suppress activity on faults in the eastern California shear zone, and vice versa, can explain the apparent switching of activity between the two fault networks. Combined with the observation that short-term geodetic and longer-term geologic rates co-vary on major southern California fault systems, this suggests that either (1) a temporal cluster of seismic displacements on upper-crustal faults increases ductile deformation on their downward extensions, or (2) rapid ductile slip in the lower crust beneath faults loads the upper crust, driving a seismic cluster. We suggest that alternating periods of rapid seismic displacement may be the expected mode of seismicity when two fault systems accommodate the same plate-boundary motion, and slip on one system suppresses slip on the other.
Late Holocene strike-slip offset of a subsurface channel interpreted from three-dimensional seismic data, eastern offshore Trinidad
M. David Soto, Paul Mann (corresponding author), University of Texas at Austin, Institute for Geophysics, Austin, TX 78759, USA; et al. Pages 859-862.
Mann et al. used three-dimensional seismic data off the east coast of Trinidad to map the main South AmericaCaribbean plate boundary strike-slip fault that was known from previous onland GPS and fault-trenching studies in Trinidad. The offshore mapping shows that the fault has right laterally offset a buried fluvial channel by a distance of 322506 meters. The channel is inferred to have formed when sea level was much lower during the Last Glacial Maximum at about 30,000 years ago. Combining the offset amount with the inferred age of the channel, a long-term slip of 1719 mm/yr can be calculated. The earthquake hazard of this fault is significant because it accommodates most of the lateral strike-slip displacement between the South America and Caribbean plates.
OPEN ACCESS: Research Focus
Paleoseismology: Why can't earthquakes keep on schedule"
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