Prelims 5025

Consider the following statement about earthquakes:
1. Intensity of earthquake is measured on Mercalli Scale.
2. Earthquakes magnitude is the measurement of energy released.
3. Magnitude of earthquake is determined from the Amplitude of earthquake waves.
Which of the statement(s) given above is/are correct?
1 and 2
1 and 3
2 and 3
1, 2 and 3
Explanation :
Earthquakes can be measured in two ways: One method is based on magnitude—the amount of energy released at the earthquake source. The other is based on intensity—how much the ground shakes at a specific location.
The Mercalli intensity scale is a seismic intensity scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake.The Richter scale describes the earthquake’s magnitude by measuring the seismic waves that cause the earthquake. Today the moment magnitude scale, abbreviated MW, is preferred because it works over a wider range of earthquake sizes and is applicable globally. Moment magnitude estimates are about the same as Richter magnitudes for small to large earthquakes. But only the moment magnitude scale is capable of measuring M8 (read ‘magnitude 8’) and greater events accurately.
The magnitude of an earthquake is determined from the logarithm (base 10) of the amplitude of waves recorded by seismographs. What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times.