Numerical simulation and first-order hazard analysis of large co-seismic tsunamis generated in the Puerto Rico trench: near-field impact on the North shore of Puerto Rico and far-field impact on the US East Coast

We perform numerical simulations of the coastal impact of large co-seismic tsunamis, initiated in the Puerto Rican trench, both in far-field areas along the upper US East coast (and other Caribbean islands), and in more detail in the near-field, along the Puerto Rico North Shore (PRNS). We first model a magnitude 9.1 extreme co-seismic source and then a smaller 8.7 magnitude source, which approximately correspond to 600 and 200 year return periods, respectively. In both cases, tsunami generation and propagation (both near- and far-field) are first performed in a coarse 2′ basin scale grid, with ETOPO2 bathymetry, using a fully nonlinear and dispersive long wave tsunami model (FUNWAVE). Coastal runup and inundation are then simulated for two selected areas, using finer coastal nested grids. Thus, a 15″ (450 m) grid is used to calculate detailed far-field impact along the US East Coast, from New Jersey to Maine, and a 3″ (90 m) grid (for the finest resolution), encompassing the entire PRNS, is used to compute detailed near-field impact along the PRNS (runup and inundation). To perform coastal simulations in nested grids, accurate bathymetry/topography databases are constructed by combining ETOPO2 2′ data (in deep water) and USGS\u27 or NOAA\u27s 15″ or 3″ (in shallow water) data. In the far-field, runup caused by the extreme 9.1 source would be severe (over 10 m) for some nearby Caribbean islands, but would only reach up to 3 m along the selected section of the East coast. A sensitivity analysis to the bathymetric resolution (for a constant 3″ model grid) of runup along the PRNS, confirms the convergence of runup results for a topographic resolution 24″ or better, and thus stresses the importance of using sufficiently resolved bathymetric data, in order to accurately predict extreme runup values, particularly when bathymetric focusing is significant. Runup (10–22 m) and inundation are found to be very large at most locations for the extreme 9.1 source. Both simulated spatial inundation snapshots and time series indicate, the inundation would be particularly severe near and around the low-lying city of San Juan. For the 8.7 source, runup along the PRNS would be much less severe (3–6 m), but still significant, while inundation would only be significant near and around San Juan. This first-order tsunami hazard analysis stresses the importance of conducting more detailed and comprehensive studies, particularly of tsunami hazard along the PRNS, for a more complete and realistic selection of sources; such work is ongoing as part of a US funded (NTHMP) tsunami inundation mapping effort in Puerto Rico

High grid resolution and parallelized tsunami simulation with fully nonlinear Boussinesq equations

Numerical simulation of tsunami propagation in large basin across the ocean demands significantly high computational capability in terms of CPU time and memory allocation. Due to this limitation, the use of sequential codes in a single scientific workstation is possible only for small-scale tsunami problem. To overcome this difficulty, a parallel Boussinesq wave model is developed based on the original FUNWAVE sequential model for efficient simulation of long wave propagation, coastal inundation and runup. The numerical resolution is decomposed into small sub-domains using domain decomposition technique for each processor to perform the calculations. The wave information is exchanged between processors via message passing interface (MPI). We show the effectiveness of this parallel code on distributed- and shared-memory computer clusters in simulating two tsunami events: the 2004 Indian Ocean and the 1999 Vanuatu tsunamis. Communication in the overlapping domains and load balancing in the partitioned domains are considered to ensure the efficiency of this method. It is found that the performance of the parallel model for both large- and small-scale tsunami problems is very satisfactory. Finally, the parallel model is applied to a spatial hierarchical grids methodology for a location-specific numerical simulation. Grid sensitivity and improved simulation results for runups along Phang Nga coastline from Takua Thung to Khao Lak are presented

Numerical Modelling of the 26th December 2004 Indian Ocean Tsunami for the Southeastern Coast of India

International audienceA numerical simulation of the 26th December, 2004 Indian Ocean tsunami of the Tamil Nadu coastal zone is presented. The simulation approach is based on a fully nonlinear Boussinesq tsunami propagation model and included an accurate computational domain and a robust coseismic source. The simulation is first confronted to available tide gauge and runup observations. The agreement between observations and the predicted wave heights allowed a reasonable validation of the simulation. As a result, a full picture of the tsunami impact is provided over the entire coastal zone Tamil Nadu. The processes responsible for coastal vulnerability are discussed

Reconstructions of the coastal impact of the 2004 Indian Ocean tsunami in the Khao Lak area, Thailand

International audienceKhao Lak, SW Thailand was severely affected by the tsunami on 26 December 2004. Here we present reconstructions of its coastal impact in this area. These are based on (1) eyewitness reports alone and (2) eyewitness reports supported by videos and photos of the tsunami and the damage it caused, field measurements, and satellite imagery. On the basis of eyewitness reports, we estimated that the sea began retreating at 1000 local time (LT) and, based also on photos, that the tsunami arrived at 1026–1029 LT. On the basis of videos of the tsunami, we estimated an offshore wave direction of 083 ± 3° and on the basis of the paths by which eyewitnesses were carried, we estimated an onshore direction of 088 ± 6°. On the basis of videos, we calculated that the velocity of the wavefront on its final approach was 33 ± 4 km/h. We obtained tsunami heights of 7.3 ± 0.8 m (relative to ground level) on the basis of eyewitness reports and 8.0 ± 0.6 m (relative to mean sea level) on the basis of field and photographic data. On the basis of eyewitness reports and photos, we concluded that Khao Lak experienced at least two main waves with a period >40 min. From eyewitness reports and satellite imagery, we measured maximum inundation ≤0.5 km in the southern part of the area, which is confined by a steeply sloping hinterland, and ≤1.5 km in the more gently sloping northern part. Comparison between these reconstructions supports the reliability of eyewitness reports as a source of quantitative data, and comparison with the numerical simulation by Ioualalen et al. (2007) supports the validity of the simulation