I have already read lots of stuff about earthquakes already so I know a fair amount like

  • Earthquakes mostly occur along tectonic plate boundaries due to convergent, divergent or transform movement
  • They can happen during or prior to volcanic activity

The definition of an earthquake – from Encyclopedia Britannica http://www.britannica.com/EBchecked/topic/176199/earthquake is:

  • earthquake –  Sudden shaking of the ground caused by a disturbance deeper within the crust of the Earth.

Doesn’t really tell me much I don’t already know – an earthquake is when the earth quakes or shakes about.  

Earthquakes are generally classified by most references as 2 distinct types – tectonic and man-made.

Tectonic Earthquakes:  

These are the ones that occur because of tectonic plate movement – and in some cases from lava/ magma movement within a volcano.

Earthquakes mainly occur at tectonic plate boundaries – and can happen at all 3 types of boundaries – the converging, diverging and transform.  Earthquakes can also occur intra-plate, like in here in Australia where we get around 200 earthquakes per year.

So why exactly do they happen???

A good explanation I found – with a video is found on the OIKOS website http://www.e-oikos.net/gmap/eng/Eq/EqMec.html?lingua=en-GB

This website talks about the sudden release of elastic energy from plate movement.  Elastic energy I know about from physics – this is a form of potential kinetic energy, from a material being distorted or pulled out of its natural shape – when tension is released the material loses potential energy to the environment.

To relate this to earthquakes…

Tectonic plate movement occurs on a continual basis – it pushes plates together, pulls them apart or makes them slide along side each other.  Rocks are not very slippery, there is an enormous amount of friction between them, so they do not take to being moved all that easily.  It is thought that during tectonic plate movements, the plate doesn’t move fluidly – stress builds up between the plates and when the tension is great enough to overcome friction there is a rapid movement of the crust to a place of lower stress.  The potential or elastic energy that had built-up in the straining rocks is then released into the environment.  The energy released can be small to extremely large depending on the amount of stress/ potential energy there was in the rocks.  The energy is released into the environment as seismic energy and is the cause of earthquakes.   Stress is designated as tensional, compressional or shear depending on the type of movement in the fault.

http://earthquake.usgs.gov/learn/glossary/?term=tensional stress

Rather than using the terms diverging, converging and transform – lots of websites classify the faults as normal, reverse or strike slip.  
Alternatively, some classify faults as either dip-slip or strike slip.
 To relate these to terms I know already…
  • At divergent plate boundaries/ constructive plate boundaries normal dip-slip faults occur.  In this type of fault the plates/ pieces of rock are generally being pulled apart causing tensional stress.  In many cases there is a hanging wall that slides down relative to the footwall as the earth’s crust lengthens.
  • At convergent plate boundaries/ destructive plate boundaries, reverse dip-slip faults occur.  In this type of fault the plates/ pieces of rock are being pushed together causing compressional stress.  In many cases there is a hanging wall that gets pushed up relative to the footwall as the crust shortens.  We of course have mentioned all this before when talking about subduction at converging plate boundaries.
  • At transform plate boundaries, strike slip faults occur.  In this type of boundary the plates/ pieces of rock are pushed transverse to each other causing sheer stress.
gosh – well considering the only place I have heard these names of normal/ reverse, dip-slip and strike-slip is in earthquake stuff – but it really refers to plate movements I have covered already.  It seems these names were generated before tectonic plate theory perhaps, which could explain the disjointedness.   But perhaps I will come up with another explanation with more research…
                                                                                                                                                                                                                                                                                  There is a map below that shows all the earthquakes that have been over 5.5 magnitude (I need to read about what the magnitude means!!!) on the world map.  Looks like the majority of them occur at tectonic plate boundaries (which we knew already).  From the map you can also see that convergent plate boundaries, as you would expect, are generally associated with the deepest focal points (e.g. you can see red/green around the north west Pacific plate and east Nazca plate – both regions of subduction/ converging plate boundaries.   (from http://www.ldeo.columbia.edu/LCSN/Eq/Global/seismicity.html)

 

So… I need to know…. what is going on at the spots not on the plate boundaries (there are not many of them, but they do exist… including, importantly, in our beloved Australia)… and I need to know what seismic activity is in scientific terms…

