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9.2 Tectonic impacts: 4. Natural disasters

Syllabus reference (October 2002 version)
4. Natural disasters are often associated with tectonic activity and environmental conditions caused by this activity may contribute to the problems experienced by people	*Students learn to:* identify where earthquakes and volcanoes are currently likely to occur based on the plate tectonic model describe methods used for the prediction of volcanic eruptions and earthquakes describe the general physical, chemical and biotic characteristics of a volcanic region and explain why people would inhabit such regions of risk describe hazards associated with earthquakes, including ground motion, tsunamis and collapse of structures describe hazards associated with volcanoes, including poisonous gas emissions, ash flows, lahars and lava flows and examine the impact of these hazards on the environment, on people and other living things justify continued research into reliable prediction of volcanic activity and earthquakes describe and explain the impacts of shock waves (earthquakes) on natural and built environments distinguish between plate margin and intra-plate earthquakes with reference to the origins of specific earthquakes recorded on the Australian continent	*Students:* gather, process and present information from secondary sources to chart the location of natural disasters worldwide associated with tectonic activity and use available evidence to assess the patterns in terms of plate tectonics gather information from secondary sources to identify the technology used to measure crustal movements at collision boundaries and describe how this is used gather information from secondary sources to present a case study of a natural disaster associated with tectonic activity that includes: an analysis of the tectonic movement or process involved its distance from the area of disaster predictons on the likely recurrence of the tectonic movement or process technology available to assist prediction of future events an investigation of possible solutions to minimise the disastrous effects of future events

Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW
[Edit: 24 Jul 08]

Prior Learning: Preliminary module 8.5 (subsections 2 and 3); Stage 5, Outcome 5.9.

Background: Earthquakes are vibrations or tremors that occur in the Earth as a result of rocks suddenly moving against each other. The epicentre of an earthquake is the point on the Earth’s surface that is directly above where the movement occurred. The focus of an earthquake is the exact position of the earthquake. The precise location of an earthquake can be described by stating the map coordinates for the epicentre and a depth for the focus.

gather, process and present information from secondary sources to chart the location of natural disasters worldwide associated with tectonic activity and use available evidence to assess the patterns in terms of plate tectonics

During the course, use a log book to gather and record information about natural disasters resulting from tectonic activity as they are reported in the news media and use a large world map to record and present their locations. You may need to use a key to present the information clearly and succinctly.
If you cannot collect enough data from media sources to assess patterns, US Geological Survey provides:
- Significant quakes of the world , from the National Earthquake Information Center (NEIC). The site provides the locations and magnitudes of global earthquake events, each year, back to 1984.
- Weekly Volcanic Activity Report , prepared by the Volcano Hazards Program and Smithsonian Institution's Global Volcanism Program.
Process the information by assessing its accuracy by comparing it with information presented in scientific journals and reliable scientific Internet sites.
Once you have enough information charted on the world map, use the available evidence gathered to formulate hypothetical plate boundaries to account for the recorded distribution of tectonic activity. Evaluate your hypothesis by comparing your findings against data published in scientific references.

identify where earthquakes and volcanoes are currently likely to occur based on the plate tectonic model

Because we know that earthquakes are caused by sudden movement of rocks that are under stress, the location of earthquakes can be predicted by using the plate tectonic model to identify places where sections of rocks are being forced to move against each other. These places would correspond to known active fault lines and plate boundaries.
Rocks that are under stress can frequently adjust to the stress by folding or sliding. However, if sections lock up, stress may be released by the rocks fracturing, creating a sudden large movement. Earthqaukes are likely to occur in places such as these.
We know that volcanoes result from the upwelling of magma generated at hot locations in the mantle, and from partial melting of crust. This means that the location of volcanoes can be predicted by using the plate tectonic model to identify typical geological settings for magma generation.

Plate boundaries were discovered by plotting past earthquakes and volcanoes on a map of the world. The following predictions can be made from the plate tectonic model.

