Birth of a fault: Connecting the Kern County and Walker Pass, California, earthquakes

A band of seismicity transects the southern Sierra Nevada range between the northeastern end of the site of the 1952 M-W (moment magnitude) 7.3 Kern C ounty earthquake and the site of the 1946 M-W 6.1 Walker Pass earthquake. R elocated earthquakes in this band, which lacks a surface expression, better delineate the northeast-trending seismic lineament and resolve complex str ucture near the Walker Pass mainshock, Left-lateral earthquake focal planes are rotated counterclockwise from the strike of the seismic lineament, con sistent with slip on shear fractures such as those observed in the early st ages of fault development in laboratory experiments. We interpret this seis mic lineament as a previously unrecognized, incipient, currently blind, str ikeslip fault, a unique example of a newly forming structure.