EESA06 - Chapter Three

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Environmental Science
Nick Eyles

Chapter Three - Page 1 of 12 Chapter Three: Earthquakes Feb 5, 1662 violent earthquake Charlevoix-Kamouraska area of Quebec o Vast landslide along rivers in the St. Lawrence valley o This area has received many seismic events over the past two centuries and is aptly named the Charlevoix-Kamouraska Seismic Zone o October 20, 1870 Baie-St-Paul earthquake (same zone) ripped open the ground along several fissures near the epicentre in Baie-Se-Paul, while tremors were felt as far south as Virginia o Among the earliest documented earthquakes in NA November 18, 1929 eastern coast of Canada o Parts of the Atlantic ocean sea floor moved in the Grand Banks earthquake o Large submarine landslide ruptured transatlantic cables, allowing scientists to record the speed of movement and erosive capabilities of a turbidity current for the first time o Large tsunami struck the Burin Peninsula of Newfoundland 28 deaths November 25, 1988 largest earthquake in eastern Canada o Saguenay region of Quebec o Compromised the engineering integrity of structures built on glaciomarine clays (quickclays) that underlie the region April 18, 1906 part of California (coastal northern cali) slid abruptly past the rest of the state o Visible scar 450km long o Soil above rock was displaced o The quake was located on a segment of the San Andreas fault near San Fran o Buildings in SF toppled; broken gas mains; fires for three days; broken water mains o 3000 deaths o 90% of destruction caused by fires October 17, 1989 San Fran o Loma Prieta earthquake o South on the San Andreas fault near Santa Cruz o Didnt tear ground surface but collapses buildings and structures built on the soft bay fill sediment in San Fran and Oakland o Bay Bridge collapsed o Raging fires; broken gas mains o 63 deaths March 27, 1964 southern Alaska Good Friday Earthquake o Force was twice as strong as the 1906 San Fran earthquake but death/damage was low because of Alaskas small population o 15 deaths from the shaking o Section of earth was raised and another sank o Slight horizontal movement o Landslides in Anchorage Chapter Three - Page 2 of 12 o Tsunami responsible for most deaths (100) o Few people drowned in Oregon and Northern Cali from the Pacific Ocean waves o Also caused damage in Port Albemi, BC Jan 17, 1994 Northridge Earthquake San Fernando Valley (north of LA) o Near Cali State University o Lots of damage o 16 deaths November 3, 2002 largest earthquake recorded in the interior of Alaska o Rupture mainly along the Denali fault Propagated eastward at more than 11,000km/h, offset streams and glaciers, thousands of landslides o No deaths; minimal damage (remote area) o Trans-Alaska Pipeline suffered minor damage (didnt break due to engineering design) December 26, 2004 o 9.3 magnitude o Second largest recorded since 1900 o Deformed the Indian ocean floor off the western coast of Northern Sumatra o Quake was so severe that it slightly changed the shape of the planet, reduced the length of the day by almost 3 microseconds, and moved the north pole by several centimetres o Tsunami caused more casualties than any other ever recorded Detected on tide gauges in the Indian, Pacific, and Atlantic oceans Quake epicentre was located to the east of the Sunda Trench, where the india plate is subducted below the Burma plate Caused by thrust faulting along the boundary between the two plates This type of destructive megathrust earthquake is possible along the western coast of Canada and the US Pacific Northwest where the Juan de Fuca plate is being subducted beneath the NA plate Feb 8, 2001 Nisqually earthquake o 6.8 magnitude o South-west of Seattle o Deep quake with such movement of the downgoing Juan de Fuca plate o Damage caused to unreinforced brick and concrete structures What Causes Earthquakes? An earthquake is a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath Earths surface Great forces deep in the earth may put a stress on the rock, which may bend or change in shape (strain) When a rock breaks, waves of energy are released and sent through the Earth (seismic waves) o These waves cause the ground to shakeChapter Three - Page 3 of 12 The sudden release of energy may cause one mass of rock to slide past another into a different position o The break between these two masses is a fault Elastic rebound theory o Sudden release of progressively stored elastic strain energy in rocks, causing movement along a fault o Deep seated internal forces (tectonic forces) act on a mass of rock over many decdes o Initially, the rocks bends, lifts, or stretches o When the rock breaks, theres an earthquake o Two masses of rock move past each other along a fault movement can be vertical, horizontal, or both Elastic rebound theory revised o Suggests that faults are weak, and need only a small stress to cause rupture and an earthquake o The weak fault model poses problems for earthquake predictions Brittle behaviour of breaking rock is only for rocks near the surface o Rocks at depths are subject to heat and pressure which reduces brittleness o Deep rocks deform plastically (ductile) instead of breaking (brittle); hence, theres a limit to the depth where faults can occur Most earthquakes are linked with movements on faults Most in eastern NA arent associated with surface displacement
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