Introduction and Methods
The Pacific Northwest region of the US sits near multiple active tectonic zones (Geist 2005, Schulz 2015). Closest to the coast, the Juan de Fuca plate subducts under the North American plate. Indeed, this geological activity is responsible for the Cascade Mountain range. Further out in the Pacific Ocean, the Pacific plate slides past the Juan de Fuca plate. Both tectonic boundaries have the potential to generate earthquakes, which in turn can result in tsunamis that may affect human populations living on the US coast. Tsunami inducing earthquakes are difficult to predict (Geist 2005). Thus, standing evacuation plans are critical for people located in potential inundation zones. The aims of this analysis are to quantify the impact of a large tsunami on the Oregon coast and identify a region for Lincoln county that could serve as a disaster recovery area.
In order to assess tsunami impact, I quantified the number of individuals, number of households, and extent of highways located in the inundation zone using data from the Oregon Geospatial Data Clearinghouse and the US Census. I used intercepts to overlay the inundation zone and then recalculated the number of individuals/households, city area, and length of highway impacted using summary statistics. This analysis was conducted for the coast overall and then the data were analyzed by county.
I determined the appropriate location to place a disaster recovery area for Lincoln County using a Multi-Criteria Evaluation (MCE) analysis. I prioritized areas 1) near the inundation zone, 2) with low slope, and 3) near highways not impact by the tsunami. Data used for this analysis include data from the Oregon Geospatial Data Clearinghouse as well as digital elevation data for Lincoln county. Individual rasters were created for each factor and reclassified using natural breaks. Figure 1 highlights the model used to run the analysis. As slope, distance from the zone, and access to highways are all relatively important, I weighted each factor equally (0.33).
Figure 1.
Results
The total city area affected by a tsunami is 1,706,034,545 sq. ft. The total length of highway impacted is 1,350,260 ft. Finally, the number of households potentially impacted is 24,347 and 30,880 people. Table 1 highlights the number of households and number of people impacted by county.
| County | # Households | # People |
| Clatsop | 9,007 | 12,593 |
| Coos | 2,664 | 4,806 |
| Curry | 2,519 | 3,816 |
| Douglas | 779 | 1,251 |
| Lane | 365 | 479 |
| Lincoln | 4,093 | 4,266 |
| Tillamook | 4,920 | 3,669 |
My analysis of an ideal recovery area for Lincoln County indicated that Newport High School is a good location. This school is located in an area with low slope and is near the impacted area. Finally, the school is not far from Highway 20, which would provide critical access to the interior of the state. Figure 2 illustrates the distance from the inundation zone. Figure 3 highlights distance from highways. Figure 4 displays the slope. In each of these figures, darker colors represent more suitable areas whereas lighter colors are less suitable. Figure 5 illustrates the resulting suitability analysis with the inundation zone highlighted and high school location denoted with a blue circle.
Figure 2.
Figure 3.
FIgure 4.
Figure 5.
Conclusion
This study highlights that a major earthquake could result in a tsunami capable of impacting many thousands of Oregonians. My analysis also describes an potential location for a disaster recovery zone for Lincoln county.
References
Geist, Eric L. Local tsunami hazards in the Pacific Northwest from Cascadia subduction
zone earthquakes. US Dept. of the Interior, US Geological Survey, 2005.
Schulz, Kathryn. The Really Big One. The New Yorker. July 2015.
http://www.newyorker.com/magazine/2015/07/20/the-really-big-one.