Stress anomaly accompanying the 1979 lytle creek earthquake: implications for earthquake prediction

An unusual stress transient was recorded 15 kilometers from the epicenter of the Lytle Creek earthquake in southern California. It was observed at the recording site as an increased shear stress parallel to the fault surface and with the proper sense of shear to have triggered the earthquake. The anomaly began 2 to 4 weeks before the earthquake and lasted for 3 months.