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- Title
Estimating Effective Normal Stress During Slow Slip Events From Slip Velocities and Shear Stress Variations.
- Authors
Kobayashi, Takuma; Sato, Toshinori
- Abstract
Theoretical analyses using a rate‐ and state‐dependent friction law have shown quasistatic and stable slip behaviors following velocity weakening. We estimated spatiotemporal slip distributions for six slow slip events (SSEs) off the Boso Peninsula, Japan, from Global Navigation Satellite System data and plotted their shear stress variations vs. slip velocity, here called "trajectories." Most trajectories are similar to theoretical stable trajectories, implying that the Boso SSEs represent a quasistatic and stable process, and that the gradient of the trajectories during slip acceleration is equal to the product of the friction coefficients of the slipping plates (a–b) and the effective normal stress (σn′). Taking (a–b) = −0.003, we estimate that the effective normal stresses during the SSEs were 10–50 MPa at 12.5–20.5 km depth. These values are much smaller than the lithostatic pressures at those depths, implying high pore pressures on the slow slip interface. Plain Language Summary: From theoretical studies, it is known that quasistatic and stable slip behaviors can occur when frictional stress decreases with increasing slip velocity. We estimated slip distributions in time and space for six slow slip events (SSEs; characterized by slow slip on the plate interface without the production of seismic waves) off the Boso Peninsula, Japan, from Global Navigation Satellite System data, and plotted slip velocities vs. shear stress changes on the plate interface. Most graphs are similar to those in the theoretical studies, implying that SSEs have quasistatic and stable behavior, and that the slopes of the graphs can be used to determine effective normal stress (the difference between normal stress and water pressure on the plate interface) given that reasonable friction coefficients are known. Taking average friction coefficients from previous studies, we estimate that the effective normal stresses during the SSEs were 10–50 MPa at 12.5–20.5 km depth. These values are much smaller than the pressure due to the weight of the overlying rock, implying that water pressure is very high on the slow slip interface. Key Points: We estimated spatiotemporal slip distributions and shear stress variations for six slow slip events from Global Navigation Satellite System dataBased on gradients in the slip velocity versus stress plot, effective normal stresses were 10–50 MPa at 12.5–20.5 km depthThese values are much smaller than lithostatic pressures at those depths and imply high pore pressures on the slow slip interface
- Subjects
JAPAN; FRICTION velocity; SHEARING force; GLOBAL Positioning System; SEISMIC waves; WATER pressure; QUASISTATIC processes
- Publication
Geophysical Research Letters, 2021, Vol 48, Issue 20, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL095690