HR: 1330h
AN: T12A-0446    [PDF]
TI: Seismic Velocities Across a Region of Continental Breakup, Woodlark Basin, Papua New Guinea
AU: * Ferris, A
EM: aferris@bu.edu
AF: Dept. of Earth Sciences Boston University, 685 Commonwealth Ave, Boston, MA 02215 United States
AU: Abers, G A
EM: abers@bu.edu
AF: Dept. of Earth Sciences Boston University, 685 Commonwealth Ave, Boston, MA 02215 United States
AU: Zelt, B C
EM: bzelt@leka.soest.hawaii.edu
AF: University of Hawaii (SOEST), 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Floyd, J S
EM: jsfloyd@ldeo.columbia.edu
AF: Columbia University (LDEO), Rt. 9W, Palisades, NY 10964 United States
AB: The Woodlark Basin rift system is one of the fastest opening continental rifts on the planet and along strike shows the full progression from continental rifting to sea-floor spreading. Seismic velocities provide information on the extent of mafic additions to the crust with increasing rifting. We report on the results from P and S wave velocity tomography across an area 350 by 350 km surrounding active metamorphic core complexes and the spreading tip. Data from 1167 local earthquakes recorded during 1999-2000 by 19 onshore PASSCAL broadband and 14 offshore OBS/OBH instruments are used to jointly solve for hypocenters and velocities. The continental crust landward of the spreading tip and around the core complexes shows uniformly low velocities of 5.9-6.4 throughout the upper 25 km. These velocities indicate felsic crust and preclude significant thickness of ophiolitic material or significant mafic additions to the crust. Near the active spreading tip velocities are 2-6% faster. This most likely reflects the thinner, more mafic crust associated with the spreading tip.Upper mantle velocities are reached by 25 km depth here, while the more continental regions still show lower crustal velocities to 35 km. The relocated hypocenters define more tightly defined clusters than with initial 1D models. The majority of seismicity appears northwest of the spreading tip, following a graben structure identified on high-resolution bathymetry. Large teleseismic earthquakes have been located near here, and the graben may represent the main normal fault system accommodating extension. Preliminary locations favor a north dip to this fault system parallel to the inferred low-angle fault planes, although the hypocentral uncertainties are large.
DE: 7200 SEISMOLOGY
DE: 7230 Seismicity and seismotectonics
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting