﻿370 
  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  It 
  so 
  happens 
  that 
  the 
  chains 
  of 
  triangles 
  of 
  the 
  great 
  triangulation 
  are 
  

   singularly 
  favourably 
  situated 
  for 
  a 
  measurement 
  of 
  the 
  displacements 
  that 
  have 
  

   taken 
  place. 
  At 
  the 
  western 
  end 
  of 
  the 
  epi 
  focal 
  area 
  a 
  chain 
  of 
  triangles 
  along 
  the 
  

   90 
  meridian 
  skirts 
  the 
  edge 
  of 
  the 
  Garo 
  hills 
  and, 
  so 
  far 
  as 
  they 
  extend, 
  is 
  based 
  

   on 
  hill 
  stations. 
  On 
  the 
  92 
  meridian 
  another 
  chain 
  of 
  triangles, 
  that 
  which 
  

   was 
  partly 
  reobserved 
  in 
  1897-98, 
  runs 
  right 
  across 
  the 
  Khasi 
  hills. 
  At 
  right 
  

   angles 
  to 
  these 
  two, 
  a 
  chain 
  of 
  triangles 
  runs 
  up 
  the 
  Brahmaputra 
  valley, 
  and 
  in 
  the 
  

   stretch 
  between 
  the 
  two 
  meridional 
  chains, 
  the 
  stations 
  are 
  almost 
  all 
  situated 
  on 
  

   rocky 
  hills 
  rising 
  out 
  of 
  the 
  alluvium. 
  

  

  A 
  retriangulation 
  should 
  start 
  on 
  the 
  92 
  meridian, 
  in 
  the 
  country 
  south 
  of 
  

   the 
  Sylhet 
  valley. 
  Any 
  triangle 
  here, 
  whose 
  three 
  angles 
  are 
  all 
  based 
  on.hill 
  

   stations, 
  would 
  probably 
  be 
  found 
  to 
  be 
  undisturbed, 
  and 
  might 
  be 
  taken 
  as 
  a 
  

   starting 
  point. 
  Should 
  it 
  be 
  found 
  to 
  have 
  suffered 
  distortion, 
  which 
  is 
  highly 
  im- 
  

   probable, 
  the 
  observations 
  would 
  have 
  to 
  be 
  carried 
  backwards, 
  away 
  from 
  the 
  

   Khasi 
  hills, 
  till 
  an 
  undistorted 
  triangle 
  was 
  found, 
  any 
  of 
  whose 
  sides 
  might 
  

   safely 
  be 
  taken 
  as 
  an 
  initial 
  base. 
  

  

  Starting 
  from 
  this, 
  triangulation 
  should 
  be 
  carried 
  northward, 
  till 
  the 
  transverse 
  

   chain 
  of 
  triangles 
  in 
  the 
  Brahmaputra 
  valley 
  was 
  met. 
  Here 
  the 
  work 
  would 
  

   turn 
  westward 
  and 
  continue 
  down 
  the 
  Brahmaputra 
  valley 
  to 
  Dhubri, 
  and 
  in 
  this 
  

   part 
  the 
  greatest 
  displacements 
  are 
  to 
  be 
  looked 
  for. 
  From 
  Dhubri 
  the 
  triangles 
  

   of 
  the 
  series 
  on 
  the 
  90 
  meridian 
  should 
  be 
  reobserved 
  as 
  far 
  south 
  as 
  they 
  are 
  

   based 
  on 
  hill 
  stations. 
  

  

  To 
  complete 
  the 
  work 
  it 
  would 
  be 
  well 
  to 
  carry 
  a 
  chain 
  of 
  triangles 
  from 
  the 
  

   neighbourhood 
  of 
  Tura 
  to 
  that 
  of 
  Cherrapunji, 
  thus 
  linking 
  the 
  two 
  meridional 
  

   series 
  and 
  forming 
  a 
  quadrilateral 
  within 
  the 
  epifocal 
  area. 
  These 
  triangles 
  

   should 
  be 
  based 
  on 
  peaks 
  fixed 
  by 
  the 
  triangulation 
  of 
  the 
  topographical 
  survey, 
  a 
  

   triangulation 
  which 
  falls 
  far 
  short 
  of 
  that 
  of 
  the 
  great 
  trigonometrical 
  survey 
  in 
  

   rigour 
  and 
  accuracy, 
  but 
  being 
  connected 
  with 
  it 
  on 
  all 
  sides 
  the 
  maximum 
  error 
  

   would 
  fall 
  far 
  short 
  of 
  the 
  displacements 
  that 
  are 
  to 
  be 
  looked 
  for 
  in 
  this 
  tract. 
  

  

  The 
  only 
  previous 
  occasion 
  on 
  which 
  displacements 
  connected 
  with 
  an 
  earth- 
  

   quake 
  have 
  been 
  actually 
  measured 
  is, 
  so 
  far 
  as 
  I 
  know, 
  that 
  of 
  the 
  earthquake 
  

   of 
  17th 
  May 
  1892 
  in 
  Sumatra. 
  1 
  The 
  principal 
  triangulation 
  was 
  then 
  in 
  progress 
  

   and 
  after 
  the 
  earthquake 
  it 
  was 
  found 
  that 
  the 
  angles 
  observed 
  would 
  not 
  

   correspond 
  with 
  these 
  observed 
  before 
  the 
  earthquake. 
  Certain 
  of 
  the 
  triangles 
  

   were 
  reobserved 
  and 
  it 
  was 
  found 
  that 
  the 
  stations 
  had 
  been 
  displaced, 
  the 
  greatest 
  

   distance 
  between 
  those 
  which 
  had 
  undergone 
  measureable 
  displacement 
  being 
  

   about 
  53 
  kilometres 
  (33 
  miles). 
  Beyond 
  this 
  some 
  other 
  stations 
  were 
  found 
  to 
  

   have 
  been 
  displaced, 
  but 
  as 
  they 
  had 
  not 
  been 
  fully 
  fixed 
  before 
  the 
  earthquake 
  

   their 
  displacements 
  could 
  not 
  be 
  measured. 
  

  

  The 
  greatest 
  measured 
  displacement 
  was 
  i"23 
  metres 
  with 
  a 
  probable 
  error 
  of 
  

   •28m.; 
  we 
  may 
  consequently 
  say 
  that 
  the 
  maximum 
  displacement 
  could 
  not 
  have 
  

  

  1 
  J. 
  J. 
  A.Muller 
  De 
  Verplaatsing 
  Van 
  einigeTrianguIati-Pilaren 
  in 
  de 
  Residente 
  Tapanceli 
  

   (Sumatra) 
  tangevolge 
  van 
  de 
  aardbeving 
  van 
  17th 
  Mai 
  1892 
  : 
  Verhandl.JK. 
  Akad 
  v. 
  VVeten- 
  

   schappen 
  te 
  Amsterdam, 
  1 
  sect. 
  Ill, 
  No. 
  2(1895) 
  abstracted 
  in 
  Peterman's 
  Mittheilungen 
  

   1895, 
  pp. 
  97-98. 
  

  

  ( 
  37° 
  ) 
  

  

  