1. Southern California Earthquake Center
Fault System Behavior
Southern California Earthquake Center
Annual Meeting
September 18, 2000

2. Themes Earthquakes and criticality Stress triggering
Rupture complexity
Complexity of earthquake sequences
Fault zone fine structure (damage, segmentation)

3. Accelerating moment release preceded M>6.5 on S.A. system
Clustering of intermediate events
Effect is clearest for largest events
Region size scales with event size
Bowman & Sammis

5. Landers Earthquake Rupture
Dynamic
Model
(Peyrat et al.)
Kinematic
Model
(Wald et al.)
Can fit strong motion waveforms with dynamic (spontaneous rupture)
model, slip-weakening friction
Rupture highly sensitive to prestress
“Criticality” condition for rupture growth
Connectivity of high prestress regions is key to event size

6. Landers Strong Motion Waveforms Dynamic Model vs. Recorded
(Peyrat et al.)

8. Accelerating seismicity, complex dynamics of individual earthquakes, both suggest long range correlations in stress field prior to largest events
Transition in ground motion modeling: from kinematic to dynamic modeling
New questions raised. Require advances in observation, and more advanced numerical models. Examples
Nature of fault friction
How much does geometrical complexity contribute to rupture complexity and strong motion characteristics?
Parametrization of dynamic model-based ground motion simulations?

11. Fault Zone Trapped Waves
Landers (Li et al., 1994)
Damage zone dimensions ~100m
Wavespeed degradation ~30-50%
Fault trace discontinuities associated with waveguide discontinuity at depth

12. Fault Zone Healing
(Li et al., 1998)

13. Important time-dependent effects recognized
Experiments + numerical simulations advanced our understanding of fault zone fine-structure
Level and extent of fault-zone damage
Persistence of fault discontinuities
Important time-dependent effects recognized
Poroelasticity?
Viscoelasticity?
Frictional dynamics?

14. But wait, . . .there’s more. . .
Long-term clustering of large events (E. Mojave)
Continuum complexity (frictional dynamics vs. geometrical disorder)
Thrust fault dynamics (theory, observation, implications for strong motion)
Lab experiments to validate numerical models of rupture