Microtremor recording techniques

For some years seismologists and engineers have been recording and measuring microtremors. In this paper a review of earlier micotremor investigations is presented and microtremor recording apparatus developed at Auckland University Engineering School is described. Two distinct methods of recording have been developed. One uses a conventional low-cost tape recorder operating at reduced speed to record the low frequency signals. The other uses a frequency modulation methods and a high quality instrumentation tape recorder to accurately record signal levels. This paper is the first of a series of three. In the second, method of analysing microtremor records, with particular emphasis on their frequency content will be presented, while in the last of the series the application of microtremor measurement to the design of earthquake resistant structures will be critically examined.