HR: 0803h
AN: NS11D-0802    [Abstracts]
TI: The October 11, 1918 Mona Passage tsunami modeled using new submarine landslide evidence.
AU: López, A M
EM: alopez@usgs.gov
AF: USGS Woods Hole Science Center, 384 Woods Hole Road, Woods Hole, MA 02543, United States
AU: * ten Brink, U
EM: utenbrink@usgs.gov
AF: USGS Woods Hole Science Center, 384 Woods Hole Road, Woods Hole, MA 02543, United States
AU: Geist, E
EM: egeist@usgs.gov
AF: USGS Western Coastal and Marine Geology, 345 Middlefield Road, Menlo Park, CA 94025, United States
AB: The October 11, 1918 ML 7.5 earthquake in the Mona Passage betweeen Hispaniola and Puerto Rico generated a local tsunami that claimed approximately 100 lives along the western coast of Puerto Rico. The area affected by this tsunami is now many-fold more populated. Although the exact cause of the tsunami is still unclear, newly-acquired high-resolution bathymetry of the Mona Passage and seismic reflection lines show a fresh submarine landslide 12 km northwest of Rincón in northwestern Puerto Rico and in the vicinity of the earthquake epicenter determined by Doser et al., (2005). The landslide area is approximately 76 km² and probably displaced a total volume of 10 km³. The landslide's head scarp is at a water depth of 1.2 km, with the debris flow extending down to a water depth of 4.5 km. The seismic profiles and multibeam bathymetry indicate that the previously suggested source of the 1918 tsunami, a normal fault along the east side of Mona Rift (Mercado and McCann, 1998), was not active recently. The fault escarpment along Desecheo Ridge, which is near the Doser et al., (2005) epicenter, and our landslide appear, on the other hand, to be rather fresh. Using the extended, weakly non-linear hydrodynamic equations implemented in the program COULWAVE (Lynett and Liu, 2002), we modeled the tsunami by a landslide with a finite duration and with the observed dimensions and location. Marigrams (time series of sea level) were calculated at locations near to reported locations of runup. The marigrams show a leading depression wave followed by a maximum positive amplitude in good agreement with the reported polarity, relative amplitudes, and arrival times. Our results suggest this newly-identified landslide, which was likely triggered by the 1918 earthquake, was the probable cause of the October 11, 1918 tsunami and not a normal fault rupture as previously suggested.
DE: 0545 Modeling (4255)
DE: 3025 Marine seismics (0935, 7294)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3070 Submarine landslides
DE: 7212 Earthquake ground motions and engineering seismology
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting