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Arguments for static stress triggering

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					                      1992 M=7.3 Landers shock
                                 increases stress
                                       at Big Bear




                         Landers
               Big
               Bear

Los
Angeles
                                             First 3 hr of
                                               Landers
                                             aftershocks
                                                plotted
from
Stein (2003)
                      1992 M=7.3 Landers shock
                         promotes the M=6.5 Big
                             Bear shock 3 hr later




                         Landers
               Big
               Bear

Los
Angeles
                                             First 3 hr of
                                               Landers
                                             aftershocks
                                                plotted
from
Stein (2003)
               …and promotes the
                 M=7.1 Hector Mine
                    shock 7 yr later




                  Hector Mine




Los
Angeles

                                First 7 yr of
                                aftershocks
                                   plotted

from
Stein (2003)
              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 ,
1999 M w=7.6 Chi-Chi,
         Tectonic setting
        earthquake
Taiwan,(CGS report, 2003)
        Tectonic setting
        (CGS report, 2003)
• Earthquake triggering
  consistent with focal
mech’sChelungpu fault can be
       taken as combination of
        ramp and décollement
• Seismicity rate drops in
              segments
 stress shadows




                                 periphery
Calculated Coulomb stress change for an idealized Chi-Chi rupture




                                                   Ma, Chan & Stein. JGR, 2005
Observed seismicity rate changes are consistent with calculated
     Coulomb stress change—including stress shadows




   decrease      Seismicity rate change (new/old)                        increase
                                                                       Ma, Chan & Stein. JGR, 2005
Taichung   Nansan




            Huatung




Kaoping



                      Chan & Stein
                      (GJI, 2009)
Focal mechanisms of earlier aftershocks are consistent
        with stress increase from mainshock




                                            Chan & Stein (GJI, 2009)
Focal mechanisms of later aftershocks are consistent with
       stress increase from afterslip and relaxation




                                              Chan & Stein (GJI, 2009)
      Postseis. stress on the focal
Later aftershocks preferentially occur where they are brought
       closer to Coulomb failure by postseismic stress
        planes of larger events




                                                                Chan & Stein (GJI, 2009)
            1997 M=6.5 &
  Japan
            M=6.3 Kagoshima
            doublet: 40 days & 4
Kagoshima
            km apart

            Do stress shadows
            inhibit earthquakes ?




              Toda & Stein (JGR, 2004)
Lin & Stein (JGR, 2004)
Lin & Stein (2004)
         2010 Mw=8.8
         Maule, Chile
          earthquake

           Outer rise
             normal
          aftershocks
         and Mw=6.9
Normal
         normal after-
events   shock above
          megathrust
          evident, but
           most are
             thrusts




           Stein, Toda, &
             Barrientos
             (in prep.)
Sites of M=6.9, outer rise, and Santiago aftershocks brought closer to failure
The long stress shadow cast by 
the 2004 M=9.2 Sumatra
earthquake




                                        Volkan Sevilgen
                                  & Ross Stein (in prep.)
 2004 Mw=9.2                  Earthquakes 
stress changes                on Andaman 
    are large                 Sea-Sagaing 
  enough to                    transform 
   influence                  system shut 
   seismicity        Rate      down after 
     300 km       drop         Boxing Day
     behind 
  the trench




                                 WAF - West 
                               Andaman Fault 
                            SEU- Seuliman Fault, 
                             SFS - Sumatra Fault 
                                    System
                                                   Decrease




                                                   Increase




Pesicek et al
(JGR, 2010)     Seismicity rate drops along right-lateral 
double-diff.
relocations
                          transform segments
 Stress drops 
on right-lateral 
   transform 
 system (top) 
 but increases 
  on back-arc 
   spreading 
      ridge 
   segments
    (bottom)




                     Back-arc 
                    transform
                    system in 
                      green
             Stress drops on 
                right-lateral 
             transform (blue
               mechansms) 
             where seismicity 
      Rate
   drop       rate also drops 

              Stress increases 
Rate            on back-arc 
drop               ridges 
             (red mechanisms)
              where seismicity 
               rates increase




             1400-patch source
              Model (shaded):
                Chlieh et al 
                (JGR 2007)
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  M≥2
 aftershocks up to 50 km away?
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
2/3 of remote aftershocks locate in large quake rupture zones or at  swarm sites
The 5 min before the mainshocks should not exhibit the   same
                decay as the 5 min afterwards
The 5 min before the mainshocks should not exhibit the   same
                decay as the 5 min afterwards
Earthquakes that occur before the waves arrive from the mainshock
         cannot be aftershocks, and so should not occur
Earthquakes that occur before the waves arrive from the mainshock
         cannot be aftershocks, and so should not occur
If the distant earthquakes are aftershocks of their mainshocks,
            they should undergo Omori temporal decay
If the distant earthquakes are aftershocks of their mainshocks,
            they should undergo Omori temporal decay
Earthquakes converse through the transfer of stress

				
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posted:7/11/2013
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Jun Wang Jun Wang Dr
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