HR: 1340h
AN: S33A-0312    [Abstracts]
TI: Receiver Function Analysis of OBS data: possibilities and drawbacks
AU: Menke, W
EM: menke@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Columbia University/LDEO, Palisades, NY 10964 United States
AU: * Levin, V
EM: vlevin@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854 United States
AU: Webb, S
EM: scw@ldeo.columbia.edu
AF: Palisades Geophysical Institute, LDEO, Palisades, NY 10964 United States
AB: Studies of near-surface Earth structure utilizing P-to-S converted seismic waves ( aka receiver function analysis) are progressively more popular, ranging from shallow crustal surveys to the studies of the transition zone. A fundamental premise in these studies is that the observed wavefield is acquired at the boundary separating rock and air (i. e. the free surface of an elastic half-space). Consequently, modeling software, as well as the intuition of technique's practitioners, is set up to treat all energy in the receiver function as either upgoing or multiply scattered within the elastic halfspace. Data collected with ocean bottom seismographs presents an added complication to the interpretation of receiver functions, as the time series constructed via standard source equalization means likely contain scattered energy from the water column. On the basis of tests with synthetic seismograms computed in realistic structures we show that properly accounting for the extra signal from the water column may be essential for correct interpretation of the seafloor receiver functions. Using data collected near the East Pacific Rise we show that, in spite of extra difficulties associated with ocean floor registration, receiver functions from OBS data may be developed to relatively high (0.5 Hz) frequency, and thus may be used to probe for relatively small-scale vertical structure of the ocean lithosphere. On the down side, we find that the number of seismic sources confidently recorded over a course of a year (5-13 per sensor) is insufficient to carry out more advanced forms of processing (e.g., studies of directional or phase velocity dependence in receiver functions). We pay particular attention to the potential signature of the phases arising from water column reverberations. Interestingly (and fortunately) their signature in data we investigated appears less prominent than synthetics would suggest. As a final test of the "validity" of detailed RF analysis on the seafloor we use a forward modeling routine that accounts for the presence of water to develop 1-D models for the structure of the ocean lithosphere that match key features of the receiver functions.
DE: 7203 Body waves
DE: 7220 Oceanic crust
SC: Seismology [S]
MN: Fall Meeting 2005