The Spectrum of Fault Slip Behaviors 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

Stick Slip vs. Stable Sliding Earthquakes and aseismic creep events

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

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

Hollister, CA

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 members of a continuous spectrum of behaviors A single fault, and perhaps even a single fault patch, may exhibit both seismic and aseismic slip 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 What causes this range of behaviors? One (earthquake) mechanism, or several? How best do we describe the rheology of brittle fault zones? Brittle fault zones exhibit complex rheologic behavior Need to monitor crustal deformation at a wide range of spatio- temporal scales

Plate Tectonics 1.Plates are rigid 2.3 types of plate boundaries: divergent, convergent, transform 3.Plates are created at divergent, destroyed at convergent plate boundaries. 4.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, , 1968.

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

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

Earthquakes and Fault Mechanics

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

Reid ’ s Hypothesis of Elastic Rebound (1910)

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

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

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

Key Observations, Outstanding Questions 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 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

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

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

Earthquake warning

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 After D. Shelly (NSF EarthScope mtg.2008)

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

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

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

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

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

True Triaxial Stress State, Direct Shear, Pore fluid

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

Fault surface Load point Stress relaxation via creep

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

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

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