Mapping the Miocene Farallon Ridge jump on the Pacific plate: a seismic line of weakness

Abstract

Bathymetric and magnetic data are used to obtain estimates, on the Pacific and Nazca plates, of the boundaries separating lithosphere generated at the old Farallon Ridge from the more recent one created at the present-day East Pacific Rise. An excellent correlation is found with the sites of known teleseismically recorded intraplate seismicity, suggesting that these boundaries, which are lines of age discontinuity in the plate, must be zones of weakness of the lithospheric plate. In particular, the so-called Region C, identified by Okal et al. as a major site of seismic release, sits on a small piece of Farallon plate, in the immediate vicinity of the northern extension of the fossil Roggeveen Rise, cut across by the East Pacific Rise during the ridge jump.