The Mw 7.1, Hector Mine, California earthquake: surface rupture, surface displacement field, and fault slip solution from ERS SAR data

The Mw7.1, Hector Mine, California earthquake of October 16, 1999 produced a 50 km-long surface rupture, ∼20 km east of the surface rupture of the 1992 Landers earthquake. ERS2 radar data acquired before and after the event provide geodetic measurements of two components of the co-seismic surface displacement field. (1) Interferometric processing of the data provides the range (radar line of sight) component of the displacement field with a precision of a few millimeters. (2) The sub-pixel correlation of the before and after amplitude images provides a second component of the surface displacement field, parallel to the satellite track, with a precision of ∼20 cm. The azimuth offset map reveals a ∼50 km long, NNW surface rupture formed of three sections: a N40°W southern section following the Bullion fault, a N10°W central section cutting through the Bullion Mountains, and a northern N40°W section extending up to the Lavic Lake. A north–south-trending, localized gradient in the azimuth offset field suggests that the central section of the fault extends to the north at depth over a distance of ∼10 km. The slip distribution curve constructed using the azimuth offsets has a bell shape, with a maximum of 6.5 m at the north end of the central fault section. The fault slip model derived from the inversion of the azimuth and from range displacement data indicates that 3–5.8 m of right-lateral slip occurred between the depths of 0 and 8 km along the northern and the central sections of the fault. The solution bears a down-dip component of slip of ∼2 m, west side down, along the southern part of the northern fault section. The down-dip component of slip is consistent with compression on a northeast dipping fault.