First of all… what is going on intra-plate – like in Australia…

It seems in 2008-2009 there was a boom in newspaper articles about Australia’s fault lines… being newspaper articles some were not terribly believable – like the Perth Sunday Times with their article “WA sits on deadly fault line” and continues with “ONE of the world’s biggest fault lines runs through WA’s back yard”.   Now that I know lots about tectonic plates, I can be safely assured that the statement is total cods-wallop since we do not have a major plate boundary running through this country http://www.perthnow.com.au/news/western-australia/wa-sits-on-deadly-fault-line/story-e6frg14u-1225782494162

We do have some minor faults running through Australia though (some of them quite extensive) – as they do the rest of the world.  There is good info about why on the Geoscience Australia website http://www.ga.gov.au/hazards/earthquakes/earthquake-basics/where.html

A minor fault, as opposed to a tectonic plate boundary major fault, is an area of fracturing of the earth’s crust bought about by stress of some kind.  The plates of the world have been moving about, pulling away from each other, slamming into each other and slipping past each other for millions of years.  Over the years, large plates have fractured from excessive stress and strain into smaller plates.  Australia has been pushed away from the Antarctic and up towards the Eurasian plate through tectonic plate movement (Sea floor spreading) – GPS data shows Australia is moving 35 degrees east of north with a velocity of 67 mm/yr.  This pushing from the sea floor spreading is slamming our Indo-Australian plate into the Eurasian plate.  As this pushing occurs, the Himalayas, the mountain range formed at the boundary of the Eurasian plate, gets taller and the Indo-Australian plate slips further under the Eurasian plate (through subduction at the converging plate boundary).  The resulting strain on the Indo-Australian plate from this continuous plate movement has been enough to cause a massive fracture in the plate which, it is thought, will eventually split the plate between India and Australia.  The Indo-Australian plate also forms a convergent boundary with the Pacific plate and a divergent boundary with the Atlantic plate, which adds to the push and pull stress.  The stress/tension can be felt at places other than the boundaries and, as a result, has resulted in small fractures forming in the crust all over the plate.  These fractures are called minor faults and, as with major faults, they can result in earthquakes from the release of stress in moving rocks/crust.  Australia is not unique in having these minor faults, they occur in every plate as a result of similar mechanisms.  These minor faults have the same slipping and sliding patterns described above – i.e. normal and reverse dip-slip faults and slip strike faults (Ahhhh – that makes sense… possibly why they call them different names than when just talking about the 3 kinds of plate boundaries!!!)

While all fault lines, including the ones in Australia, have the potential for seismic activity, the seismic activity as a result of minor faults is mild compared with major fault lines.  We have, in Australia, had a few large earthquakes.  Adelaide in South Australia is considered to be the most earthquake prone capital city in Australia – this is because South Australia bears the brunt of the slight sideways pushing.. Western Australia has quite a large fault which is prone to earthquakes but it is situated in a particularly remote area so generally does not cause widespread damage.  Australia’s most destructive earthquake occurred in Newcastle NSW in 1989 where 13 people were killed and 160 injured – it was estimated to have done about 4 billion dollars damage and is the first (and only) recorded earthquake ever to have taken a life in Australia.  This earthquake was calculated to have a magnitude of around 5.3.

This earthquake triggered the government into action monitoring and assessing earthquake activity in Australia and researching strategies to reduce potential damage in the future – there is some fantastic information on planning to reduce hazards on the Geoscience Australia website http://www.gs.gov.au – talking about building codes and soil types etc.

It is time to know more about seismic waves

What are seismic waves?  Well I found this great explanation of seismology here http://www.geo.mtu.edu/UPSeis/waves.html.  UPSeis is an educational website for budding seismologists!!! (got to love the internet…) bought to us by Michigan Technical University.

Seismic waves, as I have worked out already, is the energy formed from the breaking of rocks in the earth’s crust, or the energy released from elastic potential energy of rocks being subjected to stress in the earth’s crust, or from an explosion in the earth’s crust.

Seismic energy travels through the earth in waves is recorded by seismographs at seismic recording stations which are situated all over the world.  There are two distinct classes of seismic waves: body waves and surface waves.

Body Waves:  These can travel through the crust and mantle of the earth – they are higher frequency and travel faster than the surface waves.  There are two kinds of body waves; P waves and S waves.

P waves= also called primary waves, compressional waves or longitudinal waves.  These are the fastest kind of wave and will, therefore, reach the seismic reader first.  P waves take the push and pull form of sound waves and can travel through solid, liquid or gas at the speed of sound.  With P waves, particles move in the same direction of the wave/ energy.  Dogs can sometimes hear P waves and will start barking just before the full force of an earthquake is felt.

