Presentation on theme: "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)"— Presentation transcript:
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)
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)
…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)
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)
Tectonic setting (CGS report, 2003) Chelungpu fault can be taken as combination of ramp and décollement segments Tectonic setting (CGS report, 2003) 1999 M w =7.6 Chi-Chi, Taiwan, earthquake Earthquake triggering consistent with focal mech’s Seismicity rate drops in stress shadows periphery
Calculated Coulomb stress change for an idealized Chi-Chi rupture Ma, Chan & Stein. JGR, 2005
decrease Seismicity rate change (new/old) increase Observed seismicity rate changes are consistent with calculated Coulomb stress change—including stress shadows
The long stress shadow cast by the 2004 M=9.2 Sumatra earthquake Volkan Sevilgen & Ross Stein (in prep.)
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
Seismicity rate drops along right-lateral transform segments Increase Decrease Pesicek et al (JGR, 2010) double-diff. relocations
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 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)
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
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