Variability -
Earthquakes are unpredictable and strike without warning.
They range in strength from slight tremors to great shocks lasting from a few
seconds to as long as five minutes. They
could come in a series over a period of several days. A booklet for Students and the Community
Chapter 8
Earthquake Hazards and Disasters
WHAT ARE EARTHQUAKES?
Earthquakes are a shaking or trembling of the Earth’s crust caused by the release of huge stresses due to underground volcanic forces, the breaking of rock beneath the surface, or by sudden movement along an existing fault line. The latter type result from constant gradual movement of the tectonic plates that make up Earth’s crust which causes stress to build up in its rock layers. Small earthquakes sometimes result from human activity (eg filling of large reservoirs).
CHARACTERISTICS AND MEASUREMENT
Variability -
Earthquakes are unpredictable and strike without warning.
They range in strength from slight tremors to great shocks lasting from a few
seconds to as long as five minutes. They
could come in a series over a period of several days.
Magnitude - Energy released by (or magnitude of) an earthquake is expressed on a recording device called a seismograph, using the Richter Scale. This Scale is open-ended, as there is no upper limit to the amount of energy an earthquake might release. The most severe earthquakes so far, have not exceeded 9.5 on this Scale. It is not a simple arithmetic scale; for instance, a magnitude 7.0 creates 10 times the ground motion of a magnitude 6.0 earthquake and the total energy release is about 30 times greater. This in turn is 30 times greater than a 5.0 and so on.
Intensity - Another scale used to describe earthquakes is the Modified Mercalli (MM). It rates the amount of shaking felt and damage caused, (or intensity) and uses Roman numerals. On this Scale, I = a barely detectable tremor, and XII = total damage. Some examples appear below.
CAUSES OF INJURY AND DAMAGE
Most earthquake casualties result from falling objects or debris because shocks may damage or demolish buildings and other structures. Electricity and telephone lines, gas, sewer and water mains can be damaged; landslides, ground displacement (faulting), subsidence and even tsunamis (huge seismic sea waves) may be caused, leaving many people dead, injured or homeless (see Chapter 9).
AUSTRALIAN EARTHQUAKES
Geology
Because of Australia’s geological position, we are prone to what seismologists call ‘intra-plate’ earthquakes. These are different and poorly-understood in comparison with the more familiar ‘plate-margin’ type, common in areas like California, USA and Japan (see photos).
History
The historical record in Australia goes back only about 210 years. The first reported earthquake lasted about three seconds at Port Jackson, NSW in June, 1788. In 1837, early settlers in South Australia experienced an earthquake for 20 seconds. Similarly, in the early histories of Hobart (1827), Melbourne (1841) and Perth (1849) earthquakes were felt. The first recorded deaths (although indirect) occurred in 1902 at Warooka, SA, when two people died of shock after a Richter magnitude 6.0 earthquake, and in 1917 one miner died and 5 were injured in an underground rockfall triggered by an earthquake at Kalgoorlie, WA.
In the last 80 years there have been 17 earthquakes in Australia registering 6 or more on the Richter Scale. This is a rate of about one every five years, compared to a world average of about 140 per year. Although the larger Australian earthquakes have caused significant damage, they are, on the whole, of much smaller strength than the world’s most-damaging shocks.
Until Newcastle’s December 1989 event, the damage bill
attributed to earthquakes in Australia, during the previous 200 years, had been
comparatively low (see damage table).
Hazard Zones
The geographically-oldest western and central parts of Australia, are most seismically-active. Compared with many other countries in our region, earthquake activity in Australia is low. Our most severe earthquakes usually occur in unpopulated regions but several have caused damage in built-up areas, mainly in Western Australia, South Australia and New South Wales, although all state/territories have experienced them.
Depending on where you live, there is a chance that your area could
be hit by an earthquake. You will see from
the Hazard Map which areas are most vulnerable. If
you live in a risk area, you will need to know what to expect and what to do if an
earthquake occurs
(see page 29).
AUSTRALIAN EARTHQUAKES - CASE STUDIES
1.
