Comparison of Teleseismically and Hydroacoustically Derived Earthquake Locations along the North-central Mid-Atlantic Ridge and Equatorial East Pacific Rise

Abstract

This letter examines earthquake locations derived using independent teleseismic and hydroacoustic data sets for events along the north-central (15°-35°N) Mid-Atlantic Ridge (MAR) and equatorial (10°S-10°N) East Pacific Rise (EPR). It represents the first large-scale comparison of such data, providing ground-truth information for the teleseismic locations and insight into the process of T -wave generation. An assessment of location accuracy and catalog completeness in these remote ocean settings is critical for explosion monitoring efforts associated with the Comprehensive Test-Ban Treaty (CTBT), as well as seismotectonic studies at mid-ocean ridges (MOR's). During the last decade, the value of hydroacoustic studies in monitoring MOR seismicity has been demonstrated through work using the U.S. Navy's SOund SUrveillance System (SOSUS) ( e.g., Fox et al., 1994) and arrays of moored autonomous underwater hydrophones (AUH's) ( e.g., Fox et al., 2001; Smith et al., 2002). These studies utilize seismically generated tertiary (7) waves that propagate within the ocean's SOund Fixing And Ranging (SOFAR) channel (Tolstoy and Ewing, 1950). In locating submarine earthquakes, the main advantages of the hydroacoustic method stem from the efficiency of this low-velocity wave guide, which allows for the detection of much smaller events at longer ranges relative to that possible with waves that travel through the solid earth, as well as from the existence of a well defined ocean sound-speed model ( e.g., Teague et al., 1990). Although T waves may be produced within regions of shallow sloping bathymetry near oceanic islands, continental shelves, and subduction zones ( e.g., Shurbet and Ewing, 1957; Johnson and Norris, 1968; Talandier and Okal, 1998), here we examine their generation in association with shallow hypocenter events within a deeper-ocean or abyssal environment ( e.g., Johnson, et al., 1968; Fox et al., 1994). In this setting, the scattering of energy from a rough seafloor has emerged as the …