The State of Pore Fluid Pressure and 3-D Megathrust Earthquake Dynamics

Madden, Elizabeth H.; Ulrich, Thomas und Gabriel, Alice-Agnes (2022): The State of Pore Fluid Pressure and 3-D Megathrust Earthquake Dynamics. In: Journal of Geophysical Research JGR / Solid Earth, Bd. 127, Nr. 4

Abstract

We study the effects of pore fluid pressure (P-f) on the pre-earthquake, near-fault stress state, and 3-D earthquake rupture dynamics through six scenarios utilizing a structural model based on the 2004 M-w 9.1 Sumatra-Andaman earthquake. As pre-earthquake P-f magnitude increases, effective normal stress and fault shear strength decrease. As a result, magnitude, slip, peak slip rate, stress drop, and rupture velocity of the scenario earthquakes decrease. Comparison of results with observations of the 2004 earthquake support that pre-earthquake P-f averages near 97% of lithostatic pressure, leading to pre-earthquake average shear and effective normal tractions of 4-5 and 22 MPa. The megathrust in these scenarios is weak, in terms of low mean shear traction at static failure and low dynamic friction coefficient during rupture. Apparent co-seismic principal stress rotations and absolute post-seismic stresses in these scenarios are consistent with the variety of observed aftershock focal mechanisms. In all scenarios, the mean apparent stress rotations are larger above than below the megathrust. Scenarios with larger P-f magnitudes exhibit lower mean apparent principal stress rotations. We further evaluate pre-earthquake P-f depth distribution. If P-f follows a sublithostatic gradient, pre-earthquake effective normal stress increases with depth. If P-f follows the lithostatic gradient exactly, then this normal stress is constant, shifting peak slip and peak slip rate updip. This renders constraints on near-trench strength and constitutive behavior crucial for mitigating hazard. These scenarios provide opportunity for future calibration with site-specific measurements to constrain dynamically plausible megathrust strength and P-f gradients.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 2169-9313
• Sprache: Englisch
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 491502892