Strain effects near Palmdale associated with the San Fernando earthquake (1971)

Abstract

Abstract Field data from the southeast Palmdale network in California are the basis for a practical strain analysis, with triangulation data available for the year 1938 and 1958 and trilateration data at 1- year intervals from 1971 to date. A uniform, although small, strain accumulation over the last forty years appears to be evident from this data set. A possible soceismic strain jump of 2 μ strain in both shearing strain components, related to the 1971 San Fernando earthquake, may be postulated in the observations. However, it was already pointed out previously, that this coseismic strain jump needs further qualifications due to the corrupting influence of uncertainties in the network height differences. This particular situation arises because triangular data have to be compared with trilateration data for the computation of the coseismic strain changes. To clarify this situation, the height differences of the southeast Palmdale network were determined by trigonometric levelling in spring 1981. The effect of this new height data on the interpretation of the coseismic strain change is discussed in detail. A comparison of this result with strain model calculations is presented.