1992 M=7.3 Landers shock increases stress at Big Bear Los
Angeles Big Bear Landers First 3 hr of Landers aftershocks plotted
from Stein (2003) Slide 2 1992 M=7.3 Landers shock promotes the
M=6.5 Big Bear shock 3 hr later Los Angeles Big Bear Landers First
3 hr of Landers aftershocks plotted from Stein (2003) Slide 3 and
promotes the M=7.1 Hector Mine shock 7 yr later Los Angeles Hector
Mine First 7 yr of aftershocks plotted from Stein (2003) Slide 4
Arguments for static stress triggering Correlation of stress change
& seismicity rate change (Stein, 1999; Parsons, 2002) Tidal
triggering of quakes & tremor (Cochran et al, 2004; Tanaka et
al, 2004) Swarms triggered by creep (Vidale & Shearer, 2006;
Lohman & McGuire, 2007) Seismicity rate drop in stress shadows
(Toda & Stein, 2004; Ma et al, 2005; Marsan & Nalbant,
2005: Toda et al, 2005; Mallman & Parsons, 2008; Chan &
Stein, 2009) Arguments for dynamic stress triggering Remote
triggering by Love waves of large mainshocks (Hill et al, 1993;
Brodsky et al, 2000; Brodsky & Prejean, 2005; Gomberg &
Johnson, 2005; Velasco et al, 2008) Dynamic stress directivity may
explain asymmetry in aftershock distribution of large mainshocks
(Kilb, Gomberg & Bodin, 2000 & 2002; Doser et al, 2009) No
seismicity rate drop in stress shadows (Marsan, 2003; Felzer &
Brodsky, 2004) Slide 5 Tectonic setting (CGS report, 2003)
Chelungpu fault can be taken as combination of ramp and dcollement
segments Tectonic setting (CGS report, 2003) 1999 M w =7.6 Chi-Chi,
Taiwan, earthquake Earthquake triggering consistent with focal
mechs Seismicity rate drops in stress shadows periphery Slide 6
Calculated Coulomb stress change for an idealized Chi-Chi rupture
Ma, Chan & Stein. JGR, 2005 Slide 7 decrease Seismicity rate
change (new/old) increase Observed seismicity rate changes are
consistent with calculated Coulomb stress changeincluding stress
shadows Slide 8 Taichung Nansan Huatung Kaoping Chan & Stein
(GJI, 2009) Slide 9 Focal mechanisms of earlier aftershocks are
consistent with stress increase from mainshock Chan & Stein
(GJI, 2009) Slide 10 Focal mechanisms of later aftershocks are
consistent with stress increase from afterslip and relaxation Chan
& Stein (GJI, 2009) Slide 11 Postseis. stress on the focal
planes of larger events Later aftershocks preferentially occur
where they are brought closer to Coulomb failure by postseismic
stress Chan & Stein (GJI, 2009) Slide 12 1997 M=6.5 & M=6.3
Kagoshima doublet: 40 days & 4 km apart Do stress shadows
inhibit earthquakes? Kagoshima Toda & Stein (JGR, 2004) Japan
Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Lin & Stein (JGR,
2004) Slide 18 Lin & Stein (2004) Slide 19 2010 Mw=8.8 Maule,
Chile earthquake Outer rise normal aftershocks and Mw=6.9 normal
after- shock above megathrust evident, but most are thrusts Stein,
Toda, & Barrientos (in prep.) Normal events Slide 20 Sites of
M=6.9, outer rise, and Santiago aftershocks brought closer to
failure Slide 21 Slide 22 The long stress shadow cast by the 2004
M=9.2 Sumatra earthquake Volkan Sevilgen & Ross Stein (in
prep.) Slide 23 Earthquakes on Andaman Sea-Sagaing transform system
shut down after Boxing Day 2004 M w =9.2 stress changes are large
enough to influence seismicity 300 km behind the trench Rate drop
WAF - West Andaman Fault SEU- Seuliman Fault, SFS - Sumatra Fault
System Slide 24 Seismicity rate drops along right-lateral transform
segments Increase Decrease Pesicek et al (JGR, 2010) double-diff.
relocations Slide 25 Stress drops on right-lateral transform system
(top) but increases on back-arc spreading ridge segments (bottom)
Back-arc transform system in green Slide 26 Stress drops on
right-lateral transform (blue mechansms) where seismicity rate also
drops Stress increases on back-arc ridges (red mechanisms) where
seismicity rates increase Rate drop Rate drop 1400-patch source
Model (shaded): Chlieh et al (JGR 2007) Slide 27 Karen R. Felzer
& Emily E. Brodsky (Nature, 2006) Decay of aftershock density
with distance indicates triggering by dynamic stress Keith
Richards-Dinger, Ross S. Stein & Shinji Toda (Nature, 2010)
Decay of aftershock density with distance does not indicate
triggering by dynamic stress Are these M=2-3 mainshocks pointing to
their M2 aftershocks up to 50 km away? Slide 28 Strong evidence for
widespread triggering of very small shocks by very large ones Not
only is there triggering on the Love wave arrival, but there is
Omori decay of these remote shocks Slide 29 Slide 30 Slide 31 2/3
of remote aftershocks locate in large quake rupture zones or at
swarm sites Slide 32 The 5 min before the mainshocks should not
exhibit the same decay as the 5 min afterwards Slide 33 The 5 min
before the mainshocks should not exhibit the same decay as the 5
min afterwards Slide 34 Earthquakes that occur before the waves
arrive from the mainshock cannot be aftershocks, and so should not
occur Slide 35 Slide 36 If the distant earthquakes are aftershocks
of their mainshocks, they should undergo Omori temporal decay Slide
37 Slide 38 Earthquakes converse through the transfer of stress
Slide 39
