Final Project: Liquefaction Danger Zones in Greater Vancouver
Personal Experience:
For our final project, my team and I wanted to explore the earthquake danger zones in the Greater Vancouver area, and which healthcare facilities would be at the highest risk to liquefaction due to a high magnitude earthquake. Our goal was to create a map that showed the risk level of each healthcare facility and the nearest hospital to that healthcare facility and the danger zones to transport patients and injured civilians.
My team and I worked on the creation of the map together. We met on countless occasions to put the map together, and did research on our own time to collect data for our maps. For the written report, my group and I decided to split the work based on our strengths. For example, Hannah did the flowchart and analysis section because she had a better grasp on the analysis tools, while Rene worked on the discussion portions because he is better at explaining details and results. However, gathering the information for each written portion was a group effort, and we assisted each other along the way as well.
Along the process of creating this map, I learned that finding data is difficult. For example, geology data. My group and I had a difficult time finding geology data. Every time we thought we had found a source, something came up and we were unable to access the data. However, through the help of other groups, we were able to locate geology data and successfully clipped the layer to our project boundary. Along with learning new things about locating data, I learned about how useful the join tool is. For example, my group and I wanted to display hospital capacities on our map. However, we were unable to find data that contained both the location of the hospitals and their capacities. With the help of the join tool, we were able to individually locate the hospital capacities, insert the information onto an excel document, and join the excel document with our hospital location data, resulting in an attribute table that contained both the hospital location and the capacities.
Overall, I am satisfied with the outcome of this project, and am proud of all the effort my group members and I put into the map.
Danger Zone Map:
Population Density Map:
PopulationDensityGreaterVancouver-2
Abstract
The Pacific Northwest region of North America is at risk for an immense earthquake. Potentially, the situation may be that “… the entire fault zone ruptures from end to end, causing one great earthquake measuring magnitude 9.0… the shaking that results from this abrupt shifting of the earth’s crust will be felt throughout the Pacific Northwest – and the ground is expected to go on shaking for four to six minutes” (Cascadia Region Earthquake Workgroup, 2013). Although the exact occurrence of an earthquake of this magnitude cannot be predicted, we can anticipate the effects on the Greater Vancouver Area’s geology, infrastructure, and communities and prepare for the dark cloud that looms ahead. We chose to focus on this topic because it is an event that we have heard of our whole lives and has the potential to not only severely impact Vancouver, but the entire Pacific Coast from B.C. to California.
Cascadia Region Earthquake Workgroup predicts that if an 9.0 earthquake and it’s following tsunami happened tomorrow, the number of deaths could exceed 10,000 and more than 30,000 people could be injured. Economic impacts for Washington, Oregon, and California have been estimated upwards of $70 billion (Cascadia Region Earthquake Workgroup, 2013). A disaster event this huge has many interweaving components. To begin investigating its potential impacts, we chose to focus on outlining liquefaction danger zones based on Vancouver’s geology and which hospitals should be mitigated for within the danger zones.
Project Description
The danger of liquefaction to the Greater Vancouver Area is a concerning one, due to the soil complexion of much of the region. Some parts, more than others, are extremely susceptible to danger and infrastructure damage. Therefore, we will be creating an Earthquake Danger Zone Map that portrays the healthcare facilities that are at highest risk of earthquake damage through liquefaction. Our map will also display the population density of each danger level, hospitals within low risk areas, and road networks. The portrayal of population density will be used to show the amount of people who are at risk of liquefaction and may need medical assistant after the earthquake event. The portrayal of hospitals within low risk areas and its capacity will be used to analyze the nearest hospital to transport injured civilians and patients from high risk areas that have been affected by liquefaction. The portrayal of road networks will be used to visualize how to transport patients and civilians to the unaffected hospitals. The data used in the creation of the map are the location and capacity of hospitals, population density, the Greater Vancouver map, geology distribution, road networks and liquefaction data.
Methods
To begin prepping our data for analysis, we created a new file geodatabase in Arc Catalog and imported our data files to the geodatabase. After opening a new ArcMap document, we added in all our data layers, which included the following; a DEM of the Greater Vancouver Area (GVA), geology data, hospitals, and roads. Using the ‘reclassify’ tool, we created a mask for the GVA from the DEM. To get our final target analysis area, we clipped the geology, hospital, and road layers to the new mask.