Most volcanoes and earthquakes will occur on plate boundaries.
Shallow focused earthquakes, down to depths of seven kilometres, will occur along those sections of transform faults that are between the spreading rift axes.
Earthquakes and explosive volcanoes will be produced in subduction zones. Shallow focused earthquakes will occur near the ocean trench; deep focused earthquakes will occur further away from the trench.
Earthquakes will frequently occur at conservative boundaries, down to depths of 30 kilometres.
Volcanic eruptions occur progressively along the rifts of the mid ocean ridges. More activity will occur away from the hinge of rotation for the two plates.
Relatively passive eruptions can be expected from volcanoes located at divergent boundaries.
Mid plate volcanoes are usually the result of a hot spot under the plate. Observation of the direction of plate movement over the hot spot can assist in predicting where new volcanos will occur.

The plate tectonic model does not currently provide reliable predictions related to earthquakes in continental lithosphere.

distinguish between plate margin and intra-plate earthquakes with reference to the origins of specific earthquakes recorded on the Australian continent

The Australian continent lies entirely within the Australia-India plate, and so it does not experience plate boundary processes.
Plate margin earthquakes account for ninety percent of all earthquakes and are the result of the constant movement of the rocks at plate boundaries against each other.
Intra-plate earthquakes are those that occasionally occur in the crust of plates and away from the more active plate boundaries. The causes of intra plate earthquakes are not well understood, but they are usually caused by compressive stress in rocks.
Australia has three distinct regions of earthquake activity. These are:
- the Eastern region, covering the eastern highlands and coastal areas
- the Central region, extending from near Adelaide to the Simpson Desert
- the Western region, encompassing several distinct zones.
The most disastrous Australian earthquake in the last 200 years was the Newcastle earthquake of 28 December 1989. It was a magnitude 5.6 earthquake that caused $1.2 billion damage. The most likely cause was by readjustments along the Hunter-Mooki Thrust, a curved fault running from Newcastle and through Maitland, Murrurundi, Quirindi. Narrabri and Mackay, The fault is sporadically active due to strong easterly compression from the expanding Pacific Ocean floor.
For more detail refer to:
- Scientists debate cause of Newcastle quake Reporter, Christopher Zin; ABC 7:30 Report, 9/01/2007.
- Geohazards Fact Sheet, Australian Earthquakes Geoscience Australia
- Report into Fire Service Earthquake Preparedness Inspector Glenn Launt, New South Wales Fire Brigades: (This report is very long but most of the information you will need about earthquakes in Australia, particularly Newcastle and Sydney, can be found on page three of the report. The executive summary has interesting information about earthquakes in Kobe, Japan and the problems the fire brigade had dealing with the after effects of the earthquake.)
In the central seismic region of Australia, earthquakes have been associated with a 120 kilometre long fault as a result of north-south compressive forces.
The stress causing intra-plate earthquakes may be associated with isostasy, which is the tendency for rock masses to rise or sink to achieve a balance between downward weight forces and upward buoyancy forces. Erosion and deposition change historically balanced isostatic forces, causing new regions of stress and strain.
Some intra-plate earthquakes may be related to the stress at plate boundaries and to temperature changes in the lithosphere caused by processes in the mantle. The Australian plate has many north-south trending concentrations of earthquakes, so it may be that the Australian plate is adjusting to the twisting motion of the plate as it moves north. The forces that drive the continent may not be uniform and adjustment to the different stresses created by this may cause the earthquakes.
In Western Australia, a linear zone of seismic activity extends from near Moora, southeast to Albany. This is known as the Southwest Seismic Zone. It is the most seismically active area in Australia. The town of Meckering, that experienced a magnitude 6.9 earthquake on 14 October 1968, lies within this zone. Though the reason for the concentration of seismic activity in the Southwest Seismic Zone remains unknown, it could be caused by a major structure/discontinuity of crustal or lithospheric scale that has been reactivated.

