Anatomy of a Megathrust Earthquake Rupture: The 2010 M8.8 Chile Quake
Dr. Stephen Hicks, University of Liverpool
In February 2010, a magnitude 8.8 megathrust earthquake struck the Maule region of Central Chile - the sixth largest earthquake ever recorded. It is fast becoming one of the best-studied megathrust ruptures, allowing us a unique insight into the inner workings of subduction zone earthquakes. In the earthquake’s immediate aftermath, an international group of research institutions deployed geophysical instruments in the rupture area. A network of ~160 seismic stations on the forearc recorded over 50,000 aftershocks in the first 10 months following the earthquake.
I have used observations of P- and S-waves from aftershocks to derive a high-resolution seismic travel-time tomography of the rupture zone. Observations from ocean-bottom seismometers further improve image sharpness in the offshore portion of the seismogenic zone, where most slip occurred during the earthquake. The tomographic images reveal the distribution of P-wave velocity and Poisson’s Ratio within the earthquake rupture zone. Based on accurate aftershock locations and moment tensors, I have defined a new 3-D plate interface geometry to infer the physical structure and composition along the plate interface. I compare these velocities with the mainly geodetically observed behaviour of the fault throughout a cycle of seismic behaviour (preseismic locking, coseismic slip, postseismic deformation). This comparison allows us to understand some of the physical properties that may govern seismogenesis along the megathrust. I will reveal how both the long-lived geological structure of the forearc and the composition of the subducting oceanic plate may influence the rupture behaviour of large megathrust earthquakes. An understanding of seismic velocities along the megathrust may therefore be used to constrain the seismogenic potential of subduction zones worldwide.
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