Plate tectonics have shaped the continents for millions of years. In British Columbia, they have created the mountains, and are the source of frequent earthquakes along our coast. Many of the world's earthquakes are concentrated in specific areas along the edges of tectonic plates.
Convergent Boundary : Where two or more tectonic plates are colliding
Divergent Boundary : Where two tectonic plates are moving away from each other
Strike-Slip Fault : Where two plates are sliding past each other.
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When an oceanic plate collides with an oceanic plate or an oceanic plate collides with a continental plate, an oceanic plate will always be subducted. As the descending plate goes deeper, it gets hotter and at a certain depth, the top of the plate will partially melt. The descending basaltic oceanic plate has been sitting, soaking, in chemical rich, ocean water for millions of years. It is likely that the chemical rich ocean water, absorbed into the top of the basaltic plate, helps the rock partially melt ( produces only felsic magma, silica rich mineral melt first ).
Convergent Boundary : Where two or more tectonic plates are colliding
Divergent Boundary : Where two tectonic plates are moving away from each other
Strike-Slip Fault : Where two plates are sliding past each other.
.
When an oceanic plate collides with an oceanic plate or an oceanic plate collides with a continental plate, an oceanic plate will always be subducted. As the descending plate goes deeper, it gets hotter and at a certain depth, the top of the plate will partially melt. The descending basaltic oceanic plate has been sitting, soaking, in chemical rich, ocean water for millions of years. It is likely that the chemical rich ocean water, absorbed into the top of the basaltic plate, helps the rock partially melt ( produces only felsic magma, silica rich mineral melt first ).
New Evidence for Plate Tectonics
The new technology that has evolved and aided us in finding evidence for plate tectonics is revolutionary. The sonar mapped the ocean floor and we found deep ocean trenches and underwater mountain chains. Magnetic Detector mapped the symmetry of magnetic reversals. Volcanic islands or volcanoes on land help us understand process of subduction.
Cascadia Subduction Zone
The Cascadia Subduction Zone also knows as the "megathrust" fault is a 1000 km long dipping fault that stretches from Northern Vancouver Island to Cape Mendocino California. It separates the Juan De Fuca and North American plates. New Juan De Fuca plate is created offshore along the Juan De Fuca ridge. The Juan De Fuca plate moves toward, and eventually shoved beneath the North American plate.
At depths of around 30km the Cascadia Subduction Zone is locked by friction while strain and pressure slowly builds up as the subduction forces act, until the fault's frictional strength is reached and the rocks slip past each other along the fault in a "megathrust" earthquake. The fault frictional properties change with depth. The "slow slip events" that slip a few cm every dozen months or so. This relieves the plate boundary stresses there, but adds to the stress on the locked part of the fault. Below the transition zone the fault is stuck or slipping silently. These earthquakes have magnitudes that exceed 9.0 on the Richter Scale.
If BC had an Earthquake
A major seismic event in Vancouver could entail a cascade of problems: the collapse of buildings and other structures; the rupture of oil and gas pipelines, or water and sewage pipes; the failure of power lines, roads and bridges; the release of hazardous materials; the liquefaction of alluvial soils in the Fraser River delta; and the spread of fires through areas inaccessible to firefighters, particularly if transportation infrastructure is compromised. Finally, the potential for a tsunami is real. Road access to the Vancouver airport will be cut off during the first few critical days after the earthquake because all the bridges to Sea Island would be affected. Nanaimo’s port, on the east coast of Vancouver Island, will be damaged so much it may be out of service for many months. There will be damages to buildings in Vancouver, Richmond and New Westminster, but it will be worse on Vancouver Island, particularly in Victoria, which has many old buildings. Vancouver Island’s western edge will be hit hardest by the tsunami while Vancouver will be sheltered from the full brunt of the waves. The tsunami is estimated to hit Vancouver two hours after the quake. Just how much damage should we expect? A severe earthquake off the South coast of B.C., followed by a tsunami, would cause around $75 billion in damages to buildings, bridges, and pipelines.
Other Hazards
Factors that affect seismic risk :
Geographic location- plate boundaries, active fault lines
Topography- landscape around you ex. mountains, ocean
Ground strength- solid bedrock resist shaking more than sediments
Construction design
Hazards that can occur :
Liquefaction of soil - soil turns liquidity, sinking
Fire - ruptured gas lines, electrical lines
Tsunamis
Geographic location- plate boundaries, active fault lines
Topography- landscape around you ex. mountains, ocean
Ground strength- solid bedrock resist shaking more than sediments
Construction design
Hazards that can occur :
Liquefaction of soil - soil turns liquidity, sinking
Fire - ruptured gas lines, electrical lines
Tsunamis