Adelaide, SA, 1 March 1954
Adelaide was awakened by a loud rumbling sound. This was followed by shaking, severe enough to crack walls and loosen plaster and chimneys from many houses and other buildings. Although minor compared to many overseas, the Adelaide earthquake was (at magnitude 5.4) severe enough to cause damage estimated at $350 million (1997 values). No serious injuries were reported.
2.
Meckering, WA, October 1968
One of the more serious Australian earthquakes in fairly recent years occurred at the small town of Meckering. Residents reported seeing ground waves as well as experiencing steering difficulty when driving as the 6.9 Richter magnitude earthquake struck. Old buildings collapsed, railway lines were buckled and pipelines fractured, and a 37 km long fault scarp (up to 2.5 metres high) was caused. Although 16 injuries were reported, none were really serious. Total damage estimates reached $50 million.
3.
Tennant Creek, NT, 22 January 1988
Significant earthquakes of magnitudes 6.3, 6.4 and 6.8 occurred near Tennant Creek, NT. These resulted in large, long ground ruptures and a 35 km fault (up to 2 metre displacement) which warped underground gas pipelines, but caused only minor damage to the hospital and some homes in the town.
4.
Newcastle, NSW, 28 December 1989
At 10.27am, Newcastle, Australia’s sixth largest city, was partially devastated by a moderate earthquake measuring 5.6 on the Richter Scale. The Newcastle earthquake, the first really lethal one in Australia, claimed 13 lives. The devastation to buildings and other structures was extensive which was unusual for a relatively-small magnitude earthquake. This was due mainly to an underlying, thin layer of alluvium which appeared to magnify ground motion (shaking). The epicentre was located 15km WSW of the city centre, near Boolaroo.
End of a Myth - Despite Australia’s seemingly low-risk situation in the middle of one of Earth’s larger tectonic plates, we have been subject to many earthquakes larger than that of Newcastle. The Australian Geological Survey Organisation in Canberra estimates that on average, the Australian region experiences an earthquake of at least this size, or larger, every 13-15 months. Most of these, however, have been in areas of low population density (eg Tennant Creek, NT). For many years a view was held by most Australians that we could not be subjected to this form of natural disaster. The Newcastle experience dispelled this myth!
Deaths, Injuries and Damage - There were 13 deaths and
150 injuries, very few considering 35,000 homes and 3,000 other buildings were moderately
to seriously damaged in Newcastle, and a total of 70,000 buildings in the region suffered
some sort of damage. Older buildings suffered the most.
At the Kent Hotel in Beaumont Street, Hamilton, three fatalities occurred. Another nine resulted from partial collapse of the Newcastle Workers Club, the inner
city’s largest. Three floors collapsed
during the earthquake, trapping many people. The
timing, however, mid-morning in the Christmas holidays, may have saved many more. A pop concert, which could have attracted up to
2,000 people, was scheduled for that night in the Club.
Over 100,000 students and teachers attend educational institutions in the Hunter
Valley. There were 147 schools damaged in
some way in the Hunter region. Of these, 42
suffered structural damage and were deemed unfit for occupation. If this event had struck during school-term,
deaths and injuries could have been many times worse.
Damage Cost - Insured losses reached $1,124 million
and estimated total damage to Newcastle was $4,480 million (1997 values). One simple example of the scale of damage is that
the replacement cost of cracked footpaths alone was estimated at over $30 million!
Lessons - Newcastle revealed that a lethal earthquake
can occur in a part of Australia traditionally considered of low seismic risk and that
built-up areas on alluvial soils face greatest risk of damage. This is resulting in improved building codes and
practices, and closer monitoring of seismic activity.
Since 1994, all buildings in Australia (including homes) are required to be
constructed to resist earthquakes. A loading code published by Standards Australia
assists their safer design and construction. To
gain a more detailed understanding of geological conditions beneath our population centres
and their vulnerability to earthquake damage, a series of microzonation studies has been
completed for most major cities considered to be at risk.
5. Ellalong, NSW, August 1994
A damaging earthquake again affected the Hunter region of NSW, this time in the Ellalong-Cessnock area. Measuring 5.4 on the Richter Scale, it became our third most-damaging. Several homes, hotels and other buildings suffered seriously and up to 1,000 homes were partly damaged. Infrastructure, com-mercial and industrial losses also occurred. Insurance payouts were $38 million and total damage costs exceeded $150 million (1997 values).