An animated version of this picture can be found here… http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif

S waves = also called secondary waves, transverse or shear waves.  These are the second fastest kind of wave, being about 60% of the speed of a P wave, and can only travel through rock/ solids not liquids or gases (since liquids and gases do not support shear stress).  S waves move particles like light waves – up and down or side to side, perpendicular to the direction the wave is travelling.

An animated version of this picture can be found here… http://www.geo.mtu.edu/UPSeis/images/S-wave_animation.gif

Surface Waves:  These, as the name suggests, travel only through the upper crust of the earth’s lithosphere.  Surface waves travel more slowly, at approximately 90% of the speed of S waves.  Surface waves have a lower frequency and higher amplitude than body waves and are responsible for the physical destruction caused by earthquakes.  There are two kinds of Surface waves; Love waves and Rayleigh waves.

Love waves – These are slightly faster than Rayleigh waves and move the surface crust from side to side – they can make water vibrate a little but not to any great degree

An animated version of this picture can be found here… http://www.geo.mtu.edu/UPSeis/images/Love_animation.gif

Rayleigh waves – These waves roll along the ground like a wave rolls along the water.  Rayleigh waves cause the earth’s surface to roll up and down and side to side and, despite being a lower frequency, can be much larger than other waves.  Rayleigh waves can travel through water and rocks…

An animated version of this picture can be found here… http://www.geo.mtu.edu/UPSeis/images/Rayleigh_animation.gif

You can see by looking at the animations why Rayleigh waves are going to be destructive!!!

The velocity and propagation of the wave depends on the density and elasticity of the medium.  When an earthquake occurs, the seismographs closest to the earthquakes epicenter records the S and P waves – from the pattern they can give an indication as to where the earthquake occurred.  In the event of an earthquake happening in sea or a long distance from seismic equipment, data of P waves from several surrounding recorders can be used to determine where the earthquake was.

An earthquake has an epicenter – this is the earths surface at the point where the earthquake occurred.  The focal point or focus or hypocenter of an earthquake is the point in the crust below the epicenter, where the rock movement that generated the earthquake occurred.

Earthquakes are measured in magnitudes based on the data received from the seismograph.  The data is used to scale earthquakes in order of severity.  Different countries use slightly different scales – in Australia, Geoscience Australia  http://www.ga.gov.au/hazards/earthquakes/earthquake-basics/where.html# describe the scale as follows

The size of earthquakes is determined by measuring the amplitude of the seismic waves recorded on a seismograph. A formula is applied to these which converts them to a magnitude scale, a measure of the energy released by the earthquake. For every unit increase in magnitude, there is roughly a thirty-fold increase in the energy released. For instance, a magnitude 2.0 earthquake releases 30 times more energy than a magnitude 1.0 earthquake, while a magnitude 3.0 earthquake releases 900 times (30×30) more energy than a magnitude 1.0.

A magnitude 8.6 earthquake releases energy equivalent to about 10,000 atomic bombs of the type developed in World War II.

The effects of an earthquake depend on many factors, such as the distance from the epicentre (the point on the Earth’s surface directly above where the earthquake originated within the Earth) and the local ground conditions. Generally, for locations near the epicentre, the following effects may be observed:

       
Magnitude Description  of effect
less  than 3.4
Usually  felt by only a few people near the epicentre.
3.5  – 4.2
Felt  by people who are indoors and some outdoors; vibrations similar to a passing  truck.
4.3  – 4.8
Felt  by many people; windows rattle, dishes disturbed, standing cars rock.
4.9  – 5.4
Felt  by everyone; dishes break and doors swing, unstable objects overturn.
5.5  – 6.1
Some  damage to buildings; plaster cracks, bricks fall, chimneys damaged.
6.2  – 6.9
Much  building damage; houses move on their foundations, chimneys fall, furniture  moves.
7.0  – 7.3
Serious  damage to buildings; bridges twist, walls fracture, many masonry buildings  collapse.
7.4  – 7.9
Causes  great damage; most buildings collapse.
greater  than 8.0
Causes  extensive damage; waves seen on the ground surface, objects thrown into the  air.

There are seismic recording stations ALL over the world… A list of them can be found  here http://www.iris.edu/data/DCProfiles.htm.  This includes our own recording sites in Australia.

Earthquakes often do not occur as isolated events.  When you have a large earthquake it is common to have smaller adjustments/ earthquakes at the same point or very close over several days.  In this event the subsequent earthquakes are called aftershocks. Earthquakes can also occur in clusters, where you can see many earthquakes near each other but no one earthquake is of significantly higher magnitude than the others, or in swarms, where one earthquake triggers fault activity at a different site and triggers subsequent earthquakes.

