Robust, Extensible Representation of Complex Earth Models for Use in Seismological Software Systems

Models of geophysically important properties of the Earth, such as seismic velocity, Q and density, can become large and complex when those properties vary in three dimensions within the model. We have developed a system to represent the distribution of seismic properties in the Earth that can accommodate a wide range of local to global scale 3D Earth models with spatially variable resolution. A 2D grid of nodes is tessellated using either triangles or quadrilaterals and a profile is defined at each 2D grid node that extends from the center of the Earth to the surface. The surface of the model corresponds with the topographic/bathymetric surface of the Earth, which is referenced to the surface of the GRS80 ellipsoid. Each profile can be separated into a number of layers defined by interfaces across which geophysical properties may be discontinuous. Within the layers between interfaces, the vertical distribution of geophysical properties may be defined by a number of continuous sublayers, by arbitrary order polynomials or by various types of splines. Layer thicknesses can vary laterally and zero thickness layers and layer pinch-outs are accommodated. The distribution of nodes is very flexible, allowing model resolution to vary over a wide range in three dimensions. In this paper, we present detailed descriptions of the software algorithms used to construct, store and interpolate these models.
Published in the Proceedings of the 30th Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies, 23-25 Sep 2008, Portsmouth, VA sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.