Creating Systems Maps & Understanding Earthquakes

Learning Systems Map Activity

• Developing a systems map relies on thorough knowledge of the problem
• The best way to start is to write statements about how X leads to Y and under which conditions
• Separate information that belongs together and that does not
• Contextual factors should be separate
• Establish connections between major chunks that belong together
• Follow the chronological order gradually to develop a narrative
• Create a systems diagram
• Refine the diagram until it accurately captures the story and provides understandable information
• Refine the diagram so that the connection between main themes can be made explicit

Earthquakes

• An earthquake is a shaking of the ground caused by the release of energy stored in rocks beneath earth's surface

Causes

• Earthquakes are caused by a sudden slip on a fault
• Tectonic plates slowly move but get stuck due to friction at their edges
• When the stress overcomes the friction, an earthquake releases energy in waves

Seismic Waves

• Rocks deform only so far before breakage similar to bending stick
• When rocks break, energy waves are released
• Seismic waves are waves of energy produced by an earthquake
• Seismic waves cause the ground to tremble and shake

Faults and Focuses

• The point within the earth where seismic waves originate is the focus or hypocenter of the earthquake
• This is the center of the earthquake, the point of initial breakage and movement on a fault
• Rupture begins at the focus and spreads along the fault plane
• The point on the earth's surface above the focus is the epicenter

Earthquake Magnitude/Intensity

• Magnitude measures the energy released, like the size of the earthquake
• Magnitude is determined by measurements on seismographs
• Intensity ranks based on observed effects in a particular place
• The earthquake produces a range of intensity values, highest in the epicenter area
• Measuring the strength of shaking at certain locations determines intensity

Body Waves

• Seismic waves travel through the earth's interior
• These waves spread outward from the focus

Surface Waves

• Travel on the earth's surface away from the epicenter
• Rock movement associated waves dies out with depth into the earth

Seismic Waves

• Seismic waves are classified into three main types
• The first two, P waves and S waves, propagate within the body of the Earth
• The third, consisting of Love and Rayleigh waves, propagates along its surface

Primary Waves (P waves)

• P waves are compressional longitudinal waves where rocks vibrate back and forth parallel to propagation direction
• P waves are the fastest travelling through near-surface rocks between 4-7 kilometers per second
• The P wave is the first wave at a recording station
• The first P-wave starts at the location of the earthquake called the focus, or hypocenter
• The point at the surface is known as the epicenter

Secondary Waves (S Waves)

• Are the second waves at seismographs
• They are transverse waves, motion is perpendicular to wave propagation
• S waves can only travel through solids
• Scientists can map earth's interior by studying S wave routes

Earthquake Seismic Speed

• P waves arrive at earth's surface first
• S waves arrive after P waves
• P waves travel at 1.5-13 km/s
• S waves travel almost 1.7 times slower

Love and Reyleigh classification

• These waves are guided by the free surface of the Earth
• These follow after the P and S waves have passed through the body of the planet
• Love waves are horizontal particle motion
• Rayleigh waves are vertical ground displacements, As Love and Rayleigh waves travel, they disperse into long wave trains
• The surface cause much of the shaking felt during earthquakes

Rayleigh Wave Behaviour

• Rayleigh waves behave like rolling ocean waves
• Cause the ground to move in an elliptical path opposite to the direction of the wave
• Tend to be destructive to buildings due to the amount of ground movement produced and takes longer to pass.

Locating and Measuring Earthquakes using Seismometers

• It is used to measure seismic waves
• The seismometer keeps a heavy suspended mass as motionless as possible
• The instrument itself can't record the motion that it measures
• A seismograph records the Earth's motion detected by a seismometer, historically recorded as wiggly lines

Detecting earthquakes

• Records earth vibration
• Ground up and down movement
• A simple seismograph detects vertical rock motion
• A pen records ground motion on seismogram
• The frame and recording drum move with the ground while inertia keeps the weight and the needle motionless

P and S Waves

• Start at the focus of an earthquake at the same time
• Separate because they are travelling at different speeds

Seismography and wave time

• The first arrival of P wave is separated from the first arrival of S wave on a seismogram
• The first arrivals of these waves will record much farther apart on a seismogram

Station wave time

• As P and S waves waves with increases with distance
• The P-S time interval can determine the distance from the station to an Earthquake

Graphing seismic activity

• The P-S interval is regular allowing it to be graphed in "travel time' curve
• This can plot seismic-wave arrival time against distance

Measuring Distance

• Station records P and S waves from a quake, comparing waves to a travel-time curve
• A single station can determine only the distance to a quake, not the direction

Station pinpointing

• Multiple stations can pinpoint the location of a quake
• Mapping with multiple stations circles intersect at the epicenter

Earthquake depth

• Seismograms can indicate at what depth a quake occurred
• Earthquakes are classified into shallow, intermediate, and deep based on the depth
  • Shallow: 0-70 km
  • Intermediate: 70-350 km
  • Deep: 350 – 670 km
• Earthquakes are classified into 3 groups according to their depth of focus
• Shallow-focus quakes are most common releasing 85% of quake energy

Magnitude measurement

• Measuring earthquake intensity by the amount of damage that has been caused
• Measure of earthquake's effect on people and buildings
• The amount of energy released can indicate magnitude
• Measuring the height (amplitude) of one of the wiggles on a seismogram to determine its magnitude
• The more the ground vibrates The larger the wiggle the larger the quake is

Ground movement

• Ground motion is the shaking of land
• it can cause buildings to vibrate
• It can be strong enough to topple large structures
• Falling debris from buildings generally harms the most people

Earthquake Related Hazards

• Fire is a serious problem during the event
• Shaking causes which can crack gas pipes
• Power electrical and household appliances may have ignite damage

Landslides

• Shaking can trigger land slides
• Liquefaction is a type of ground failure caused by shaking
• Water saturated soil turns into a liquid
• Permanent displacement of land surface comes from a fault
• Faults can cause landmass one end to rise, the other end to drop
• Often leaves trace of a fault

Foreshocks

• Earthquakes smaller than the main shock follow after the event

Aftershocks

• Small quakes often less common and less damaging
• Can precede a main shock

Earthquake movement

• The sea floor movement upward during causes large sea waves
• seismic sea waves" or tsunamis
• Caused by 7+ magnitude earthquakes
• Submarine landslides are also a large factor