JANUARY 9th to 13th 2017

16th World Conference on Earthquake Engineering
Santiago - Chile

Session: General Session “Subduction Earthquakes” (ID 3019 )Date: Monday, January 9th
Time: 15:15 - 15:30
Room: Terraza Manquehue I Room (11)Broadband ground motion simulations ofmega-thrust subduction earthquakes
based on multi-scale heterogeneous-source model
Kojiro Irikura and Susumu Kurahashi
Aichi Institute of Technology, Japan

Presentation content
1.

Methodology of simulating ground motions from mega-thrust
subduction earthquakes
Segmentation
Ground motion characteristics
Period-dependent source model2.

Source dynamics of mega-thrust subduction earthquakes
Source model with a multi-scale heterogeneity
Ground motions from multi-scale heterogeneity sources3.

Simulation of strong ground motions from mega-thrust subduction
earthquakes using kinematic source modelLong-period ground motions
Short-period ground motions

4.

Conclusion

1. Methodology: Segmentation 1

Seismic Segmentation used in long-term evaluation of earthquake
occurrence by the Headquarter of Earthquake Research Promotion
Seismic activity in Japan and its vicinity

Koyama et al. (2012)

1. Methodology: Segmentation 2

Epicenters of earthquakes from 1950 to 2010 by JMA(Yellow symbols classified by magnitude)

Koyama st al.(2012）

1. Methodology: Ground motion characteristics 1

Strong ground motion records (acceleration) near the source area ofthe 2011 Mw 9 Tohoku earthquake
Wave pachet 2

Wave packet 3
Wave packet 4
Wave packet 1

Wave packet 5

After Irikura and Kurahashi (2011)1. Methodology: Ground motion characteristics 2

Short-period source model for the 2011 Tohoku earthquake
consisting of five strong-mition-generation-areas (SMGAs)

SMGA2
SMGA1

SMGA4
SMGA5

SMGA3

LxWL,W(km2)

MoMo(Nm)Stress Drop
Stress drop(MPa)

SMGA1

34×34

2.68E+2016SMGA2

23.1×23.1

1.41E+2020SMGA3

42.5×42.5

6.54E+2020SMGA4

25.5×25.5

1.24E+2025.2

SMGA5

38.5×38.5

5.75E+2025.2

1. Methodology: Ground motion characteristics 3

Comparison of observed motions and synthetic ones using
five-SMGAs’ model and the empirical Green’s function method
Black：Obs.
Red：Syn.

MiyagiOnagawa
site1. Methodology: Period-dependent source model 1

Period-dependent source rupture behavior of 2011 Tohoku earthquakeby Kubo, Asano and Iwata (2014)

Rewrite Kubo et al. (2015)

1. Methodology: Period-dependent source model

Comparison between SMGAs in this study and source locations ofpast earthquakes off the Pacific coast of Tohoku

2. Source dynamics: Multi-scale heterogeneous source model 1

Multi-scale Heterogeneous Earthquake Model (Aochi and Ide2014)
Parametric Study of Multi-scale Heterogeneous Earthquake Model2. Source dynamics: Multi-scale heterogeneous source model 2

Ground motion comparison for three scenarios (Aochi and Ide, 2014)

Small patchesのパラメータ case 1 case 2 case 3
510Stress excess Δτexcess [MPa] 15
Stress drop Δτ [MPa]51510

3. Simulation of ground motions: Long-period source model 1

An illustrative source model with multiscale heterogeneity
combining tsunami and strong motion generation(Long-Period Motion Evaluation Committee of Cabinet Office, Japan)

3. Simulation of ground motions: Long-period source model 2

Empirical relationships between seismic moment Mo
and rupture area S for subduction earthquakes

Cabinet Office (2015)

3. Simulation of ground motions: Long-perios source model 3

Empirical relationships between seismic moment Mo andcombined area of asperities Ss for subduction earthquakes

Cabinet Office (2015)

3. Simulation of ground motions: Long-perios source model 4

Comparison between observed and synthetic long-period motions
Ohmiya（SIT016)
Observed
Synthetic

F. Spectra

SMGA models by different authors

NSEW

UD

Shinjuku (TKY007)

Observed
Synthetic

F. Spectra

NSOhmiya(SIT016)

EW

Shinjuku(TKY007)
UD3. Simulation of ground motions: Short-period source model 1

Impulsive acceleration motions in near-source areas
Horizontal NS

Horizontal EW

3. Simulation of ground motions: Short-period source model 2

Heterogeneity inside ‘strong motion generation areas’ (SMGAs)

3. Simulation of ground motions: Short-period source model 3

Simulated motions from a heterogeneous model, varying rise-timesof slip velocity time functions at subfaults inside the SMGAs.

(a) Uniform model with uniform rise time of 3.7 s in all subfaults.
(b) Heterogeneous model with rise time of 2.5 s in one of the subfaults(c) Heterogeneous model with rise time of 1.0 s in one of the subfaults(d) Heterogeneous model with rise time of 0.25 s in one of the subfaults.

Conclusion 1
1. Six segments in the Pacific coast region off Tohoku from Middle
Sanriku-Oki to Ibaragi-Oki were related to the 2011 Mw 9 Tohoku
Earthquake, which are characterized by along-dip double
segmentation (ADDS). The segmentation tends to control thecharacteristics of ground motions judging from the rupture process
inversion results of near-field strong motion data as well as of thisevent.
2. Short-period motions radiated from five strong-motion-generationareas (SMGAs) in the down-dip areas closer to the Pacific coastinside the source fault of this earthquake, while extremely longperiod motion data such as tsunamis and geodetic variations weregenerated in the shallow segment closer to the trench based on theslip distributions inverted from long-period (more than 20 s) strongmotions data.

Conclusion 2
3. Long-period motions in the range of 2 – 10 s of engineeringinterest have successfully been simulated taking radiation mainly
from the same SMGAs as the short-period motions less than 2 s
into account. Impulsive motions with high accelerations whose
amplitudes are large at onsets of the wave-packets were simulated
taking heterogeneity of slip durations inside the SMGAs intoaccount.
4. We propose a multi-scale heterogeneous model as a recipe ofpredicting strong ground motions for mega-thrust subduction
earthquakes. This model provides broadband ground motions
from 0.1 s to 10 s that are engineering interest for aseismic design
and base-isolation.