Evidence for weak oceanic transform faults

Abstract

We present the results of a series of 3-D boundary element calculations to investigate the effects of oceanic transform faults on stress state and fault development at adjacent mid-ocean ridge spreading centers. We find that the time-averaged strength of transform faults is low, and that on time scales longer than a typical earthquake cycle transform faults behave as zones of significant weakness. Specifically, mechanical coupling of only ∼5% best explains the observed patterns of strike-slip and oblique normal faulting near a ridge-transform intersection. On time scales shorter than a typical earthquake cycle, transient "locked" periods can produce anomalous reverse faulting similar to that observed at the inside corner (IC) of several slow-spreading ridge segments. Furthermore, we predict that extensional stresses will be suppressed at the IC due to the shear along the transform resisting ridge-normal extension. This implies that an alternative mechanism is necessary to explain the preferential normal fault growth and enhanced microseismicity observed at many ICs.