Regional tsunami hazard assessment for Shemya, Alaska

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What does this data set describe?

Title: Regional tsunami hazard assessment for Shemya, Alaska
Abstract:
We assess potential tsunami hazards for Eareckson Air Station on Shemya Island, Alaska. The primary tsunami hazard for this installation is considered to be near-field, with the major threat originating from tsunamigenic earthquakes along the Alaska-Aleutian megathrust. We numerically model tsunamis generated by three different megathrust earthquakes, analyze tsunami wave dynamics, and develop approximate tsunami hazard maps for Eareckson Air Station (formerly "Shemya Station"). The hypothetical tsunami scenarios that we examined simulate Mw9.0 megathrust earthquakes with a slip distribution in the 5-54 km (3-33 mi) depth range along the Alaska-Aleutian megathrust. The maximum runup heights are 40 m (131 ft) on the northern side of Shemya Island, and 58 m (190 ft) on the southern side of the island. Results presented here are intended to provide guidance to local emergency management agencies in initial tsunami inundation assessment, evacuation planning, and public education for mitigation of future tsunami hazards. The complete report and digital data are available from the DGGS website: <http://doi.org/10.14509/30193>.
Supplemental_Information:
hazard-boundary: Shapefile depicting maximum assumed runup heights with an included safety factor. These lines are intended to be utilized as a basis for local tsunami hazard planning and development of evacuation maps.
  1. How should this data set be cited?

    Suleimani, E.N., Salisbury, J.B., Nicolsky, D.J., and Koehler, R.D., 2019, Regional tsunami hazard assessment for Shemya, Alaska: Report of Investigation RI 2019-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 13 p., 1 sheet

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: 174.086326
    East_Bounding_Coordinate: 174.142775
    North_Bounding_Coordinate: 52.738448
    South_Bounding_Coordinate: 52.716574

  3. What does it look like?

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

    Beginning_Date: 2015
    Ending_Date: 2019
    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?

    ri2019-4-hazard-boundary-shemya-north-shore.shp, ri2019-4-hazard-boundary-shemya-south-shore.shp
    Shapefile depicting maximum assumed runup heights with an included safety factor. These 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)


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, which is part of the National Tsunami Hazard Mitigation Program (NTHMP), received support from the National Oceanic and Atmospheric Administration (NOAA) under Reimbursable Services Agreement ADN 952011 with the State of Alaska's Division of Homeland Security & Emergency Management (a division of the Department of Military and Veterans Affairs).

  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 5)
    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: 2015 (process 2 of 5)
    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 Shemya. 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: 2015 (process 3 of 5)
    Numerical simulations of hypothetical tsunami scenarios - We assessed hazard related to tectonic tsunamis in Shemya by performing model simulations for each 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.

    Date: 2015 (process 4 of 5)
    Tsunami hazard boundary - After calculating the maximum tsunami height for every grid point in the vicinity of community, we multiply each highest value grid point by a safety factor of 1.3 (30%) and define it as the maximum runup height. Then we find an elevation contour on the DCRA community map that corresponds to this maximum runup height. This contour is the tsunami hazard boundary.

    Date: 2015 (process 5 of 5)
    To create a shapefile for the post-earthquake shoreline resulted from coseismic subsidence - We calculated the amount of coseismic ground subsidence in the community for each scenario considered in the report and select the largest value among all scenarios. Then we subtracted this amount from the community DEM used to model tsunami inundation, and calculated the new shoreline position from the boundary between positive (land) and negative (water) values using Matlab.

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

    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., and Koehler, R.D., 2014, Tsunami inundation maps of the villages of Chenega Bay and northern Sawmill Bay, Alaska: Report of Investigation RI 2014-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 50 p., 7 sheets
    Nicolsky, D.J., Suleimani, E.N., and Koehler, R.D., 2016, Tsunami inundation map for the village of Nikolski, Alaska: Report of Investigation RI 2016-7, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 34 p., 1 sheet, scale 1:12,500
    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
    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
    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
    Suleimani, E.N., Nicolsky, D.J., and Koehler, R.D., 2017, Updated tsunami inundation maps of the Kodiak area, Alaska: Report of Investigation RI 2017-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 38 p., 10 sheets
    Suleimani, E.N., Salisbury, J.B., Nicolsky, D.J., and Koehler, R.D., 2019, Regional tsunami hazard assessment for False Pass and Perryville, Alaska: Report of Investigation RI 2019-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p., 2 sheets
    Suleimani, E.N., Salisbury, J.B., Nicolsky, D.J., and West, M.E., 2019, Tsunami inundation maps for Adak and Atka, Alaska: Report of Investigation RI 2019-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 63 p., 6 sheets


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

  1. How well have the observations been checked?

    The hydrodynamic model used to calculate propagation and runup of tectonic tsunamis is a nonlinear, flux-formulated, shallow-water model and has passed the required tests for official use in producing tsunami inundation maps. Most of the uncertainties in the numerical calculations originate from the tsunamigenic earthquake sources used in the models. Uncertainties in the earthquakes, such as the precise location, magnitude, and slip distribution, are the largest sources of error. The direction, amplitude, and arrival times of incoming waves are determined by the initial ocean surface conditions immediately following the earthquake. Therefore, the modeling results are particularly sensitive to the details of the tsunamigenic earthquake rupture, and when the earthquake occurs close to a community, discrepancies can be exacerbated. Furthermore, our assessment of potential earthquake scenarios is by no means exhaustive but represents the best estimate of the locations and sizes of potential tsunami-generating events. It is possible that other unrecognized earthquake scenarios could present hazards to these communities. 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?

    We use a series of nested computational grids to calculate inundation with sufficiently high resolution for each community. The bathymetry and topography in each nested grid are based on digital elevation models (DEMs) developed at the National Centers for Environmental Information (NCEI) of the National Oceanic & Atmospheric Administration (NOAA). The spatial resolution of the fine-resolution grid cells, with about 83 x 137 m (272 x 450 ft) dimensions, satisfies NOAA minimum recommended requirements for estimation of the tsunami hazard zone; however, no DEM verification efforts were conducted to reduce uncertainties in the fine-resolution (level 3) Near Islands grid. Therefore, in this report we do not perform high-resolution runup modeling, but provide an estimation of the approximate tsunami hazard zone by extrapolating the maximum composite tsunami wave height on land according to the tsunami scenarios described in the accompanying report. We account for uncertainties inherent to this method by applying a safety factor of 1.3 (30 percent) to the estimated hazard zone.

  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?

    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 &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 2019-4

  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: 11-Oct-2019
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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