Heterogeneous slab thermal dehydration driving warm subduction zone earthquakes

Area of Science:

• Geophysics
• Tectonics
• Seismology

Background:

• Changing thermal regimes influence seismicity at cold megathrusts.
• Interpreting seismicity in warm subduction zones like Vanuatu is challenging due to high temperatures.
• Understanding thermal structures is key to explaining tectonic activity in these regions.

Purpose of the Study:

• To clarify the thermal structure controlling tectonic seismicity in Vanuatu.
• To investigate the relationship between thermal conditions and seismicity in a warm subduction zone.
• To determine the primary drivers of seismicity in the Vanuatu subduction system.

Main Methods:

• Construction of a 3-D thermomechanical model.
• Analysis of the thermal structure of the subducting slab.
• Correlation of seismicity with plate interface thermal processes.

Main Results:

• Revealed a heterogeneous subducting slab with temperatures ranging from 300°C to over 900°C.
• Identified a strong correlation between subduction seismicity and the plate interface, particularly where dynamic thermal dehydration occurs.
• Observed that the transformation of hydrated basalts to eclogites facilitates intense earthquakes and slips.
• Noted that multistage mineralogical metamorphism impacts megathrust stability and generates large interplate events.

Conclusions:

• Slab thermal dehydration is a more significant factor than slab temperature in influencing subduction earthquake distribution in warm subduction systems.
• The mineralogical transformations within the subducting slab play a crucial role in generating large seismic events.
• Dynamic thermal dehydration processes are central to understanding seismicity in warm subduction zones.