Strain accumulation north of Los Angeles, California, as a function of time, 1977–1992

No significant change in the rate of strain accumulation in a 40×120 km trilateration network spanning the San Gabriel mountains was observed from 1977.5 to 1991.8 despite an apparent increase in seismicity (M_L > 4.5) beginning in late 1987 in the northern Los Angeles basin immediately to the south. The observed deformation (0.13±0.01 µstrain/yr right‐lateral shear across a vertical plane striking N63°W±1°) can be attributed to strain accumulation on the San Andreas fault (local strike N65°W). No significant accumulation of compression normal to the strike of the San Andreas fault was observed in the network as a whole.