Accession Number : ADA308603

Title :   Development of Improved Geophysical Imaging Techniques for Environmental Site Characterization.

Descriptive Note : Final rept. 1 Jul 93-1 Oct 95,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH ATMOSPHERIC AND PLANETARY SCIENCES

Personal Author(s) : Greaves, Robert J. ; Haartsen, Matthijs W. ; Kutrubes, Daria L. ; Lee, Jung M. ; Lesmes, David P.

PDF Url : ADA308603

Report Date : 31 DEC 1995

Pagination or Media Count : 183

Abstract : The objective of this research was to develop geophysical techniques for environmental site characterization: (1) a multi-offset ground penetrating radar profiling technique; (2) a nonlinear seismic refraction traveltime tomography; (3) a 3-D d.c. resistivity tomography; and (4) an electroseismic method. The goals of this project were accomplished successfully and a large amount of field data were collected and modeled for characterizing actual environmental sites. Specifically, we demonstrate that performing GPR surveys with multi-offset geometry can improve the signal-to-noise ratio of subsurface radar reflections. We formulate a nonlinear seismic refraction traveltime tomography to precisely delineate bedrock topography that fits not only traveltime data but also the gradients of traveltime curves. A 3-D d.c. resistivity tomography technique is described for characterizing conductivity distribution in the shallow earth that can map surface measurements to the subsurface. Finally, we present theoretical and numerical techniques for modeling electroseismic waves from a poin source by solving coupled equations of seismic wave propagation, fluid flow, electrical streaming current, and the resulting electromagnetic field. The usefulness of these four techniques for characterizing environmental sites is demonstrated by applications to field data from various sites. The new approaches and algorithms introduced for GPR, seismic refraction tomography, and 3-D resistivity inversion have received wide interest from both the scientific and user communities. The electroseismic method is still a new and potentially powerful technique for subsurface characterization. The theoretical modeling that was done is the first of its kind in this field.

Descriptors :   *GEOLOGICAL SURVEYS, *TOMOGRAPHY, *TERRAIN ANALYSIS RADAR, ALGORITHMS, COUPLING(INTERACTION), ELECTROMAGNETIC FIELDS, SIGNAL TO NOISE RATIO, RADAR IMAGES, TOPOGRAPHY, ELECTRICAL CONDUCTIVITY, PROBLEM SOLVING, NONLINEAR SYSTEMS, WAVE PROPAGATION, RADAR REFLECTIONS, SEISMIC WAVES, USER NEEDS, MAPS, ELECTRIC CURRENT, NUMERICAL METHODS AND PROCEDURES, GEOPHYSICS, SUBSURFACE, RADAR MAPPING, SHALLOW DEPTH.

Subject Categories : Geology, Geochemistry and Mineralogy
      Magnetic & Electric Fld Detection & Detectors
      Active & Passive Radar Detection & Equipment
      Seismic Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE