Earthquakes

MANAGEMENT

Our Active Earth
Over a period of time, stresses build beneath the Earth's surface.  From time to time, stress is released resulting in the sudden, and sometimes disastrous shaking we call an earthquake.  It could last seconds, or minutes and come in a series over several days. 

What Can Happen 
An earthquake is often announced by a loud noise like that of a train.  Initial earth movements and swaying of structures caused by the earthquake could be followed some time later (after hours or days) by after-shocks, usually of decreasing severity. 

Injuries and Structural Damage 
The actual movement of the ground in an earthquake is seldom the direct cause of death or injury.  Most casualties result from falling objects and debris because the shocks can shake,  damage or demolish buildings and other structures. Buildings do not automatically collapse in earthquakes. Some such as timber framed houses, may withstand shock very well. However, chimneys, parapets, ceiling plaster and light fixtures may fall.  There could be flying glass from broken windows.  Fallen power lines are another hazard, and could leave communities without power for days. 

Fire 
Fires may be caused by broken chimneys and gas lines or by chemical spills and the danger aggravated by broken water mains. 

Other Effects 
Earthquakes can also trigger landslides, ground displacement (faulting) subsidence and even huge ocean waves called tsunamis (seismic sea waves), each of which can cause great damage. 

Australian Earthquakes 
The historical record in Australia goes back only about 200 years.  The first reported earthquake was felt for about 3 seconds at Port Jackson, NSW in June, 1788.  In 1837 the first settlers in South Australia experienced an earthquake which lasted 20 seconds.  Similarly in the early histories of Hobart (1827), Melbourne (1841) and Perth (1849) were felt. 

Until Newcastle’s December 1989 event, the damage bill attributed to earthquakes in Australia, during the previous 200 years, had been comparatively 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.