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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

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Contents Keyword: Crustal deformation, Japanese Islands, Earthquakes Secular crustal movement Tokai Earthquake Vertical movements, long- and short-term buying real estates in Japan Transient crustal movement Afterslip and silent earthquakes Where do they occur? a natural creepmeter Periodic crustal movement Seasonal change of surface loads Seasonality of seismicity radio astrometry What should we do next?

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

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I was here In 1994 December, there was an earthquake

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House Front yard North ! Surveyed in 1994 Summer Earthquake in 1994 December (M w ~ 8 including afterslip) My case …

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Global Positioning System (GPS) ArrayDense

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1998- Mt.Iwate volcano-seismic crisis 1995 Hyogoken-Nanbu coseismic + postseismic 1995,6,7,8 Seismic Swarm + Dike Injection time-dependent inversion Events that occurred 1994-now 1996 Boso Silent Eq. 1994 Sanriku-Haruka-Oki year-long afterslip comparable to the main rupture 1994 Hokkaido-Toho-Oki coseismic jump + northward migration of the postseismic transient 1997 Kagoshima Eqs. 1997 Yamaguchi 1996 Hyuganada Eq. sequence two earthquakes, afterslip + creep event Normal/slow earthquake Silent earthquake Magma activity 2000 Miyake-Kozu events Eruption, earthquakes, dike injection 2000- Tokai silent event Still in progress 2000 Tottori 2001 Geiyo Hirose et al., GRL, 26, 3237, 1999.

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Events to occur (interplate) Tokai 197X Seismic gap at Suruga Trough Miyagi-Oki 201X An asperity at the Japan Trench Last rupture 1978 (80% probability in the next 20 yrs) Nankai, Tonankai 202X Interplate events at the Nankai Trough Last rupture 1946,1944 Normal/slow earthquake Silent earthquake Boso silent 2008 Similar events in 1983, 1990, 1996, 2002 Off-Aomori 20XX Last rupture 1968

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1944 1946 T o k a i EU PH AM NA Izu microplate

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19461944 1854 1707 1605 1498 1361 1099 1096 887 684 Year (AD) A A B B C C D D E (Tokai region) E 20XX slower convergence rate longer recurrence interval ！

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Secular movement Secular Transient periodic Vertical velocities available now

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Taneichi Shizugawa Reference

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Tide Gauge Combine horizontal and vertical velocities to estimate slip deficits (backslips)

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Slip deficit (backslip) Savage [1983] = +

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Everywhere is Coupled Along-strike Difference in Coupling Strength asperity Epicenter (stronger at asperities) Seismo zone genic Yamanaka and Kikuchi, 2001

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Subsidence Uplift Neutral Uplift Subsidence Surface projection of down-dip edge max. uplift

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Interseismic (backslip) Coseismic (forward slip) Averaged to zero ?? Slip deficit (backslip) model

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Sanriku Coast North South Tanesashi Coast Kitayamazaki uplift subsidence

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Transient movement Transient secular periodic

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Slow Slips Silent Earthquake Afterslip X X

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Interseismic (decades to centuries) Coseismic (seconds to minutes) afterslip Stable slide Fast rupture Postseismic (days to years) asperity locked

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From Heki et al., 1997 Slip of asperity Slip of the region surrounding the asperity ?

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Heki and Tamura, 1997. GPS Kuji

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Heki and Tamura, 1997. Strainmeter

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Large asperity (large interplate earthquake) Small asperity (characteristic small-earthquake sequences) = Natural Creepmeter Matsuzawa et al. (2002)

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Characteristic small-earthquake sequence (= a small isolated asperity) Afterslip of 1994 Sanriku Eq. 1993.0 1995.0 1997.01999.0 Cumulative slip (cm) 0 10 20 year After Igarashi et al. (2001) 1994 Dec.Sanriku Eq. Accelerated slip at depth

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Hamamatsu w.r.t. OhgataSecular + Transient + PeriodicTransient + PeriodicTransient A Silent Earthquake

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Dike intrusion (2000/Jun-Sep) Slow slip Mw 6.8 (2000/Sep- now) Tokai region

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Nankai Trough 5 km 35 km 30 km 25 km 15 km 100% 25% 75% 1997 Bungo-Channel Silent Eq. Mw~6.6 2000Fall - Now Tokai Silent Eq. Mw=~6.8 at 2003.0 Hyuganada 1996 Oct.19 Mw~6.7 Hyuganada 1996 Dec. 3 Mw~6.7 Relationship with rupture updip

