Fault System Behavior Southern California Earthquake Center Annual

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

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

• 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

Landers Earthquake Rupture Dynamic Model (Peyrat 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 Kinematic Model (Wald et al. )

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

• 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?

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

Fault Zone Healing (Li et al. , 1998)

• 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?

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