In order to identify the areas of Greater Vancouver that are at risk of liquefaction, we began by changing the symbology in the geology layer to display by soil material. Then, using the danger classifications found on CGEN’s ‘Geomap Vancouver’ site, we performed the merge function on all polygons with a material that was at high risk of liquefaction. We repeated the merge with the moderate risk materials as well as those with low/no risk. In the symbology tab of the geology properties, we chose a colour gradient to represent the risk from high to low. Finally, we calculated the areas of each risk polygons by selecting by attribute and then using the statistics tab.
The next stop was to identify which hospitals lay in high risk areas and assess the capacity of the hospitals. We began by creating a new layer from the high risk polygons. We performed the intersect function on the new high risk layer and the hospital layer. Then, with the selected hospitals, created a new layer of ones that lay within the high risk zones. In the symbology tab, we represented these with a crossed circle. Using the join function, we joined an excel we created that held capacities, represented by beds, to the hospital layers. Then, we used the proportioned symbol option in the symbology lab so that the size of the circle represents to capacity of the hospitals.
To analyze the population densities to compare the hospital locations, we first joined census population data to the GVA mask. Using a query, we selected each risk (high to moderate and low) and created separate layers. We joined the population data to these layers. We created a new column in the attribute tables. Then, using the field calculator, we calculated the population density (population/area) then in symbology represented the density with 5 classes and a colour gradient. Finally, we performed a union between the bedrock and risk area layers, then used the intersect to find which hospital lay in safe areas. We created a layer from these hospitals and changed their symbology to a circle with a dot, as well as represented by the proportioned symbol.
Analysis
Which hospitals are at risk to liquefaction during a Cascadia Subduction Zone Earthquake and how are they mitigated for? The goal of our study was to determine the hospitals within the medium to high risk zones of liquefaction. Then based on the certain environmental factors around these hospitals and the cities they are in, particularly on underlying soil type, we predict the possible impacts that may occur during the earthquake, and then propose feasible strategies to mitigate the risk of further deaths and injuries during and after an earthquake. As well, we take into account the particular soil types that dominate cities in medium to high danger zones and their characteristics in terms of liquefaction in order predict the magnitude of casualties that may occur. Although, we weren’t able to find reliable sources that describe the specific impacts of each soil type and their sensitivity to liquefaction. We did find a general characteristic for soils sensitive to liquefaction, where soils that are young and poorly layered with weak plasticity, cohesion, and water drainage often lead greater fracturing and hence more subjected to liquefaction (Rauch, 13). Based on these particular set of characteristics, we will judge the magnitude of casualties in these cities during an earthquake and how Vancouver’s hospitals; particularly those in the danger zones, will be affected by this.
Based on our data which is represented on the map, approximately 54% of Vancouver’s land area lies within moderate to high risk zones of liquefaction. Out of greater Vancouver’s population we found that, approximately 891,768 people live within these zones of medium to high danger areas, while 1,288,428 live in low danger zones, and 86,402 live in bedrock areas which we classified as ‘nil’. Although it is true that certain factors may lead to ensuing impacts on bedrock during and after an earthquake, in this study we assume that bedrock has no detrimental impacts on the city’s population.
Based on the map, we have found that there are four hospitals in greater Vancouver that are located within medium to high danger zones. These hospitals are located in the cities of Richmond, Delta, Surrey, and White Rock, where each city has one hospital in a danger zone. Maple Ridge’s hospital is in a safe zone, but is too small considering the fact that a major portion of the city is in a danger. Each of these cities as well are key areas for concern as they are heavily populated; particularly for the cities of Richmond and Delta. As well, most to all of the land area within the boundaries of these cities are within medium to high risk areas.
