HR: 0830h
AN: T51D-0197    [PDF]
TI: NEW SIMULATION OF THE 1755 TSUNAMI SOURCE USING A COMPOSITE SUBDUCTION SOURCE
AU: * Baptista, M A
EM: mabaptista@sa.isel.ipl.pt
AF: ISEL, R Cons Emidio Navarro 1, Lisboa, 1900 Portugal
AU: * Baptista, M A
EM: mabaptista@sa.isel.ipl.pt
AF: CGUL, FCUL, Campo Grande, Ed C8, Lisboa, 1749-016 Portugal
AU: Gutscher, M A
EM: gutscher@univ-brest.fr
AF: UBO/IUEM, Pl Nicolas Copernique, Plouzane, F29280 France
AU: Miranda, J M
EM: jmirabda@fc.ul.pt
AF: CGUL, FCUL, Campo Grande, Ed C8, Lisboa, 1749-016 Portugal
AB: A recent marine seismic survey, together with tomographic data, provides compelling evidence for an active east dipping subduction zone beneath the Gibraltar Arc, which can be thought as a candidate for the 1755 Lisbon earthquake. If we consider a convergent rate of 1 to 2 cm/yr and a co-seismic slip of 20 m (to account for the 1755 earthquake magnitude), we get a recurrence interval between 1000 and 2000 years, that seems compatible with available geological information. Previous attempts to model the tsunami wave that could be generated by such structure concluded that synthetic amplitudes are lower and arrival times longer than observed, particularly for locations along the west coast of Portugal. This suggested a second source segment, closer to the Portuguese margin, which should have also contributed to the tsunami waves that ravaged the coast of SW Portugal and the Gulf of Cadiz, and were reported as far as the Lesser Antilles and SW England. This possibility is also reinforced by some historic documents that report the occurrence of at least a second large shock. In this paper we present the simulation of a composite 1755 source, where the main shock is attributed to dipping subduction beneath the Gibraltar Arc, modelled as a 180 km (N-S) x 210 km (E-W) rectangular fault with a 20 m co-seismic slip, followed by a second shock, 10 minutes later, beneath the southern flank of Gualdalquivir Bank, modelled as a 250 km (WNW-ESE) x 71 km (WSW-ESE) rectangular fault with 5 m co-seismic slip. Tsunami wave heights are computed for all locations where reliable historical information is available and comparison is made between synthetic values and observations.
DE: 8105 Continental margins and sedimentary basins
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting