Frequency-dependent seismic radiation of megathrust earthquakes and depth-varying properties of the subducting plate
Abstract
Megathrust earthquakes rupture a broad zone of the subducting plate interface in both along-strike and along-dip directions. The along-dip rupture characteristics of these giant events, e.g., their slip distribution and seismic energy radiation, reflect depth-varying frictional properties of the slab interface. We use a compressive sensing (sparse signal recovery) method (Yao et al., 2011, GRL) and dense seismic array data in the United States and Japan to systematically analyze the spatial and temporal distribution of the coseismic radiation in the frequency band 0.6 - 0.06 Hz for four recent megathrust earthquakes (2011 Mw 9.0 Tohoku, 2010 Mw 8.8 Maule, 2005 Mw 8.6 Sumatra, 2004 Mw 9.2 Sumatra). Our results reveal a frequency-dependent and depth-varying radiation pattern during the mainshocks, with generally lower frequency radiation closer to the trench at shallower depths and higher frequency radiation farther from the trench at greater depths. Together with coseismic slip models and early aftershock locations, our results suggest depth-varying frictional properties at the subducting plate interfaces. The shallower portion of the slab interface (above ~15 km) is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip, deficient high-frequency radiation, and few early aftershocks. The slab interface at intermediate depths (~15 - 35 km) is the main unstable and seismogenic zone for the nucleation of megathrust quakes, typically with large coseismic slip, abundant early aftershocks, and intermediate- to high-frequency seismic radiation. The deeper portion of the slab interface (~35 - 45 km) is seismically unstable, however with small coseismic slip, dominant high-frequency radiation, and relatively fewer aftershocks.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S21B2471Y
- Keywords:
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- 7209 SEISMOLOGY / Earthquake dynamics;
- 7215 SEISMOLOGY / Earthquake source observations;
- 7240 SEISMOLOGY / Subduction zones;
- 8163 TECTONOPHYSICS / Rheology and friction of fault zones