We found that the city of Richmond would be an area for most concern because it has a high population of 190,470 and a very high population density of 1473.5 with only one hospital that isn’t that large. As well, we project that all of the city’s area lie within medium to high danger zones. Based on these factors alone, we believe that a high magnitude earthquake would have devastating effects on the city’s population and infrastructure and would lead to the city’s only hospital being completely overwhelmed due to high injuries. The majority of Richmond’s underlying soil is composed of very young sand: all of its western side as well as most coastal land is composed of this (EMPR). Young sand have a very high susceptibility to liquefaction compared to other soil types. Because of the lack of assimilation of different soil layers in these areas, there is poor structure and cohesion as sand grains are generally larger and less cohesive than more assimilated and structured clays and silts (Rauch, 13). Such a lack of foundation in the soil will lead to high fluidity during a high magnitude earthquake making the ground unstable leading to liquefaction. As the majority of Richmond live on its western side, this would mean there is a high risk of deaths and injuries as it is expected that a significant number of homes and other buildings will collapse. Consequently, because we discovered that the city of Richmond only has one hospital; it is highly likely that this hospital will be overwhelmed. The number of available beds in this hospital is roughly within 500 which supports a population of 190,470 according to the 2011 census. This means that that there is roughly one bed for every 384 people in Richmond. The closest hospital to the city within a low risk area is B.C. Children’s Hospital which is 10 kilometers away, and the larger Vancouver General Hospital nearby; both of which are in Vancouver. Getting to these areas may be a challenge as Vancouver is connected to Richmond by only 3 bridges. As a result, there is a high possibility of traffic bottlenecks occurring towards these areas due to the large volume of emergency vehicles and evacuating residents This could be aggravated even more if one these bridges collapses. Finding a suitable location for another hospital in Richmond would be pointless as the whole island is prone to liquefaction. The only alternative it seems is to strengthen the foundation of the existing hospital through earthquake proof engineering, increasing the number of beds from 500 to 750, as well as increasing the resilience of roads, electricity, and water networks throughout the city. Also, we believe it is ideal to create a makeshift emergency area along with extra supplies, and beds which can respond rapidly in the event of an earthquake. These extra supplies can be kept in an earthquake proof storage. We also propose that by strengthening local infrastructure, and buildings; and a system of rapid emergency response, casualties can be minimized.
The city of Delta is another area of major concern as all of its area is located within medium to high danger zones. It has a population of 102,238 (2016), and a population density 546.7 per square kilometer. We found that the city only has one hospital with about 100 beds. This is even smaller than the hospital in Richmond. As a result, there is only one bed for every 1023 people in the city. Quite similar to Richmond, the majority of the underlying soil is composed of young sand, silt, and clay with poor soil structure and cohesion. Consequently, we predict there will be medium to high liquefaction here as well; therefore leading to building collapses and more casualties. As a result, we believe that the hospital in Delta will be more overwhelmed than Richmond’s. The long distance towards hospitals within low risk areas would make it very difficult to transport patients to other hospitals. The closest hospital in a low risk zone is in the city of Surrey. However, as the map reveals, there is only one major road artery that connects Surrey with Delta, so the swiftness of emergency response may be hindered. It would be quite impractical to build a new hospital. However, we propose to increase the size of the current hospital to about 250-500 beds to support the inevitable large volumes. We also propose to make the hospital and its facilities earthquake proof, and to have an emergency response area; just like in Richmond, with facilities, beds and supplies that can be set up quickly.
The other two hospitals within medium to high danger areas are located within the cities of White Rock and Surrey. As the population density map reveals, many dense areas of the city are within danger zones as well. However, the road network map reveals that roads are more interconnected opposed to Richmond and Delta. There is also a major hospital in Surrey with approximately 750 rooms that is within a low risk area. Again similar to Richmond, we propose strengthening the resilience of the hospital structure and facilities, as well as increasing the number of beds in both hospitals from 500 to 750 as well as the one in the low risk area from about 750 to 1000. Although this study does not take into account tsunamis, we also propose to move the hospital in White Rock more inland to a low risk area, just in case of tsunami and the risk of liquefaction near coastal areas.
Compared to other cities in metropolitan area, we believe that Vancouver city proper is in the best position to withstand the impacts of a deadly earthquake. Other than a few areas, the majority of the city is located within a low risk area. The density map reveals that areas such as downtown are high density areas; but the decreased risk will make mitigation much easier. As well, there are 6 hospitals located in the city; including Vancouver General hospital which is the largest in the metropolitan area. This means there will be a large supply of beds for the city’s residents. However, from what we discovered in our study. Other cities such as in the North Shore, and Coquitlam are similar. However, towards Maple Ridge, there is only one small hospital to support the city where a significant portion of it is in danger zones. Thus we believe doubling or even tripling the size would be a good way to mitigate injuries, and perhaps even construct another hospital.
