GEOPHYSICAL DIFFRACTION TOMOGRAPHY AT A DINOSAUR SITE

In 1979 two hikers discovered the partially exposed bones from the tail of a dinosaur in the high desert of New Mexico. Excavation in 1985 led to the recognition that the dinosaur, informally named "Seismosaurus," was new to science. It is by far the longest dinosaur on record. Excavations continued in 1986 with the discovery that additional bones leading forward from the middle region of the tail, potentially toward the remainder of the skeleton, remained entombed in the 145 million year old sandstone. The site has been the subject of intensive experimentation to assess the feasibility of geophysical remote sensing in exploration paleontology. The efforts of numerous investigators at the site may serve to change the century-old methods of hammer and chisel, in part, to those based on more modern technology. One of the methods tested is geophysical diffraction tomography (GDT). Unlike the more common straight-ray algorithms of geophysical tomography that map subsurface properties by projecting received signal amplitude or time of the first signal arrival back to the source, GDT treats the problem as one of wave propagation by inverting the linearized wave equation to compute the spatial distribution of refractive index. Excavation of the "Seismosaurus" skeleton continues. The purpose of our most recent GDT study is to further test the method and to guide paleontologists in their future excavations by locating and identifying the buried skeletal remains. A total of eleven imaged vertical cross-sections displayed features of sufficient acoustic contrast to be tentatively identified as dinosaur bone. Although the GDT resolution is insufficient to characterize bone shape, bone identification was subjectively accomplished on the basis of size, aspect ratio, and position. Based on this interpretation, it is believed that much of the remaining skeleton exists and is in near articulation.