The Spectrum of Fault Slip Behaviors

1. 18 Sep. 2013, C. Marone, Geosc500 • Mechanics of Earthquakes and Faulting • Stick-slip dynamics and Instability. Introduction to "normal earthquakes” • Fault models and the spectral signature of (normal) earthquakes • Aseismic creep and creep events, slow tectonic slip • Slow earthquakes, Low frequency earthquakes • Non-volcanic tremor: tectonic fault tremor The Spectrum of Fault Slip Behaviors

2. Stick Slip vs. Stable Sliding Earthquakes and aseismic creep events

3. Stick Slip vs. Stable Sliding THE SPECTRUM OF FAULT SLIP BEHAVIORS Incomplete

4. THE SPECTRUM OF FAULT SLIP BEHAVIORS Discrete & Fast: m/s Continuous & Slow: cm/yr Seismic: earthquake Aseismic: fault creep 10 seconds 3 km Borehole casing deformation along the San Andreas 2 years The Anime Sante church after the MW = 6.3 L’Aquila earthquake (2009) The Anime Sante church (1713) after the MW = 6.3 L’Aquila earthquake (2009) 15 m After Collettini, 2010

6. Hollister, CA http://earthquake.usgs.gov/research/creep/index.php

7. Fault Mechanics & Earthquake Physics • Aseismic slip • Creep events • Strain transients • Slow earthquakes • Episodic tremor • Silent earthquakes • Afterslip and transient postseismic deformation • Slow precursors to “normal” earthquakes • Earthquakes with a distinct nucleation phase • Normal (fast) earthquakes • Earthquakes with supersonic rupture velocity Seismic slip and aseismic faulting are end membersof a continuous spectrumof behaviors A single fault, and perhaps even a single fault patch, may exhibit both seismic and aseismic slip

8. Brittle fault zones exhibit complex rheologic behavior • Need to monitor crustal deformation at a wide range of spatio-temporal scales • Aseismic slip • Creep events • Strain transients • Slow earthquakes • Episodic tremor • Silent earthquakes • Afterslip and transient postseismic deformation • Slow precursors to “normal” earthquakes • Earthquakes with a distinct nucleation phase • Normal (fast) earthquakes • Earthquakes with supersonic rupture velocity • What causes this range of behaviors? • One (earthquake) mechanism, or several? • How best do we describe the rheology of brittle fault zones?

9. Plate Tectonics Plates are rigid 3 types of plate boundaries: divergent, convergent, transform Plates are created at divergent, destroyed at convergent plate boundaries. Transform faults form small circles to poles of rotation. Isacks, B., J. Oliver, and L. Sykes, Seismology and the New Global Tectonics J. Geophys. Res., 73, 5855-5899, 1968.

10. What is the strength of a major, plate boundary tectonic fault? Average frictional strength at seismogenic depth (10-15 km) Is it 100-200 MPa, µ ≈ 0.6, or 10-20 MPa, µ ≤ 0.3 ?

11. SAFOD The San Andreas Fault Observatory at Depth NSF EarthScope, MREFC SAFOD The San Andreas Fault Observatory at Depth $25M

12. Earthquakes and Fault Mechanics

13. 6 m M7.3 1992 Landers Earthquake, Wald, 1996 Dynamic Rupture Propagation Velocities are several km/s, as expected for elastic wave propagation February 2010 Mw 8.8 Maule EQ. Lange et al., EPSL 2012

14. Reid’s Hypothesis of Elastic Rebound (1910)

17.  s  d Static-Dynamic Friction sd Slip slip duration = rise time • Brittle Friction Mechanics, Stick-slip • Stick-slip (unstable) versus stable shear Stick-slip dynamics N x x´ K F s f

18.  Slip Weakening Friction Law s N x x´  d K F  (v) s ≠ d f L Slip Slope = -K B  s f Force x´ x C Slip Displacement Laboratory Studies Plausible Mechanisms for Instability Quasistatic Stability Criterion K< Kc; Unstable, stick-slip K > Kc; Stable sliding

