Seismic anisotropy evidence for dehydration embrittlement triggering intermediate-depth earthquakes

Area of Science:

• Geophysics
• Seismology
• Tectonics

Background:

• Intermediate-depth earthquakes in subducting slabs are a significant seismic hazard.
• Dehydration embrittlement of hydrous minerals is a proposed mechanism for triggering these earthquakes.
• Seismic anisotropy is sensitive to mineral hydration, pressure, and temperature, offering insights into slab processes.

Purpose of the Study:

• To investigate the relationship between seismic anisotropy and intermediate-depth seismicity in the Japan subduction zone.
• To develop a high-resolution tomographic model of P-wave radial anisotropy.
• To test the hypothesis that dehydration embrittlement drives intraslab seismicity.

Main Methods:

• High-resolution P-wave radial anisotropy tomography.
• Utilized arrival-time data from local and teleseismic events.
• Modeled seismic structures down to approximately 400 km depth in the Japan subduction zone.

Main Results:

• Revealed a strong correlation between intermediate-depth seismicity patterns and anisotropic structures within the subducting slabs.
• Identified positive radial anisotropy (faster horizontal than vertical velocity) in seismically active regions, linked to dehydration.
• Observed negative radial anisotropy (faster vertical than horizontal velocity) in aseismic regions, suggesting anhydrous conditions.

Conclusions:

• Intermediate-depth earthquakes in the Japan subduction zone are likely triggered by dehydration embrittlement of hydrous minerals.
• Anisotropic structures provide crucial evidence for the role of water content in controlling seismicity within subducting slabs.
• The study supports the double seismic zone model and highlights the importance of fluid-induced processes in deep earthquakes.