Tsunami inundation maps of Anchorage and upper Cook Inlet, Alaska

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Title:
Tsunami inundation maps of Anchorage and upper Cook Inlet, Alaska
Abstract:
Tsunami inundation maps of Anchorage and upper Cook Inlet, Alaska, Report of Investigation 2023-2, evaluates potential tsunami hazards for upper Cook Inlet, including Anchorage, Girdwood, and Hope, Alaska, by numerically modeling the extent of inundation from tsunami waves generated by hypothetical earthquakes. We define an updated suite of earthquakes, including Tohoku-style megathrust ruptures and other sources in the eastern part of the Alaska-Aleutian megathrust, to calculate vertical seafloor displacements and model resulting tsunami dynamics. We also perform a numerical analysis of tsunami-tide interactions for the 1964 Great Alaska Earthquake in upper Cook Inlet, an area with some of the most extreme tidal ranges in the U.S. This analysis reveals why the 1964 earthquake-generated tsunami largely went undetected in upper Cook Inlet and highlights that the tidal stage at the time of future great earthquakes determines the severity of tsunami impacts around Anchorage. A rare combination of earthquake magnitude, location, and timing must be satisfied for tsunami wave energy to reach upper Cook Inlet coincident with a natural high tide. A hypothetical earthquake with maximum slip distributed between depths of 17 and 32 km (10.6 and 19.9 mi) results in worst case tsunami inundation for Anchorage. If the tsunami arrives to the Anchorage area at high tide, the maximum predicted overland flow depths in the community can reach up to 10 m (32.8 ft), and the currents could be as strong as 4 m/sec (7.8 knots). Dangerous wave activity is expected to last for more than 24 hours. The results presented here are intended to provide guidance to local emergency management agencies for tsunami inundation assessment, evacuation planning, and public education to mitigate future tsunami damage. The complete report and digital data are available from the DGGS website: http://doi.org/10.14509/31018.
Supplemental_Information: 
max-flow-depth:    Raster image depicting maximum composite flow depths over dry land. For each grid point, the pixel value provides the modeled depth of water (in meters) over previously dry land, representing the maximum depth value of all calculated tsunami scenarios.	
max-inundation:    Estimated, maximum credible scenario inundation line(s) that encompasses the maximum extent of flooding based on model simulation of all credible source scenarios and historical observations. The maximum credible scenario inundation lines are intended to be utilized as a basis for local tsunami hazard planning and development of evacuation maps.	
scenario-01:    Mw 9.2 earthquake in the KI-KP region: Predominantly shallow slip with maximum slip at a depth of 10-15 km (6.2-9.3 mi)	
scenario-02:    Mw 9.2 earthquake in the KI-KP region: Predominantly shallow slip with maximum slip at a depth of 0-10 km (0-6.2 mi)	
scenario-03:    Mw 8.7 earthquake in the KP region: maximum slip at a depth of 35-45 km (21.7-27.9 mi)	
scenario-04:    Mw 8.8 earthquake in the KP region: maximum slip at a depth of 28-42 km (17.4-26.0 mi)	
scenario-05:    Mw 8.8 earthquake in the KP region: maximum slip at a depth of 5-7 km (3.1-4.3 mi)	
scenario-06:    Mw 9.0 earthquake in the PWS-KP-KI region: maximum slip at a depth of 28-42 km (17.4-26.0 mi)	
scenario-07:    Mw 9.1 earthquake in the PWS-KP-KI region: maximum slip at a depth of 25-35 km (15.5-21.7 mi)	
scenario-08:    Mw 9.1 earthquake in the PWS-KP-KI region: maximum slip at a depth of 18-32 km (11.2-19.9 mi)	
scenario-09:    Mw 9.2 earthquake in the PWS-KP-KI region: maximum slip at a depth of 17-32 km (10.6-19.9 mi)	
scenario-10:    Mw 9.1 earthquake in the PWS-KP-KI region: maximum slip at a depth of 20-40 km (12.4-24.8 mi)	
scenario-11:    Mw 9.3 earthquake with 50 m (164 ft) of maximum slip close to the trench	
scenario-12:    Mw 9.3 earthquake with 35 m (114.8 ft) of maximum slip in most of the rupture	
scenario-13:    Mw 9.0 earthquake offshore AP region: SAFRR scenario	
scenario-14:    Mw 8.9 earthquake in the KI-AP region: maximum slip at a depth of 15-25 km (9.3-15.5 mi)	
scenario-15:    Mw 8.8 earthquake in the KI-AP region: maximum slip at a depth of 25-35 km (15.5-21.7 mi)	
scenario-16:    Mw 9.1 rupture of the Cascadia subduction zone, including the entire megathrust between British Columbia and northern California