19. Friction Laws and Their Application to Seismic Faulting n (a  b) Frictional Instability Requires K < Kc Kc= Dc (a-b) > 0 Always Stable, No Earthquake Nucleation, Dynamic Rupture Arrested (a-b) < 0 Conditionally Unstable, Earthquakes May Nucleate if K < Kc, Dynamic Rupture Will Propagate Uninhibited a  b Earthquake Stress Drop Seismicity ( - ) ( + ) ( - ) ( + ) Seismogenic Zone

20. Aseismic slip • Slow earthquakes, Creep events, Tsunamogenic earthquakes • Slow precursors to “normal” earthquakes • Earthquakes with a distinct nucleation phase • Afterslip and transient postseismic deformation • Normal (fast) earthquakes Key Observations, Outstanding Questions Seismic and Aseismic Faulting: End Members of a Continuous Spectrum of Behaviors What causes this range of behaviors? One (earthquake) mechanism, or several? How best do we describe the rheology of brittle fault zones? Marone, 1998

21. Stick Slip vs. Stable Sliding 2. THE SPECTRUM OF FAULT SLIP BEHAVIORS Tremor, Slow Slip, Swarms, Low frequency earthquakes, Creep, Geodetic transients, Dynamic triggering, Postseismic slip Incomplete

22. Southwest Japan Obara et al., 2004 Rogers and Dragert, 2003 Episodic Tremor and Slip Cascadia After D. Shelly (NSF EarthScope mtg.2008)

23. Earthquake warning

24. A Weeklong Tremor and Slip Episode • April 15-21, 2006 • Moment Magnitude=6.0 (April 17-20) • Average slip = 1.2 cm Sekine and Obara, 2006 Sekine and Obara, 2006 After D. Shelly (NSF EarthScope mtg.2008)

25. Family of slow, shear-slip events LFEs VLFEs SSEs Megathrust Ide et al., Nature, 2007 After D. Shelly (NSF EarthScope mtg.2008)

26. Tectonic Tremor is modulated by Love wave shear stress (Denali) and Tides Rubinstein et al., Nature, 2007 * * * * Rubinstein et al., Science, 2008

27. Faults exhibit a wide spectrum of slip behaviors • EarthScope Facility: • Fault Mechanics • Frictional Rheology • Earthquake Physics • Earthquake Hazzard

28. Laboratory Evidence for Complex Friction Behavior accelerometer wave source Effects of acoustic waves on stick–slip friction Johnson, Savage, Knuth, Gomberg & Marone, Nature, 2008. apparatus • 5 MPa normal stress • background shearing rate of 5 µm/sec

29. Stress drop in slow, quasi-stick-slip events scales with acoustic vibration amplitude Johnson, P., Carpenter, B. M., Knuth, M.,Kaproth, B. M., Le Bas, P.-Y., Daub, E. G.; and C. Marone, JGR, 2012

30. True Triaxial Stress State, Direct Shear, Pore fluid

31. Load point Fault surface Frictional Healing Steady state friction & the rate of healing vary with sliding velocity Angular quartz particles (100-150 µm), 3 mm thick, 25 MPa normal stress. Marone, 1998

32. Load point Fault surface Stress relaxation via creep

33. Sliding Friction   c Coulomb, 1785

34. Empirical laws, based on laboratory friction data V=2 V=1m/s (a-b)  Velocity weakening frictional behavior in granular fault gouge Thermally-activated process Rate and State FrictionDieterich, Ruina, Rice Dieterich State Evolution

35. n (a  b) Kc= Dc (a-b) < 0 Conditionally Unstable, Earthquakes May Nucleate if K < Kc, Dynamic Rupture Will Propagate Uninhibited Earthquake Stress Drop ( - ) ( + ) Friction Laws and Their Application to Seismic Faulting Frictional Instability Requires K < Kc (a-b) > 0 Always Stable, No Earthquake Nucleation, Dynamic Rupture Arrested a  b Seismicity ( - ) ( + ) Depth Seismogenic Zone