Where do Earthquakes Occur?
No part of Earth's surface is free from earthquakes, but some regions experience them more frequently. They are most common at tectonic plate boundaries where different plates meet. The largest events usually happen where two plates are colliding, or colliding and sliding past one another, particularly around the edge of the Pacific Plate, for example in New Zealand, Vanuatu, the Solomon Islands, Papua New Guinea, Japan and the Americas, and in Indonesia, where the Indo-Australian Plate collides with the Eurasian Plate. The depths of focus in these collision zones can range from 0-700km.
Large shallow earthquakes also happen where two plates are pulling apart with the creation of new oceanic crust along mid-ocean ridges and on the transform faults that intersect them.
Shallow intraplate earthquakes occur in the relatively stable interior of continents away from plate boundaries. They are less common and do not follow easily recognisable patterns. This type of earthquake generally originates at shallow depths.
Although Australia is not on the edge of a plate, the continent experiences earthquakes because the Indo-Australian plate is being pushed north and is colliding with the Eurasian, Philippine and Pacific plates. This causes the build up of mainly compressive stress in the interior of the Indo-Australian plate which is released during earthquakes.
Adelaide has the highest earthquake hazard of any Australian capital. It has experienced more medium-sized earthquakes in the past 50 years than any capital because South Australia is being slowly squeezed in an east-west direction by about 0.1mm/yr. Although earthquakes cannot be predicted accurately, measuring these changes and combining that information with Adelaide's earthquake history helps to develop an understanding of when the next big earthquake might happen.
Australia's largest recorded earthquake was in 1941 at Meeberrie in Western Australia with an estimated magnitude of 7.2 but it occurred in a remote, largely unpopulated area. A magnitude 6.8 earthquake at Meckering in 1968 caused extensive damage to buildings and was felt over most of southern Western Australia. Earthquakes of magnitude 4.0 or more are relatively common in Western Australia with one occurring approximately every five years in the Meckering region.