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Scenario Earthquake Shaking Mapsin Japan
Nobuyuki Morikawa
National Research Institute for Earth Science andDisaster Prevention (NIED), JAPAN2

Scenario Earthquake Shaking Maps (SESMs)
The shaking maps are evaluated for about 500 scenario
earthquakes of almost all of major active faults in Japan.

Selection of a specified scenario is essential to make a shaking map. The basic policy of the selection of ascenario earthquake is that we choose the most probable case.
For treatment of uncertainties, we assume several cases of source model and compare the results of them toshow deviation of strong-motion evaluation due to uncertainties.

Scenario Earthquake Shaking Mapsfor specified seismic-source fault
on the engineering bedrockon the ground surface

1 km × 1km

0.25 km × 0.25 km

Peak acceleration△

×

Peak velocity○△

Spectrum△×

JMA seismic intensity (IJMA)○○Time history of waveform○×

Mesh size

Peak velocity on the engineering bedrock.

JMA seismic intensity on the ground surface.

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4Strong-motion evaluation method (Recipe)
Modeling of source fault

Modeling of underground structure(Characterized source model)・Outer source parameters
・Inner source parameters
・Other source parameters

・Deep underground structure from the crust up
to seismic bedrock
・ Structure of sediments from the seismic
bedrock up to the engineering bedrock

Waveform simulation (Hybrid method)・Finite difference method (for low frequency range)
・Stochastic Green’s function method (for high frequency range)

Waveforms on the engineering bedrock
Amplification factor based on subsurface shallow
structure from the engineering bedrock to the ground surface

JMA seismic intensity on the ground surface

5Characterized source modelComplicated source model

The complicated source model is simplified by thecharacteristic source model for strong-motion prediction.
Characterized source models are composed of asperities and abackground slip area surrounding the asperities. Asperities are
the main rupture areas in the fault zone.
Source parameters required to evaluate strong-motions byusing the characterized source model are classified into threeparts.
The first part is the set of outer parameters that show themagnitude and the fault shape of the earthquake.
The second part is the set of the parameters that describe thedegree of fault heterogeneity.
The third part is the set of the parameters to define thecharacteristics of the rupture propagation.

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Determination of outer source parameters
Fault length (L) by the long-term evaluation ⇒ Outer source parameters
FormulaeM = (log L +2.9) / 0.6 (Matsuda, 1975)(4) log M0 = 1.17・M + 10.72 (Takemura, 1990)(2)’ S = 2.23・10-15・(M0×107)2/3 (M≧7)(3)’ S = 4.24・10-11・(M0×107)1/2 (M<7)(Irikura & Miyake, 2001)(5) W = S / L

7Determination of dip angle

8Determination of outer source parameters
Thickness of seismogenic zone (H) is mainly determined from activities of small or
micro earthquakes(6) If W≦H/sin δ, Wmodel = W, Lmodel = L
If W＞H/sin δ, Wmodel = H/sin δ, Lmodel = S / Wmodel(7) Smodel = Lmodel・Wmodel

9Modeling of underground structure
Surfacesoil

Seismic bedrock（Vs=3km/s）•The deep underground structure from the crust andplates up to seismic bedrock;•The structure of sediments from the seismic bedrock
up to engineering bedrock (Vs=0.4km/s～0.7m/s);•The structure of surface soils from the engineering
bedrock up to the ground surface.
Flowchart of structure modeling

SedimentSource

Deep undergroundstructureEngineering bedrock（Vs=0.4～0.7km/s）

10Structure model deeper than the seismic bedrock
Contour of the top depth of each velocity layer based on
the 3D velocity structure by Matsubara et al. (2008)(Top of the lower cruct)(Top of the mantle)

11Structure model for deep sedimentary layers
To improve the initial model, with a focus on
predominant periods, by comparing the H/V spectral
ratio of seismic records (for M5.5 or greater) obtainedby the Kyoshin Network (K-NET, KiK-net) and theH/V spectral ratio of fundamental to 4th higher-mode
Rayleigh waves obtained from velocity structure
models.
Comparing calculated waveforms with observed
waveforms for middle-scale earthquakes (around M5),
the validity of adjustments using H/V spectral ratios
was reviewed.

