Tsunami inundation maps for the city of Sand Point, Alaska

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Title: Tsunami inundation maps for the city of Sand Point, Alaska
Abstract:
Staff from Alaska Earthquake Center, Geophysical Institute and Alaska Division of Geological & Geophysical Surveys evaluated potential tsunami hazards for the city of Sand Point, on Popof Island in the Shumagin Islands archipelago. We numerically modeled the extent of inundation from tsunami waves generated by local and distant earthquake sources. We considered the results in light of historical observations. The worst-case scenarios are defined by analyzing results of the sensitivity study of the tsunami dynamics with respect to different slip distributions along the Aleutian megathrust. For the Sand Point area, the worst-case scenarios are thought to be thrust earthquakes in the Shumagin Islands region with magnitudes ranging from Mw 8.8 to Mw 9.0. We additionally consider a Mw 9.0 rupture between Shumagin Islands and Kodiak Island, a Mw 9.0 rupture of the Cascadia subduction zone, and a Mw 8.6 outer-rise rupture in the area of the Shumagin Islands. Conducted numerical experiments reveal that a tsunami might start to arrive to Sand Point in about 15 minutes after the earthquake with a strong positive wave reaching in 1 hour the height of 7-8 m (23-26 ft) with respect to the pre-earthquake sea level. Consecutive waves might have the same of height or even be higher. The highest predicted wave height is 12-14 m (39-46 ft); a vertical difference between the trough and crest could be as much as 16 m (53 ft) and a time period between the water withdrawal and runup could be as short as 15 minutes. At least three devastating waves can reach the community in the first 2.5 hours after the earthquake. The first wave may not be the highest; the later waves might be more damaging and produce larger inundation. Results from the numerical modeling are intended to provide guidance to local emergency management agencies in tsunami inundation assessment, evacuation planning, and public education to mitigate future tsunami hazards. Users can access the complete report and digital data from the DGGS website: <http://doi.org/10.14509/29706>.
Supplemental_Information: 
border: Outline of the study area. 
max-flow-depth: Raster image depicting maximum composite flow depths over dry land. Pixel values provide the modeled depth (in meters) of maximum inundation. 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-tectonic-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. 
scenarios: Collection of shapefiles that depict the modeled potential maximum inundation by tectonic waves for each modeled scenario. Detailed information about each scenario can be found in the accompanying report. 
time-series-points: To help emergency management personnel assess tsunami hazards, we supplement the inundation maps with the time series plots of the modeled water level and velocity dynamics at some on-land and some offshore locations in the communities. The plots are provided in the appendices of the report. These shapefiles provide the location of each time series point.
  1. How should this data set be cited?

    Nicolsky, D.J., Suleimani, E.N., and Koehler, R.D., 2017, Tsunami inundation maps for the city of Sand Point, Alaska: Report of Investigation RI 2017-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 61 p., 4 sheets, scale 1:15,000

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -160.551594
    East_Bounding_Coordinate: -160.462593
    North_Bounding_Coordinate: 55.370603
    South_Bounding_Coordinate: 55.276042

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 2013
    Ending_Date: 2017
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: report and digital 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 World Geodetic System of 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563000025.

      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: Mean Higher High Water
      Depth_Resolution: 1
      Depth_Distance_Units: meter
      Depth_Encoding_Method: Attribute values

  7. How does the data set describe geographic features?

    ri2017-3-border.shp
    Outline of the study area. File format: shapefile (Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and Alaska Earthquake Center, Geophysical Institute, University of Alaska)

    ri2017-3-max-flow-depth-sand-point.tif
    Raster image depicting maximum composite flow depths over dry land. Pixel values provide the modeled depth (in meters) of maximum inundation. 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. File format: GeoTIFF (Source: Alaska Earthquake Center, Geophysical Institute, University of Alaska, this report)

    ri2017-3-max-tectonic-inundation-sand-point.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. File format: shapefile (Source: Alaska Earthquake Center, Geophysical Institute, University of Alaska, this report)

