A sea-level recorder for tectonic studies

In the past tide gauges have provided valuable information concerning the vertical ground deformation associated with major earthquakes. Although tide-gauge data contains numerous sources of noise; a spacing of less than 40 km between gauges is indicated for a useful study of dilatant behaviour, and a spacing of less than 80 km may be adequate for the study of crustal downwarping in island arcs. An inexpensive tide gauge is described which is designed to provide a continuous record of sea level with a measurement precision of 1 mm. Hydraulic filtering is incorporated into the instrument in order to attenuate daily tides relative to longer period variations of sea level, The instrument is designed to operate from flashlight batteries for a year unattended and to withstand temporary submersion as might be caused by tsunamis. Several of these sea-level recorders have been installed in seismic gaps in the Aleutians and in the Caribbean.