Tsunami Preparedness in Los Angeles
For my final GIS presentation, I investigated Tsunami preparedness in the areas along the coastline of Los Angeles County. Before doing this investigation, I first surveyed the Japanese Tsunami preparedness policy since northeastern part of Japan was hit by a massive earthquake and Tsunami on March 11, 2011. Since then, Japanese government has started examining various new policies for Tsunami preparedness.
What caused so big damages in the coastal areas of Japan? There are two major causes. One is that the height of Tsunami was much larger than that had been expected. The Tsunami was higher than two or three story buildings. As a result, the Tsunami easily overflowed the Tsunami barriers constructed by governments. The other is that the local people were not prepared for so big Tsunami
As one of the Tsunami preparedness schemes after the 2011 Tsunami, a scheme of using existing tall buildings as Tsunami evacuation buildings is becoming popular in local governments of Japan (Fig.1). Among the tall buildings existing in the expected inundation areas, local governments selected the buildings that meet the requirements as Tsunami evacuation building. Each evacuation buildings are expected to cover the communities that are 200 m from the buildings. Once an earthquake occurs, community people are able to reach these buildings within a short time. The above Tsunami preparedness scheme hereinafter referred to as “the Tsunami evacuation building scheme” is mainly intended for near-field earthquakes where the evacuation time is very much limited. Under severe budget, this approach is very attractive to local governments.
By examining statistical data concerning Los Angeles coastal areas, I herein examine the problems and possibility of applying the Tsunami evacuation building scheme to these areas. I hope my maps could shed some new light on Tsunami preparedness policy of Los Angeles. My research focuses on the following three points.
- Which areas are lacking in multistory buildings for evacuation?
- Which areas will be seriously damaged by Tsunami?
- Which areas need Tsunami evacuation buildings?
In the present study, it is assumed that Tsunami inundation area is within 2,000 m from coastline as shown in Map. 1.
Map 2 shows the multistory buildings over 65 feet currently existing in the inundation area (Total number of buildings: 254,391). In this map, 200 m and 500 m buffers are taken for the respective buildings to show the covered areas. To reach the buildings of 200 m and 500 m distances, average male adults need 2.5 and 6.25 minutes, respectively, on foot, if their averaged walk speed is assumed 80 m/ minutes. It can be seen from Map 2 that there are many areas that are not covered by tall building. Here, I did not consider whether or not these buildings have been upgraded for earthquakes.
Next, I investigated which areas are strongly damaged by Tsunami. This is to look for the areas that among others need Tsunami evacuation buildings. As possible factors that increase the magnitude of Tsunami damage, I chose four factors; low elevation, old buildings, high percentage of elderly people, close distance from coastal line.
1. Elevation (Map. 3)
I selected areas with elevation (including structure height) under 100 feet. Especially, larger part of Santa Monica is located in lower elevation, compared to other areas.
2. Age of buildings(Map. 4)
I choose this factor because old buildings have a higher possibility of collapse during the earthquake prior to Tsunami and people in the community cannot make use of these buildings. According to previous research, buildings before 1940 are reported to have a high possibility of collapse when earthquake occurs (Yoshimura, 2005). Therefore, I classified the building in two categories, that is, the buildings constructed in and after 1940, and those before 1940. It is observed from Map 4 that there is low correlation between height of buildings and age of buildings.
3. Proportion of elderly people (Map.5)
When the 2011 Tsunami hit Japan, many old people could not start the quick action of escape and failed to reach evacuation areas. From Map.5, it can be seen that the southern part of the study area has a higher proportion of elderly people.
4. Distance (Map.6)
As a distance , I herein used a straight-line distance from the coastline.
Next, I proceeded to figure out the areas with higher possibility of damages by considering the four factors shown in Maps 2~6. I employed spatial analysis in order to find out the heaviest damage areas. Parameters and weight are summarized in Table. 1. The smallest weighed of 10% is herein set to the age of buildings because the minimum survey size is limited to the average age of buildings existing in a block. In addition, it cannot be identified whether or not old buildings originally constructed before 1940 were upgraded for earthquake preparation after 1940.
In Map. 7, blue color denotes higher expected damage areas, while yellow color denotes lower expected damage areas.
To find out high priority areas for Tsunami preparedness, I overlaid Map. 2 showing the areas covered by existing tall evacuation buildings on Map. 7of Tsunami damage areas. The result is shown in Map.8. It is demonstrated by Map. 8 that the areas close to Malibu Beach coast, around Santa Monica Airport, areas nestled between Marina Del Rey and Lax and coast areas close to Manhattan and Hermosa Beach have higher damage possibility of Tsunami but not covered by Tsunami evacuation buildings.
In conclusion, Malibu Beach coast, around Santa Monica Airport, areas nestled between Marina Del Rey and Lax and coast areas close to Manhattan and Hermosa Beach have higher priority for Tsunami preparedness. I would like to say that the proposed scheme for Tsunami preparedness using existing tall buildings as evacuation areas is feasible to adopt since the government does not need bigger budget. My analysis is still rough and insufficient. However, I hope that the present research suggest something to the real world.
All maps are created by Nobuko Goto
Sources: Guideline of Tsunami evacuation building, Cabinet Office, Japanese Government, http://www.bousai.go.jp/oshirase/h17/tsunami_hinan.html
Los Angeles County Tsunami Inundation Map, http://www.conservation.ca.gov/cgs/geologic_hazards/Tsunami/Inundation_Maps/LosAngeles/Pages/LosAngeles.aspx
Miho Yoshimura, The introduction of incentives to earthquake vulnerability of buildings (September, 2005) http://repository.dl.itc.u-tokyo.ac.jp/dspace/handle/2261/50136
Model Used: reclassify rasters