University of Tokyo, Japan

During Ocean Drilling Program (ODP) Leg 179, we recorded drill string vibration data to investigate the subseafloor environment as part of two seismic-while-drilling experiments in May 1998. Holes 1105A and 1107A were drilled in 714 and 1660 m water depth, respectively, in the Indian Ocean, where these experiments were conducted. To our knowledge, such measurements have never before been recorded by ODP or on other deepwater drilling rigs. By comparison of vertical and horizontal drill string acceleration with wireline logs and core data, variations in the formation properties are correlated to drilling parameters. Drill string acceleration signals vary inversely with porosity measured from logs and core data. The signal amplitude in sediments is roughly half that in either basalt or gabbro. These signals illustrate characteristics of the advancing drill bit- significant energy radiates through the seafloor and differently through various formations; thus, it may provide a useful tool to evaluate drilling conditions and formation properties encountered at the bit. Determining these properties while drilling, therefore, could assist both drillers and geologists in identifying lithologic contacts and sediment/ rock interfaces, even in cases where core and log data are not available.