Abstract

The amplification of a strainmeter is frequency dependent. As the wavelength λ approaches the length L of the strainmeter, the amplitude vanishes, because the two extremes of the strainmeter are in phase. The sign of the response is inverted at zero crossings such that λ = L/n, n = 1, 2,…. Between L < λ < 2L, the amplitude of an incoming signal may be reduced by 60% or more. Filtering of the output may worsen the problem. Thus, strainmeters may be poorly suited for certain research purposes, including surface-wave studies and first-motion studies. The output of long-base strainmeters sited on low-velocity materials (such as the 732-m-long strainmeters at Piñon Flat Observatory) may require correction for amplitude distortion.

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