TTT MAPS

Tsunami Travel Time Maps

Questions: haz.info@noaa.gov

Travel time map for a hypothetical magnitude 9.2 earthquake off the coast of central Chile at 30^oS, 72^oW. This scenario was used for the Pacific-wide Tsunami Drill Exercise Pacific Wave '06 that took place 16-17 May 2006.

https://www.ngdc.noaa.gov/hazard/tsu_travel_time.shtml

https://www.ngdc.noaa.gov/hazard/tsu_travel_time_events.shtml

NCEI, as the World Data Service for Geophysics (including Tsunamis), and the UNESCO-IOC International Tsunami Information Center, collaborate to provide tsunami travel time maps.

NCEI, as the World Data Service for Geophysics (including Tsunamis), and the UNESCO-IOC International Tsunami Information Center, collaborate to provide tsunami travel time maps.

·       Maps generated using Tsunami Travel Time (TTT) software: calculates first-arrival travel times on a grid for a tsunami generated at an earthquake epicenter

·       Map contours: 1-hour intervals:

• Red: 1-4 hour arrival times
• Yellow: 5-6 hour arrival times
• Green: 7-14 hour arrival times
• Blue: 15-21 hour arrival times

·       Maps were generated from earthquake epicenters in the NCEI Global Historical Tsunami Database using NCEI 2-Minute Gridded Global Relief Data bathymetry

·       NOTE: Maps do not provide the height or the strength of the wave, only the arrival times

·       "Event Details" links to runups (observed wave locations). In some cases, runups have observed tsunami arrival times, which can be compared with the map calculated arrival times. Calculated times are usually within 1 hour of the observed travel times, but can differ by more than 1 hour, particularly when the location is across the Pacific Basin (why times may be different)

Tsunami Source Maps

Estimated travel times for historical tsunamis based on earthquake epicenters

Coastal Locations Maps

Estimated tsunami travel times from any point in the ocean to selected coastal locations

Maps were generated using Tsunami Travel Times (TTT) software (see below) developed by Paul Wessel, Geoware. TTT software calculates first-arrival travel times on a grid for a tsunami generated at a given earthquake epicenter or coastal location.

• Maps do not provide information on the height or the strength of the wave, only the arrival times
• There are several situations in which the estimated arrival times may not match observed arrival times of the tsunami waves, including but not limited to the following:

1.    Bathymetry is not accurate in the vicinity of the epicenter

2.    Epicenter is not well located, or its origin time is uncertain

3.    Epicenter is on land and a pseudo-epicenter off the coast must be selected

4.    Bathymetry is not accurate in the vicinity of the reporting station

5.    Nonlinear propagation effects may be important in shallow water

6.    Observed travel times do not represent the first wave but instead are later arrivals

Maps were generated using Tsunami Travel Times (TTT) software (see below) developed by Paul Wessel, Geoware. TTT software calculates first-arrival travel times on a grid for a tsunami generated at a given earthquake epicenter or coastal location.

• Maps do not provide information on the height or the strength of the wave, only the arrival times
• There are several situations in which the estimated arrival times may not match observed arrival times of the tsunami waves, including but not limited to the following:
  1. Bathymetry is not accurate in the vicinity of the epicenter
  2. Epicenter is not well located, or its origin time is uncertain
  3. Epicenter is on land and a pseudo-epicenter off the coast must be selected
  4. Bathymetry is not accurate in the vicinity of the reporting station
  5. Nonlinear propagation effects may be important in shallow water
  6. Observed travel times do not represent the first wave but instead are later arrivals

Tsunami Travel Time Software

The technique to compute travel times is an application of Huygen's principle. It 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. earthquake epicenter). 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. This technique is explained in Shokin, et al., 1987, Calculations of tsunami travel time charts in the Pacific Ocean, Science of Tsunami Hazards, vol. 5, p. 85-113.

Tsunamis are categorized as long waves, therefore, tsunami travel times can be computed with water depth as the only variable (Murty, T.S., Seismic Sea Waves Tsunamis, Bulletin 198) Long waves are where the distance between wave crests is much greater than the water depth through which the wave is traveling. 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.

The technique to compute travel times is an application of Huygen's principle. It 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. earthquake epicenter). 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. This technique is explained in Shokin, et al., 1987, Calculations of tsunami travel time charts in the Pacific Ocean, Science of Tsunami Hazards, vol. 5, p. 85-113.

Tsunamis are categorized as long waves, therefore, tsunami travel times can be computed with water depth as the only variable (Murty, T.S., Seismic Sea Waves Tsunamis, Bulletin 198) Long waves are where the distance between wave crests is much greater than the water depth through which the wave is traveling. 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.

These maps were generated by the Pacific Warning Center using Paul Wessel's TTT software. The first image shows one-hour travel times from simulated seismic zone off the Sumatra-Andaman coasts, Indian Ocean. A 100-kilometer distance around the seismic zone is also shown on the map as a dashed line. The other image shows zoomed in image of the area.