  1. How might this data set be cited?
    Suleimani, E.N., Salisbury, J.B., and Nicolsky, D.J., 2023, Tsunami inundation maps of Anchorage and upper Cook Inlet, Alaska: Report of Investigation RI 2023-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 56 p., 9 sheets
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -150.370758
    East_Bounding_Coordinate: -148.887405
    North_Bounding_Coordinate: 61.628145
    South_Bounding_Coordinate: 60.757040
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2023
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: report, data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a vector data set.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest .000001. Longitudes are given to the nearest .000001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is WGS84.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.
      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: Mean Higher High Water
      Depth_Resolution: .01
      Depth_Distance_Units: meter
      Depth_Encoding_Method: Attribute values
  7. How does the data set describe geographic features?
    ri2023-2-upper-cook-inlet-max-flow-depth.tif
    Raster image depicting maximum composite flow depths over dry land. For each grid point, the pixel value provides the modeled depth of water (in meters) over previously dry land, representing the maximum depth value of all calculated tsunami scenarios. (Source: Alaska Earthquake Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-upper-cook-inlet-max-inundation.shp
    Estimated, maximum credible scenario inundation line(s) that encompasses the maximum extent of flooding based on model simulation of all credible source scenarios and historical observations. The maximum credible scenario inundation lines are intended to be utilized as a basis for local tsunami hazard planning and development of evacuation maps. (Source: Alaska Earthquake Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-01-upper-cook-inlet-inundation.shp, ri2023-2-scenario-01-upper-cook-inlet-flow-depth.tif
    Mw 9.2 earthquake in the KI-KP region: Predominantly shallow slip with maximum slip at a depth of 10-15 km (6.2-9.3 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-02-upper-cook-inlet-inundation.shp, ri2023-2-scenario-02-upper-cook-inlet-flow-depth.tif
    Mw 9.2 earthquake in the KI-KP region: Predominantly shallow slip with maximum slip at a depth of 0-10 km (0-6.2 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-03-upper-cook-inlet-inundation.shp, ri2023-2-scenario-03-upper-cook-inlet-flow-depth.tif
    Mw 8.7 earthquake in the KP region: maximum slip at a depth of 35-45 km (21.7-27.9 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-04-upper-cook-inlet-inundation.shp, ri2023-2-scenario-04-upper-cook-inlet-flow-depth.tif
    Mw 8.8 earthquake in the KP region: maximum slip at a depth of 28-42 km (17.4-26.0 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-05-upper-cook-inlet-inundation.shp, ri2023-2-scenario-05-upper-cook-inlet-flow-depth.tif
    Mw 8.8 earthquake in the KP region: maximum slip at a depth of 5-7 km (3.1-4.3 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-06-upper-cook-inlet-inundation.shp, ri2023-2-scenario-06-upper-cook-inlet-flow-depth.tif
    Mw 9.0 earthquake in the PWS-KP-KI region: maximum slip at a depth of 28-42 km (17.4-26.0 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-07-upper-cook-inlet-inundation.shp, ri2023-2-scenario-07-upper-cook-inlet-flow-depth.tif
    Mw 9.1 earthquake in the PWS-KP-KI region: maximum slip at a depth of 25-35 km (15.5-21.7 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-08-upper-cook-inlet-inundation.shp, ri2023-2-scenario-08-upper-cook-inlet-flow-depth.tif
    Mw 9.1 earthquake in the PWS-KP-KI region: maximum slip at a depth of 18-32 km (11.2-19.9 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-09-upper-cook-inlet-inundation.shp, ri2023-2-scenario-09-upper-cook-inlet-flow-depth.tif
    Mw 9.2 earthquake in the PWS-KP-KI region: maximum slip at a depth of 17-32 km (10.6-19.9 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-10-upper-cook-inlet-inundation.shp, ri2023-2-scenario-10-upper-cook-inlet-flow-depth.tif
