Direction of faulting in the Ancash, Peru, earthquake of November 10, 1946, from Teleseismic Evidence*

Abstract

Silgado has reported that the Ancash earthquake resulted in two parallel fault systems trending approximately N 45° W and separated by a distance of about two kilometers. The observed displacements were such that the intermediate ground appeared to have subsided, the two fault planes dipping toward this central ground.The careful observation of the fault appeared to offer an opportunity for checking the techniques of the fault-plane project. A solution has been carried out on the basis of information obtained from questionnaires. It agrees with the strike direction but not with the dip, and shows the motion to have been largely transverse rather than vertical as actually observed.Silgado has shown that the first motion, which is that determined by the teleseismic determination, originated at a depth of 30 to 40 kilometers. The observed surface displacements are therefore a secondary effect. The earthquake thus does not offer the hoped-for check on the theory of the fault-plane project.