Questions on Earth's Behavior

Question: What is epicenter of an earthquake? 

Answer: It is the point on the surface of the earth vertically above the place of origin (hypocentre) 
of an eartquake. This point is expressed by its geographical latitude and longitude. 

Question: What is Hypocentre or Focus of an earthquake? 

Answer: It is the point within the earth from where seismic waves orignate. Focal depth is the 
vertical distance between the hypocentre and epicentre. 

Question: What is Magnitude and intensity of an earthquake? 
Answer: Earthquakes are quantified either in terms of magnitude or intensity. The strength of an 
earthquake, or strain energy released by it is usually measured by a parameter called “Magnitude” determined from the instrumental (Seismograph) records. 
Intensity of an earthquake is a subjective measure of the force of an earthquake at a 
particular place as determined by its effects on persons, structures and earth materials. The intensity at a point, depends not only upon the strength of the earthquake (i.e. magnitude) but also upon the distance from the earthquake to the point and the local geology at that point. While the intensity decreases with the distance from the epicenter, magnitude for an earthquake remains the same, irrespective of where it is measured. 


 Question: What is Richter Scale?

Answer: The local magnitude is defined as the logarithm of the maximum amplitude measured in 
microns on a seismogram written by Wood-Anderson seismograph with free period of 0.8 second, 
magnification of 2,800, damping factor of 0.8 calculated to be at a distance of 100 kms. The relative size of events is calculated by comparison to a reference event of ML=0, using the formula, ML =log A - log Ao  where A is the maximum trace amplitude in micrometer recorded on a standard seismograph and Ao is a standard value which is a function of epicentral distance (Δ) in kilometers. 

Question: How will you classify the earthquakes? 
Answer: Earthquakes can be classified as below: 
Classification of earthquakes 

• Slight Magnitude upto 4.9 on the Richter Scale. 
• Moderate Magnitude 5.0 to 6.9 
• Great Magnitude 7.0 to 7.9 
• Very Great Magnitude 8.0 and more.  

Question: What are the causes of earthquakes? 

Answer: From the concept of plate tectonics, the Indian plate is moving in a north-north-east 
direction and colliding with Eurasian plate along the Himalayan mountain range. This collision is 
responsible for the formation of faults such as Main Boundary Thrust, Main Central Thrust, etc in and along the Himalaya. Almost all the major earthquakes in India and its adjoining region occur along these faults. In brief, earthquakes occur due to forces of geological origin along weak planes called, faults. The earthquakes occurring near plate boundaries such as Himalaya are known as interplate earthquakes. Apart from earthquakes from the Himalayan belt, there have been earthquakes of relatively lesser magnitude and lesser frequency in the Peninsular India also. Such earthquakes are known as intraplate earthquakes and are attributed to the stresses building up in this area on account of compressive forces arising out of north-northeastward movement of the Indian plate.  


Question: What is seismic hazard? 

Answer: Seismic hazard is a physical phenomenon, such as surface faulting, ground shaking, 
landslides, liquefaction, tectonic deformation, tsunamis, or seiches, that is associated with an 
earthquake and that may produce adverse effects on the normal activities of the people. 


Question: What is Vulnerability? 

Answer: Vulnerability is the degree of damage caused by various levels of loading. The 
vulnerability may be calculated in a probabilistic or deterministic way for a single structure or groups of structures. 


Question: Can you predict earthquakes? 
Answer: No scientific technique is available anywhere in the world so far to predict the 
occurrence of earthquakes with reasonable degree of accuracy with regard to space, time and 
magnitude.