The October 19, 2020, Sand Point, Alaska tsunami was generated by a Mw 7.6 earthquake (54.617°N 159.635°W), at 2020-10-19 20:54:39 UTC (according to the USGS). The earthquake generated a tsunami that arrived approximately 18 minutes later at the closest DART 46403, located approximately 290 km away from the epicenter. The proximity of DART 46403 to the epicenter resulted in the tsunami signal being contaminated by seismic noise. While DART 46403 has DART 4G capabilities, meaning it should have been able to filter the tsunami signal from the seismic noise, those capabilities were not activated at the time of the event. The next available DART buoy to detect the tsunami was DART 46402, showing a maximum wave amplitude in deep water of just above 5 cm approximately 40 minutes after the earthquake. A DART inversion was performed with data from DART 46402 and DART 46403. The largest coastal tsunami amplitude was ~74 cm and was detected at the Sand Point tide station 2 hours 15 minutes after the earthquake. Model results shown below were created with the NOAA forecast method using the MOST model via inversion of the source with NOAA's TFS (Tsunami Forecast System).

The graphics display preliminary modeling analysis, showing qualitative and quantitative information about the tsunami, including tsunami wave interaction with ocean floor bathymetric features, and neighboring coastlines. Tsunami model amplitude information is shown color-coded according to the scale bar.

Modeling Results

Model amplitudes calculated with the MOST forecast model. Click to see large image.

Propagation animation Click for animation.

• " Model amplitudes are calculated with the MOST forecast model. Filled colors show maximum computed tsunami amplitude in cm during 24 hours of wave propagation.
  • Maximum wave amplitude
    
• Propagation animation on YouTube

Preliminary Model

Comparison of the October 19, 2020 Sand Point, Alaska tsunami recorded at tsunameter/DARTs and tide gauges with model results computed using the DART-inverted source (red) and the USGS moment-tensor solution (blue) is presented in the graphics. The DART model time series are obtained from the pre-computed generation/propagation forecast database in real time, after automatically fitting models to tsunami records from DARTs 46402 and 46403.

• DART® comparisons with model data
  • Composite plot: DARTs 46402, 46403, 46409, 46410 and 46414
• Coastal sea-level gauge comparisons with model data
  • Composite plot: Sand Point, AK; King Cove, AK; Atka, AK; Kahului, HI; Hilo, HI; Crescent City, CA; Port San Luis, CA
• Source Inversion: 2.375*ac28a

It is noted that all above model results are preliminary. The tsunami source is estimated from inversion of observed waveforms at DARTs using a limited number of unit sources. The discrepancies between model results and tide gauge observation are mostly due to the limited knowledge of the earthquake/tsunami source configuration at this point.