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How Tsunamis Are Generated
• Most tsunamis are caused by earthquakes
generated in a subduction zone (where
oceanic plate is being forced down
by tectonic forces)
• Others by underwater volcanoes or
landslides
Wave Propagation
SF Bay
Treasure Island Development Project
SF Bay Vulnerable To Distant Sources
> 4 hrs to
SF Bay
> 5 hrs to
SF Bay
Less vulnerable to tsunamis
from Cascadia or So America
Treasure Island Development Project
SF Bay’s Local Fault Structure Limits Tsunami Generation
• San Andreas is a transform,
strike-slip type fault (adjacent
plates not subducting below
each other)
• Little to no vertical
displacement
Treasure Island Development Project
Width of Golden Gate Restricts
Tsunami Propagation Into SF Bay
Treasure Island Development Project
Waves Diffract As They Pass Through Gate
1. Tsunami height reduces due to “energy spreading” as a result of:
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Restricted Opening (Golden Gate)
Shallow Depth of Bay
Shape of Bay
2. Tsunami profile changes after passing the Golden Gate due to:
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Wave diffraction
Not a “wall of water”
Treasure Island Development Project
Measured Tsunamis In SF Bay
1960 Chile
Presidio, SF
8
6
4
4
2
2
0
0
Predicted
-2
Alameda
8
6
1964 Alaska
Observed
-2
0:00
6:00
12:00
18:00
0:00
6:00
12:00
18:00
0:00
0:00
2011 Japan
6:00
12:00
18:00
0:00
6:00
12:00
18:00
0:00
Treasure Island Development Project
Tsunamis Included in Design of Treasure Island
1. Analyses and modeling based on:
• FEMA Guidance
• Tsunami Risk studies conducted by CalEMA for SF Bay Marine
Oil Terminals
2. Extreme high water level modeling:
• Included coincident events (tides + storm surges + tsunamis +
waves)
• Used a 157-yr record of tsunamis in SF Bay, extrapolated over a
1008-yr period to determine probability of tsunami occurring
jointly with tides and storms
• Highest water level including tsunamis over the 1008-yr
simulation was +9.5‘
• 100-yr return period high water level was 9.2’
• 100-yr return period wave runup was 10.5’ to 16.5’
Treasure Island Development Project
Proposed Design Criteria For Treasure Island
1. Base Flood Elevation = 9.2’
(based on combined 100-yr return period high water level including high
tides, wind-waves, ocean swell and tsunamis)
 Finish floors of buildings will be 3.5’ higher (12.7’
minimum) to accommodate sea level rise
2. Design Wave Runup = 10.5’ to 16.5’
(based on combined 100-yr return period runup elevation including
wind-waves, ocean swells, and tsunamis)
 Perimeter elevations will be 1.33’ higher (11.8’ to 17.8’)
as an allowance for sea level rise and more extreme
event occurrence, including tsunamis.
Treasure Island Development Project
Lower Probability Tsunami Events
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CalEMA map shows inundation up to 15’ elevation for
emergency scenario planning (not for design)
Return period for such an event (10’ tsunami occurring at a 5’
tide in SF Bay) is over 1000 years
Significantly beyond the standard of practice included in
Building Codes (472-yr earthquake, 100-yr flood, etc.)
SF Bay will have 4 to 5 hour advance warning of such an event
Typical tsunami wave after coming through Golden Gate rises
to full height in about 20 minutes (not a wall of water)
Structures on TI will be modern, multi-story buildings & built to
present codes
TI-specific emergency response planning appropriate
Treasure Island Development Project