THESIS, Munich, 13.06.2006

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THESIS, Munich, 13.06.2006
Using Numerical Greens Function Method to
Investigate Ground Motion Variation
Haijiang Wang LMU
In collaboration with Heiner Igel, LMU, Alain
Cochard, LMU, Michael Ewald, LMU.
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Outline

• Motivation (source related ground motion
  uncertainty)
• Numerical Greens Function approach
• Uncertainty due to hypocentre location
• Uncertainty due to varying slip distribution
• Conclusions

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Motivation
Basin effect
But few attention was paid on source complexity
(3D) ...
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Motivation

• For large earthquake, point source is not
  sufficient and at least kinematic finite source
  is necessary to describe the source process
• Special attention should be paid to the
  directivity
• Source complexity
• Static displacement (asperity)
• Rupture velocity
• Slip velocity

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Numerical Greens Function

• Theory
• Optimal largest subfault size
• Study area and fault
• Database created

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Numerical Greens Function
Theory
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Numerical Greens Function
Optimal subfault size homogeneous case
Spatial discretization (km) 1000
Temporal discretization (s) 0.0822
S-wave velocity (km/s) 3.9
Simulation time (s) 50
Study area (km) 150130x60
PML Nodes 10
Constant slip rate (m/s) 1

• Accuracy increases with the increase of
• cut-off frequency
• rupture velocity
• magnitude

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Numerical Greens Function
Study area
N
SCEC cvm version3
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Numerical Greens Function
Newport Inglewood Fault

• M6.4 Long Beach earthquake in 1933 (Hauksson and
  Gross, 1991)
• Probable source for a damaging earthquake
• Near-vertical plane and predominant right-lateral
  slip (SCEC cfm)

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Numerical Greens Function
Verification heterogeneous case
subfault size 1.5 km can be applied as the
principal subfault size to the generation of the
NGF data base
Spatial discretization 300 m
Temporal discretization 0.018 s
Lowest S-wave velocity 1.4 km/s
Simulation time 65
Number of cells 550500x150
PML Nodes 10
Magnitude 7.0
Fault dimension 16 x36 km
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Numerical Greens Function
Database
Spatial discretization (km) 0.300
Temporal discretization (s) 0.01811
Lowest S-wave velocity (km/s) 1.400
Simulation time (s) 65
Number of cells 550500x150
Fault length dimension (km) 6019
Surface grid distance (m) 600
Ground motion components 6
Total database size (Tb) 1.5
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Summary 1

• Equation for synthesization of NGFs is developed.
• Optimal subfault size is investigated both for
  homogeneous media and heterogeneous media.
• Database is created for the Newport Inglewood
  fault embedded in the Los Angeles basin with
  appropriate setup.

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Uncertainty - Hypocentre

• Outline

• Motivation
• Hypocentre locations
• Velocity snapshots
• Basin amplification
• PGV characteristics variation with hypocentre
  location

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Uncertainty - Hypocentre
Static displacement and hypocentres
Guatteri et al., 2005
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Uncertainty - Hypocentre
Velocity snapshots
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Uncertainty - Hypocentre

• Velocity Profiles

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Uncertantity - Hypocentre
PGV characteristics
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Uncertantity - Hypocentre
Varying source depth
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Summary 2

• Horizontal hypocentre variation influences the
  ground motion
• Vertical hypocentre variation has only slight
  influence on the ground motion
• In the area far from the fault, the medium plays
  main role on ground motion variation while in the
  area very close to the fault plane the hypocentre
  does

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Uncertainty - Slip

• Outline

• Quasi-dynamic rutpure process generation
• Directivity effect
• Slip variation effect
• PGV characteristics

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Uncertantity - Slip
Quasi-dynamic rutpure process
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Uncertantity - Slip
Wang et al., 2006, submitted to ESG
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Uncertantity - Slip
Directivity
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Uncertantity - Slip
Different directivity on different components
the fault perpendicular component is dominated by
the directivity effect and the fault parallel and
vertical components have significant contribution
from the 3-D structure (basin effects) and slip
distribution.
Wang et al., 2006, submitted to ESG
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Uncertantity - Slip
Three individual slips
Wang et al., 2006, submitted to ESG
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Uncertantity - Slip
PGV characteristics maximum value and standard
deviation
Wang et al., 2006, submitted to ESG
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Summary 3

• Directivity effect dominates the fault
  perpendicular component
• Fault parallel and vertical components have
  significant contribution from the 3-D structure
  (basin effects) and slip distribution.
• Slip asperity elevates the ground motion in its
  nearby area.
• The maximum seismic motion variation on the
  surface is dominated by directivity.

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Conclusions

• We investigate the ground motion variations due
  to sets of parameters using our new-developed
  method Numerical Greens Function
• Horizontal hypocentre location variations
  influence the ground motion.
• Dominant directivity effect on the fault
  perpendicular component is confirmed by our
  simulations while fault parallel components are
  controled by both the source properties and the
  basin structure, for this specific case.
• Slip asperity elevates the ground motion in its
  nearby area.
• The maximum seismic motion variation on the
  surface is dominated by directivity.

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Future Works

• Investigation of rotational motions
• Peak rotational motions
• Attenuation relations for rotations
• Source vs. 3D effects for rotations

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End Thanks