Researchers from the Scripps Institution of Oceanography, Boston College, and the Woods Hole Oceanographic Institution mapped 2,323 earthquakes along the westernmost Gofar transform fault on the East Pacific Rise. Reporting in Nature Communications, the team showed that along-strike variations in faulting styles correspond to mechanical weakness and elevated fluid pressure within creeping fault segments.
Oceanic transform faults display mixed slip behaviors, hosting both creeping patches and characteristic earthquakes. At the Gofar fault, earthquakes of magnitude 5.5 and larger are bounded by creeping segments that serve as persistent rupture barriers.
To analyze the mechanical properties across the fault, the scientists used one year of continuous seismic data recorded by the WHOI Ocean Bottom Seismology Laboratory through the Ocean Bottom Seismograph Instrument Pool. Pure strike-slip earthquakes made up approximately 31% of the cataloged events. Oblique earthquakes appeared pervasively across the area, alongside pure normal and reverse events.
The study found that faulting types directly correlate with fault segmentation. Reverse and oblique-reverse earthquakes clustered inside the creeping rupture barriers. Coulomb failure modeling indicated that this clustering pattern is diagnostic of elevated pore-fluid pressure and localized mechanical weakness.
The team also observed that a magnitude 6 mainshock in 2008 increased the diversity of focal mechanisms across the entire fault, pointing to the activation of secondary structures during the seismic cycle. Comparisons with the Blanco and Chain transform faults suggest that diverse faulting and along-strike mechanism clustering are widespread characteristics of oceanic transform faults.
The research was authored by Fengzhou Tan, Wenyuan Fan, Peter M. Shearer, Mark D. Behn, and Jeffrey J. McGuire. Project funding was provided by the Natural Sciences and Engineering Research Council of Canada and the U.S. National Science Foundation.
