A portable seismograph utilizing a magnetic tape recorder and capable of recording both long- and short-period seismic information is described. The field system which is housed in two weatherproof steel containers is completely self-contained and incorporates both a radio and an internal clock for timing. Eight data channels can record in either AM or FM mode which allows a frequency range from dc to 200 Hz. A feature of the field system is that it incorporates a test panel that enables a check to be kept on all of the recording functions. The field system power consumption is less than 7.5 watts and two 6-volt batteries power the system for up to 12 days. The replay electronics are primarily designed to digitize the analog tapes and the process utilizes an “aspect clock” dividing system that links the recorded clock time to the digitization time.