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Open-File Report O-22-01, Tsunami Evacuation Analysis of Astoria and Nearby Unincorporated Communities, Clatsop County, Oregon,
by Laura L. S. Gabel, Fletcher E. O’Brien, and Jonathan C. Allan; 51 p. report, one Esri® geodatabase with internal metadata, external metadata in .xml and .html formats.

Learn more about Beat the Wave series maps.

 

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ABSTRACT
Pedestrian evacuation routes were evaluated for a local tsunami generated by an earthquake on the Cascadia Subduction Zone (CSZ) in the City of Astoria and nearby unincorporated communities of Clatsop County, Oregon. Our analyses focused on a maximum-considered CSZ tsunami event, termed XXL, that could be produced by a locally generated magnitude (Mw) 9.1 earthquake. Evacuation paths were limited to established roads, trails, and pedestrian pathways designated by local government reviewers as the most likely routes.

To assist in pedestrian tsunami evacuation, we produced maps and digital data that include the following:

The Beat the Wave maps depict the minimum evacuation speed required to stay ahead of the tsunami wave for each scenario. For planning purposes, we present a variety of scenarios that increase and decrease evacuation difficulty (due to additional complications and mitigation options, respectively). Model assumptions include: 

In addition to the assumptions listed above, the current-conditions scenario also assumes the failure of non-retrofitted bridges. In all cases, the identified minimum speeds must be maintained for the entire time it takes to evacuate from the inundation zone.

Given the model limitations defined in the Methods section and summarized above, results show that evacuation for nearly the entire region examined is achievable at a walk (4 fps, or 2.7 mph) or faster. This is due to steep terrain creating a very narrow XXL tsunami zone and short evacuation distances as well as long wave arrival times (~40 minutes). Evacuation distances in Jeffers Garden are much longer and present a greater challenge. Evacuees in western Jeffers Garden must travel at a fast walk (6 fps, or 4.1 mph) to reach safety prior to the arrival of the tsunami. Liquefaction, landslides, and lateral spreading could present additional challenges to evacuation across the region and are not examined in detail.

In this report, tsunami mitigation refers to actions used to improve the survivability of a local population. This project is about evaluating ways to help move people out of the tsunami zone in the shortest amount of time possible between the start of earthquake shaking and the arrival of the tsunami. Mitigation options may include adding new evacuation routes, constructing earthquake-hardened roads and trails (that is, built or remodeled to withstand shaking from a major earthquake and liquefaction), enhancing tsunami wayfinding signage along core routes, and/or installing a tsunami refuge, otherwise known as a tsunami vertical evacuation structure.


GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA

Geodatabase is Esri® version 10.7 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml and .html formatted files.

Astoria_Tsunami_Evacuation_Modeling.gdb (GIS data bundle zip file)
XXL1_EvacuationFlowZones This polygon feature class shows the nearest safety destination for every point in the inundation zone (on the road and trail network) assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This layer was created based on the Extra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years. .xml
.html
XXL1_EvacuationRoutes This line feature class shows the most efficient routes to safety for every point in the inundation zone (on the road and trail network) assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. Symbolize in ArcGIS with arrow at end of each segment to see direction of line. This layer was created based on the Extra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years. .xml
.html
XXL1_WalkingSpeeds_Roads This polygon feature class shows minimum evacuation speeds, in feet per second, needed to stay ahead of the wave assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains data on paved roads. A separate feature class contains data for trails and beach networks. This layer was created based on the Extra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years. .xml
.html
XXL1_WalkingSpeeds_Trails This line feature class shows minimum evacuation speeds, in feet per second, needed to stay ahead of the wave assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains data on trails and beach networks. A separate feature class contains data for paved roads. This layer was created based on the Extra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years. .xml
.html