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CSIR-NET 2015 DEC

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87) A Seismic observatory closest to the epicentre of an earthquake recorded the travel times of PcP, ScS and PKiKP phases of the earthquake as 9.0, 15.5 and 16.5 minutes respectively. The travel time of the SKiKP phase would be

1. 17.5 minutes 


2. 23.0 minutes

3. 24.5 minutes 

4. 32.0 minutes



Solution:
P - a P-wave in the mantle
S – an S-wave in the mantle
c – a reflection from the mantle-outer core boundary
K - a P-wave through the outer core
PKiKP - a P-wave that travelled down through the mantle and outer core, was reflected at the outer-core-inner-core boundary and travelled back up through the outer core and mantle.
PcP = 9.0 minutes
ScS = 15.5 minutes
PKiKP = 16.5 minutes
ScS-PcP = 15.5-9.0 = 6.5 minutes
SKiKP = (ScS-PcP) + PKiKP = 6.5+16.5= 23.0 minutes



Reference: The Solid Earth , An Introduction to Global Geophysics by C.M.R.Fowler
CSIR-NET 2015 DEC

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5 comments

  1. Anupama Sharma12 November 2019 at 00:58

    Please solve question no. 87- csir net 2013 june paper.

    ReplyDelete
    Replies
    1. Anupama Sharma12 November 2019 at 01:03

      The following figure shows an E-W cross-section of a topography with a sudden rise in elevation by 1OOm at a location B, and which is otherwise even everywhere. Gravity observations were made at widely separated stations A, B, C and D .and also at E in a borehole at a depth of 1OOm below D. The topographic material has an average density d such that 2piGd=120 mgal/km, where G is the Newton's gravitational constant

      A) Compared to A, the gravimeter reading at B is
      (1) same as that of A
      (3) smaller by 6 mgals
      (2) smaller by 12 mgals
      ( 4) larger by 12 mgals .

      B) Compared to B, the gravimeter reading at C is smaller by
      (l) 31 mgals {2) 25 mgals (3) 19 mgals (4) 12mgals

      C). Compared to D, the gravimeter reading at E is
      ( l) smaller by 31 mgals
      {2) sma!ler by 17 mgals
      (3) smaller by 7 mgals
      (4) larger by 7 mgals

      Delete
  2. Shivjay Volvoikar8 February 2023 at 09:35

    Sir, i think the solution is wrong... Answer should be 19.75.
    Please do check and notify me whether I am right or wrong

    ReplyDelete
  3. guruchandigarh25 July 2023 at 10:34

    Guru Institute is theBest institute for CSIR NET Life Science Coaching in Chandigarh. We have a team of well-qualified Instructors who are not only trained assessors but also very well-qualified instructors.

    ReplyDelete

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