    ri2017-3-scenarios-sand-point-01.shp, ri2017-3-scenarios-sand-point-02.shp, ri2017-3-scenarios-sand-point-03.shp, ri2017-3-scenarios-sand-point-04.shp, ri2017-3-scenarios-sand-point-05.shp, ri2017-3-scenarios-sand-point-06.shp, ri2017-3-scenarios-sand-point-07.shp, ri2017-3-scenarios-sand-point-08.shp, ri2017-3-scenarios-sand-point-09.shp
    Collection of shapefiles that depict the modeled potential maximum inundation by tectonic waves for each modeled scenario. Detailed information about each scenario can be found in the accompanying report. File format: shapefile (Source: Alaska Earthquake Information Center, Geophysical Institute, University of Alaska, this report)

    ri2017-3-time-series-points-sand-point.shp
    To help emergency management personnel assess tsunami hazards, we supplement the inundation maps with the time series plots of the modeled water level and velocity dynamics at some on-land and some offshore locations in the communities. The plots are provided in the appendices of the report. These shapefiles provide the location of each time series point. File format: shapefile (Source: Alaska Earthquake Center, Geophysical Institute, University of Alaska, this report)

    Number
    Numbers correspond to labeled points and graphs shown in the accompanying report. (Source: this report)

    Figures A-2 through A-4

    Label
    Values correspond to graphs shown in the accompanying report. (Source: this report)

    Figures A-1 and A-2

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 project was supported by the National Oceanic and Atmospheric Administration (NOAA) under Reimbursable Services Agreement ADN 0931000 with the State of Alaska's Division of Homeland Security and Emergency Management (a division of the Department of Military and Veterans Affairs). Some of the research in this publication is sponsored by the Cooperative Institute for Alaska Research with funds from NOAA under cooperative agreement NA08OAR4320751 with the University of Alaska Fairbanks. Numerical calculations for this work were supported by a grant of High Performance Computing (HPC) resources from the Arctic Region Supercomputing Center (ARSC) at the University of Alaska Fairbanks. We thank Zebulon Maharrey for his help with the RTK GPS survey in Sand Point. We also express our gratitude to Douglas Christensen, Michael West, and Natasha Ruppert for their help in assessing potential earthquakes along the Alaska Peninsula and the Aleutian Islands, and for sharing the data with us. Rob Witter provided valuable contributions to discussions on subduction-type tsunamigenic earthquakes along the Shumagin Islands. Reviews by Jason Patton and an anonymous reviewer improved the report and maps.

  3. To whom should users address questions about the data?

    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK 99709-3707
    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

Why was the data set created?

Results presented here are intended to provide guidance to local emergency management agencies in tsunami inundation assessment, evacuation planning, and public education to mitigate future tsunami hazards.

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: 2011 (process 1 of 6)
    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 Sand Point. 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. Because the high-resolution topography in the NOAA DEMs can have large vertical errors near the shoreline, prediction of potential tsunami inundation using only this data can be inaccurate. Hence, this topographic dataset is augmented with a real-time kinematic (RTK) GPS survey in the harbor areas and along nearshore areas in Sand Point. The survey in Sand Point was conducted September 7-9, 2011. The extent of each grid used for our tsunami inundation mapping is listed in the accompanying report. See Methodology and Data section of the accompanying report for more detail and additional grid development source information.

    Date: 2011 (process 2 of 6)
    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: 2011 (process 3 of 6)
    Model verification - To estimate tsunami propagation and runup in the Sand Point area, we verified our model against the observed tsunami generated by the March 11, 2011, Mw 9.0 Tohoku earthquake in Japan.

    Date: 2016 (process 4 of 6)
    Numerical simulations of hypothetical tsunami scenarios - We assessed hazard related to tectonic tsunamis in Sand Point by performing model simulations for each hypothetical source scenario. Numerical results for each scenario include extent of inundation, sea level and velocity time series calculations, tsunami flow depth over land, and the maximum water level above the MHHW tide level offshore and within the potential inundation area. We create raster files of model results. For each grid point, the pixel value provides the modeled depth of water (in meters). See the accompanying report for more detail and additional information.