    Mw 9.1 earthquake in the PWS-KP-KI region: maximum slip at a depth of 20-40 km (12.4-24.8 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-11-upper-cook-inlet-inundation.shp, ri2023-2-scenario-11-upper-cook-inlet-flow-depth.tif
    Mw 9.3 earthquake with 50 m (164 ft) of maximum slip close to the trench (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-10-upper-cook-inlet-inundation.shp, ri2023-2-scenario-12-upper-cook-inlet-flow-depth.tif
    Mw 9.3 earthquake with 35 m (114.8 ft) of maximum slip in most of the rupture (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-13-upper-cook-inlet-inundation.shp, ri2023-2-scenario-13-upper-cook-inlet-flow-depth.tif
    Mw 9.0 earthquake offshore AP region: SAFRR scenario (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-14-upper-cook-inlet-inundation.shp, ri2023-2-scenario-14-upper-cook-inlet-flow-depth.tif
    Mw 8.9 earthquake in the KI-AP region: maximum slip at a depth of 15-25 km (9.3-15.5 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-15-upper-cook-inlet-inundation.shp, ri2023-2-scenario-15-upper-cook-inlet-flow-depth.tif
    Mw 8.8 earthquake in the KI-AP region: maximum slip at a depth of 25-35 km (15.5-21.7 mi) (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)
    ri2023-2-scenario-16-upper-cook-inlet-inundation.shp, ri2023-2-scenario-16-upper-cook-inlet-flow-depth.tif
    Mw 9.1 rupture of the Cascadia subduction zone, including the entire megathrust between British Columbia and northern California (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    This report was funded by the U.S. Department of Commerce/National Oceanic and Atmospheric Administration (NOAA) through National Tsunami Hazard Mitigation Program Awards NA21NWS4670003 and NA22NWS4670012 to the Alaska Division of Homeland Security and Emergency Management. This does not constitute an endorsement by NOAA. Numerical calculations for this work were supported by High Performance Computing resources at the Research Computing Systems unit at the Geophysical Institute of the University of Alaska Fairbanks. We thank our reviewers, Peter Haeussler and Rob Witter, for their insightful comments, suggestions, and discussions, which helped improve the report.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

DGGS manages the DNR portion of the federally funded National Tsunami Hazard Mitigation Program (NTHMP). The program identifies at-risk coastal Alaska communities and provides tsunami hazard maps for hazard mitigation and emergency response training.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 2014 (process 1 of 3)
    Model validation - The numerical model that we used for simulation of tsunami wave propagation and runup was validated through a set of analytical benchmarks and tested against laboratory data. The model solves water equations using a finite-difference method on a staggered grid. See the accompanying report for more detail and additional model information.
    Date: 2022 (process 2 of 3)
    Development of nested grids - To support inundation modeling of coastal areas in Alaska, we used a series of nested telescoping grids, or digital elevation models (DEMs), as input layers for tsunami inundation modeling and mapping. These grids of increasing resolution allowed us to propagate waves generated by various sources to Anchorage, Girdwood, and Hope. In order to propagate a wave from its source to various coastal locations, we used embedded grids, placing a large, coarse grid in deep water and coupling it with smaller, finer grids in shallow water areas. The extent of each grid used for our tsunami inundation mapping is listed in the accompanying report.
    Date: 2022 (process 3 of 3)
    Numerical simulations of hypothetical tsunami scenarios - We assessed hazards related to tectonic tsunamis in Anchorage, Girdwood, and Hope by performing model simulations for each historic hypothetical source scenario. For each tsunami scenario, we first calculate the maximum tsunami wave heights in the highest-resolution grid over the course of the entire model run in the following way: at each grid point, the tsunami wave height is computed at every time step during the tsunami propagation time and the maximum value is kept. Then we compute the composite maximum tsunami wave height from all considered scenarios by again choosing the maximum value for each grid point among all scenarios, and plot the results.
