UTIG investigators apply seismic refraction and reflection surveying to a wide range of problems: from large-scale experiments designed to study the structure of the Earth’s entire crust to investigations of targeted geologic settings. Besides marine geophysical surveying, UTIG researchers have also conducted aerogeophysical surveys.

Seismic refraction surveying uses seismic energy that returns to the surface after traveling through the ground along refracted ray paths. Because this energy travels at different speeds through different types of rocks, refracting interfaces separate layers of different seismic velocity. Seismologists use seismic refraction data to develop detailed images of the crust and the upper mantle below the seafloor.

To carry out seismic refraction work on the seafloor, UTIG has developed a specialized ocean-bottom seismograph (OBS) contained in a glass ball seated in a polyethylene hemisphere. Experiments using OBS instruments may be passive, in which the energy generated by earthquakes is detected and used to create an image of the Earth’s interior, or active, in which seismic sources (high-energy sound waves) are generated from research ships.

Seismic Reflection
Seismic reflection surveying uses seismic energy initially generated from a sound source on board a research ship that returns to the surface after being reflected from subsurface rock and sediment layers. The reflected sound provides an image of sub-seafloor layers as the speed and direction of the sound waves are altered by the physical properties of the sediments or rocks. Seismic reflection surveys provide a specified depth of penetration and a particular degree of resolution of the subsurface geology in both the vertical and horizontal dimensions. A conventional reflection detector system consists of an array of geophones or hydrophones arranged in a specific pattern and connected together in series/parallel. The assembly, known as a streamer, is towed behind the research vessel.

In 1986, UTIG became the first academic institution to collect and process three-dimensional (3-D) seismic data. The collection of such data involves very detailed seismic reflection profiling in combination with satellite navigation to produce a detailed portrait of the Earth’s interior. With 3-D seismic data, investigators can select specific surfaces within the surveyed zone that are of special interest and use sophisticated visualization software programs to generate maps of them.

UTIG maintains an archive of marine seismic reflection data collected worldwide by UTIG investigators from 1974 to the present. These data are in demand by the international marine geophysical community and industry. UTIG Senior Research Scientist Tom Shipley has created the UTIG Marine Seismic Data Center (SDC) web site to facilitate access to the Institute's 26-year global archive of seismic reflection data and to serve as the prototype for an international equivalent.

Multibeam Bathymetry
UTIG researchers also use sidescan sonar and high-resolution, multibeam bathymetric systems to image seafloor morphology and texture. The multibeam bathymetric systems available on some UNOLS vessels consists of two hull-mounted instrument arrays. One array transmits a succession of sonic pulses in a swath; the sound reflected from the seafloor is received by a second array. Advances in data acquisition and image processing have made it possible to generate mosaiced topographic maps of the seafloor in real time. Such maps provide a regional view the geologic framework, fundamental for research and sound management of the coastal ocean. The simultaneous collection of conventional high-resolution seismic reflection profiles of the structure beneath the seafloor and high-resolution side-scan data provides a four-dimensional view of the seafloor. The interpretation of these data yields insights into past and present processes responsible for shaping the seafloor.