HIGH-RESOLUTION BATHYMETRIC MAPPING AND SEISMIC PROFILES OF FAULTS ON THE OUTER RISE OF THE MARIANA TRENCH: NEW INSIGHTS INTO FAULT FORMATION

The Mariana trench in the western Pacific is the southernmost trench along the 2800-km-long Izu-Bonin-Mariana (IBM) arc system. The subduction rate of the Pacific plate at the Mariana trench is ~35 mm/yr in a westerly direction, and the downgoing plate has an extensive fault system on the outer rise area within 70 to 100 km of the trench. A February 2012 cruise on the R/V Marcus G. Langseth acquired high-resolution bathymetric and multichannel 2D seismic reflection data in this faulted region on the incoming Pacific plate. The survey consisted of two east-west lines from the Mariana forearc, across the trench, and onto the faulted outer rise region. A deepwater Kongsberg EM122 1x1 array was used to retrieve new high resolution bathymetry data (11 km swath width, about 10 cm spatial resolution) for the region, and a Syntrak 960-24 recording system along with a single 8-kilometer long hydrophone array was used to record seismic profiles along these swaths. These new combined data have allowed for unprecedented visualization of the extensive fault systems near the trench. The faults are parallel to the trench and caused by flexure of the plate as it is drawn toward the trench, and the seismic data show that some penetrate >10 km into the crust. These data have allowed for a detailed analysis of the density and depth of faulting relative to the distance from the trench, and provide insight into the rate and mechanisms of fault formation. These faults likely serve as conduits for water into the crust, and a better understanding of the faults can also provide insight into the water budget of the Mariana trench system and serpentinization in the forearc.