  3. What similar or related data should the user be aware of?
    Newell, J.T., Maurits, S.A., Suleimani, E.N., Koehler, R.D., and Nicolsky, D.J., 2015, Tsunami inundation maps for Alaska communities: Digital Data Series DDS 10, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Salisbury, J.B., and Janssen, K.A., 2022, Tsunamis in Alaska: Information Circular IC 85 v. 2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    The maps showing the results of our modeling have been completed using the best information available and are believed to be accurate, however, their preparation required many assumptions. We described several scenarios and provide an estimate of maximum credible tsunami inundation. Actual conditions during a tsunami event may vary from those considered, so the accuracy cannot be guaranteed. The limits of inundation shown should be used only as a guideline for emergency planning and response action. Actual areas inundated will depend on specifics of the earth deformations, on-land construction, and tide level, and they may differ from areas shown on the map. The information on this map is intended to provide a basis for state and local agencies to plan emergency evacuation and tsunami response actions in the event of a major tsunamigenic earthquake. These results are not intended for land-use regulation or building-code development. This DGGS Report of Investigations is a final report of scientific research. Several scientists familiar with the subject matter provided technical reviews. Uncertainties associated with the depiction or interpretation of various features are discussed in the manuscript.
  2. How accurate are the geographic locations?
    The hydrodynamic model used to calculate propagation and runup of tsunami waves is a nonlinear, flux-formulated, shallow-water model that has passed the validation and verification tests required for models used in the production of tsunami inundation maps. The uncertainties in tsunami modeling include bottom friction, the presence or absence of buildings and vegetation in DEMs, the time delay between the observed and computed tsunami arrivals discussed above, the lack of horizontal deformation in the displacement models, and the assumption of instantaneous displacement. The tsunami scenarios we calculate in this report are considered sufficient to capture the worst-case tsunami event. However, there are still an infinite number of possible slip distributions. Further details about the limitations of the employed modeling approach are described in earlier reports by Suleimani and others and Nicolsky and others, as well as in National Tsunami Hazard Mitigation Program guidelines. See the accompanying report for more detail.
  3. How accurate are the heights or depths?
    The vertical accuracy of the inundation modeling is dependent on the accuracy and resolution of the digital elevation models (DEMs) and tidal datum values that were used to compile the computational grid. We provide additional details about DEM and grid development in the accompanying report. Prior to scenario modeling, bathymetric data were shifted to use Mean Higher High Water (MHHW) as the vertical datum. The depths of inundation shown should be used only as a guideline for emergency planning and response action. Actual inundation water depth will depend on specifics of the earth deformations, on-land construction, and tide level, and they may differ from areas shown by this data. The information is intended to permit state and local agencies to plan emergency evacuation and tsunami response actions in the event of a major tsunamigenic earthquake. These results are not intended for land-use regulation or building-code development. For additional information, please reference the sources of errors and uncertainties section of the accompanying report.
  4. Where are the gaps in the data? What is missing?
    Our modeling results have been completed using the best information available and are believed to be accurate; however, their preparation required many assumptions, and actual conditions during a tsunami event may vary from those considered.
  5. How consistent are the relationships among the observations, including topology?
    Not applicable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
This dataset includes results of numerical modeling of earthquake-generated tsunami waves for a specific community. Modeling was completed using the best information and tsunami modeling software available at the time of analysis. They are numerical solutions and, while they are believed to be accurate, their ultimate accuracy during an actual tsunami will depend on the specifics of earth deformations, on-land construction, tide level, and other parameters at the time of the tsunami. Actual areas of inundation may differ from areas shown in this dataset. Landslide tsunami sources may not be included in the modeling due to unknown potential impact of such events on a given community; please refer to accompanying report for more information on tsunami sources used for this study. The limits of inundation shown should only be used as a general guideline for emergency planning and response action in the event of a major tsunamigenic earthquake. These results are not intended for any other use, including land-use regulation or actuarial purposes. Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  1. Who distributes the data set? (Distributor 1 of 1)
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? RI 2023-2
  3. What legal disclaimers am I supposed to read?
    The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 14-Aug-2023
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:
Generated by mp version 2.9.50 on Mon Aug 14 17:40:16 2023