Abstract
Recent studies have documented the occurrence of shallow very low frequency earthquakes (VLFE) in subduction zones. The heterogeneity of the materials or stresses that act on the plate interface results in the variable slip rate. Stress on the décollement can be controlled by the décollement geometry and the regional stress, which is also able to control the material properties. We determined the distribution of stress along the shallow portion of the décollement in the Nankai Trough using a three-dimensional (3D) seismic survey and regional stress analysis to construct maps of normalized slip tendency (Ts′) and dilation tendency (Td). Alignments of VLFEs trend parallel to the trends of {T}_{s}^{^{prime}} and {T}_{d}. On the other hand, very low {T}_{s}^{^{prime}} and {T}_{d} areas probably act as barriers that limit the number of VLFEs that can migrate towards the trench. Because the {T}_{s}^{^{prime}} and {T}_{d} distributions are derived only from the décollement geometry and the regional stress without incorporating any data on sediment properties, the consistency between the trends suggests that the décollement geometry is the primary control on VLFE activity.
Highlights
The number of reports of slow earthquakes including slow-slip events (SSE), tremor, and very low frequency earthquakes (VLFE), in shallow subduction zones has increased4,5, and those studies show that slow earthquakes occur in the same areas where tsunamigenic-fast earthquakes are observed
A conceptual model for variable slip has been proposed, suggesting that small unstable patches surrounded by a ductile matrix along the plate interface can result in complex seismic energy r elease6
VLFE alignments can be expressed as the trend of map scale distributions for comparison of distributions between
Summary
The number of reports of slow earthquakes including slow-slip events (SSE), tremor, and very low frequency earthquakes (VLFE), in shallow subduction zones has increased, and those studies show that slow earthquakes occur in the same areas where tsunamigenic-fast earthquakes are observed. A conceptual model for variable slip has been proposed, suggesting that small unstable patches surrounded by a ductile matrix along the plate interface can result in complex seismic energy r elease. A conceptual model for variable slip has been proposed, suggesting that small unstable patches surrounded by a ductile matrix along the plate interface can result in complex seismic energy r elease6 This model is supported by numerical experiments showing that rheological heterogeneity along the plate interface explains slip variability. A two-dimensional model used to examine the effects of subducting plate topography, including seamounts, showed the heterogeneous distribution of physical properties and stress around the features.
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