You can investigate recent Australian earthquake activity by referring to the Geohazard page of the web site of Geoscience Australia.

gather information from secondary sources to identify the technology used to measure crustal movements at collision boundaries and describe how this is used

You need to identify data that is useful and current. To help you to do this in a limited time, consider sharing the task by working as part of a group. This will spread the workload, improve the identification of, and access to, an appropriate range of sources. It also allows a more thorough collection of data about specific technologies. Secondary sources you refer to could include internet, textbooks, video series about natural disasters.
Decide on a useful data collection technique to be used consistently across the group to gather the data. You may need to decide on the structure and components of a table and the language to be used by each team member.

The following table is an example of one way to gather data. It can be used as a starting point for the collection of more detailed information. The table describes some of the developed or experimental technologies currently used to measure crustal movements. Many of these exhibit potential as technologies which might contribute to more accurate prediction of volcanic eruptions and earthquakes.

Technology used to measure crustal movements	How this is used
Laser geodimeter	Measures changes in the distance between stable units on either side of the fault
Wire strain meter (10 m long)	Measures the deformation of the ground surface around a fault
Tilt meter	Monitors ground tilting
Data gathered by satellite global positioning systems (GPS) is being used to analyse deformations in the Earth's crust	Monitoring the relative and absolute motion of stations set up across plate boundaries enables the determination of regional-scale deformation and associated stress fields.
Two-colour geodimeter	Measures crustal deformation along faults and near volcanoes. It is an ultra-precise, distance-measuring instrument that employs light pulses. It has a precision of 0.5 to 1.0 mm for ranges between 1 and 12 km.

describe methods used for the prediction of volcanic eruptions and earthquakes

The following are descriptions of some of the developed or experimental technologies currently used to predict volcanic eruptions and earthquakes. No reliable method of predicting volcanic eruptions and earthquakes has yet been developed.

Local seismic recording stations: used with artificially generated micro-earthquakes to produce precise estimates of the P-wave and S-wave velocities in a test region. An earthquake may be expected when the ratio of these velocities changes slightly.
Modern seismic monitoring networks including the use of seismic instruments placed down boreholes (to depths of 500 m): Some large earthquakes are preceded by foreshocks. Knowledge of past earthquake patterns allows scientists to estimate the odds that an earthquake striking is a foreshock to a larger mainshock in the same area. Additionally, characteristic levels of background seismicity may drop substantially in the months or years prior to a large earthquake. Tiny changes in seismic velocity in the stressed region may be due to cracks forming just before failure.
The VAN Technique measures changes in the earth’s electric field prior to an earthquake: Three Greek scientists, P. Varotsos, K. Alexopoulos, and K. Nomicos, (VAN) have pioneered methods of detecting, recording, and interpreting signals from the earth that precede an earthquake. These electromagnetic signals are apparently generated through piezoelectric processes, induced by tectonic stress. Other similar research is investigating if changes in the Earth’s background noise in the low (LF), very low (VLF), and extremely low (ELF) frequency bands may indicate a pending earthquake.
Geochemical samplers: detect increases in the radioactive gas radon in the ground water prior to an earthquake. It is believed that changes in stress in the crust enables radon trapped in cracks to move toward the surface.
Because increased earthquake activity is an indicator of an imminent volcanic eruption, the methods above can all be used to predict eruptions. Additionally, systematic seismic monitoring of activity before, during and after an eruption is used in some situations. Volcano monitoring consists of keeping a detailed record of the changes in a volcano over time. Scientists look for:
- increase or decrease in steaming of vents
- emergence of new steaming areas
- development of new ground cracks or widening of old ones
- unusual or inexplicable withering of plant life
- changes in the colour of minerals encrusting fumaroles
- increase in volume of the volcano (swelling)
- precise location of earthquakes associated with magma movement
- localised changes in the Earth’s magnetic field
- any other obvious and recordable change.

gather information from secondary sources to present a case study of a natural disaster associated with tectonic activity that includes:

an analysis of the tectonic movement or process involved
its distance from the area of disaster
predictions on the likely recurrence of the tectonic movement or process
technology available to assist prediction of future events
an investigation of possible solutions to minimise the disastrous effects of future events

Select a recent natural disaster associated with tectonic activity to research as your case study. You will find it easier to find information you need for your case study than for earlier natural disasters.
Gather the required information by using an efficient technique such as:
- skimming and scanning for key words
- "find" facility of your computer application.
Present your case study effectively by:
- providing the audience with an introuction to the selected event, its time and location
- the appropriate use of subheadings in a written report.