Man-Made Earthquakes:

Seismic activity can be triggered by explosions and bombs – A good explanation I found on the Michigan Technical University website UPSeis http://www.geo.mtu.edu/UPSeis/why.html:

  • “Earthquake-like seismic waves can also be caused by explosions underground. These explosions may be set off to break rock while making tunnels for roads, railroads, subways, or mines. These explosions, however, don’t cause very strong seismic waves. You may not even feel them. Sometimes seismic waves occur when the roof or walls of a mine collapse. These can sometimes be felt by people near the mine. The largest underground explosions, from tests of nuclear warheads (bombs), can create seismic waves very much like large earthquakes. This fact has been exploited as a means to enforce the global nuclear test ban, because no nuclear warhead can be detonated on earth without producing such seismic waves.

There are also some references to man made activity near faults triggering earthquakes.  Some geologists appear in favour of this being possible, although it is not mentioned at all on many geological websites so the hypothesis possibly doesn’t have enough substantial evidence to support it totally.  The man made activities thought to be responsible, by some, for triggering earthquakes, includes damming and mining near fault lines.  Some of the major earthquakes postulated to have been “man triggered” include the 2008 earthquake in Sichuan, China that killed 80,000 people – the earthquakes epicenter was just 550 yards from a dam holding 315 million tonnes of water – from the UK Telegraph (http://www.telegraph.co.uk/news/worldnews/asia/china/4434400/Chinese-earthquake-may-have-been-man-made-say-scientists.html).    Closer to home, the Newcastle Earthquake was the subject of a review by Christian D. Klose of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York (http://www.abc.net.au/am/content/2007/s1823833.htm), who linked 200 years of underground coal mining,in Newcastle to the reactivation of a fault and the trigger of the 1989 earthquake that killed 13 and caused around 1 billion dollars worth of damage.  The hypothesis is that these man-made activities can be the trigger of adjustments in rocks at fault lines or can contribute to increased stress near fault lines.  The debate is still out on this but I am sure we will hear more about it in the future…      

oooh oooh oooh – I just found reference to this on Geoscience Australia – but not in the section on what causes earthquakes.  It said coal mining in Newcastle could have been a potential trigger for the 1989 Newcastle earthquake. 

SO… Interesting knowing the theory… and gosh – I have seen the effect on TV!!! with the Christchurch NZ earthquake and the Japanese earthquake… The two things that struck me about these earthquakes… with the Christchurch one it was the mud bellowing up through cracks in the roads/ ground, and with the Japanese one… THE TSUNAMI!!! massive wave… These would be classified as effects of earthquakes… Along with shaking and landslides which also occurred in New Zealand.  

Effects of Earthquakes:

 Aside from obvious damage bought about by the ground shaking and rippling with the surface waves, which naturally can cause extensive damage to structures such as buildings, houses, bridges and roads (also, of course, what is in and on these structures).  There are a few other less direct things that can cause damage from earthquakes.   

Liquefaction

This is what that muddy stuff was that was oozing out of cracks in New Zealand following the Earthquake a couple of months ago.  Liquefaction of silt it was…

A good explanation of liquefaction can be found here http://www.es.ucsc.edu/~es10/fieldtripEarthQ/Damage1.html – in summary it says that liquefaction occurs when saturated sandy, silty or gravelly soils are exposed to seismic shear waves during an earthquake.  The seismic waves change the properties of the soil so it behaves more like a viscous liquid or cement slurry than a solid.  Hydrated soil normally has a consistent amount of strength to support its structure – due to the grains physically touching each other and from the consistent water pressure between the pores.  Seismic waves cause the soil particles to vibrate and, as a result, the water is forced out of the soil particles into the pores – thus increasing water pressure between the grains.  The process continues as earthquake vibrating continues – constantly reducing the soils ability to “stick” together and eventually allowing it to collapse into a liquid (i.e. it loses shear strength because of the lack of interaction/ friction between the grains).  Because the water pressure has increased significantly, the liquid also wants to escape… and because of this it will often spurt up through cracks formed by earthquake activity (called sand volcanoes).

