Scripps Institution of Oceanography will undertake a project to develop an absolute gravity meter that will operate on the ocean-bottom. The instrument will be based upon the design of an existing terrestrial absolute gravity meter. The work involves development, construction and field testing of the new instrument off the California coast. Absolute gravity measurements are useful for ocean-floor geodesy to infer vertical seafloor motions. Two physical mechanisms for vertical motions: inflation events, and dilatant expansion, produce changes in gravity that are several times larger than a change in sea level. If an ocean bottom gravimeter can achieve the same 3 to 10 micro-Gal accuracy as the land instrument, vertical motions on the order of two to six cm could be measured. Such measurements at sea would be the first of their kind to shed light on important processes such as magma motions and dike intrusions at or near ridge crests, deformation near subduction zones, and the large scale behavior of plates. The ocean bottom absolute gravity meter addresses present data requirements. The resulting information on vertical seafloor motion will be useful in testing existing tectonic models, as well as possibly prompting new ones associated with the RIDGE global geoscience initiative.