Depth contour of seismic bedrock12

Subsurface shallow structure modelEngineering
geomorphologicClassification(Wakamatsu &Matsuoka, 2008)

AVS30(Matsuoka &Wakamatsu,2008)

Amplification
factor for peakvelocity(Fujimoto &Midorikawa, 2006)

Site amplification factor for IJMA
from engineering bedrock (Vs=0.6km/s)
to the ground surface

Calculation of JMA seismic intensity (IJMA)
on the ground surface
Waveforms on theengineering bedrock

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Engineering
geomorphologic
classification
Average S-wave
velocity up to 30m
depth (AVS30)

IJMA on the engineering
bedrock

Amplification factor
for peak velocity

Relation between
peak velocity and IJMA

Site amplification factor
for IJMA

IJMA on the groundsurface

Consideration of surface structure(engineering bedrock ～ ground surface)

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Hybrid method for evaluation of strong-motion
Low frequency range

Matching filter
Lowfrequency
range

Finite Difference MethodHighfrequency
range
High frequency range

Stochastic Green’s function method

Superposition

deterministic

Stochastic

The technical details on the hybrid method are summarized as the‘Recipe for strong-motion evaluation’, which are published by theearthquake research committee of Japan.

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Verification of the ‘Recipe’
For inland crustal earthquakes
・ The 2000 western Tottori earthquake on October 6, 2000
(MJMA = 7.3, Mw = 6.8, Depth = 9 km)
・ The 2005 west off Fukuoka earthquake on March 20, 2005
(MJMA = 7.0, Mw = 6.6, Depth = 9 km)
・ Simulated strong-motion intensity distribution matched well toobserved one.
・ Simulated spectral level also matched well to observed one
if the location of asperity and velocity structure model could be
set up appropriately.
Uncertainty of asperity location should be considered because it isvery difficult to know the location in advance.16

Example of SESMs
Southeastern part of the Kego fault zone
・ Fault length = 27km (⇒ M = 7.2)
・ Strike-slip fault

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Characterized source model
Outer source parameters ⇒ Inner source parameters
For details, see ‘Recipe’(http://www.j-shis.bosai.go.jp/map/JSHIS2/text/news_en.html)

Deep sediments structure model

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Seismic bedrock (Vs=3.1 km/s) ～ engineering bedrock (Vs = 0.6 km/s)(Vs=1.1km/s)(Vs=1.4km/s)(Vs=1.7km/s)(Vs=2.1km/s)(Vs=2.7km/s)(Vs=3.1km/s)

19Results-1
Peak velocity distribution on the engineering bedrock (Vs=0.6km/s)
・ peak velocities atnear source fault incases 1a and 1b arelarger than cases 2aand 2b・ large peak velocity
region extends tosoutheastern of thesource fault in cases 1band 2b(forward directivity
effect andamplifications bysediments)

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Results-2
Comparison of simulated peak velocity on the engineering bedrockwith an empirical attenuation relation by Si and Midorikawa (1999)

・ Simulated peakvelocities have a tendency
small compared with theattenuation relation. The
depth to seismic bedrock isshallow (200m or less) at
the near fault region.
・ Extremely large peakvelocities are simulated incases 1b and 2b.

Results-3
Examples of velocity waveforms on the engineering bedrock(site A located just on the source fault)○ cases 1a & 1b (1 asperity model)
large amplitudes with a short duration○ cases 2a & 2b (2 asperities model)
relatively small amplitudes with a longduration

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Results-4
Examples of velocity waveforms on the engineering bedrock(site C located on a direction extending from the source fault)○ cases 1a & 2asmall amplitudes○ cases 1b & 2blarge pulse with period of about 3s(forward directivity effect+ amplification by sediments)

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Results-5
Examples of velocity waveforms on the engineering bedrock(site E located on very thick sediments)○ all cases
remarkable later phases with large
amplitudes○ cases 1b & 2b
relatively large peak amplitude(forward directivity effect)

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Site amplification factor for IJMA
from engineering bedrock (Vs=0.6km/s)
to the ground surface
IJMA on the ground surface
can be obtained by adding thevalue to the IJMA on theengineering bedrock
calculated from simulated
waveforms

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Results-6
JMA seismic intensity distribution on the ground surface

・ Large amplification
in basins causes verylarge JMA seismic
intensity on the groundsurface for all cases.
・ Difference between
basin and mountainregions is more
remarkable comparedwith peak velocity on
the engineering
bedrock.
IJMAConclusions
Scenario Earthquake Shaking Maps can understand strong groundmotion distribution if the target earthquake occurs. The maps have anadvantage that the influences of the rupture processes of the source
fault and detail underground structure, especially the deep
sedimentary layers structure, are expressed.
Problems remain:・It is not enough to consider uncertainties because only one or few
cases have been carried out for each fault.
・The underground structure models should be improved much more.
・SESMs for huge subduction-zone earthquakes are also required.
・Forward directivity effect may be overestimated because simple
rupture propagation (circular rupture propagation with a constantrupture velocity) is assumed in the simulation.

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Thank you for your attention !