Title:

Anatomy of a predictable seismic cycle at the Gofar oceanic transform fault

Abstract:

Oceanic transform faults host some of the most regular earthquake
cycles observed on Earth. At the Gofar transform fault on the East Pacific
Rise, characteristic Mw 6 earthquakes repeatedly rupture the same fault
patches every 5 to 6 years, and adjacent barrier zones consistently arrest
these ruptures. The short recurrence interval makes Gofar a natural
laboratory for observing the full seismic cycle within a human
observational timescale. In this talk, I will synthesize results from two
ocean-bottom seismometer experiments in 2008 and 2019–2022 to examine the
controls of fault architecture, damage, healing, and fluids on the seismic
cycle. High-resolution seismicity catalogs show that the eastern (G1) and
western (G3) segments share a structured architecture, in which locked
rupture patches are separated by persistent barrier zones that host
elevated background seismicity and foreshocks before mainshocks and become
quiescent afterward. Within the G3 barrier, episodic seismicity bursts
frequently migrate along diffusion-like fronts, consistent with coupled
fluid-pressure transients and aseismic creep regulated by dilatancy in a
fluid-saturated, damaged fault zone. Elevated pore-fluid pressure
mechanically weakens such barriers relative to the locked rupture patches,
as indicated by microearthquake focal mechanisms whose faulting types vary
systematically along strike within a nearly uniform stress field, and this
contrast explains the distinct slip modes of the two fault elements. The
characteristic Mw 5–6 earthquakes consistently produce abrupt seismic
velocity reductions, but the fault zones heal within 1 to 3 months, much
faster than stress reaccumulates over the recurrence interval. Because the
barriers isolate the rupture patches and the fault zones heal rapidly, each
cycle begins from a similar fault-zone state. These patterns repeat across
segments and seismic cycles, rendering a predictable earthquake cycle.