Terms in this set (76)
Contributions from Scientists
observation and experimentation permit them to explain some phenomenon
Observe, Explain, Predict, recommend
Observations about Local Earthquakes
Occurrence patterns in South west British Columbia
all the small earthquakes are close to, or on land, while the larger quakes are offshore and appear to cluster around specific areas
How observations are made
In the instrumentation
Detecting Ground Motion
A framework fixed to the Earth supports a mass (weight) hanging on a spring and attached to a pen. So when the ground moves, the weight and pen also move relative to the ground.
Locating Ground Motion
detect motion from two sensors, then use the different in time when seismic energy (ground motion) reaches the two instruments to estimate the location
how many seismometer are needed to estimate of the source of the seismic energy
Three seismometer are needed to get a unique estimate of the source of the seismic energy
1. The earth is spherical so travel times must be recorded accurately, Need to be sure that what was recorded at different locations actually came from the same event
2. the Earth's composition is complex. The signals travel through many different types of materials, The challenge is to know about these materials in order to estimate travel times, but it turns out that we need to know the travel times in order to guess what the materials are
Questions to consider when viewing maps of earthquake locations
1) how many observations of earthquake signals were needed to generate this map
2) how long might it have taken to build this map
Global Distribution of Earthquakes
The majority of earthquakes occur at the margins of Earth's tectonic plates
Connecting earthquakes to plate Tectonics
How many lithosphere on Earth
9 major plates: oceanic and continental plates
Which plates move faster, Oceanic and continental plates
Four types of boundaries
Convergent type 1
Convergent type 2
plates are moving apart, leading to tension (stretching). Due to the tension forces, rocks break and many small earthquakes occur. Divergence occurs at mid-ocean ridges
plates move past each other, leading to shearing forces between plates, Shearing forces are those that push one part of a body in one direction and the other part in the opposite direction. Rocks are being shears, thus many earthquakes occur here, There are moderate to large earthquakes, But not as large as those that occur in the next 2 boundry types below
Convergent type 1
plates move toward each other and collide, leading to compression. In this type, one of the plate is less dense than then other. Thus, one plate subducts or dives under the other at subduction zones. Rocks are compressed and extensive small to very large earth quakes occur, In fact, the largest earthquakes occur at subduction zones
Convergent type 2
same as type one. but here, both plates are of the same density so neither plate is subducting or plunging. Thus the plate crumple up like a rug being pushed together. Rocks are compressed and extensive small to very large earthquakes ovcur
force directed parallel to a surface
Stress that stretches rock so that it becomes thinner in the middle
Stress that squeezes rock until it folds or breaks
Q1. Which of the plate boundaries above would you expect to be associated with the LARGEST earthquakes?
e. all of them
CYU EQ.2 Check Your Understanding
Juan de Fuca plate
The map of the west coast of North America above illustrates 3 out of the 4 plate boundary types closer to home. This figure is from Kious and Tilling (Links to an external site.)Links to an external site., USGS.
a. On the southern end of the map is the San Andreas Fault, a transform boundary. Here, plates are sliding past each other (note the thin black arrows indicating the direction of movement). Can you tell which plates are sliding past each other?
b. There is another transform boundary on the northern end of this region (beyond the map). Find out the name of this fault and the plates that are involved.
c. Note the Juan de Fuca and Explorer Ridges at the northern end of the map. What type of boundaries are they and what plates are involved?
d. In which direction are these plates moving?
e. To the east of these ridges is a subduction zone, another plate boundary. What plates are involved in this convergent zone?
f. Which plate(s) is/are subducting?
g. Consider the situation of the plate bounded by the Juan de Fuca Ridge and the subduction zone. This plate is growing on its western side as it is being consumed on its eastern side! Is this plate growing or shrinking overall? What is a good way of determining this?
Continue with Back to SW BC
The ability of an object to change shape when forced, but to spring back to its original shape when the force is released. e.g., rubber band, spring
The ability to permanently change shape or deform when forced. e.g. ice in glaciers, soft metals, even some rocks
Very plastic. e.g., gold
not plastic; fractures/breaks instead of bending e.g., ceramic dishes
Three types of ground motion
- permanent shifts in ground position
- show plastic movement
- short oscillations after which ground returns to its origin
- the forces acting on a rock are relatively small; therefore, the resulting shape of the rock is not permanently changed
- the shape is restored once the force is removed
- very similar to the behavior of a rubber ball as it bounces
- as long as the motion does not cause damage b4 its over it should be fine, but because of elastic behaviour, the damage can be at great distances
permanently changes the shape of a rock without breaking it
- consider a wooden stick being bent until it breaks. This is effectively a catastrophic release of energy
- earthquake occurs when accumulating stress over time
Types of faults
dip-slip, strike-slip, oblique-slip
vertical motion along a slanting plane
those where the side leaning on its neighbour moves up
those where the side learning on its neighbour drops down
motion that is horizontal
motion that is a combination of the vertical and horizontal directions of motion
What type of fault is shown in the photo below?
strength of rocks x
area involved in the breakage x
distance the fault moved
Moment Magnitude (Mw)
how much stronger an earthquake of magnitude 7 compared to magnitude 6
Q4 1. How much more ENERGY does a magnitude 7 quake release than a magnitude 4?
