Case Study :
Earthquake along the Cascadia Subduction Zone
There
are MANY links related to Earthquake risks and hazards in Vancouver posted in
Edmodo in the Internal Processes folder. You should read and be aware of these
before beginning the assignment.
Scenario :
A magnitude 9.0 earthquake has occured along the Cascadia subduction zone with
the epicenter being near Haida Gwaii in the Juan de Fuca straight. There has
been significant damage to the Metro Vancouver area.
1) Describe how we
knew that a major earthquake would occur in this area based on evidence of past
earthquakes (10 marks)
Cascadia subduction zone is a convergent plate
boundary that stretchs from the northern Vancouver island to northern California. It
separates the Juan de Fuca and North America plates. Tectonic processes active
in the cascaia subduction zone region include acceleration subduction and deep
earthquakes.
The Cascadia subduction zone can produce very
large earthquakes with the magnitde 9 or greater. If rupture occurs over its
whole area of the Great Subduction Zone the earthquakes are known to be deadly. Over there the earthquakes are the largest earthquakes in the
world, and can exceed the magnitude 9. Earthquake magnitude is proportional to area of fault
rupture, and the Cascadia Subduction Zone is a very long sloping fault that
stretches from mid-Vancouver Island to Northern California. Because of the very large fault area,
the Cascadia Subduction Zone could produce a very large earthquake. The last known great earthquake in the
northwest was the 1700 Cascadia earthquake. Geoglgical evidence indicates that great earthquakes may have occurred
at least seven times in the last 3,500 years, Geologist are suggesting a return time of 300
to 600 years for the deadly earthquake. There is also evidence of accompanying tsunamis with every
earthquake that had taken place. One strong line of evidence for these earthquakes is convergent
timings for fossil damage from tsunamis in the Pacfic Northwest and historical Japanese records of tsunamis.
The
next rupture of the Cascadia Subduction Zone is anticipated to be capable of
causing widespread destruction throughout the Pacific
Northwest!
Other similar subduction
zones in the world usually have such earthquakes every 100 to 200 years; the
longer interval here may indicate unusually large stress buildup.
Scientists have
found that at least seven earthquakes around magnitude 9 have occurred over the
last 3,500 years, an average of one every 500 years. But recent research has
shown that many magnitude 8 quakes have shaken the area during the same period
of time, bringing the average time between very large earthquakes down to 270
years.
2) Briefly describe
the geologic setting of the area. (5 marks)
The
cascadia subduction zone is a 1,000 km long dipping fault that stretches from
Northern Vancouver island to cape Mendocino in northern California. The juan de
fuca plate moves toward and eventually shove beneath the continent (north American Plate). The width of the Cascadia subduction zone
varies along its length, depending on the temperature of the subducted oceanic
plate. As it
becomes hotter and more molten, it eventually loses the ability to store
mechanical stress and generate earthquakes.
3) Describe the
impact that a major earthquake would have on the Metro Vancouver area.
a. Consider the
following hazards where the following would be major concerns and explain why.
(3 marks each. Total 12)
i.
Liquefaction
During seismic shaking the groundwater and soil combine to form liquefaction. This usually happens when the earthquake is very powerful and strong. The result of this process is like quicksand. This is a hazard because buildings that have liquefaction under it, can potentially sink(thus the reason its like quicksand)and the buildings would collapse/break. Collapsing infrastructure not only damages the city but is a hazard for the lives of humans or animals if they get stuck underneath.
ii.
Landslides
Landslides happen when the ground starts shaking. They are usually more damaging than earthquakes because they can cause lots of property damage and death. Varieties of resources can also be ruined because of a landslide! For instance water supplies, fisheries,sewage disposal systems, forests and roadways can be ruined. This would also have a negative impact on the economy to repair and pay for all the damages.
iii.
Tsunami
Another dangerous effect of an earthquake is a tsunami. They are giant waves that can cause floods and can become very tall in height. These deadly waves strike a great distance from the epicentre. They often result from sub sea faulting of the ocean floor which sends seismic shocks through the water. They can cause lots of property and environmental damage. Also peoples lives are in danger because of tsunamis.
iv.
Flooding
Flooding occur from many various reasons. Such as broken water pipes, or earthquake-generated tsunamis. Flooding is very dangerous since it can damage buildings, sweep away cars and drown people. It negatively impacts the area where the earthquake already has done so much damage.
b. Consider the
impact on the following areas. Use as much detail as possible and specific
examples in your explanations.
i.
Social
Impact (Impact on humans) (5 marks)
Earthquakes can have huge social impact on humans. Whether the earthquake be short or long term impacts. The short term impacts include people being killed, homes being destroyed, transportation links to be disrupted, water pipes bursting and water supplies to be contaminated with toxic chemicals. Long term impacts may involve disease, people having to rebuild their house and building the city to what it use to be.
ii.
Economic
Impact (Money) (5 marks)
Earthquakes can cause economic impacts. Short term impacts may be small shops and business places being destroyed and damage to transport links (bridges) which could cause trading to become difficult. Long term impacts involve the cost of rebuilding the city which can be very expensive! Investment in the area may be focused on repairing damages which can be even more costly and lots of income or major insurance losses due to the earthquake.
iii.
Impact
on Infrastructure (Buildings, bridges, tunnels, roads, airports, water
reservoirs, skytrain) (10 marks)
Earthquakes negatively impact the infrastructure as well. It can cause large buildings to collapse which can result in the wreckage of many urbanized areas. Bridges, skytrains and roads would be destroyed and blocked, which would make it an obstacle for goods, ideas and for people to move around. It would especially make it difficult for fire-fighters, police officers, and many more public service workers to help if roads were blocked. Water reservoirs would become contaminated and not drinkable to the public. Airports would get destroyed resulting in planes to not be able to enter or leave the terminal. Public places would be ruined such as schools and hospitals. Less people would get the education they need which could help the public learn what to do in earthquakes. If hospitals were destroyed, it would be difficult to treat injured people and save lives of the innocent people.
4) Describe some of
the ways that communities in Metro Vancouver are preparing for the impending
earthquake. Think about the things in part 3) a. and b. in your explanation. (8
marks)
Some ways communicates in Vancouver are preparing for the big bam!
- Having first aid kids ready at home
-Storing canned gods and fresh water in their homes, workplace and cars
-Planning a safe meeting spot for families when the earthquake will occur
-Having shelves and various other objects securely screwed into the wall
-Putting heavy items away from top shelves to help save from damages
-Stocking up on flashlights and batter packs
-Creating more secure buildings and fixing hanging lighting fixtures
-Hanging items like mirrors away from siting areas
-putting flammable liquids and bottles further from high shelves or far from people for safety reasons
-educating the public on how to survive an earthquake
Some links below explain this case study!
http://www.ctvnews.ca/pacific-northwest-at-risk-for-a-mega-earthquake-1.516808
http://www.cbc.ca/player/News/TV%20Shows/The%20National/ID/1511465234/
https://www.youtube.com/watch?v=Bq1VHnq0Yvk
