Earthquakes Flashcards
Earthquake focal depths are…
- Deep
- Intermediate
- Shallow
Earthquake Belts are generally parallel plate boundaries but..
Some are within plates.
What is an Earthquake?
An Earthquake is a shaking or vibration of the ground
Earthquakes represent a release of built-up stress which occurs when rocks being deformed suddenly
break along a _____. The energy arises because friction prevented the ___ ________ _____ on either side of a fault from sliding past one another easily.
- Break along a fault
- Two opposing rocks
What happens during step one of an earthquake, draw it.
-Stress begins
-fault is locked
-elastic deformation begins
What happens during step two of an earthquake, draw it.
- Stress builds
- deformation continues
What happens during step 3 of an earthquake, draw it.
- Fault slips
- Stress released
- Rocks return to undistressed dimension
What was the fault offset of the 1906 San Francisco Earthquake
- Approx. 2.5 meters
There are _ main types of fault movements that initiate earthquakes and the stresses that cause them.
- 3 main types of fault movements
What are the main types of fault movements that initiate earthquakes.
- Dip-slip
- Thrust Faults
- Strike-slip faults
What is the stress that causes a dip-slip fault?
tensile stress (pull apart or stretch a material, lengthened)
What is the stress that causes a thrust fault?
compressive stress (pushes a material-squeezed or shortened)
What is the stress that causes a strike-slip fault?
Shearing stress (material is twisted or experiences forces that cause different parts of it to move in different directions or at different speeds)
Label a diagram with
- focus
- epicenter
-seismic waves
-slip
The point on a fault at which the first movement or break occurs during an
earthquake is called the _____.
The Focus
The point on the Earth’s surface directly
above the focus is called the _________.
- Epicenter
When the blocks slip suddenly at the time of the earthquake, intense vibrations called _______ _____ travel outwards from the focus much as
waves ripple outward from the spot a stone was dropped in a still pond.
- Seismic waves
With sudden displacement and release of ______, the rocks snap back elastically to their previous dimensions. What is this behaviour known as?
-Release of stress
- Elastic Rebound
The distance of displacement is known as the ____.
- Slip
Energy released by an earthquake will send
_______ _____ out from the _____.
- Seismic waves
- Focus
“Body Wave” travels…
- through the interior of the earth
What kind of body waves are compression waves?
- P Waves
What kind of body waves are shear waves that only pass through solid rock (not magma)
- S Waves
What are some features of surface waves?
- Travels along the surface
- Larger ground displacement than body waves
- Results in most earthquake damage
- Why do we need to understand seismic waves?
- We need to understand in order to build EQ resistant structures.
How do the different seismic waves move? (p-wave vs s-wave motion)
What do the two types of surface waves look like in motion?
Energy released from an earthquake must travel…
- Through the earth
– Density of rock will affect the travel time for seismic waves, describe the relationship.
- Waves move fast through high density rocks
- Waves move slow through low density rocks
What detects ground movement and can be useful in calculating the location of an epicenter?
- Seismograph
What does a seismograph do?
- Records arrival of different seismic waves
- Interval of time between the first arrivals of P waves
and S waves is a function of distance to the epicenter
How many seismographs are required to locate an
earthquake?
-At least 3 seismographs
______ is released during an earthquake
- Energy
What happens when waves of energy are transmitted through rock in an earthquake?
- As the waves of energy are transmitted through
the rock, this energy with be felt by people at
the surface
What is magnitude when talking about an earthquake?
– the amount of ground motion related to an earthquake
What is intensity when talking about an earthquake?
- effect on humans, and their structures, caused by the energy released
by an earthquake
Energy released by
earthquake will be
related to the ________
__ _____ and ____ __
_____ (length x depth).
- Strength of rock and area of break
The damage an earthquake causes can be measured in
two ways. What are the ways?
- Magnitude and/or 2. Intensity
Explain measuring “Richter magnitude”
- measures the amount of ground displacement or shaking it produces at the epicentre.
- The scale is logarithmic (means that an earthquake of
magnitude 5 causes ten times as much ground movement as one of magnitude 4)
Explain measuring “Moment magnitude”
- measures what
happened at the earthquake source NOT how much the ground shakes at a distant point - takes into account the area of break on the fault surface, the displacement along the fault, and the strength of the rock.
What/how does Mercalli Intensity scale measure earthquakes?
- Measures the impact of an earthquake event on humans and surface features
-Many local factors are considered such as local geology, construction practices, and distance to the epicenter
Modified Mercalli Intensity Scale is widely used in ______ and the _______ _______.
- Canada and the United States
Intensities in the Mercalli Intensity Scale are reported as ______ _________ ranging
from _ (___ ____ _____) to ___ (_______ _____ ______)
- Roman Numerals
- I (for ‘not felt’) to XII, for (‘damage nearly total’)
The Mercalli Intensity Scale can be used to measure _______ __ _____ __ ___ _____ ___ ________ (useful knowledge for EQ prediction)
-ancient EQ based on old texts and folklore
Modern cellphones and laptops have built in ______________ so general population can “tweet” in both ____________ ____ _____________ to seismologists.
-accelerometers
- observations and measurements
Based on seismicity charts it has become evident that earthquakes originate both at shallow depths (__ _________ ______) and deep in the Earth (_____ _________ ______)
- At spreading ridges
- Along subduction zones
Describe earthquakes that happen at shallow depths.
-associated with divergent boundaries and transform faults, as well as on continents due to crustal movements
Describe earthquakes that happen at deep depths.
- at subduction zones they occur because the
brittle lithosphere is forced deep into the
asthenosphere (to about 700 km)
What are the 3 types of earthquake tectonic plate boundaries? Draw them.
Some earthquakes are unusual in that they are not associated with _____ _______. They often occur on
___ ______ that were once part of______ ______ ___________ (e.g., the South Carolina earthquake in
1886). Others may arise as a result of _________ _______ (e.g., those occasionally in eastern Canada in the Ottawa to Montreal region)
- plate margins
- Old faults they were once apart of ancient plate boundaries
- isostatic rebound
What are the 4 things that cause damage in earthquakes?
Earthquakes damage
1. Ground motion
2. Ground failure
3. Fire
4. Tsunamis
( also remember Mitigating EQ damage
Man induced EQ
EQ risk in Canada)
What causes ground motion in earthquakes?
- Ground shaking
- Fault movement
What happens during earthquake ground failure?
- Landslides
- Cracks
- Liquefaction
Liquefaction at depth can lead to _______ __ ________.
- collapse of surface
How do we mitigate earth quake damage?
Avoidance:
- Better to build away from earthquake
zones
Engineering:
- Use better construction designs and materials
Predicting/giving warnings!
What do we use for prediction and forecasting?
- Geological field work (find ancient EQ example. japan)
- Seismic gaps(highlight the major gaps we know of)
- Precursors
- Prediction (date, place, and magnitude
of next big one) - Forecasting (Forecast chance of given size EQ, along a given fault, or in given time interval)
- Watching animal behaviour
Examples of Induced earth quakes
- Fluid injection & Withdrawal
- Hydraulic fracturing
- Dams
- Engineered earth quakes??
The suggestion that fluid injection can case
earthquakes was tested and proven in ____ !
- in 1972
AN earthquake in a place where oil and gas are produced and in an area where there are no precious earthquakes, is a very _______ ________.
- Very unusual ocurence
What are the causes of man made earthquakes?
