HR: 0830h
AB: Seismic activity associated with deformation along the active northeastern North America-Caribbean plate boundary poses a serious threat to the growing population on the island of Puerto Rico, in particular the rapidly developing western and southern regions. Studies of seismicity and associated hazards in western Puerto Rico have identified areas onshore of active and historically significant seismic risk. While these studies provide a general description of potential seismic hazards onshore, an understanding of the distribution and nature of active fault structures offshore has been lacking. Existing multichannel seismic profiles offshore western and southern Puerto Rico, collected by Western Geophysical in 1972, show numerous east-west trending normal and strike-slip faults offsetting Oligocene-Pliocene age carbonates and the underlying Cretaceous basement. A systematic high-resolution sidescan sonar mapping and seismic profiling effort of the shallow insular shelf of Puerto Rico was conducted in May 2000, to provide a better understanding of the seismogenic potential of the submarine deformation zone. During a 10-day period, over 728 km of along-track single-channel and sidescan sonar data were collected. Preliminary analyses of these data identify three zones of active deformation within the survey area: 1) extensions of the Cerro Goden and Algarrobo fault zones which lie offshore the Rio de Añasco and Mayagúez Bay of western Puerto Rico, respectively (see Del Greco et al., this poster session); 2) a half-graben structure in Boqueron Bay and east-west trending lineaments offshore Cabo Rojo of southwestern Puerto Rico that may be part of a system faults that extend onshore to the tectonically controlled Lajas Valley (see Prentice and Mann, this poster session); and 3) southeast trending lineaments on the southern insular shelf offshore Guanica and Guayama, which are possible active extensions of the Great Southern Puerto Rico Fault Zone. This offshore study will improve assessments of seismic hazards in Puerto Rico by identifying targets for onshore paleoseismic studies and by better defining the total length of offshore Holocene faults.
AN: T11B-05 INVITED
TI: A High-Resolution Sidescan and Seismic Survey Reveals Evidence of late Holocene Fault Activity Offshore Western and Southern Puerto Rico
AU: Grindlay, N R
EM: grindlayn@uncwil.edu
AF: Center for Marine Science, Univ. of North Carolina at Wilmington, One Marvin K. Moss Lane, Wilmington, NC 28409 United States
AU: Abrams, L J
EM: abramsl@uncwil.edu
AF: Center for Marine Science, Univ. of North Carolina at Wilmington, One Marvin K. Moss Lane, Wilmington, NC 28409 United States
AU: Mann, P
EM: paulm@ig.utexas.edu
AF: Institute for Geophysics, Univ. of Texas at Austin, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759-8500 United States
AU: * Del Greco, L
EM: delgrecol@uncwil.edu
AF: Center for Marine Science, Univ. of North Carolina at Wilmington, One Marvin K. Moss Lane, Wilmington, NC 28409 United States
DE: 8150 Plate boundary--general (3040)
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: T
MN: Fall Meeting 2000