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Stephen Hicks*, Andreas Rietbrock, Isabelle Ryder School of Environmental Sciences, University of Liverpool, UK
Chao-Shing Lee National Taiwan Ocean University, Taiwan
Matt Miller Universidad de Concepción, Chile
*Email: [email protected]
A high-resolution 3D seismic velocity model of the 2010 Mw8.8 Maule, Chile earthquake rupture zone Using land and OBS networks
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The overriding / underlying question…
Can we physically identify asperities and barriers along the megathrust?
Megathrust dynamics Material properties
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6th largest recorded earthquake
magnitude 8.8 rupture length 500 km max slip 16m a heterogeneous megathrust?
Mainshock hypocentre location: Hayes et al. (2013), GJI
Co-seismic slip model: Moreno et al. (2012), EPSL
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Tomographic inversion algorithm: SIMUL2000 (Thurber,1983, JGR)
An unprecedented dataset
160 land + 37 OBS stations
670 aftershocks
38,000 P-wave picks
14,000 S-wave picks
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Forearc 2D velocity structure
Focal mechanisms from: Agurto et al. (2012), EPSL Hayes et al. (2013), GJI Coastline
Resolution limits
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Forearc 2D velocity structure
Focal mechanisms from: Agurto et al. (2012), EPSL Hayes et al. (2013), GJI Coastline
Resolution limits
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Forearc 2D velocity structure
Coastline
Resolution limits
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Forearc 2D velocity structure
Coastline
Resolution limits
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Down-dip segmentation of the megathrust
Automatic picks from Rietbrock et al. (2012)
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3D velocity structure
Coastline
Resolution limits
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3D velocity structure
Coastline
Resolution limits
Automatic picks from Rietbrock et al. (2012)
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Shedding light on megathrust dynamics
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Pre-seismic locking (90%, 95%): Moreno et al., 2010
Post-seismic Afterslip: Lin et al., 2013
Interface aftershocks: Rietbrock et al., 2012
Co-seismic rupture Nucleation: Hayes et al., 2013
Slip: Moreno et al., 2010
High freq: Kiser & Ishii (2011)
Shedding light on megathrust dynamics
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Shedding light on megathrust dynamics
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Post-seismic Afterslip (>1m): Lin et al., 2013
Interface aftershocks: Rietbrock et al., 2012
Pre-seismic locking (90%, 95%): Moreno et al., 2010
Co-seismic rupture Nucleation: Hayes et al., 2013
Slip: Moreno et al., 2010
High freq: Kiser & Ishii (2011)
Shedding light on megathrust dynamics
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Forearc body: composition & origin
Gravity model from Hicks et al. (2012), GRL
vp ~ 7.7 km/s; vp/vs ratio ~ 1.8 Positive gravity anomaly
Observations
Ultramafic - weakly serpentinised Christensen & Mooney (1995), JGR; Hacker & Abers (2004), G3
Composition
Origin Subducted topographic anomaly? Hicks et al. (2012), GRL
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Forearc body: composition & origin
vp ~ 7.7 km/s; vp/vs ratio ~ 1.8 Positive gravity anomaly
Observations
Ultramafic - weakly serpentinised Christensen & Mooney (1995), JGR; Hacker & Abers (2004), G3
Composition
Origin Subducted topographic anomaly? Hicks et al. (2012), GRL
Root of Paleozoic granite batholith?
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Forearc body: composition & origin
vp ~ 7.7 km/s; vp/vs ratio ~ 1.8 Positive gravity anomaly
Observations
Ultramafic - weakly serpentinised Christensen & Mooney (1995), JGR; Hacker & Abers (2004), G3
Composition
Origin Subducted topographic anomaly? Hicks et al. (2012), GRL
Root of Paleozoic granite batholith?
Mantle upwelling during Triassic extension Vásquez et al. (2011), J. Geol.
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Ultramafic bodies beneath coast inhibit rupture propagation
Low vp gradient and lower vp/vs values associated with high slip
High vp/vs controls up-dip limit of seismogenesis
4 Afterslip may be compositionally-driven
Implications for Maule seismogenesis
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Can we physically identify asperities and barriers along the megathrust?
Up-dip barrier: Fluid-saturated sediments
Down-dip barrier: Long-lived
ultramafic bodies in crust
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3D velocity structure
Coastline
Resolution limits
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A segmented seismogenic zone!