Large creep events on the Imperial fault, California

Abstract

During September 1975, three creepmeters were installed across the Imperial fault and one across the southern end of the Brawley fault, two members of the San Andreas fault system in the Imperial Valley of southeastern California. These supplement earlier installations in the Imperial Valley of one dial-gauge creepmeter and six alignment arrays (Figure 1 and Table 1). Each creepmeter uses either an invar or a stainless steel wire suspended in a horizontally buried pipe, and crosses the fault at an angle of about 45°. Those at Heber Road and Tuttle Ranch are of the design described by Yamashita and Burford (1973), using a linear variable differential transformer as the displacement transducer, and are 20 m long. The three more northerly creepmeters are similar in design to that described by Smith and Wyss (1968), and are between 12 and 15 m in length. Those at Harris Road and Ross Road use a potentiometer in a bridge circuit as the displacement transducer for continuous recording. The Superstition Hills creepmeter is equipped with a dial-gauge micrometer, which is read periodically.