What is a synthetic ShakeMap?
The USGS ShakeMap represents a map of the intensity of ground shaking that is derived from data recorded by a seismographic network, i.e., it is derived directly from seismographic data. The map is interpolated between stations, so in areas with few seismographic stations the map is less reliable, whereas in areas with lots of stations the map is more reliable. A "synthetic ShakeMap" is a ShakeMap derived from a numerical simulation of an earthquake, i.e., it is the result of a calculation. How well the "synthetic ShakeMap" captures the actual shaking intensity is determined by the quality of the three-dimensional model that was used to perform the numerical simulation. Because the numerical simulation has the same resolution across the entire region, the "synthetic ShakeMap" does not involve interpolation between seismographic stations.