3.1.4.4. Measuring Earthquakes

The earthquake events are scaled either according to the magnitude or intensity of the shock. The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the quake. The magnitude is expressed in numbers, 0-10. The intensity scale is named after Mercalli, an Italian seismologist. The intensity scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.

Earthquakes are measured using two main types of scales: magnitude and intensity. The Richter scale measures the energy released during an earthquake, using a numerical scale from 0 to 10, where higher numbers indicate stronger earthquakes. The intensity scale, developed by Mercalli, focuses on the observable damage that results from the earthquake, ranging from 1 (not felt) to 12 (total destruction). While magnitude provides a numeric value of the earthquake's strength, intensity measures the effects experienced on the surface.

Think of magnitude as the volume of music from a speaker. The louder the music, the higher the number on the volume scale (like Richter scale). Intensity, on the other hand, is like the number of people dancing around you after that music starts. A massive concert might have high volume (high magnitude), but whether people are dancing vigorously or just tapping their feet varies — that’s the intensity.

Earthquake is a natural hazard. The following are the immediate hazardous effects of earthquake: (i) Ground Shaking (ii) Differential ground settlement (iii) Land and mud slides (iv) Soil liquefaction (v) Ground lurching (vi) Avalanches (vii) Ground displacement (viii) Floods from dam and levee failures (ix) Fires (x) Structural collapse (xi) Falling objects (xii) Tsunami.

Earthquakes can lead to various hazardous effects immediately after they occur. Ground shaking is the most obvious effect, which can cause buildings and infrastructure to sway or collapse. Differential ground settlement occurs when the ground beneath structures settles unevenly, which can exacerbate damage. Mudslides and land sliding may happen, especially in hilly areas, leading to further destruction. Soil liquefaction can turn solid ground into a fluid state, affecting the stability of buildings. Other possible effects include flooding from dam failures, fires igniting from ruptured gas lines, and even tsunamis if the earthquake's epicenter is under the ocean.

Imagine a jenga tower. When you pull out blocks (like during an earthquake), some lower blocks might settle unevenly when the ‘tower’ shakes, causing a collapse — that’s similar to ground shaking and differential settlement in buildings during an earthquake. Just like a domino effect, one fallen block can lead to others falling, similar to how one hazard can lead to another during an earthquake.

The earthquake is a natural hazard. If a tremor of high magnitude takes place, it can cause heavy damage to the life and property of people. However, not all the parts of the globe necessarily experience major shocks. We shall be discussing the distribution of earthquakes and volcanoes with some details in the next chapter. Note that the quakes of high magnitude, i.e. 8+ are quite rare; they occur once in 1-2 years whereas those of ‘tiny’ types occur almost every minute.

Earthquakes happen frequently around the world, but the impact varies significantly based on location and magnitude. High-magnitude earthquakes ( rating 8 and above) are extremely rare and typically occur once in a couple of years. In contrast, minor earthquakes can happen almost every minute globally, but they usually go unnoticed due to their low intensity. The distribution of earthquake activity isn't uniform; some regions are more prone to significant tremors depending on geological factors.

Consider an old clock in your house; it ticks quietly most of the time, representing the small earthquakes. But occasionally, the clock strikes the hour loudly (a major earthquake), affecting only those nearby. Just like the clock's quiet ticking — invisible to most — little tremors occur constantly without everyone being aware of them, but when it strikes, it grabs attention.

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