EARTHQUAKE SURVIVAL AND DAMAGE REDUCTION
Know Your Local Earthquake Risk - Ask your State or Territory Emergency Service (S/TES), council and insurance company for this information:
Whether tremors or earthquakes have occurred in your area and what
damage resulted.
Ask your S/TES for a free pamphlet or poster showing Australia’s earthquake hazard zones.
Even if you’re in a slight-risk zone, ask your council how to make your house safer.
Check that your insurance covers earthquake damage.
Emergency Kit and Plan - Needed for during and after an earthquake:
Have candles, matches, a torch and a portable radio with fresh batteries.
Have containers of fresh water, a first aid kit and basic first aid knowledge.
Know safe areas to shelter, and danger areas to avoid (see below).
Plan with family how and where to meet if separated. List emergency contact numbers.
Watch for Possible Warning Signs
Erratic Animal Behaviour - Watch for frightened or confused pets running around, or a bird-call not usually heard at night.
Ground-Water Levels - Watch for sudden changes of water level in wells or artesian bores.
During the Earthquake
If indoors stay there. There could be falling debris outside.
Take cover under an internal door frame, sturdy table, bench or bed.
Keep away from windows, mirrors, chimneys, overhead fittings and tall furniture.
In high-rise buildings, stay clear of windows and outer walls. Get under a desk near a pillar or internal wall. Do not use elevators.
In crowded areas, do not rush for doors. Stay clear of roof and wall fittings.
If outside, keep well clear of buildings, walls, power lines, trees, etc.
In a city street, with tall buildings, shelter from falling debris under strong archways or doorways of buildings. Don’t stand under awnings or parapets as they may collapse.
If in a vehicle, stop in the open until shaking stops. Beware of ‘downed’ powerlines and damage to roads, overpasses or bridges. Listen to radio for warnings before moving.
After the Earthquake - Tend injuries and watch for hazards as follows:
Check for injuries. Apply first aid. Do not move the seriously injured unless in danger.
Do not use telephone (avoid congestion) unless there is a serious injury or fire.
Turn off electricity, gas and water. Check for gas/fuel leaks before lighting matches.
Check for water or sewerage leaks, broken electrical wiring etc.
Check for cracks and damage, including roof, chimneys and foundation.
Be prepared for aftershocks. Evacuate if house is badly damaged.
Do not waste food and water as supplies may be interrupted. Collect emergency water from heaters, ice cubes, toilet tanks and canned foods.
Listen to local radio and heed warnings and advice on damage and service disruptions.
Avoid driving unless for emergency (keep streets clear for emergency vehicles).
Do not go sight-seeing or enter damaged buildings. Stay calm and help others if possible.
What Are Your Chances of Survival?
You can survive an earthquake and minimise its damage by being aware of, and prepared for, potential hazards. An earthquake will be over before you can do much about it. Most people are killed or injured as they attempt to move prematurely during the earthquake and are struck by falling or flying objects. Your chances of avoiding serious injury are high if you remain calm and take cover as recommended above. Follow this advice and by being well-prepared, you could be a potential resource for your community, not a potential casualty requiring help.
FIND FURTHER INFORMATION
1. As an earthquake project, find out about:
earthquake waves, and seismographs;
the San Andreas Fault, and the San Francisco earthquake, 1906;
the earthquake in Armenia, 1988 or the Kobe, Japan earthquake, 1995; and
compare the Newcastle earthquake, 1989, with major overseas ones in Annex A.
2. Refer to a geological map to discover on what rock/soil type your house/school/workplace is built? How might this affect the building’s chance of withstanding an earthquake?
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EMERGENCY MANAGEMENT AUSTRALIA, PO
Box 1020 Dickson, Australian Capital Territory 2602, AUSTRALIA Telephone: + 61 (0) 2 6266 5402 Facsimile: +61 (0) 2 6266 5029 Email: ema@ema.gov.au AUSTRALIAN EMERGENCY MANAGEMENT INSTITUTE,
Mount Macedon Road, Mount Macedon, Victoria 3441, AUSTRALIA |
| This page was last updated May 31, 2001 |
