Abstract
ODP borehole observatory 1200C, drilled into the South Chamorro seamount and instrumented with Circulation Obviation Retrofit Kit (CORK), provided information about natural fluid pressure within this forearc crust. The seafloor and formation pressure data recorded hourly and shown fluctuations that are caused largely by the ocean tides. The data also shown two transient pressures increase at the time of two earthquakes. Harmonic analysis provides a simpler way to analyze the periodic tidal signals that constitute the pressure records. By using the result of the harmonic analysis and applying simple theory of formation response to tidal loading, developed by Wang & Davis, the hydrogeologic character of the non-accretionary forearc environment, particularly permeability, can be determined. In this thesis, the way to calculate the permeability of the South Chamorro seamount using CORK-pressure response to tidal loading method and its implication is explained. The resultant bulk permeability of the seamount is 1.42 x 10-13 m2, with a range between about 1.18 to 1.79 x 10-13 m2, that represent the permeability of this formation within the scale of about 176 meter around the CORK-borehole. By using this method we could determine the permeability that represent the formation over the larger scale of investigation relative to other methods, especially the core-based method as the most common method used to determine permeability. In order to test whether the earthquake would be a factor that would change the permeability of this formation, an analysis is performed, adopting the way that was used in oceanic crust. From the analysis, we could imply that earthquake has negligible effect in changing the formation permeability and it is suggested that this is caused by the elastic behavior of the formation. The matrix frame of this formation, as the component that affect the elastic behavior, is implied to be highly compressible, with its calculated bulk moduli of 0.652 ± 0.15 GPa. The forearc crust has more elastic behavior if compare to the oceanic crust.