An earthquake hazard map provides, at any location, the value of a ground motion intensity measure (for example, horizontal peak ground acceleration, PGA) that is expected to be exceeded at least once in 100 year mean return period. The earthquake hazard maps are developed by determining the simulated ground motion intensities at every gridded location for 10,000 realizations of next-year activity of earthquake events. At each grid location, the intensities are ranked and the ground motion intensity of the mean return period of interest is recorded.
Nauru, in the central Pacific Ocean, is a raised atoll capping a volcanic seamount arising from an ocean floor depth of 4300m. The land area is 22km, and the island rises to 70m above sea level. Drilling has proved dolomitised limestone of upper Miocene or younger age to a depth of 55m below sea level. Gravity and magnetic surveys indicate that the limestone probably overlies volcanic bedrock at a depth of about 500m.