Shaking and Flooding by the Tohoku-Oki earthquake Shengji Wei*, Rob Graves**, Don Helmberger*, Jean-Philippe Avouac* and Junle Jiang* * Seismological Lab, Division of Geological and Planetary Science, Caltech ** United States Geological Survey AGU annual fall meeting 2011 U41D-07

An unexpected earthquake! Earthquake in the last 100 yrs (M>7.5) 6 meter wall for fukushima N-plant fukushima Hashimoto, 2009, Nature Geoscience Raw data

Frequency Content in the Data MYGH12: strong motion 0550: High-rate GPS displacement velocity acceleration Easy Hard Impossible

Outline 1. Use strong motion and geodetic data constrain the kinematic rupture process of the earthquake 2. Prediction: 2.1 Tsunami 2.2 High-rate GPS 3. 3D strong motion simulation 3.1 Refinements to source to enhance shorter period energy radiation 3.2 Use 3D crustal model to improve fits to observed motions 4. Conclusion

Ji et. al., 2002a, BSSA Ji et. al., 2002b, BSSA Finite Fault Inversion Method A simulated annealing algorithm is used to simultaneously invert for the: slip amplitude, slip direction, rise time, rupture velocity Chi-Chi Earthquake We need a layered crustal model to calculate synthetic seismogram:

Data resolution Data used: 14 Strong motion stations Over 1000 GPS stations (static) 5 ocean bottom GPS station 5 Ocean bottom GPS data from: Sato et. al., 2011, Science

Tsunami waveforms prediction: -COMCOT simulation with nonlinear shallow-water equation w/o dispersion -instantaneous seafloor deformation

Strong motion fits >2s

Shaking produce by the earthquake Strong motion High-rate GPS In velocity In displacement MYGH12

Prediction for the High-rate GPS

Summary of all High-rate GPS fits Cross-correlation between High-rate GPS and synthetics (>5s)

Peak-Ground Shaking and 3D Geological Feature

Japan 3D Crustal Seismic Velocity Model (NIED): Mid to upper crust only (< 20 km) Horizontal resolution about 1 km 34 isovelocity layers (V s : 0.35 – 3.4 km/s) Onshore and offshore regions Superpose on background 1D crust and upper mantle structure

Refine source model to enhance shorter period energy (following Graves and Pitarka, 2010, BSSA) Retain longer wavelength slip features (> 40 km) Retain original rupture initiation times Add stochastic slip features at shorter length scales (K -2 falloff) Replace symmetric slip-rate function with “Kostrov-like” representation including slip and depth dependence of rise-time

Effect of source refinement on shorter period energy radiation Similar radiation on shallow fault Enhanced radiation on deeper fault

PGV prediction with refined source and 3D velocity model 4s and longer original

Original source model 1D seismic velocity model Refined (rough) source model 3D seismic velocity model

Conclusion 1, Shaking came from the deeper (>30km) portion of the rupture. 2, The large tsunami originated from very large slip at shallow depth. 3, Using refined source model with 3D crustal model provides improved fit to observed motions.

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