Data from: Signatures of localization control transition between rupture styles on basaltic megathrusts

Megathrust faults at subduction zones slip at a broad spectrum of rates
from slow creep (centimeters per year) to
dynamic rupture (meters per second), with large excess
fluid pressures implicated as a control on nucleation style. We
report friction measurements on oceanic basalt gouges
(IODP Expedition 368X) at elevated temperatures (150-450 °C),
stresses (150 MPa), and large fluid overpressures
(30-120 MPa) to represent conditions along the descending slab
and to link observed rheology to microtextural evolution. With reducing
effective stress, slip instabilities are first manifested as slow-slip and
evolve through dynamic stick-slip as a result of reduced shear
zone width. This transition in rupture style is
driven by an increase in effective fault stiffness
k'c and a decrease in nucleation length L. Increased
intergranular pressure dissolution at elevated effective stress
mediates the shear localization
width, controls the dynamics of strain
localization, and leaves a structurally discernible fingerprint. Our
results imply that effective stress-controlled mass
transfer, together with strain
localization, dictates the styles of
instability nucleation manifest as slow earthquakes
rationally evolving into
dynamic megathrust ruptures.