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ABSTRACT Oceanic transform faults are a significant component of the global plate boundary system and are well known for generating fewer and smaller earthquakes than expected. Detailed studies at a handful of sites support the hypothesis that an abundance of creeping segments is responsible for most of the observed deficiency of earthquakes on those faults. We test this hypothesis on a global scale. We relocate Mw ≥5 earthquakes on 138 oceanic transform faults around the world and identify creeping segments on these faults. We demonstrate that creeping segments occur on almost all oceanic transform faults, which could explain their deficiency of earthquakes. We also find that most of the creeping segments are not associated with any large-scale geological structure such as a fault step-over, indicating that along-strike variation of fault zone properties may be the main reason for their existence. 

The Line Islands Ridge (LIR), located south of the Hawaiian Islands between 7°N and 1°S, is one of the few large central Pacific regions shallower than the regional carbonate compensation depth. Thick sequences of carbonate sediments have accumulated around the LIR despite it being located in the sediment-starved central tropical Pacific. The LIR is an important source of carbonates to the surrounding region and deposition around the LIR has expanded the equatorial Pacific carbonate sediment tongue by about 5% of its total area. Furthermore, sediments on the ridge are potentially important paleoceanographic archives. A recent survey at the crest of the LIR finds evidence for high current activity, significant erosion, but overall net sediment deposition. Currents are strong enough to form sediment waves and lee drifts in the Palmyra Basin, at the northern terminus of the LIR. Sediments along the LIR are pelagic foraminiferal sands that are easily eroded and flow out into the surrounding abyssal plain in active submarine channel systems. As channels migrate, pelagic sediments fill in the abandoned channel arms. Despite significant sediment losses from the top of the ridge, 1.3 km of sediment has accumulated in the upper Palmyra Basin over basement formed 68 to 85 million years ago (Ma). Late Neogene erosion may be more extensive than earlier erosion cycles, in response to reduced sediment production as the Palmyra Basin exited the high productivity equatorial latitudes. Sediments with good stratigraphic order needed for paleoceanographic study are limited in this dynamic sedimentary environment, but can be found with proper survey. 

Abstract Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminiferaGlobigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio ofG. ruberbetween the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).