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Final

GG231 Study Guide - Final Guide: Monte Carlo Method, Takers, Volcanic Bomb


Department
Geography
Course Code
GG231
Professor
Rob Milne
Study Guide
Final

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GG 231 Review
Introduction
Hazard: probability that a specific damaging event will happen within a particular period
of time
Risk: vulnerability and coping capacity. The product of the probability of a hazardous
event and the expected damage if the event occurred
Disaster: brief event that causes great damage or loss of life in a limited geographic area.
Catastrophe: event that causes damage to people and property on such a scale that
recovery is long and complex
Module 1
Lesson 1- Earthquakes
Earthquakes
-Result from rupture of rocks along a fault
-Rocks on either side of the fault shift and create friction, releasing seismic waves
Fault: fracture in the Earth’s crust
Seismic waves: energy released when tectonic plates rub together.
Epicentre: point on the surface of the Earth directly above the fault rupture.
Focus (hypnocentre): location of the initial rupture along the fault, directly below the
epicentre.
-Seismic waves radiate outward in all directions from the focus.
Seismologists: scientists who study earthquakes
Magnitude: terms used to express the amount of energy an earthquake releases
Intensity: a measure of the effects of the earthquake on people and structures.
Magnitude
-Kiyoo Wadati, 1931, devised first quantitative magnitude scale
-Charles F. Richter, 1935, California Institute of Tech, further developed the
scale.
-Richter scale quantified magnitude of local earthquakes as log base 10 of the
max signal wave amplitude recorded, 100 km from epicentre.
-Body-wave scale (Mb) is based on the strength of a type of earthquake wave
that travels through the Earth. Used to measure deep earthquakes.
-Surface-wave scale (Ms) based on waves that travel along Earth’s surface.
-Moment Magnitude (Mw): most common; determined from:
oArea that ruptured along fault plane
oAmount of movement or slippage along fault
oRigidity of rocks near focus
Increase of 1 whole number= 10 x increase in amount of
shaking & 32 x increase in amount of energy released.

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Intensity
-Intensity depends on the magnitude of the quake, distance from the epicentre,
and the nature of the ground at the site.
-Modified Mercalli Intensity Scale: measures the degree to which an
earthquake affects people, property, and the ground.
o12 categories of intensity, each assigned Roman Numerals.
oContains description of how people perceive the shaking and extent of
damage to structures.
-Conventional Modified Mercalli Intensity maps takes day or weeks to create,
so the Internet is used to expedite the process.
oReal-time recordings and user input to Geological survey of Canada
and US Geological Survey used to create maps at a faster rate.
-Instrumental intensity: measures from seismic stations scattered around fault
areas used to immediately produce a shake map.
-Shake Map: showing both perceived shaking and potential damage. Valuable
for emergency teams who must locate and rescue people in collapsed
buildings & identify nat gas lines and other utilities.
Faulting
-can be compared to 2 rough boards sliding past each other.
-Lithospheric plates moving past each other are slowed by friction along the
boundaries
oFriction exerts forces on rocks
oCauses strain and deformation
oWhen rocks exceed breaking point (strength) they suddenly move
along fault
-Rupture starts at focus and propagate up, down, and laterally along fault plane
oProduces waves of vibrational energy called seismic waves.
-Faults are seismic sources
Types of Faults
(Horizontal) Strike-slip
Strike slip faults: horizontal displacement along the
fault plane
(Vertical) Dip-Slip
Thrust fault: hanging wall has moved up and over the
footwall. Angle of fault plane is less than 45 deg
Reverse fault: hanging wall moved up relative to
footwall along plane. Angle is steeper than 45 deg
Normal fault: hanging wall has moved downward
relative to the footwall.
Fault Activity
Active: moved during the Holocene Epoch (past 11,600)

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Potentially active: shows evidence of movement during the Pleistocene Epoch
(past 2.6 mil years)
Inactive: not moved during the past 2.6 million years
Tectonic creep (fault creep): gradual movement along a fault without
accompanying felt earthquakes.
-Can slowly damage roads, sidewalks, foundations, and other structures.
Slow earthquakes: similar to other quakes; they are produced by a fault rupture;
can last from days to months as opposed to
instantaneous.
Seismic Waves
Body Waves
- Include P and S waves
- P waves: aka compressional or primary waves,
faster than the two types and can travel through
any material. Velocity in solids is much higher
than liquids
-Avg velocity in earths crust is 6km/s; 1.5
km/s in water
- Propagated by repeated compression and
expansion of the medium through which
they are moving
- Swaves: shear or secondary waves; only
through solid materials.
-Avg velocity through earths crust 3km/s;
cannot travel through water
-Similar to whipping motion of long rope
Surface Waves
-Occurred when P & S waves reach surface
and move along it.
-Causes much of the damage at epicentre
-Complex horizontal & vertical movement or rolling motion
-Love wave: horizontal shaking that is especially damaging to foundations
-Rayleigh wave: travels in elliptical motion, rolling ocean waves
Shaking and Amplification
Epicentre Distance & Seismograph
-Seismogram: analog or digital record of various seismic waves.
- Difference between arrival times of P and S waves determine the distance of the quake
from the epicentre
Triangulation
- Epicentre is calculated for each seismograph
- A circle is drawn with the radius equal to that distance.
- The circle of 3 or more seismic stations will intersect at a point, the epicentre.
Focal Depth
-Depth of focus influences severity of the resulting ground shaking.
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