This picture from http://www.semp.us/publications/biot_reader.php?BiotID=330 provides a great diagram of the soil grain interactions.  If there are houses, roads, bridges or buildings built on sandy/ silty or gravely soil then liquefaction could be a potential nightmare because the once solid surface suddenly turns into a liquid.  Liquefaction is one of the main causes of structural damage from earthquakes because it can cause entire buildings to sink and topple over.  Luckily Christchurch, built on hydrated silt, was aware of its potential for liquefaction prior to the 2011 earthquake, so their building code ensures it is considered in newer buildings and houses.  There was extensive liquefaction flooding in yards and many roads and some bridges in Christchurch were destroyed as a result of liquefaction – but this could potentially have been far worse without the building codes.  There is an excellent video which explains the cement-like properties of liquefied silt here http://mandenomusings.wordpress.com/2011/03/03/christchurch-earthquake-liquefaction-explained/

Manden, in this blog, uses the analogy of a tent to describe the liquefaction process – if you take the inside frame out of a tent then it collapses and no longer has any shear strength – being more like a liquid…

In the video above, a guy puts the solid looking wet silt into a wheelbarrow and wheels it out of his front yard – by the time he gets to the front it is liquid again due to the bumping motion of the wheelbarrow on the brick paving.  This is a good demonstration of the structure – when stationary it appears solid, when moving it turns into liquid.  

Another cause of destruction from the 2011 Christchurch earthquake was landslides

Landslides

Landslides are just what they sound like – slippage of part of the structure of a hill or mountain.  Landslides can be caused by destabilization through shaking, can be caused by rock crushing near the earthquake epicenter or can also be due to liquefaction.  The earthquake, particularly if at a converging plate boundary, can contribute significantly to the height of a mountain within a few short seconds – this can also be enough to destabilize the mountain and cause major avalanches/ landslides.   There were two major landslides resulting from the 2011 Christchurch earthquake.  Landslides and avalanches can cause extensive damage to houses and roads and if they are large enough and fall into a body of water they may even potentially trigger tsunamis.

Tsunamis

On Boxing day in 2004 a 9.1 magnitude earthquake occurred off the coast of Sumatra, Indonesia (n.b. this is in the ring of fire and was at a subduction zone…).   The earthquake triggered a series of deadly tsunamis that killed over 200,000 people in 12 countries with waves up to 30 meters high.  Those of us who remember this earthquake were horrified by the numbers of dead and missing, and until this time I had NEVER heard of a tsunami.  So what is it exactly, aside from a giant wave…

Well Geoscience Australia does quite a good job trying to explain tsunamis http://www.ga.gov.au/hazards/tsunami/tsunami-basics/what.html as does the EarthScience website at http://earthsci.org/education/teacher/basicgeol/tsumami/tsunami.html.  Tsunamis can be triggered by anything with the potential to displace large amounts of water in the ocean.  This would include earthquakes under or next to oceans, landslides/ avalanches, volcanoes or meteorites hitting the ocean.   The most common cause of tsunamis are underwater earthquakes with a magnitude over 6 (cause around 3/4 of all tsunamis) occurring underwater at subduction zones (converging plate boundaries).

I like the idea of the step-by-step to tsunami… this has helped me understand what it is all about…

1. Initiation!!!   [ Image of Tsunami Generation ]

During a large submarine earthquake there is a rapid jolting/ displacing of a column of water upward.  For the case shown above, the earthquake rupture occurred at the base of a subduction zone in deep water. Note: In the figure the waves are greatly exaggerated compared to water depth! In the open ocean, the initial tsunami wave is at most, several meters high.

2. Split!!! [ Image of Tsunami Wave Split ]

Within several minutes of the earthquake, gravity splits the initial tsunami into two separate tsunami waves which travel in opposite directions – one that travels out into deep ocean and the other that travels towards the nearby coast.  The two tsunami waves are approximately half the height of the original wave.  The speed which the tsunami waves are travelling at depends on the depth of the water the wave is travelling according to the following the equation

c is equal to the square root of gH where c = the speed of the wave, g is the acceleration due to gravity (= 9.8 m/s2) and H is the depth of water.

i.e. from this we can see that tsunami waves travel more quickly in deep water – if we are talking about water 4000m deep, which would be common, the tsunami wave is travelling at 198m/sec.  The deep water tsunami will travel faster than the tsunami near shore.

3. Amplification!!! [ Image of Tsunami Amplification ]

As the tsunami travels over the continental slope towards land, the sea depth (H) gets smaller – and as a result of the equation above, the hight (amplitude) of waves increases (since the energy of the tsunami is maintained) and the tsunami waves slow down (the wavelengths decrease).   Note that the deep ocean tsunami has travelled much farther than the local tsunami because of the higher propagation speed (again because of the equation above). As the deep ocean tsunami approaches a distant shore, amplification and shortening of the wave will occur, just as with the local tsunami shown above.

