Which statement describes the Mercalli scale?
A. This scale measures seismic waves based on their size. B. This scale rates an earthquake according to how much damage it causes. C. This scale produces a single rating for earthquakes that reach the surface. D. This scale measures the magnitude of an earthquake based on the size of seismic waves.
The Correct Answer and Explanation is :
The correct answer is B. This scale rates an earthquake according to how much damage it causes.
The Mercalli scale is a qualitative scale used to assess the intensity of an earthquake based on its observed effects on people, buildings, and the Earth’s surface. Unlike quantitative scales, such as the Richter or moment magnitude scales, which measure the energy released at the earthquake’s source, the Mercalli scale focuses on the impact of the earthquake on communities and structures.
Developed by Italian seismologist Giuseppe Mercalli in 1902, the scale ranges from I (not felt) to XII (total destruction). Each level describes specific effects, such as the degree of shaking felt, the damage inflicted on structures, and the reactions of people. For example, at intensity level III, people may feel a light tremor, while at level VIII, significant structural damage occurs, with walls cracking and some buildings collapsing.
The scale is particularly valuable for historical earthquakes for which no instrumental data are available, as it relies on eyewitness accounts and physical damage to estimate the earthquake’s intensity. This makes it an essential tool for assessing the effects of seismic activity on communities, guiding emergency response efforts and recovery strategies.
In contrast to the Mercalli scale, the Richter and moment magnitude scales provide a more objective measurement of an earthquake’s size based on seismic wave data. These scales are crucial for understanding the energy released during an earthquake but do not directly convey the human experience or structural damage caused by the event. Thus, while the Mercalli scale may not measure the magnitude or energy of an earthquake, it plays a vital role in understanding its societal impact.