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AGU annual fall meeting 2011 U41D-07. 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

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shaking and flooding by the tohoku oki earthquake

AGU annual fall meeting 2011

U41D-07

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

slide2

An unexpected earthquake!

Earthquake in the last 100 yrs (M>7.5)

6 meter wall for fukushima N-plant

http://www.snptc.com.cn/Lists/xwzx/Attachments/712/%C8%D5%B1%BE.jpg

fukushima

Raw data

Hashimoto, 2009, Nature Geoscience

slide3

Frequency Content in the Data

MYGH12: strong motion

0550: High-rate GPS

acceleration

Impossible

velocity

Hard

displacement

Easy

outline
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
slide5

Finite Fault Inversion Method

We need a layered crustal model to calculate synthetic seismogram:

A simulated annealing algorithm is used to simultaneously invert for the:

slip amplitude,

slip direction,

rise time,

rupture velocity

Jiet. al., 2002a, BSSA

Ji et. al., 2002b, BSSA

Chi-Chi Earthquake

slide6

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

slide7

Tsunami waveforms prediction:

    • COMCOT simulation with nonlinear shallow-water equation w/o dispersion
    • instantaneous seafloor deformation
slide9

Shaking produce by the earthquake

MYGH12

Strong motion

High-rate GPS

In velocity

In displacement

slide11

Summary of all High-rate GPS fits

Cross-correlation between High-rate GPS and synthetics (>5s)

slide13

Japan 3D Crustal Seismic Velocity Model (NIED):

  • http://www.j-shis.bosai.go.jp/map/?lang=en
  • Mid to upper crust only (< 20 km)
  • Horizontal resolution about 1 km
  • 34 isovelocity layers (Vs: 0.35 – 3.4 km/s)
  • Onshore and offshore regions
  • Superpose on background 1D crust and upper mantle structure
slide14

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
slide15

Effect of source refinement on shorter period energy radiation

  • Similar radiation on shallow fault
  • Enhanced radiation on deeper fault
slide17

Original source model

  • 1D seismic velocity model
  • Refined (rough) source model
  • 3D seismic velocity model
conclusion
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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