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  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  the 
  assumption 
  that 
  rock 
  expands 
  to 
  an 
  equal 
  degree 
  for 
  an 
  equal 
  

   increase 
  of 
  temperature 
  at 
  all 
  temperatures, 
  and 
  that, 
  if 
  allowance 
  is 
  

   made 
  for 
  the 
  increase 
  of 
  the 
  coefficient 
  of 
  expansion 
  with 
  an 
  increase 
  

   of 
  temperature, 
  this 
  estimate 
  must 
  be 
  raised 
  to 
  nearly 
  8 
  miles. 
  1 
  

  

  In 
  both 
  these 
  mathematical 
  investigations 
  a 
  number 
  of 
  assump- 
  

   tions 
  have 
  necessarily 
  to 
  be 
  made 
  which 
  either 
  do 
  not, 
  or 
  are 
  not 
  

   known 
  to, 
  accurately 
  represent 
  the 
  facts 
  of 
  nature, 
  so 
  that 
  neither 
  can 
  

   be 
  accepted 
  as 
  a 
  rigidly 
  accurate 
  estimate. 
  But, 
  after 
  making 
  

   allowance 
  for 
  all 
  these 
  sources 
  of 
  error, 
  it 
  is 
  evident 
  that 
  the 
  level 
  of 
  

   no 
  strain 
  lies 
  at 
  a 
  depth 
  of 
  only 
  a 
  few 
  miles 
  from 
  the 
  surface 
  ; 
  and 
  as 
  

   it 
  is 
  highly 
  improbable 
  that 
  in 
  the 
  depths 
  below 
  it 
  the 
  conditions 
  are 
  

   such 
  as 
  will 
  allow 
  of 
  the 
  production 
  of 
  an 
  earthquake, 
  we 
  may 
  take 
  it 
  

   that 
  all 
  estimates 
  of 
  the 
  depth 
  of 
  focus, 
  which 
  exceed 
  some 
  five 
  or 
  six 
  

   miles 
  must, 
  ipso 
  fact 
  o 
  t 
  be 
  regarded 
  with 
  suspicion. 
  

  

  In 
  the 
  case 
  of 
  the 
  earthquake 
  at 
  present 
  under 
  consideration 
  the 
  

   faults 
  described 
  in 
  Chapter 
  IX 
  show 
  that, 
  in 
  part 
  at 
  least, 
  the 
  focus 
  

   extended 
  right 
  up 
  to 
  the 
  surface, 
  and 
  the 
  presumption 
  is 
  that 
  the 
  

   great 
  thrust-plane, 
  which 
  may 
  be 
  looked 
  upon 
  as 
  the 
  principal 
  

   focus, 
  does 
  not 
  lie 
  at 
  a 
  very 
  great 
  depth. 
  A 
  similar 
  conclu- 
  

   sion 
  might 
  be 
  drawn 
  from 
  the 
  local 
  irregularities 
  of 
  the 
  permanent 
  

   displacements 
  of 
  level 
  and 
  position 
  which 
  have 
  been 
  detected 
  over 
  so 
  

   large 
  an 
  area, 
  and 
  it 
  is 
  probably 
  an 
  outside 
  estimate 
  if 
  we 
  suppose 
  

   the 
  principal 
  focus 
  to 
  have 
  been 
  as 
  much 
  as 
  5 
  miles 
  below 
  the 
  

   surface. 
  

  

  There 
  is 
  one 
  indication 
  which 
  points 
  to 
  a 
  great 
  depth 
  of 
  origin, 
  

   and 
  that 
  is 
  the 
  alleged 
  simultaneous 
  arrival 
  of 
  the 
  aftershocks 
  at 
  

   Shillong, 
  Sylhet 
  and 
  Gauhati, 
  as 
  described 
  in 
  Mr. 
  T. 
  D. 
  LaTouche's 
  

   report. 
  2 
  This 
  statement 
  was 
  so 
  striking 
  that 
  an 
  application 
  was 
  

   made 
  to 
  the 
  Telegraph 
  Department 
  to 
  have 
  the 
  observations 
  

   continued 
  and 
  extended. 
  They 
  were 
  carried 
  on 
  over 
  two 
  months, 
  

   but 
  unfortunately, 
  owing 
  to 
  a 
  failure 
  on 
  the 
  part 
  of 
  the 
  Telegraph 
  

   Masters 
  to 
  appreciate 
  the 
  real 
  object 
  of 
  the 
  observations, 
  have 
  only 
  

  

  1 
  Phil. 
  Mag, 
  5th 
  series, 
  XL1, 
  136 
  (1896). 
  

   * 
  Appendix 
  A. 
  

  

  ( 
  >78 
  ) 
  

  

  