Seismicity, Fault Architecture, and Slip Mode of the Westernmost Gofar Transform Fault.

Oceanic transform faults accommodate plate motions through both seismic and aseismic slips. However, deformation partition and slip mode interaction at these faults remain elusive mainly limited by rare observations. We use 1‐year ocean bottom seismometer data collected in 2008 to detect and locate earthquakes at the westernmost Gofar transform fault. The ultra‐fast slipping rate of Gofar results in ∼30,000 earthquakes during the observational period, providing an excellent opportunity to investigate interrelations between the slip mode, seismicity, and fault architecture at an unprecedented resolution. Earthquake distribution indicates that the ∼100‐km‐long Gofar transform fault is distinctly segmented into five zones, including one zone contouring a M6 earthquake that was captured by the experiment. Further, a barrier zone east of the M6 earthquake hosted abundant foreshocks preceding the M6 event and halted its active seismicity afterward. The barrier zone has two layers of earthquakes at depth, and they responded to the M6 earthquake differently. Additionally, a zone connecting to the East Pacific Rise had quasi‐periodic earthquake swarms. The seismicity segmentation suggests that the Gofar fault has multiple slip modes occurring in adjacent fault patches. Spatiotemporal characteristics of the earthquakes suggest that complex fault architecture and fluid–rock interaction play primary roles in modulating the slip modes at Gofar, possibly involving multiple concurrent physical processes. Plain Language Summary: Oceanic transform faults are apparently simple tectonic plate boundaries. However, their structures are surprisingly complex as manifested through various seismic and aseismic slip modes. The deformation partition mechanism is not well understood due to a lack of near‐field observations. Here, we use 1‐year ocean bottom seismometer data to study earthquakes at the westernmost Gofar transform fault and use these earthquakes to infer the fault slip modes. Spatiotemporal evolution of the earthquakes suggests that the fault has five distinctive zones along strike, including one zone hosted a magnitude (M) 6 earthquake captured by the experiment. The remaining zones are dominated by either seismic or aseismic slip. Such distinct variations of slip mode along strike likely originated from the complex, heterogeneous fault structure, and extensive fluid–rock interactions. Key Points: The westernmost Gofar transform fault is composed of distinct seismic and aseismic zonesThese fault zones are controlled by different slip modes and they possibly interact with each other via multiple mechanismsThe slip mode variations may result from the complex fault architecture and fluid–rock interactions at multiple scales [ABSTRACT FROM AUTHOR]