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Slab temperature controls on the Tonga double seismic zone and slab mantle dehydration
S Shawn Wei1, Douglas A Wiens2, Peter E van Keken3
1Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA.; Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
Science Advances
|January 19, 2017
Summary
Double seismic zones reveal deep earthquake patterns in the Tonga subduction zone. Colder slab temperatures and faster subduction correlate with deeper earthquake activity, offering insights into mantle processes.
Area of Science:
- Geophysics
- Seismology
- Tectonics
Background:
- Double seismic zones are characterized by two distinct layers of intermediate-depth earthquakes.
- These zones provide crucial information about the thermomechanical conditions within subducting tectonic plates.
Purpose of the Study:
- To precisely locate intermediate-depth earthquakes in the Tonga subduction zone.
- To investigate the depth, structure, and thermal controls of double seismic zones.
Main Methods:
- Utilized data from island-based, ocean-bottom, and global seismographs for precise hypocenter determination.
- Analyzed earthquake distribution and correlated it with subduction parameters and thermal models.
Main Results:
- Identified a double seismic zone in Tonga extending to ~300 km depth, deeper than previously observed.
- Observed a compressional upper plane and a tensional lower plane, separated by ~30 km.
- Found a distinct seismic belt in the upper plane linked to a constant temperature of ~500°C, suggesting dehydration of mantle minerals.
Conclusions:
- Tonga's double seismic zone is deeper due to colder slab temperatures from faster subduction.
- Temperature, rather than pressure, appears to be a primary trigger for intermediate-depth earthquakes in this region.
- Metamorphic dehydration of subducting mantle minerals likely facilitates faulting and seismic activity.
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