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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
- IIT JAM
- Geology (GG)
Question below
2 Answer(s)
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Owishi Sarkar
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The answer should be A) no brittle material is present below 650 km. The other options are incorrect as Seismic waves from all depths do reach the Earth surface. Mantle is not completely liquid, it allows P and S waves to travel through it, the S waves only cannot travel through outer core which is completely liquid and the fourth option is also incorrect as instruments can record Seismic waves from deeper depths.
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Rahul kumar
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Answer (A) No brittle material is present deeper than that depth Earthquake is a term used to describe sudden slip on a fault. Earthquake occurs because of movement along fractures of brittle rocks in the upper parts of the Earth. In deeper part of the Earth (below 700km), earthquake can't occur in normal conditions because of unavailability of brittle rocks. Also, Option-C is wrong because S wave can propagate from partially melted mantle. S wave can't travel from liquid core. Seismic waves travelling deeper can be easily recorded by high accuracy seismograms.
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Saurabh 1
Correct answer has to be (A) . As it was seen and observed deeply that no earthquake has been observed below 650km. At such depths rocks do not undergo brittle deformation (no breaking or faulting) , as it is already known at these depths rock would be in high pressure and temperature, thereby leading to deformation by flowing(plastic deformation you can say), other options are not that much pronounced for explaining this fact of unavailability of earthquakes deeper than 650km. Always remember brittle regimes are the most important factor for the earthquakes to develop. Deep focus earthquakes aren't that catastrophic (which can lead to minimal damage) and have less attenuation of body waves.