Large creep events on the Imperial fault, California

Abstract

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