A pressure solution flow law for the seismogenic zone: Application to Cascadia

Area of Science:

• Geophysics
• Tectonics
• Rheology

Background:

• Pressure solution is a key deformation mechanism in sedimentary rocks at subduction zones.
• Understanding the rheology of subducting sediments is crucial for modeling seismic and aseismic processes.
• Previous models lacked detailed incorporation of pressure and temperature effects on silica solubility.

Purpose of the Study:

• To develop a linear viscous constitutive relationship for pressure solution.
• To incorporate pressure and temperature dependence on silica solubility using a van't Hoff relationship.
• To apply this flow law to predict interseismic behavior in subduction zones, specifically Cascadia.

Main Methods:

• Developed a linear viscous constitutive relationship for pressure solution.
• Parameterized silica solubility using a practical van't Hoff relationship, including pressure and temperature dependence.
• Applied the derived flow law to the Cascadia subduction zone, utilizing existing data on thermal structure, geometry, plate velocity, and GPS data.

Main Results:

• The developed flow law is consistent with ductile strain in subducted mudstones near the updip limit of the seismogenic zone.
• Results indicate that relative plate motion is accommodated by viscous deformation near the downdip limit of the seismogenic zone.
• The flow law successfully predicts the observed forearc tapering of slip rate deficit with depth.

Conclusions:

• The new linear viscous flow law provides a robust framework for understanding pressure solution in subduction zones.
• This model enhances predictions of interseismic deformation and slip deficit distribution.
• The findings have significant implications for seismic hazard assessment and subduction zone dynamics.