A global survey of along-strike heterogeneity of seismic behavior on oceanic transform faults

Abstract:

Oceanic transform faults are a significant part of the global plate boundary system and exhibit along-strike variation of seismic behavior. Main mechanisms of such heterogeneity include (1) geological structure such as inter-transform spreading centers and step-over valleys and (2) along-strike variation of fault zone properties. Both mechanisms have been proposed for detailed studies of faults at the East Pacific Rise. Here, we expand the study to all the 79 major oceanic transform faults. We use surface wave cross-correlation to relocate major earthquakes and identify major seismic segments on these faults. We also include the USGS catalog earthquakes to calculate along-strike seismic moment release rate. For the 79 oceanic transform faults studied, we observe four general types according to the seismic segmentation. The majority (45 or 57%) of the faults exhibit multiple distinctive segments distributed along-strike with various length and seismic moment release rate. Another 22 or 28% of the faults have only one seismic segment, which is less than half of the fault length and not necessarily in the middle of the fault. Seven or 9% of the faults have two distinctive segments near each end while the middle segment is aseismic. Four or 5% of the faults have no distinctive segments and seismic moment release rate is quite uniform along-strike. One fault has no large earthquake and might be totally aseismic. For the 46 faults with high-resolution bathymetry data, we observed that 20 have seismic segmentation that is associated with geological structures. Also, 59 faults have clear quasi-periodic large earthquakes, and 35 faults show earthquake synchronization across multiple adjacent faults. Five fault segments show dual-mode slip behavior, which is the same segment switching between seismic and aseismic slip on the time scale of decades.