Some sources of information about recent natural disasters:

The National Earthquake Information Center (NEIC) site, is a part of the US Geological Survey. The site provides information on global earthquake events and is a good site to search for information on specific earthquakes. The site includes Significant quakes of the world .

describe hazards associated with earthquakes, including ground motion, tsunamis and collapse of structures

Ground motion can cause built structures to collapse, can damage and displace vehicles, can cause water in harbours to be displaced, and can trigger other devastating events such as landslides and mudslides. People and other animals can be buried in crevasses.
Major earthquakes in the lithosphere below oceans can trigger tsunamis. Such earthquakes can change the level of the ocean floor by several metres and displace an enormous volume of water. The waves produced contain the energy of the earthquake as it lifts up to 14 kilometre of ocean above it. A wave generated has twice the wavelength of the diameter of the affected area and it travels very fast (800 km per hour). Upon reaching shallow water, the front of a tsunamis wave-set slows down while the back catches up to produce a massive wall of water. Tsunamis devastate low lying coastal areas. Houses and other structures are usually hit by a wall of water from the ocean and again as the water rushes back out to sea. Floating debris increases the impact on life and property.

Some information about the December 2004 Tsunami.

The Sumatran tsunami, Boxing day 2004 USGS Earthquake Hazards Program.

describe hazards associated with volcanoes, including poisonous gas emissions, ash flows, lahars and lava flows and examine the impact of these hazards on the environment, on people and other living things

One of the greatest hazards of volcanoes is the explosive eruption. At least 200 000 people have lost their lives as a result of explosive volcanic eruptions in the past 500 years. Well known examples of explosive eruptions are:
- Mt Pelée, Martinique, in which erupted in 1902, killing 30 000 people
- Mt St Helens, USA, which erupted in 1980 resulting in 57 dead or missing and $1.2 billion damage.
Poisonous gas emissions from volcanoes include carbon monoxide (CO), sulfur dioxide (SO₂), sulfur trioxide (SO₃), hydrogen sulfide (H₂S) hydrochloric acid (HCl), hydrofluoric acid (HF), sulfurous acid (H₂SO₃) and boric acid (H₃BO₃). Carbon dioxide (CO₂), although not poisonous, can asphyxiate by displacing air that contains oxygen. Most of these emissions are associated with eruptions. One specific example recently occurred in Lake Nyos, in Africa, where the crater-lake became saturated with carbon monoxide gas. A minor disturbance in the lake caused about one cubic kilometre of gas to be released, killing 1700 people in a nearby village and all livestock in surrounding areas.
Ash flows can kill because of heat and poisonous gas. In March and April 1982, El Chichon in Mexico erupted three times producing high velocity incandescent ash flows that levelled villages up to eight kilometres away. The number of deaths exceeded 500. In 79 AD, Mt Vesuvius buried the cities of Pompeii and Herculaneum so completely that they weren’t discovered again until 1700 years later.
Different types of lava flow at different speeds. Highly viscous lava tends to block volcanic vents and lead to explosive eruptions. High temperature, low viscosity lava flows freely and is often associated with hot spot volcanoes and sea floor rifts. These lavas do not usually endanger human life because there is time for evacuation. However all property in their path is destroyed by the lava. Lava flows regularly from Mt Etna in Italy and Kilauea in Hawaii. Villages are buried but people have enough time to escape the flow.
Lahars are mud and ash flows generated from the melting of an ice cap on a volcano or associated with release of water from a crater lake. Flows of volcanic debris can have the consistency of wet cement. They can sweep down the sides of a composite volcano burying everything in their path. Nevada del Ruiz Volcano, in Colombia, buried the city of Armero with a lahar, killing 25 000 people.
A nuée ardente is a highly mobile, turbulent gaseous cloud erupted from a volcano. It can be incandescent. The most infamous nuée ardente occurred when Mt Pelée erupted in 1902, killing 30 000 people.

