Natural disaster impacts have increased worldwide in the last decades. Earthquakes are one of the disasters that have been studied for real-time analysis and crisis management. Disaster- related losses have been examined by damage extent of the houses, infrastructures, fatalities and injuries converted to financial losses. WebGIS technologies provide a wide range of solutions to map those damages, analyse data and publish the results. Open-Source tools and data have been widely used today because they stay free and facilitate access to data especially significant in developing countries. This research presents a WebGIS prototype using Open-Source Geo-Spatial technologies such as PostGIS, Geoserver, Geoexplorer and OpenStreetMap (OSM) to evaluate the rapid impact of naturally produced disasters for total damages. For this purpose, expert knowledge such as earthquake intensities and vulnerability inputs are imported into the system and the loss of the damage is rapidly estimated. This work is part of a project for catastrophe modeling based on Open-Source data and software. We hope that involving Open-Source knowledge into our application will decrease the time and efforts needed for rapid disaster and catastrophe management.