Slip-parallel seismic lineations on the northern Hayward fault, California

A high-resolution relative earthquake location procedure is used to image t he fine-scale seismicity structure of the-northern Hayward fault, Californi a. The seismicity defines a narrow, near-vertical fault zone containing hor izontal alignments of hypocenters extending along the fault zone.: The line ations persist over the 15-year observation interval, implying the localiza tion of conditions on the fault where brittle failure conditions are met. T he horizontal orientation of the Lineations parallels the slip direction of the fault, Suggesting that they are the result of the smearing of friction ally weak material along the fault plane over thousands of years.