Coupled Seismic Slip on Adjacent Oceanic Transform Faults - Figure 1

Coupled Seismic Slip on Adjacent Oceanic Transform Faults - Figure 1 Figure 1. Locations and focal mechanisms of earthquakes in the swarm. Ellipses represent 95% confidence limits of locations relative to reference event (star). Filled ellipses are largest events for which mechanisms have been determined. Area of mechanism diagram is proportional to seismic moment, shaded quadrants represent compressional arrivals, and labels above diagrams indicate origin time or year and Julian day for events not part of the swarm. Colors indicate depth to seafloor, with red shades. Double yellow lines indicate location of spreading centers, dashed where uncertain. Inset shows location of seismometers (triangles) and differential pressure gauges (circles) of the MELT Experment, Global Seismic Network station RPN, location of swarm (star) and plate boundaries.

In a 4.5 hour period, more than 60 events in an earthquake swarm on the western boundary of the Easter microplate were detected by an array of ocean bottom seismometers and GSN station RPN on Easter Island. The larger events of the swarm were recorded by many GSN stations; the surface wave radiation patterns indicate that these events were strike-slip earthquakes located on two transform faults separated by about 25 km. Slip on the faults was closely coupled, with activity alternating back and forth randomly between the two transforms. Coupled seismic activity is usually attributed to triggering by static stress changes or dynamic stresses in propagating shear waves generated by another earthquake, but these earthquakes are too small for either mechanism to be plausible. The swarm may have been the seismic manifestation of a larger, primarily aseismic, slip event or slow earthquake involving both transforms, perhaps triggered by dike injection on the Easter-Pacific spreading center.

Forsyth, D.W., Y. Yang, M.-D. Mangriotis, and Y. Shen, Coupled seismic slip on adjacent oceanic transform faults, Geophys. Res. Lett., 30(12), 1618, doi:10.1029/2002GL016454, 2003.

This work was supported by National Science Foundation grants OCE-98912208 and CE-9896393.


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