4. Run-up!!! [ Image of Tsunami Runup ]

As the tsunami wave travels from the deep-water, to the near-shore region, tsunami run-up occurs. Run-up is a measurement of the height of the water onshore observed above a reference sea level. Contrary to many artistic images of tsunamis, most tsunamis do not result in giant breaking waves (like normal surf waves at the beach that curl over as they approach shore). Rather, they come in much like very strong and very fast tides (i.e., a rapid, local rise in sea level). Much of the damage inflicted by tsunamis is caused by strong currents (in and out, and floating debris. The small number of tsunamis that do break often form vertical walls of turbulent water called bores. Tsunamis will often travel much farther inland than normal tidal waves.  Because of the amplification and slowing down process, some of the shore water is sucked in help amplify a tsunami wave – this is why it is often mentioned that the water disappears from the beach before a tsunami hits.  Tsunamis are associated with lots of energy – after run-up part of the tsunami energy is reflected back to open ocean and can generate edge waves that travel back and forth, parallel to the shore.  As a result of long wavelength and ability of tsunami to transfer energy, a second tsunami wave often occurs which is larger than the first (not always the case but does sometimes happen.

Tsunamis are often inconspicuous at sea – since they are really quite shallow in deep water- often only a meter tall.  Because earthquakes are rather unpredictable, tsunamis are unpredictable – but measuring instruments can measure changes in water which may indicate a tsunami, and these measuring instruments have been situated near the coasts of Australia to give us some forewarning.  Seismic activity is also measured to help us monitor earthquakes that have the potential of generating tsunami waves which may affect us.  Tsunamis have drowned hundreds of thousands of people and animals in the past decade and have caused more destruction than any other natural events.

oh another note on tsunamis I read somewhere – the shallower the underwater (submarine) earthquake, the more potential for the tsunami… this is actually pretty logical…

All because of a simple equation huh!!! tsunamis would make a good maths class 

Mountain Building

This isn’t necessarily a bad thing – like the other consequences of earthquakes.  Earthquakes are a result of moving and cracking rocks – if this movement involves an upward displacement of rock (like with subduction zones or dip-slip faults), then you have mountain making occurring.  A large scale example of this is the Himalayas at the convergent plate boundary – a small scale of this is in our own backyard – it is thought there is some very slow active mountain building going on in South Australia as a result of minor dip-slip fault activity.  http://cooberpedyregionaltimes.wordpress.com/2008/09/26/faultlines-weaving-their-way-across-southern-australia/ is an interesting newspaper article on this – written for the Coober Pedy Regional Times Newspaper.    The mountain building is occurring very slowly.
Mountain building most commonly occurs when convergent boundaries meat on land rather than the usual case of oceanic crust and continental crust.
SO… that ends my earthquake investigation… the other thing interesting to note… is the monitoring of earthquakes http://earthquake.usgs.gov/earthquakes/recenteqsww/ This is the most fantastic site!!! it is a map of earthquake activity up to the current time – showing all earthquakes in the world that have happened in the last hour – day – week and their magnitude… FASCINATING… Earthquakes are monitored very closely in an effort to make some predictions about when and where they may occur.  While they are unpredictable, many faults have a certain amount of regular activity… if the activity begins to slow down or stops then it is thought there is potentially lots more stress building up in the fault which leads to the possibility of a major earthquake.  We have earthquake monitoring going on in Australia – and we have earthquake safe building codes in most places now – much of this was triggered by the 1989 Newcastle earthquake which gave evidence to how poorly prepared Australia was for such an event.    There is an earthquake overlay in Google Earth which is a fantastic learning tool – it links to this website.  There is a more specific Australian version of this earthquake monitor on the Geoscience Australia website http://ga.gov.au/earthquakes.

So how would I teach students about earthquakes… well I think I would start out by getting them to explore where they occur – where the biggies more often occur, what is meant by magnitude and perhaps do an activity where we simulate an earthquake and tsunami – best done in the explore phase… then cover the more detailed information about seismic readings, liquefaction, how tsunamis work and how they are monitored in the explain phase… perhaps adding to the jigsaw activity previously mentioned… 

This knowledge can then be used to look at seismic activity in Australia and what Australia is doing in the way of disaster management.  



Advertisements