    Date: 2016 (process 5 of 6)
    Calculation of the potential inundation lines - For each grid cell in the high-resolution DEMs Sand Point, we determined whether the cell was inundated by waves or stayed dry throughout the entire simulation. Then, we defined a function such that it is equal to one at the center of each wet cell and is negative one at the center of each dry cell. Using a linear interpolation algorithm in Matlab, we plotted a zero-value contour that delineates dry and wet cells from each other. The resultant contour line (or a collection of lines) was directly exported to the ArcGIS using WGS84 datum.

    Date: 2016 (process 6 of 6)
    Compilation of composite maximum inundation zone, flow depths over land, and water level above the MHHW tide level offshore and within the potential inundation area - We interpret the maximum, geologically credible, worst case scenario by combining the maximum calculated inundation of all scenarios. See the accompanying report for more detail and additional information.

  3. What similar or related data should the user be aware of?

    Nicolsky, D.J., Suleimani, E.N., Combellick, R.A., and Hansen, R.A., 2011, Tsunami inundation maps of Whittier and western Passage Canal, Alaska: Report of Investigation RI 2011-7, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 65 p., 4 sheets
    Nicolsky, D.J., Suleimani, E.N., Freymueller, J.T., and Koehler, R.D., 2015, Tsunami inundation maps of Fox Islands communities, including Dutch Harbor and Akutan, Alaska: Report of Investigation RI 2015-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 67 p., 2 sheets, scale 1:12,500
    Nicolsky, D.J., Suleimani, E.N., Haeussler, P.J., Ryan, H.F., Koehler, R.D., Combellick, R.A., and Hansen, R.A., 2013, Tsunami inundation maps of Port Valdez, Alaska: Report of Investigation RI 2013-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 77 p., 1 sheet, scale 1:12,500
    Nicolsky, D.J., Suleimani, E.N., and Koehler, R.D., 2014, Tsunami inundation maps of Cordova and Tatitlek, Alaska: Report of Investigation RI 2014-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 49 p., 2 sheets
    Nicolsky, D.J., Suleimani, E.N., and Koehler, R.D., 2016, Tsunami inundation maps for the communities of Chignik and Chignik Lagoon, Alaska: Report of Investigation RI 2016-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 48 p., 2 sheets, scale 1:12,500
    Suleimani, E.N., Hansen, R.A., Combellick, R.A., and Carver, G.A., 2002, Tsunami hazard maps of the Kodiak area, Alaska: Report of Investigation RI 2002-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p., 4 sheets, scale 1:12,500
    Suleimani, E.N., Nicolsky, D.J., and Koehler, R.D., 2013, Tsunami inundation maps of Sitka, Alaska: Report of Investigation RI 2013-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 76 p., 1 sheet, scale 1:12,500
    Suleimani, E.N., Nicolsky, D.J., and Koehler, R.D., 2015, Tsunami inundation maps of Elfin Cove, Gustavus, and Hoonah, Alaska: Report of Investigation RI 2015-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 79 p., 3 sheets
    Suleimani, E.N., Nicolsky, D.J., Koehler, R.D., Freymueller, J.T., and Macpherson, A.E., 2016, Tsunami inundation maps for King Cove and Cold Bay communities, Alaska: Report of Investigation RI 2016-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 73 p., 2 sheets, scale 1:12,500
    Suleimani, E.N., Nicolsky, D.J., West, D.A., Combellick, R.A., and Hansen, R.A., 2010, Tsunami inundation maps of Seward and northern Resurrection Bay, Alaska: Report of Investigation RI 2010-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 47 p., 3 sheets, scale 1:12,500

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 production of tsunami inundation maps. The uncertainties in tsunami modeling include bottom friction, 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 assumption of instantaneous displacement. The tsunami scenarios that we calculate in this report are considered to be sufficient to capture the worst-case tsunami event, but 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. The accuracy of the later waves is limited by the accuracies of the bathymetry and coastline that are outside the extent of the high-resolution DEM but still impact the modeling. See 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 associated manuscript.

  4. Where are the gaps in the data? What is missing?

    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 and actual conditions during a tsunami event may vary from those considered.

  5. How consistent are the relationships among the observations, including topology?

    Model validation for this report included comparison of the modeled results to observations that were recorded during historic events.

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 &amp; 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 99709-3707
    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
  2. What's the catalog number I need to order this data set?

    RI 2017-3

  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: 30-Nov-2017
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
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:

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