TRENCH-PARALLEL VARIATIONS IN SUBDUCTION ZONE FLUID PRESSURE AND FAULT STRENGTH RESULTING FROM TEMPERATURE DIFFERENCES

Trench-parallel differences in the thermal state of subducting crust offshore Nicoya Peninsula, Costa Rica cause along-strike differences in subduction zone temperature. These temperature differences result in along-strike differences in fluid viscosity and hydraulic conductivity that lead to variations in fluid pressure on the plate boundary fault. Along-strike differences in fluid pressure, in turn, affect fault strength and may partly control the updip limit of seismicity. Because temperatures along the upper 5 km of subduction zone megathrusts generally span a range of temperatures over which fluid viscosity changes substantially, this process may be important in any subduction zone with along-strike variability in the thermal state of subducting crust. This includes subducting crust with along-strike differences in plate age, patchy hydrothermal circulation, or local off-axis volcanism.