USGS 3D EARTHQUAKE MAP SOFTWARE
Fortunately, advances in computer hardware and geologic modeling and visualization software now provide us with the potential to construct 3D geologic maps that retain all the information in a traditional geologic map while quantitatively extending this information into the subsurface. However, these maps, even enhanced with GIS capabilities, are insufficient for storing and transmitting subsurface information, information that is critical in the role of the map as a window into the subsurface. The introduction of Geographic Information Systems ( GIS) enhanced traditional geologic maps in terms of ease of use and communication of surface geologic information. Traditional geologic maps, which show the distribution and orientation of geologic materials and structures at the ground surface, have served for many decades as effective tools for storing and transmitting geologic information. Examples of immediate applications of 3D maps include ground shaking estimation, refined earthquake relocation, fault segmentation analysis for probabilistic earthquake forecasting, resource exploration, contaminant source and dispersion pathway definition, and ground water flow modeling for resource management. One important application unique to 3D geologic maps is predictive process modeling of geologic, tectonic, and hydrologic processes needed for land-use planning, hazard mitigation, and resource management. Such 3D databases and appropriate computer software will allow even the inexperienced user to figuratively "walk around" in the earth to examine the data and extract needed information. This framework allows us to progressively refine the individual surfaces in an iterative fashion without altering the fundamental model architecture.Ĭomputer-based representations of areal geology extended into the subsurface as 3-dimensional geologic maps can now be developed to provide continuous quantitative 3-D geologic information for a variety of practical needs. The present 3D map includes the fundamental geometry, architecture, and interaction instructions, though many of the surfaces are as yet only approximately defined. The 3D map exists in the computer as 1) a set of numerical grids (large cell raster datasets) that quantitatively define the positions and shapes of the critical surfaces, 2) a set of instructions that specify how these surfaces interact when they encounter each other, and 3) the software to assemble the surfaces according to the specified instructions and to assign properties to the map volume. It is divided by 11 major faults into blocks, within which the Cenozoic section is represented by up to three layers, and the Mesozoic section by more than six units. The map volume is 45X45 km by 14 km deep, and spans the valley floor and surrounding hillsides between the San Andreas and Calaveras faults. Critical surfaces are assembled into a 3D map using earthVision (Dynamic Graphics, Inc.) modeling software. Quantitative definition of critical surfaces is based mainly on surface geology, drillhole data, cone penetrometer testing, gravity and magnetic modeling, seismic reflection and refraction profiling, and earthquakes. The fundamental map architecture is defined by critical surfaces (faults, intrusive contacts, unconformities, other depositional contacts) interacting to form volumes, which ultimately are assigned measurement-based properties according to geologic identity, geometric position, or both. This multipurpose map is intended to provide a quantitative basis for modeling processes including groundwater flow, contaminant dispersion from naturally occurring mercury and asbestos, ground shaking, seismic wave propagation, and tectonic strain accumulation. This is part of a larger project that also involves developing techniques for constructing 3D models, defining uncertainties associated with geologic elements and properties, and designing procedures for visualizing, accessing, and releasing 3D geologic information. The USGS recently began a long-range project to construct a 3D geologic map of the Santa Clara ("Silicon") Valley, southern San Francisco Bay area, California. Geological Survey Open-File Report 01-223 3D Geologic Maps and Visualization: A New Approach to the Geology of the Santa Clara (Silicon) Valley, California By R.C. USGS OFR 01-223: 3D Geologic Maps and Visualization Digital Mapping Techniques '01 - Workshop Proceedings
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