Context:
A devastating 7.1 Scale earthquake hits China’s remote area of Tibet, 75km from Everest region. It resulted in killing of at least 126 people.
Earthquake and Causes
- Earthquakes are natural occurrences due to the unleashing of energy, which radiates seismic waves in all directions.
- Epicentre
- The point on the earth’s surface where the effects of a sudden movement (earthquake) are felt most strongly
- Fault Zones:
- Energy is released along a sharp break in the crustal rocks, thus causing the blocks to move apart and slide past each other.
- Tectonic Earthquakes:
- The most common type of earthquake, these tectonic earthquakes occur because tectonic plates are in constant motion. This causes tension on Earth’s crust.
- Volcanic Earthquakes:
- These are caused by stress changes in solid rock due to the injection or withdrawal of magma, which causes land to subside and produces large ground cracks.
- Human Induced Earthquakes:
- These can occur in areas of intense mining activity, ground shaking may occur due to the explosion of chemical or nuclear devices, or in areas of large reservoirs.
- India
- India has been divided into four seismic zones (II, III, IV, and V) based on scientific inputs relating to seismicity, earthquakes occurred in the past and tectonic setup of the region.
- Distribution of Earthquakes
- Earthquakes can hit any place anytime but repeat in the same general patterns every year.
- The circum-Pacific seismic belt, the Alpide earthquake belt, and the mid-Atlantic Ridge are the three large zones of the earth.
- Measurement of Earthquakes
- The energy from an earthquake travels through Earth in vibrations called seismic waves.
- Seismometers
- Seismometers detect seismic waves below the instrument and record them as a series of zig-zags.
- The earthquake events are scaled either according to the magnitude or intensity of the shock.
- Seismic Waves
- Earthquake waves are the waves of energy caused by earthquakes or an explosion.
- They are divided into body waves (P-waves) and surface waves (S-waves).
- Effects of Earthquake
- Earthquakes are a natural hazard, causing heavy damage to life and property.
- Direct hazardous effects include ground shaking, differential ground settlement, land and mudslides, fires, ground lurching, avalanches, ground displacement, floods from dam and levee failures, structural collapse, and tsunamis.
