Abstract
This study investigates the spatial and temporal distribution of energy
release of large, intermediate-depth earthquakes using a modified
back projection technique first used to study the 2004 Sumatra-Andaman
megathrust event. Multiple seismic phases are included in the back
projection analysis, which provides the capability to determine the
energy distribution with respect to depth and time. A total of 22
intermediate-depth earthquakes with moment magnitudes greater than
or equal to 6.5 are investigated with hypocentral depths between
100 and 300 km. For most of these events, the vertical extent of
energy release is either below the resolution of this study (<=5
km) or slightly above (<=15 km). This observation agrees with previous
studies that find large, intermediate-depth earthquakes have subhorizontal
rupture planes. The results also show a significant portion of the
events have multiple rupture planes that are well separated in depth.
The closeness in time of the ruptures on separate planes and the
distance between the planes suggest dynamic triggering where the
P waves from the first rupture initiate rupture on the second plane.
We propose that a dehydration embrittlement mechanism combined with
preferentially hydrated subhorizontal faults can explain the observations
of dominant subhorizontal rupture planes and the frequent occurrence
of rupture complexity involving multiple subevents.
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