The main issue we found in this study is the transport of injured patients in the cities of Richmond and Delta. Although we propose makeshift emergency shelters, these may also eventually be overwhelmed. Increasing structural resilience and size within these hospitals may be the best method to mitigate impacts. As well, as pinpointing key areas of concern within these cities where high casualties may occur based on population density, liquefaction sensitivity, and structural resilience of buildings; thus finding strategies to mitigate them. The same can be said for the cities of White Rock and Surrey. Large parts of Surrey are in low risk zones, so the construction of another hospital may be a feasible proposition.
Error and Uncertainty
With the collection of data and creation of our map, many errors and uncertainties had risen along the process. One error and uncertainty of our map is the inconsistently in the dates of the data. All of the data used in our map originate from different years. For example, our census data is from 2011, but our hospital capacity data is from 2017. This causes uncertainties and errors because older data excludes details and features that are present in more recent data. In other words, this can lead to an error in the interpretation of the map. A way we could mitigate this issue is to find data from the same or similar years. Another uncertainty that arose in the creation of our map was our data on the capacity of each hospital. We were unable to locate the capacity of each hospital, so we used the number of beds each hospital contains instead. This causes error because, although it provides us with a rough estimate of the hospital’s capacity, hospitals are typically capable of holding more patients than the number of beds it contains. Indeed, we are also unable to estimate how many patients currently occupy each hospital. Therefore, we are unable to capture the true capacity of each hospital, which ultimately affects the transportation network of patients and injured citizens. A third uncertainty and error is our geology data. Our geology data table contains missing data. This means that the data does not provide us with a full geological coverage of our study area, which can result in a misinterpretation of the map. One way to mitigate this issue is to find another data set on the geology of Greater Vancouver, and use it to verify the available data and fill the missing data of the data set that was used. Another error and uncertainty was our inability to fully predict the magnitude of the earthquake and its effects on each geology type. This led us to use a classification set for each danger zone type. However, with the classification method used, we were unable to differentiate the areas between moderate risk and high risk. This resulted in the map’s inability to pinpoint the exact hospitals that are at the most risk. Additionally, due to our inability to predict the magnitude of the earthquake, we were unable to account for the hospitals outside of the danger zone that may also be affected. For example, the hospitals located near or beside areas of bedrock may be affected by land slides. This causes a disruption in the transportation network of patients from hospitals and injured citizens within the danger zone. This issue could have be mitigated by creating a buffer around areas of bedrock. Overall, although many errors arose along the process, we were still able to portray our map in a concise and effective manner.
Further Research/Recommendations
We cannot be exactly sure the intensity and extent of a Cascadia Subduction Zone earthquake in the Vancouver area as there’s no exact documentation from the last occurrence in 1700. In terms of further research, we could look into a range of past earthquakes, such as the one in Chile that occurred in 2004, that have magnitudes similar to the predicted Cascadia Subduction Zone earthquake. We can examine the type of geology found in those earthquake locations and see how the shaking and duration of the quake affected the buildings and other infrastructure. With this information, we can adjust our danger ratings with geology found in the Vancouver area. We could go even further into testing each type of geology/sediment found in the Vancouver region in a lab with different shaking intensities and duration to examine how liquefaction effects each different sediment. We can also look at the preparedness of each city and their mitigation techniques after an earthquake to understand how to ensure the health and safety of citizens that are in a danger zone.
A buildings age and how they are constructed also affects their ability to withstand shaking; we can further investigate the ages of each hospital in the Vancouver area and their placement throughout our proposed danger zone. We could research what type of buildings are capable of withstanding high magnitudes of shaking, and mark hospitals with less structurally sound material, along with their age. Older hospitals that are less structurally sound for earthquakes and in the danger zone could have a more in depth emergency plan, and be highly mitigated for in case of a Cascadia Subduction Zone earthquake.