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Periodic movement periodic secular transient

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Tateyama (late April)

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Earth Subsidence extension contractionLoad Earth’s response to a surface load

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Gojoume Naruko Tobishima Shizukuishi Onagawa Yamada Snow belt Contraction in winter Extension in winter Subsidence in winter

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Estimated snow depth (density 0.4 g/cm 3 )

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atmosphere Soil moisture All cause contraction in winter Seasonal Change of Surface Loads snow Sea surface height (0-10kPa) whole (0-10kPa) (100kPa) 1-2 kPa (100kPa) (5kPa) 1-2 kPa (5kPa) (0-1GPa) 1-2 kPa (0-1GPa)

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AMeDAS snow depth meter The Snow AMeDAS average max. snow depth 1997-2001 Snow density: 0.4 g/cm 3 Underestimated

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The Atmosphere Winter value w.r.t. summer value 1kPa = 10 cm water

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The Soil Moisture Winter value w.r.t. summer value Calculated using (1) potential evapotranspiration (2) precipitation

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The Ocean negative positive after Sato et al., PEPI, 123, 45-63, 2001

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fixed x 2 atmosphere snow ocean soil moisture

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Tobishima-Naruko Kamitsushima-Susaki

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Why do we care ? periodic secular transient It masks transient/secular signals It may influence seismicity Hamamatsu w.r.t. Ohgata

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….. 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.)

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Seasonal variation of earthquake occurrence 8 12 M > 7.9 [Ohtake & Nakahara, 1999] 11 8 12 2 9 2 9 10 12 High offshore seismicity in autumn/winter 4 6 2 7 7 5 8 1 5 5 3 8 5 10 6 68 3 6 M > 7.0 [Okada, 1982] High seismicity in snow-covered area in spring/summer

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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

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Snow Load Clamps Faults NE Japan ~ Reverse Central Japan ~ Strike-slip

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Triggering of Earthquakes n CFF = 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

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P 0 : background seismicity P m : time-varying seismicity Expected Seasonal Variation of Seismicity P m 3/5 P 0

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Snow depth and Inland earthquake epicenters More eq. in spring/summer in snowy area Little seasonality in snow-free area snowy not snowy

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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 of Seasonal Crustal Deformation A speculation: larger/smaller earthquakes may respond only to longer-/shorter- term disturbances However

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Blewitt et al., A New Global Mode of Earth Deformation: Seasonal Cycle Detected, Science, 294, 2342, 2001. Degree 1 deformation Load Seasonal Mass Redistribution (snow, groundwater, atmosphere, etc.) Load Geocenter variation

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Global Mode of Secular Crustal Deformation

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J 2 > 0 (Spin) Cox & Chao, Science, 2002 Dickey et al., Science, 2002 Ocean 、 Glacior, CMB ?? J 2 < 0 (PGR). J 2 > 0 (1997-).. Change in the Earth’s Oblateness (J 2 )

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Secular Transient Periodic seasonal tidal seismic Temporal aspects Spatial aspects Local Regional Global Plate motion Interseismic Degree 2 (J 2 ) Geocenter variation Degree 2 (C 22 ) Snow/atom. /hydro. loading PGR Ocean loading Pole tide Background free oscillation GPS seismometer (dJ 2 /dt) Postseismic (aseismic) Crustal Movements -1970’s Geodetic Survey Tide gauge Strainmeter 1980’s VLBI, SLR 1990’s GPS, inSAR SCG 2000’s GPS dense array SST Gravity Coseismic

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Geodesy Proper Motion Astrometry (r.a., decl., distance) Astronomy Crustal Movement dX/dt dY/dt dZ/dt Positioning XYZ Beyond Global

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National Astronomical Observatory Dark matter

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Satellite Laser RangingVery Long Baseline Interferometry Two big brothers of GPS

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V E R A VLBI Exploration of Radio Astrometry Angular resolution 0.01 mas Separation 2 A.U. Ranging with annual parallax Differential VLBI with dual-beam

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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

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What should we do next ?

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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

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2001 Aug.14 M6.2 (depth 38km) A B B position w.r.t. A 2002 Oct.14 M5.9 (depth 53km) Asperity (last rupture 1968) Asperity (ruptured 1968, 1994) 1994 afterslip

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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.

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