UTIG
Ocean-Bottom Seismometer Program

UTIG investigators apply seismic refraction surveying to a wide range of problems, from large-scale experiments designed to study the structure of the entire crust, to investigations of targeted geologic settings. Seismic refraction surveying utilizes seismic energy that returns to the surface after traveling through the ground along refracted ray paths. The refracting interfaces (refractors) separate layers of different seismic velocity. Sound travels at different speeds through different types of rocks and seismologists can use these 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 seismometer (OBS). This is a microprocessor- controlled instrument that is placed on the seafloor to record seismic signals generated by seismic sources. The OBS instrument and control electronics are contained in a glass ball (sphere) encased in a yellow polyethylene housing called a hard hat. The instrument is deployed from a surface ship, free-falls to the seafloor, and while on the seafloor detects and records seismic signals. Commercially available hard disks store the data in the instrument. Experiments 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 a sesimic source (i.e. sound) is generated from research ships. After the data acquisition is completed, the system receives a sound signal from a surface ship, which triggers the OBS to release itself from the seafloor and float to the surface for recovery.  On board the ship, the data can be downloaded to standard computer workstations and evaluated. UTIG researchers are currently using OBS instruments in offshore seismic investigations with diverse geological/geophysical targets in many parts of the world.

A sample record section from offshore Costa Rica illustrates OBS data collection.

In 1999, a lost OBS was found - 20 months and across the Atlantic Ocean from where it was last seen.

Since 1995, UTIG has made 394 OBS deployments at 9 experiment sites. Listed below are some of the recent studies using the instruments.