2002/05/07ACES Workshop Spatio-temporal slip distribution around the Japanese Islands deduced from Geodetic Data Takeshi Sagiya Geographical Survey Institute

2002/05/07ACES Workshop Earthquake Simulations and Data Assimilation Earthquake phenomena occur in the real world. Incorporation of observational information is indispensable in order to make a forecast using simulation models. What data can be assimilated? How can we assimilate those data?

2002/05/07ACES Workshop Observation Data in Earthquake Studies Seismicity –Related to stress Seismicity rate stressing rate LURR –Assimilation model needs global applicability More studies needed. Crustal deformation –Well established model Maruyama, Okada, etc. Groundwater, SEMs, … –Needs for establishing quantitative model

2002/05/07ACES Workshop Assimilation of Deformation Data Deformation data can be modeled in terms of stress/strain change in the earth. –Dislocation theory, FEM, FDM, etc. GPS and InSAR provide deformation data with good accuracy and high (spatially and temporally, but not enough) resolution. Conventional geodetic data are available for more than a century, which is comparable to a typical recurrence interval of subduction earthquakes.

2002/05/07ACES Workshop Assimilation of Geodetic Data Limitations –Observations only at the Earth’s surface Estimate on internal stress/strain/slip has limited resolutions. –Assumptions are necessary Deformation caused by slip (or slip deficit) on the fault (or plate boundary). Fault configuration needs to be assumed. Isotropic elastic half-space is assumed in many cases. –Underdetermined problem Introduce a priori constraints

2002/05/07ACES Workshop GPS Data Daily coordinates Accuracy: 2-3mm Horizontal, 10-20mm vertical Near real-time: 2-14 days time lag Average site interval in Japan: 20-25km Network solution – systematic errors 2000 Wesrwen Tottori Earthquake (M w =6.6) Velocity GPS site Length EW NS UD

2002/05/07ACES Workshop Vertical data by GPS High temporal resolution Rate estimates is getting reliable Problems –Seasonal signal –Large scattering –Local effects, artificial subsidence Comparison with InSAR will be a good solution.

2002/05/07ACES Workshop Leveling Data Relative height change between neighboring benchmarks High (~2km) spatial resolution along leveling routes. Poor (1-10years) temporal resolution Almost uniform quality for 100 years Systematic errors Still provides the best accuracy for vertical

2002/05/07ACES Workshop Horizontal Movements of Japan revealed by GPS Earthquakes(M>5) Exaggeration: X500,000

2002/05/07ACES Workshop Data Assimilation with deformation data Representation theorem Observational equation Response functions G includes time- dependent effects (viscoelasticity). Linear equation is to be solved. A priori constraints on smoothness –ABIC minimum criterion for optimum solution

2002/05/07ACES Workshop The Nankai Trough and the Philippine Sea Plate Subduction Deformation can be attributed to slip (or slip deficit) on plate boundary interface M M M M6.7 20?? 1923 M M6?

2002/05/07ACES Workshop 1996 Boso Silent Earthquake Detected by continuous GPS monitoring Up to 20mm displacements within a week

2002/05/07ACES Workshop Inversion of A Slow Earthquake Inversion of daily coordinates at 30 GPS stations Elastic response functions Constraints on spatio- temporal smoothness Attribute to plate interface Slip migration

2002/05/07ACES Workshop 2001 Tokai Slow Event Estimated source region of the Tokai Earthquake Hamamatsu(93054) Please check our updates at (Captions in Japanese only, sorry)

2002/05/07ACES Workshop 2001 Tokai Slow Event Moment release comparable to a M6.7 earthquake Slip may slow down and slightly migrate to the east recently. Results by Ozawa et al. (2002)

2002/05/07ACES Workshop Tokai Slow Events Recorded in Legacy Data ±0mm/y -10mm/y -5mm/yr After Kimata and Yamauchi(1998) GPS: w.r.t Length East North Up -2mm/yr -4.5mm/yr

2002/05/07ACES Workshop Earthquake Deformation Cycle Coseismic, postseismic, and interseismic deformations documented by leveling in Shikoku Island, southwest Japan

2002/05/07ACES Workshop Viscoelastic Inversion of Earthquake Deformation Cycle Data analyzed –Vertical displacement in Shikoku and surrounding areas Parameters estimated –Spatio-temporal distribution of slip rate on the plate interface –All the parameters for 100 years are estimated at once. Response functions –Viscoelastic –Analytically calculated from a layed structure

2002/05/07ACES Workshop Viscoelastic Inversion of Earthquake Deformation Cycle Preliminary results –Spatio-temporal distribution of slip deficit (blue color corresponds to plate locking) Optimum solution is not yet obtained

2002/05/07ACES Workshop Obstacles in Data Assimilation: Problems to be solved BEM-type problem –Need to solve a dense matrix –Parallelization Assimilation in a spatio-temporal space –Large number of parameters/data –Kalman filtering Viscorlastic (time-dependent) response functions applicable? Faults/PBs may not be the only sources of deformation. Only gives us kinematic conditions –Interpretation is not straightforward

2002/05/07ACES Workshop Asperities and Slip Deficits on Plate Boundary Interpretation of kinematic Inversion results is not straightforward. It may not be a direct indication of mechanical coupling.