For example, an earthquake that shows 5 on the Richter scale is ten times stronger than an earthquake that shows 4 on the Richter scale. The modified Mercalli scale This measures the amount of damage caused by an earthquake, so where an earthquake rates on this scale is dependent on human factors, such as the strength of buildings and population density. The moment magnitude scale This scale is used by seismologists today to measure the total amount of energy released during an earthquake and is more accurate, particularly with larger earthquakes, than the Richter scale. The moment magnitude scale ( M W ) reflects the distance a fault is moved and the force required to move it. For media purposes, seismologists convert the recording on the M W to a Richter scale number, because that is the measurement most people are familiar with ( FIGURE3 ).
FIGURE3 Earthquake magnitude scale, from 1.0 to over 3.0
CASESTUDY What caused the 2015 Nepal earthquake?
On 25 April 2015, a 7.8-magnitude earthquake struck Nepal. The epicentre of this earthquake was quite shallow — only 15 kilometres below the Earth’s surface. It occurred approximately 80 kilometres to the north-west of Kathmandu, Nepal’s capital. At this location, the Indian Plate to the south is subducting under the Eurasian Plate to the north (see FIGURE2 ). This is occurring at a rate of approximately 45 millimetres per year and is causing the uplift of the Himalayas (see the case study in lesson 14.3). During the Nepal earthquake event, nearly 9000 people were killed and nearly 18 000 were injured. FIGURE4 shows that the earthquake released a large amount of energy and caused large slips of up to 4 metres of the Earth’s surface. The shaking from this earthquake was felt in China, India, Bhutan and much of western Bangladesh. On 12 May 2015, a huge aftershock with a magnitude of 7.3 occurred near the Chinese border with Nepal (between Kathmandu and Mount Everest). More than 160 people died and more than 2500 were injured as a result of this aftershock.
382 Jacaranda Humanities Alive 8 Victorian Curriculum Third Edition
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