1. A computer system for determining a damage index indicative of the damage caused by an earthquake to a portfolio of objects associated with a geographical area, the system comprising: means for storing local portfolio replacement value indices representing a value of the portfolio of objects, the local portfolio replacement value indices assigned to grid coordinates of a grid covering the geographical area; means for receiving and storing location, depth and magnitude data associated with the earthquake; means for calculating a local damage index for each grid coordinate having a local portfolio replacement value index assigned to it, the local damage index being calculated from the location, depth and magnitude data of the earthquake, and from the assigned local portfolio replacement value index; and means for calculating the damage index by aggregating the local damage indices for the grid coordinates, wherein the means for calculating the local damage index is configured to calculate, for each grid coordinate having a local portfolio replacement value index assigned to it, a local shaking intensity value index from the location, depth and magnitude data, a local mean damage degree index from the local shaking intensity value index, and the local damage index from the local mean damage degree index and the local portfolio replacement value index.