﻿THE 
  SEISMIC 
  FOCUS. 
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  These 
  indications 
  of 
  a 
  northern 
  extension 
  of 
  the 
  thrust-plane 
  are 
  

   further 
  supported 
  by 
  the 
  very 
  large 
  number 
  of 
  secondary 
  earthquakes 
  

   recorded 
  at 
  Borpeta 
  and 
  Bijni, 
  which 
  point 
  loan 
  extension 
  of 
  the 
  

   focus 
  in 
  that 
  direction. 
  We 
  may, 
  accordingly 
  place 
  the 
  northern 
  

   limit 
  to 
  the 
  north 
  of 
  Borpeta 
  with 
  some 
  degree 
  of 
  certainty. 
  Further 
  

   east 
  the 
  observations 
  of 
  the 
  Great 
  Trigonometrical 
  Survey 
  show 
  that 
  

   Shillong 
  lay 
  within 
  the 
  limit 
  of 
  the 
  area 
  over 
  which 
  permanent 
  

   displacement 
  has 
  been 
  observed, 
  which 
  may 
  be 
  taken 
  to 
  practically 
  

   coincide 
  with 
  the 
  epicentre. 
  It 
  is 
  not 
  impossible 
  that 
  this 
  may 
  have 
  

   extended 
  as 
  far 
  north 
  as 
  Gauhati, 
  which 
  was 
  certainly 
  not 
  far 
  beyond 
  

   the 
  limits 
  ; 
  but 
  however 
  this 
  may 
  be, 
  the 
  area 
  over 
  which 
  displacement 
  

   has 
  taken 
  place 
  broadens 
  rapidly 
  a 
  short 
  way 
  to 
  the 
  west 
  of 
  Shillong 
  

   and, 
  as 
  shown 
  in 
  Chapter 
  IX, 
  Bordwar, 
  at 
  the 
  northern 
  foot 
  of 
  the 
  

   hills, 
  is 
  within 
  the 
  epicentral 
  area. 
  Between 
  here 
  and 
  Borpeta 
  we 
  

   have 
  no 
  certain 
  indications 
  of 
  its 
  boundary, 
  and 
  to 
  the 
  west 
  of 
  

   Borpeta 
  the 
  indications 
  are 
  even 
  more 
  imperfect. 
  

  

  It 
  is 
  evident, 
  however, 
  from 
  the 
  observations 
  in 
  the 
  Garo 
  Hills, 
  

   that 
  the 
  zone 
  of 
  maximum 
  permanent 
  change 
  lies 
  just 
  west 
  of 
  the 
  

   91 
  meridian, 
  and 
  it 
  is 
  reasonable 
  to 
  suppose 
  that 
  the 
  zone 
  of 
  

   maximum 
  displacement 
  would 
  correspond 
  to 
  the 
  greatest 
  width 
  of 
  

   the 
  area 
  of 
  displacement, 
  that 
  is 
  of 
  the 
  epicentre. 
  Assuming, 
  for 
  the 
  

   moment, 
  that 
  the 
  displacement 
  was 
  mainly 
  in 
  a 
  north 
  and 
  south 
  

   direction, 
  we 
  should 
  expect 
  the 
  northern 
  boundary 
  to 
  trend 
  south 
  

   and 
  west 
  from 
  about 
  91 
  E. 
  longitude, 
  in 
  a 
  manner 
  corresponding 
  

   to 
  its 
  southerly 
  and 
  easterly 
  trend 
  to 
  the 
  east 
  of 
  that 
  line, 
  while, 
  to 
  

   judge 
  from 
  the 
  accounts 
  of 
  the 
  effects 
  of 
  the 
  shocks 
  in 
  the 
  Borpeta 
  

   subdivision 
  and 
  in 
  the 
  Bhutan 
  hills, 
  it 
  would 
  seem 
  that 
  the 
  northern 
  

   limit 
  of 
  the 
  epicentre 
  must 
  have 
  reached 
  nearly 
  to 
  the 
  foot 
  of 
  the 
  

   Himlayas, 
  even 
  if 
  it 
  did 
  not 
  run 
  still 
  further 
  north, 
  on 
  this 
  meridian. 
  

  

  Turning 
  now 
  to 
  the 
  southern 
  boundary. 
  This 
  may 
  be 
  approximate- 
  

   ly 
  fixed 
  with 
  some 
  approach 
  to 
  accuracy, 
  though 
  we 
  have 
  no 
  direct 
  

   evidence. 
  

  

  In 
  the 
  first 
  place, 
  it 
  is 
  reasonable 
  to 
  suppose 
  that 
  this 
  earthquake 
  

   was 
  directly 
  connected 
  with 
  the 
  tectonic 
  processes 
  to 
  which 
  the 
  

  

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