20

year

After Igarashi et al. (2001)

1994 Dec.Sanriku Eq.

Accelerated slip at depth

Hamamatsu w.r.t. Ohgata Secular + Transient + PeriodicTransient + PeriodicTransient

A Silent Earthquake

Dike intrusion(2000/Jun-Sep)

Slow slip　Mw6.8

(2000/Sep- now)

Tokai region

Nankai Trough

5 km

35 k

m30

km

25 k

m15

km

100%

25%

75%

1997 Bungo-ChannelSilent Eq.

Mw~6.6

2000Fall - Now Tokai Silent Eq.Mw=~6.8 at 2003.0

Hyuganada 1996 Oct.19Mw~6.7

Hyuganada 1996 Dec. 3

Mw~6.7Relationship with rupture updip

Periodic movement

periodic

secular

transient

Tateyama(late April)

Earth

Subsidence

extensionextension

contraction

LoadLoad

Earth’s response to a surface load

Gojoum

e

Naruko

Tobishim

a

Shizuku

ishi

Onagaw

a

Yamada

Snow belt

Contraction in winter

Extension in winter

Subsidence in winter

Estimated snow depth(density 0.4 g/cm3)

atmosphere

Soil moisture

All cause contraction in winter

Seasonal Change of Surface Loads

snow

Sea surface height

whole (0-10kPa)(0-10kPa)

1-2 kPa (100kPa)(100kPa)

1-2 kPa (5kPa)(5kPa)1-2 kPa (0-1GPa)(0-1GPa)

AMeDAS snow depth meter

The Snow

AMeDAS average max. snow depth 1997-2001

Snow density: 0.4 g/cm3

Underestimated

The Atmosphere

Winter value w.r.t. summer value1kPa = 10 cm water

The Soil Moisture

Winter value w.r.t. summer value

Calculated using (1) potential evapotranspiration(2) precipitation

The Ocean

negative

positive

after Sato et al., PEPI, 123, 45-63, 2001

fixed

x 2

atmosphere

snow

ocean

soil moisture

Tobishima-Naruko

Kamitsushima-Susaki

Why do we care ? periodic

secular

transient

It masks transient/secular signals

It may influence seismicity

Hamamatsu w.r.t. Ohgata

…..….. When crustal strain gradually accumulates and reaches a critical condition, relevant secondary factors, such as atmospheric pressure change, would surely induce an earthquake. Hence, at one hand measuring crustal strain, and investigating major secondary factors at other hand, it seems to me possible to forecast earthquakes. How far would this expectation realistic?…..

from “Modern Science”, 1916 March (in Japanese) by T. Terada (Physicist, founder of the Earthquake Research Inst., Univ. Tokyo.)

Seasonal variation of earthquake occurrence

812

12

M > 7.9 [Ohtake & Nakahara, 1999]11 8

12

2

92

912

10

12

12

High offshore seismicity in autumn/winter

4627

75815

538510

6

6 83

6

M > 7.0 [Okada, 1982]

High seismicity in snow-covered area in spring/summer

time

Stress drop(~1MPa)

Recurrence interval(~100 yr)

Stress build-up(~30 Pa/day or ~10 kPa/yr)

Critical stress

Stress

Probability of earthquake occurrence Stress rate

Snow Load Clamps Faults

NE Japan ~ Reverse

Central Japan ~ Strike-slip

Triggering of Earthquakes

nCFF =

shear stress(positive in the direction of fault slip)

t

normal stress(positive for unclamping)

t

friction coeff. (0.2 ~0.5)

Coulomb Failure Function

10 kPa/yr

±3 kPa

0.3

P0 : background seismicity

Pm : time-varying seismicity

Expected Seasonal Variation of Seismicity

Pm 3/5 P0

Snow depth and Inland earthquake epicenters

More eq. in spring/summer in snowy area

Little seasonality in snow-free area

snowy not snowy

Does not pass the Schuster’s statistical test

Correlation ambiguous for smaller earthquakes

Opposite to ocean tidal case: correlation more significant for smaller earthquakes (Tanaka et al., JGR, 2002)

Due to small number of earthquakes

Global Mode ofSeasonal Crustal Deformation

A speculation: larger/smaller earthquakes may respondonly to longer-/shorter- term disturbances

However

Blewitt et al., A New Global Mode of Earth Deformation: Seasonal Cycle Detected, Science, 294, 2342, 2001.

Degree 1 deformation

LoadLoad

Seasonal Mass Redistribution(snow, groundwater, atmosphere, etc.)

LoadLoad

Geocenter variation

Global Mode ofSecular Crustal Deformation

J2 > 0 (Spin)

Cox & Chao, Science, 2002Dickey et al., Science, 2002

Ocean 、 Glacior, CMB ??

J2 < 0 (PGR).

J2 > 0 (1997-)..

Change in the Earth’s Oblateness (J2)

Secular Transient Periodicseasonal tidal seismic

Temporalaspects

Spatialaspects

Local

Regional

GlobalPlate motion

Interseismic

Degree 2 (J2) Geocenter variation

Degree 2 (C22)

Snow/atom./hydro. loading

PGR

Ocean loading

Pole tide

Background free oscillation

GPS seismometer

(dJ2/dt)

Postseismic(aseismic)

Crustal Movements

-1970’sGeodetic SurveyTide gaugeStrainmeter

1980’sVLBI, SLR

1990’sGPS, inSARSCG

2000’sGPS dense arraySST Gravity

Coseismic

Geodesy

Proper MotionAstrometry(r.a., decl., distance)

Astronomy

Crustal MovementdX/dt dY/dt dZ/dt

PositioningXYZ

Beyond Global

National Astronomical Observatory

Dark matter

Satellite Laser Ranging Very Long Baseline Interferometry

Two big brothers of GPS

V E R AVLBI Exploration of Radio Astrometry

Angular resolution 0.01 mas

Separation 2 A.U.

Ranging with annual parallax

Differential VLBI with dual-beam

Ranging with error of 10 %

Galactic centerWe are here

Already ranged by Hipparchus

Our Galaxy

Mizusawa Astrogeodynamics Observatory

Synergy of Geophysics and Astronomy

mm accuracy of annual crustal movement models needed

What should we do next ?

What should we do next ?

Seafloor geodesy (Positioning, strain, etc.)

Secular vertical velocity

Wait and see matter of time

Deploy the denser the array, the less ambiguous the interpretation

2001 Aug.14 M6.2(depth 38km)

AB

B position w.r.t. A

2002 Oct.14 M5.9(depth 53km)

Asperity(last rupture 1968)

Asperity(ruptured 1968, 1994)

1994 afterslip

Thank you for your attention

References

Blewitt et al., Science, 2001.

Cox and Chao, Science, 2002.

Dickey, et al., Science, 2002.

Heki, Science, 2001 (reprints available)

Heki, Earth Planet. Sci. Lett., 2003.

Heki and Miyazaki, Geophys. Res. Lett., 2001 (reprints available)

Heki, Miyazaki and Tsuji, Nature, 1997.

Heki and Tamura, Geophys. Res. Lett., 1997.

Hirose, et al., Geophys. Res. Lett., 1999.

Igarashi et al., SEISMO, 2001.

Matsuzawa et al., Geophys. Res. Lett., 2002.

Miyazaki and Heki, J. Geophys. Res., 2001.

Ozawa et al., Science, 2002.

Sato et al., Phys. Earth Planet. Inter., 2001.

Savage, J. Geophys. Res., 1983.

Tanaka et al., J. Geophys. Res., 2002.

Yamanaka and Kikuchi, 2001.