Offsets in the regional strain field, generated by the October 1, 1987 Whittier Narrows earthquake, were recorded with large amplitudes on two deep-borehole dilational strainmeters at distances of 46.7 and 65.5 km from the hypocenter and marginally on instruments at greater distances in the Parkfield area and at Pinon Flat, where laser extensometers also recorded small offsets. These data are insufficient to solve for the location and physical parameters of the earthquake, but by also using the measured elevation changes in the epicentral area, we are able to invert for source models consistent with all available observations of crustal deformation. The source models obtained indicate that slip extends to a depth of about 30 km, well below the recorded aftershock zone. The requirement for deeper (and presumably aseismic) slip derives from the large negative dilation experienced by the nearest strainmeter (PUBS), but high-frequency data from the same site exclude any significant slow component of moment release. By ignoring PUBS we obtain a moment of about 0.7¿1018 N m on a fault that has a strike and dip of about N60 ¿W and 40¿ down to the north, respectively, and extends to a depth of about 16 km. The most likely reason for the anomalous offset at PUBS appears to be sympathetic slip triggered on a nearby fault by the main shock. Precursive strain during the month prior to the earthquake is not apparent at the nanostrain level in the data from the closest instrument, but the event was accompanied by a change in strain rate at the two nearer sites. ¿ American Geophysical Union 1989