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Segmentation of transform systems on the East Pacific Rise: Implications for earthquake processes at fast-slipping oceanic transform faults

¹ Massachusetts Institute of Technology/WHOI Joint Program in Oceanography, Woods Hole, Massachusetts 02543, USA
² Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

Seven of the eight transform systems along the equatorial East Pacific Rise from 12° N to 15° S have undergone extension due to reorientation of plate motions and have been segmented into two or more strike-slip fault strands offset by intratransform spreading centers (ITSCs). Earthquakes recorded along these transform systems both teleseismically and hydroacoustically suggest that segmentation geometry plays an important role in how slip is accommodated at oceanic transforms. Results of thermal calculations suggest that the thickness of the brittle layer of a segmented transform fault could be significantly reduced by the thermal effect of ITSCs. Consequently, the potential rupture area, and thus maximum seismic moment, is decreased. Using Coulomb static stress models, we illustrate that long ITSCs will prohibit static stress interaction between transform segments and limit the maximum possible magnitude of earthquakes on a given transform system. Furthermore, transform earthquakes may have the potential to trigger seismicity on normal faults flanking ITSCs.

Key Words: seismology • earthquake stress triggering • Siqueiros transform fault • transform faults • East Pacific Rise • Clipperton transform fault