describe and explain the impacts of shock waves (earthquakes) on natural and built environments

Shockwaves from earthquakes are of three main types:
1. P-waves are compression waves.
2. S-waves are transverse or shear waves.
3. L-waves are surface waves and can be transverse or elliptical. The elliptical waves are the slowest, but often the largest and most destructive, of the wave types caused by an earthquake.
The impact of shockwaves is related to their intensity.
Factors affecting intensity include the location of the focus, the triggering mechanism, the quantity of energy released and the nature of the local geology.

Earthquake intensity is measured using a relative scale, such as the modified Mercalli scale.

The magnitude of an earthquake is an absolute value and is related to the amount of strain energy released, as recorded by seismographs. Magnitude is measured on the Richter scale, a numerical scale that describes an earthquake independently of its effects on people or objects such as landforms or buildings.

The following table relates some of the Modified Mercalli scale of earthquake intensities to some well-known examples. The Richter scale values are provided for comparison.

Intensity (Mercalli)	Title	Effects on natural and built environments	Example (Richter magnitude)
II	Feeble	Suspended objects sway
IV	Moderate	Windows and dishes rattle	Port Jackson, 1788
	Rather strong	Dishes and windows broken	Lithgow, 1985 (4)
VI	Strong	Chimneys topple
VIII	Destructive	Weak structures severely damaged; strong structures slightly damaged
IX	Ruinous	Total destruction of weak structures. Foundations damaged. Underground pipes broken	Meckering, 1968 (5) Newcastle, 1989 (5.6)
X	Disastrous	Only best buildings survive. Ground badly cracked
XI	Very disastrous	Few masonry structures remain standing. Broad cracks in ground	Kobe, 1995 (7.2) Western India, 2001 (7.9)
XII	Catastrophic	Total destruction. Waves seen on the ground	Chile, 1960 (9.5)

describe the general physical, chemical and biotic characteristics of a volcanic region and explain why people would inhabit such regions of risk

Volcanic regions have extremely fertile soils. Volcanic rocks break down physically and chemically very quickly. Volcanic rocks weather readily producing soils rich in iron and magnesium . Soil formation can occur in as little as a few hundred years, but there are instances recorded of seeds germinating on erupted rock soon after cooling. Volcanic mountains often have very high altitudes resulting in favourable conditions for plentiful rainfall.
There is generally a great diversity of biota in volcanic regions. If adequate rainfall is available, natural vegetation and crops grow quickly and these can support a great variety of animal species.
Volcanic landscapes have aesthetic attraction for people. Mountains create beautiful scenery and symmetrical volcanic cones have been important to many cultural beliefs.
People are often willing to take the risk that eruptions will not occur in their lifetime. Many people who live in volcano and earthquake prone regions accept earthquake activity, like climate, as a condition of life.

justify continued research into reliable prediction of volcanic activity and earthquakes

Some possible arguments for continued research are:

There are large populations in many areas prone to volcanic activity and earthquakes. Given that prediction of impending volcanic eruptions and earthquakes are currently unreliable, people will not move until it is too late. Thus reliable early warning would save many lives and reduce losses due to poor preparation for a disaster.
Although research and the use of new technologies are expensive, the cost is small compared to the possible savings in lives, the provision of emergency services and loss of work, after a devastating event.
The use of new technologies, such as modern microcomputers, and remote sensing technologies, offer great potential for reliable methods of prediction to be developed in the near future.

Some alternative arguments:

Earthquakes are difficult or impossible to predict because of their inherent random behaviour. Efforts should be channelled into hazard mitigation.
Providing warnings can cause panic in a population, potentially causing more problems than if an earthquake or a volcanic eruption was not predicted.
The geological hazards of most regions are now known and the choice to live in a potentially hazardous area is an individual one. Education about ways to survive and cope with the effects of a natural disaster is more appropriate than continued research into prediction.