An assessment of the probability that a tsunami will reach, or exceed, a given size within a specified interval of time at a particular location. The tsunami size may be measured in various ways, such as: run-up height, flow depth, or tsunami height at the coast. Usually a PTHA would provide probabilities for a range of different time spans, for example from 50 to 2500 years. The assessment may cover a single location, a stretch of coastline, or an area of land (if inundation is included). See also ‘Tsunami Hazard Assessment’ which provides information on some of the techniques that may be used to make a PTHA.