workshop on the seismogenic zone at trenches snowbird, utah march 16-21, 2003
DESCRIPTION
Workshop on the Seismogenic Zone at Trenches Snowbird, 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. - PowerPoint PPT PresentationTRANSCRIPT
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.