A) 3 times
B) 32 times
C) 100 times
D) 1,000 times
E) 33,000 times
2. How much more SHAKING does a magnitude 7 quake cause than a magnitude 4?
A) 3 times
B) 32 times
C) 100 times
D) 1,000 times
E) 33,000 times
1. Which of the two types of faults (thick or thin red lines) are likely to release as much energy as the Mount St. Helens eruption? What could the MW for this event be?
2. Which of the two types of faults will likely experience an earthquake of MW 4.0? How much energy will likely be involved relative to the 'quake from (1) above?
the force per unit area
describes how materials change shape as a result of the stresses involved
Q 6 1. Describe the sequence of events shown in the series of images below:
earthquake stress knowledge test
2. What type of stress is shown in (d) above?
CYU EQ.7 Check Your Understanding
Use the figure below to answer the following questions:
cascadia eq sources-mod.jpg
Which tectonic boundaries will accumulate more stress before breaking: convergent, divergent, or strike-slip boundaries?
Consider Cascadia... Which boundaries are convergent, divergent, strike-slip?
Consequently, which boundaries are likely to have the biggest earthquakes?
The focus point within the ground where the strain energy of the earthquake stored in the rock is first released
CYU EQ.8 Wave Behaviour
After waves pass, the ground returns to its original position. Does this mean that the ground is exhibiting elastic, plastic, or brittle behaviour?
If the ground does return to it's original position, how can seismic waves be so dangerous?
seismic waves that travel through the Earth's interior
pressure or primary wave
Travels about 1.7 times faster than S waves
shear or sevondary wave
those that travel only along surfaces
These above types are most dangerous. These are the waves with the largest amplitude of motion
travels, particles experience a backward-rotating motion that is in line with the wave's direction
cause the most damage because they are largest and clearly helot beause they travel along the Earth's surface
side-to-side motion that is perpendicular to the wave's direction
CYU EQ.9 Check Your Understanding
1. Which earthquake wave travels the fastest?
C) Rayleigh waves
D) Love waves
2. Match the following descriptions (A to E) to the correct wave type listed below (1-5):
A) first wave recorded on a seismogram
B) travels through solids only
C) surface waves with a rolling motion
D) slowest and most damaging seismic waves
E) surface waves with a side-to-side motion
1) Surface waves
2) S waves
3) Love waves
4) P waves
5) Rayleigh waves
characterizing seismic waves
frequency, velocity, and wavelength
depend upon the use of seismic signals
- determining the location of distant earthquakes
- estimating earthquake magnitudes
- learning about our planet's internal structure
CYU EQ.10 Check Your Understanding
Which of seismograms below was recorded furthest from the earthquake?
Ritcher magnitude scale
Scale defines earthquakes based on amplitude of largest ground motion recorded on seismogram
correct only if a particular type of sesmometer was used and if were in Southern California
Forecasting vs Prediction
prediction is too general term
Forecasting is more reasonable term to predict something within a specific time period
- where will earthquakes occur
- what effect should we expect
-- probability of occurrence
-- possible precursors
- specific predictions about cascadia
stress increases gradually, then the chance of a shock grows as time passes
Lights in the sky
Changing electrical resistivity in ground, air, and ionosphere
Spontaneous radio noise
Changing height of the ionosphere
Changes in infrared light visible from satellites
The evidence of Cascadia earthquakes in Jan 26, 1700
Record of Tsunami in Japanese coastal communities
Btw what about Cascadia
- large quakes have occured and scientific evidence exist
- oral history confirms the most recent event occurred on jan 26, 1700
- plate dynamics is being carefully studied to inform us about cascadia
Formula for force
mass x acceleration
factors influencing intensity (5)
duration of shaking
distance from epicentre/hypocentre
The act of minimizing risks by reducing them or avoiding them, or planning a strategy for recovery if an event occurs.
two general approaches to making buildings better able to withstand side-to-side stresses
simply adding strength in the form of cross braces, shear walls, and shear cores
- absorbing energy
- changing the resonant frequency: adding mass has the effect of reducing the resonant frequency
- allowing the earth to move without dragging the structure with it: isolation at the foundation of a structure
Some of the aspects engineers must consider when employing good general construction practices
Firmly attach cosmetic brick
Use reinforced concrete properly
Use of shear walls
Hillsides can be dangerous
Other contributors to catastrophe
Destruction of infrastructure
Liquefaction of soils
- retrofit your home
- keep your home safe
- identify safe spots
- prepare an earthquake kit
- stay calm
- get out of areas where flying objects could cause injury
- strong under tables
- if not, under archways or the inside corner of a room
- avoid doorways
- don't move
- deep breaths
- help the injured
- get out of damaged building
- don't use phone
-- find food, water, supplies, equipment
-- fill a bathtub with water as your reserve
-- use other sources of water: water heaters, melted ice cubes, the toilet tank
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