Earthquakes, the usual cause of tsunamis, cannot be predicted in time,
but can be predicted in space.
- Historical records show where earthquakes frequently occur.
- Plate tectonic theory also predicts where earthquakes will occur.
- Neither historical records nor current scientific theory can accurately tell us when earthquakes will occur.
- Therefore, tsunami prediction can only be done after an earthquake has occurred.
Tsunami waves behave in a predictable way.
- The speed of a tsunami is controlled by ocean depth (deeper=faster).
- Sensors in the path of a tsunami can measure its characteristics before it arrives at other coastlines.
Pacific Tsunami Warning Center (PTWC) Procedures:
- Step 1: Locate the earthquake
- Is it local (in Hawaii) or teleseismic (anywhere else)?
- Is it under or near the ocean?
- Is it shallow or deep within the earth? (shallow is <100 km or ~60 miles deep)
- How big is it? (What is its magnitude?)
- Step 2: Determine tsunami travel time
- Tsunami travel time is dependent on seafloor depth.
- We know seafloor depth for the entire earth.
- Therefore, once we know when and where an earthquake as occurred, we can determine when a tsunami will arrive at any given coastline.
- Step 3: Check sea level gauges for evidence of a tsunami.
- Sea level gauges measure and record sea level at a given location (usually a pier).
- Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys are a deep-ocean pressure sensor-type of sea level gauge.
- Step 4: Issue messages as appropriate
- If the earthquake is in a PTWC area of responsibility and meets a magnitude threshold, PTWC will issue a tsunami message.
- Initial tsunami bulletins for Pacific Rim earthquakes are issued in 10-20 minutes.
- Initial tsunami bulletins for Hawai’i earthquakes are issued in 2-5 minutes.
The success of the above procedures is predicated on public awareness. Public awareness and tsunami preparedness to save lives is the primary mission of the Pacific Tsunami Museum (PTM). Read about what you should know regarding “Tsunami Safety“.
Information above is excerpted from presentation given by Dr. Gerard Fryer of the Pacific Tsunami Warning Center.