DEM

TIN

Surface modeling

Buffer layers • 1906 Earthquake (500 feet) • Water bodies (200 feet) • Buildings > 200 feet (400 feet) • Coastline (2000 feet) • Highways/freeways (300 feet)

Service areas (5 min)

• Police stations • Fire stations • City facilities

Slope

Constraints Opportunities

Suitability Map

‘Safe Zone’ facilities &

‘Vulnerable’ population

Location-Allocation

Surface Modeling Suitability Analysis Network Analysis

Contours

Derek Chin, Maneet Kaur, Chloe Tarrasch December 11, 2015

Background

Client: The City of San Francisco government has commissioned a project to determine the safest locations to egress in the event of a pre-warned earthquake.

Problem: Over 800,000 people live in San Francisco. After watching the fictional film San Andreas depicting collapsing skyscrapers, explosions, tidal waves, and rupturing of the Earth’s crust, the citizens of San Francisco are very concerned. In the film, the cast receives a 10-20 minute warning of the earthquake and attempts to travel to what they deem as a safe location. Under the false premise that there will be such a warning, the citizens have pressed the city government to determine safest locations to go in the event of such a natural disaster.

Methods Data: The Digital Elevation Model (DEM) came from the USGS National Map Viewer. Data for the Network in the network analysis, such as population or transportation data, came from the GEOG C188 Lab 10. Data on buildings, coastline, highways/freeways, police stations, fire stations, and city facilities were downloaded form SF OpenData, a central clearinghouse for data published by the city and county.

Overview: Surface modelling and network analyses were performed in order to inform the suitability analysis which determined the safest location during an earthquake. The final network analysis used the suitability analysis to identify individuals in non-suitable locations and allocate them to evacuation facilities.

Suitability: The factors for the suitability analysis were created in 3 possible ways: 1) horizontal proximity buffering, 2) surface modelling, and 3) network analysis. Buffering by Euclidean distance was performed in order to designate horizontal proximity to certain areas. Surface modelling was performed on DEM data to find slope. Service area network analysis was used to define a custom accessibility buffer for Fire, Police, and city facilities.

Constraints: City districts with tall buildings are hazards because they could collapse. The city coastline is dangerous due high liquefaction and potential flooding.. The 1906 Earthquake zone was considered a constraint because it experienced the most damage from the magnitude 7.8 earthquake in 1906. Bodies of water could also experience high liquefaction. Highways and freeways are susceptible to collapsing and crowding. Slopes greater than 20% were deemed unsafe for travel.

Opportunities: Being closer to emergency services like police and fire stations allows for a faster response time. City facilities include hospitals, schools, etc., which could serve as sources of refuge for stranded individuals.

Location-Allocation: The final network analysis was performed to identify facilities in the most suitable areas (‘Safe Zone’ facilities) to serve populations outside of the safe zone (‘Vulnerable’ population). Using selection and clipping we created these two new layers and used location allocation (minimize facilities, 5 minute impedance) to find the least amount of facilities in the suitable area to serve the vulnerable population. Five minute impedance was assumed to be a reasonable amount of time to egress to the nearest facility in the event of pre-warned earthquake.

Conclusions & Limitations Conclusion: Our suitability shows that many San Francisco residents already live in the purple safe zone. Nine facilities out of 43 total are needed to serve the vulnerable population. In the event of a massive earthquake in San Francisco, the population that we identified to be in dangerous zones should egress to one of the nine designated places, while everyone who is already in the safe zone should stay put.

Spatial Limitations: Actual times used in the network analysis may not be accurate in the mayhem before and after an earthquake. The area at the top of Twin Peaks was deemed a suitable location by our suitability analysis, but the needed gain in elevation may be too difficult to achieve.

Egress to Safety During an Earthquake in San Francisco

Credit Sara Kustera

Credit Common Floor

Questions

Where are the safest areas of San Francisco during an earthquake? For individuals not in safe areas, where should they egress to?

Projection: NAD 1983 State Plane CA III FIPS 0403 Feet Datum: D_North_American_1983

Slope from Surface Modelling

Suitability Analysis Weight Table Constraints Opportunities

water bodies -1 SFPD +2 1906 earthquake -3 SFFD +2

Freeways/highways -1 SF Facilities +1 Buildings over 200’ -2 Slope <20% +1

Coastline -2 Slope >20% -2