We discuss the development and application of Web-service-based geographical information system (GIS) Grids. Following the WS-I+ approach of building (,rids on Web service standards, we have developed data Grid components for archival and real-time data. map generating services that can be used to build user interfaces. infomation services for storing both stateless and stateful metadata, and service orchestration and management tools. Our goal is to support dynamically assembled Grid service collections that combine both GIS services with more traditional Grid capabilities such as file transfer and remote code execution. We are applying these tools to problems in earthquake modeling and forecasting, but we are attempting to build general purpose tools by using and extending appropriate standards. Copyright (C) 2008 John Wiley & Sons, Ltd.