Measuring crustal deformation using contemporary geodetic surveying techniques

Geophysical processes such as earthquakes and volcanoes occur on different spatial and temporal scales. To understand the behaviour of these processes, scientists look closely for precursory signals. One of these signals is ground deformation, which can be geodetically measured and then described by strain rate. To measure horizontal or vertical strain rate accurately, very precise geodetic observations of distance, position or height must be made, preferably with a high level of repeatability. The most precise estimations of strain rate are achieved with geodetic observations collected and averaged for periods extending up to a decade. Presently, a number of geodetic instruments are used for this purpose, which include differential levelling, the Electronic Distance Measurement (EDM) and Global Positioning System (GPS). Each of these instruments is capable of detecting very small amounts of strain and ground movement; however they may be limited by their spatial and temporal resolution. This paper examines the use of these instruments and techniques and critically examines their advantages and disadvantages in this field. The increasing use of large-scale geodetic monitoring networks around the world is investigated. Recent catastrophic events in Sumatra, Haiti and Japan highlight that measuring and correctly interpreting ground deformation from these networks in the years, months, days or hours leading to these events is critically important.