Since tsunamis can be categorized as long waves, tsunami travel times can be computed with water depth as the sole variable (see, e.g., Murty, 1977). Long waves are those in which the distance between crests of the wave is much greater than the water depth through which the wave is travelling. Wave speed is computed from the square root of the quantity water depth times the acceleration of gravity. So, tsunami travel times can be computed without any knowledge of the tsunami's height, wavelength, etc. At the WC/ATWC, travel times are pre-computed for over 200 locations around the Pacific and Atlantic basins. Pre-computing these times helps decrease warning response time.
Travel times for the Pacific are computed on a finite-difference grid with an increment of 15'x10'. This increment is appropriate for the open ocean, but is not fine enough for near-shore resolution. In the near-shore around the point of interest, finer grids of 1' or 12" increment are included within the Pacific-wide 15'x10' grid. Atlantic travel times are computed using a 2'x2' grid with finer 1' or 3" grids included in near-shore areas.
The technique used to compute travel times over the entire grid is an application of Huygen's principle which states that all points on a wavefront are point sources for secondary spherical waves. Minimum travel times are computed over the grid starting at the point of interest (e.g., Los Angeles). From the starting point, times are computed to all surrounding points. The grid point with minimum time is then taken as the next starting point and times are computed from there to all surrounding points. The starting point is continually moved to the point with minimum total travel time until all grid points have been evaluated. A brief explanation for this technique is given in Shokin, et al. (1987).
Due to source uplift size in an actual event, travel times shown on the maps may
be in error up to 30 minutes.
| Location | Latitude | Longitude |
| La Jolla, CA | 32.87N | 117.257W |
| Los Angeles, CA | 33.71N | 118.25W |
| Pt. San Luis, CA | 35.17N | 120.75W |
| Monterey, CA | 36.62N | 121.87W |
| San Francisco, CA | 37.8067N | 122.465W |
| Mendocino, CA | 39.28N | 123.79W |
| Crescent City, CA | 41.745N | 124.833W |
| Coos Bay Mouth, OR | 43.36N | 124.35W |
| Seaside, OR | 45.99N | 123.94W |
| Gray's Harbor Mouth, WA | 46.92N | 124.14W |
| Neah Bay, WA | 48.368N | 124.6167W |
| Bamfield, BC | 48.84N | 125.14W |
| Cape Scott, Vancouver I., BC | 50.77N | 128.42W |
| Cape St. James, Queen Charlotte Is., BC | 51.94N | 131.03W |
| Langara I., BC | 54.25N | 133.08W |
| Sitka, AK | 57.04N | 135.3383W |
| Yakutat, AK | 59.5467N | 139.735W |
| Cordova, AK | 60.5583N | 145.7533W |
| Seward, AK | 60.12N | 149.4267W |
| Kodiak, AK | 57.745N | 152.4833W |
| Sand Point, AK | 55.33N | 160.50167W |
| Unalaska, AK | 53.88N | 166.5383W |
| Adak, AK | 51.863N | 176.63167W |
| Shemya, AK | 52.73N | 174.103E |
| Southeast Coast, HI | 19.25N | 155.25W |
| Mexico-Texas Border | 25.92N | 97.13W |
| San Juan, PR | 18.46N | 66.08W |
| Galveston, TX | 29.28N | 94.78W |
| New Orleans, LA | 29.95N | 90.08W |
| Apalachicola, FL | 29.72N | 84.98W |
| St. Petersburg, FL | 27.73N | 82.77W |
| Miami Beach, FL | 25.78N | 80.13W |
| Cape Canaveral, FL | 28.45N | 80.53W |
| Savannah, GA | 31.95N | 80.90W |
| Cape Hatteras, NC | 35.18N | 75.50W |
| Ocean City, MD | 38.33N | 75.05W |
| New York, NY | 40.62N | 74.05W |
| Provincetown, MA | 42.10N | 70.18W |
| Portsmouth, NH | 43.10N | 70.70W |
| Halifax, NS | 44.40N | 63.50W |
| St. Pierre & Miquelon | 46.83N | 56.35W |
| St. John's, NL | 47.57N | 52.67W |
| Nain, NL | 56.53N | 61.10W |
| Cape Chidley, NL | 60.38N | 64.43W |
References
Murty, T.S. (1977). Seismic Sea Waves Tsunamis, Bulletin 198, Dept. of Fisheries and the Environment, Fisheries and Marine Service, Ottawa, Canada, 337 pp.
Shokin, Y.I., L.B. Chubarov, V.A. Novikov, and A.N. Sudakov (1987). Calculations of tsunami travel time charts in the Pacific Ocean - models, algorithms, techniques, results, Sci. Tsunami Hazards, 5, 85-113.
