Lecture 4 - Natural Hazards

earthquakes

release of seismic energy at fault zones in the earth

seismic events

acoustic events so transfer of energy moving through the solid earth

ground motion

shaking that occurs from earthquakes is caused by the sudden release of energy in the lithosphere, this happens along geologic faults

geologic faults

planar fractures in the earth, the way earthquakes work is the tectonic stress/energy builds up when the faults are locked and when they rupture or slip, seismic energy is released in the form of an earthquake

normal faults

when you have extensions, pulls rock apart so one rock extends along another

reverse faults

squeezing the rock so forcing the other block to push up and over another rather than falling back down

strike-slip fault

when rock is sliding back and forth against itself rather than having overextension, build up of tectonic stress and energy so faults not always continuously moving, builds up enough energy so they do move so they slip and release the pent up seismic energy

seismometers

measures earthquakes, responds to ground motion like a pendulum that is sensitive to vibrations so draws waves, there’s a ticker tape and pen that moves with vibrations and draws the seismic waves

mapping earthquakes

this is done with seismometers, the map shows there’s a ring of earthquakes around the pacific ocean which are all subduction zones, in canada on the east there is only one plate tectonic despite many earthquakes occurring there, same thing in the north so unexpected movement recorded there

richter scale

this measures the strength of an earthquake based on amplitude of seismic waves, this was developed based on earthquakes in California which ranges from 2.0 to 10.0 but its not really used much anymore because it was based on small data set , the scale is logarithmic so each whole number increase represents a multiplication by factor of 10

moment magnitude scale (Mw)

this is what we use now to measure earthquakes and its based on seismic moment of an earthquake, it takes into consideration large earthquakes,

modified mercalli intensity scale

measures off what actually happens when the earthquake occurs, based on intensity so how many people felt the effects of the earthquake, its ahrd to relate magnitude back to this scale because its qualitative

historic large earthquakes

the smaller magnitude ones happen much more often and all around the pacific ocean due to having lots of subduction zones and big plates being forced back down into the mantle, the big ones happened in places like ecuador, chile, sumatra and japan

active plate boundaries in Canada

they are mostly located in the north american plate, when you have big iceages crust gets pushed down and that causes smaller earthquakes to occur

eastern canada earthquake activity

there is lots of seismic activity that can be broken down into different sections, there are only 3 moderately sized ones in the region 1929 in attica, new york, 1986 near cleveland ohio and 1998 near the pennsylvania/ohio border, but none of these areas have active plate boundaries so instead stresses are due to glacial isostatic adjustment or background intraplate stresses, reactivation of pre-existing structural faults could also be another reason

seismic hazard map

shows how likely a location will experience ground motion caused by earthquakes

can we predict earthquakes?

when they happen in intraplate regions rather than subduction zones its harder to predict them cause there isnt much data, might not know when they will occur but we can still get a general idea

what are common earthquake hazards?

unstable buildings, exposed electrical wiring, natural gas leaks, water system breaks, hazardous materials, falling, lifting injuries and confined space work hazards

major earthquake in turkiye

they had back to back earhquakes of magnitude 7.8 and 7.5 causing fault system rupture along east anatolian fault

fracking

drilling for oil and natural gases that can cause earthquakes, it affects the subsurface

tsunami

ocean wave triggered by large earthquakes that occur near or under the ocean or other events where large volumes of debris fall into the water,

how does a tsunami occur?

what happens is the rock is compresses and in the middle of it you have an earthquake due to eventual slip causing release in energy, movign rock underneath, the seafloor is then offset and its very fast but as you get close to the shore it slows down and grows in size so you get large volumes of water, basically go from having flat tomography then push the rock up which pushes the water up, even a small displacement of the seafloor causes a tsunami

deep ocean

the tsunamis occurring here have very small amplitude but long wavelength and high speed making them very hard to detect

tohoku earthquake

this was a megathrust earthquake, the triangle/teeth shows where the subduction zone is, it built up energy and slipped 10-20 meters

fukushima nuclear incident

there were 13-14 meter high waves that damaged the nuclear power plant’s emergency diesel generators leading to a loss of electric power, the waves had blew over the seawall, the generators were required to provide electrical power to the pumps that circulated coolant through the reactors’ cores, the loss of the core cooling led to 3 nuclear meltdowns, 3 hydrogen explosions and the release of radioactive contamination in 3 different units

fukushima tsunami warning system

the warning was delivered 8 seconds after first P wave or about 31 seconds after earthquake occurred, the second wave is S wave, the warning system is called deep-ocean assessment and reporting of tsunami

tsunami preventative measures

drop cover and hold on, automatically open fire hall and ambulance bay doors, stop traffic onto bridges and into tunnels, automatically open fire hall and ambulance bay doors, close valves, halt trains, divert planes from landing, move elevators to the nearest floor and open doors, halt surgery

laurentian slope seismic zone

in 1929, large magnitude 7.2 earthquake occurred near grand banks and was responsible for large tsunami, 27 ppl died when it came ashore on burin peninsula in southern newfoundland, one of the few incidents involving loss of life in any Canadian earthquakes

radon

radioactive gas that comes from breakdown of uranium in soil and rock, its invisible, odourless and tasteless

radon hazards

when inhaled into lungs it decays inot radioactive particles that release small bursts of energy, exposure to it is the number one cause of lung cancer in non-smokers, the gas moves through the ground and escapes outside or into buildings, radon levels are higher in areas where there’s a higher amount of uranium in underlying rock and soil

radon in rock

the ordovican camp nelson limestone correlated with high indoor radon levels in kentucky, homes on limestone, dolostone and some shales have higher indoor radon concentrations than homes on siltstones, sandstones and surficial deposits

radon in sedimentary rocks

it derives from decay of uranium atoms and uranium typically ends up in sedimentary environments through weathering of igneous rocks and eventual transport of sediment through the hydrosphere

how do we accommodate for radon in our homes?

opening windows or running an air exchange system can temporarily reduce radon levels, finishing unfinished basements, sealing foundation cracks and active soil depressurization can also help