﻿^ol' 
  53*] 
  GREAT 
  JAPANESE 
  EARTHQUAKE 
  OP 
  1891. 
  3 
  

  

  joining 
  the 
  centres 
  of 
  two 
  rectangles 
  in 
  the 
  proper 
  proportion. 
  

   Taking, 
  for 
  example, 
  the 
  curve 
  marked 
  5, 
  if 
  the 
  numbers 
  in 
  two 
  

   consecutive 
  rectangles 
  are 
  3 
  and 
  7, 
  the 
  curve 
  bisects 
  the 
  line 
  joining 
  

   their 
  centres; 
  if 
  the 
  numbers 
  are 
  1 
  and 
  6, 
  the 
  line 
  joining 
  the 
  

   centres 
  is 
  divided 
  into 
  five 
  equal 
  parts, 
  and 
  the 
  curve 
  passes 
  through 
  

   the 
  first 
  point 
  of 
  division 
  reckoned 
  from 
  the 
  centre 
  of 
  the 
  rectangle 
  

   in 
  which 
  six 
  epicentres 
  are 
  found. 
  

  

  4. 
  In 
  Prof. 
  Omori's 
  maps, 
  the 
  meaning 
  of 
  the 
  curves 
  is 
  obvious. 
  

   At 
  every 
  point 
  of 
  the 
  curve 
  marked 
  100, 
  for 
  instance, 
  one 
  hundred 
  

   shocks 
  were, 
  or 
  would 
  have 
  been, 
  felt 
  during 
  the 
  period 
  embraced 
  by 
  

   the 
  map. 
  

  

  The 
  meaning 
  of 
  the 
  curve 
  marked 
  100 
  in 
  the 
  accompanying 
  maps 
  

   (pp. 
  5, 
  6, 
  & 
  7) 
  is 
  as 
  follows 
  : 
  — 
  Let 
  any 
  point 
  in 
  the 
  curve 
  be 
  imagined 
  

   as 
  the 
  centre 
  of 
  a 
  rectangle 
  whose 
  sides 
  are 
  directed 
  north-south 
  and 
  

   east-west, 
  and 
  are 
  respectively 
  1 
  of 
  a 
  degree 
  of 
  latitude 
  and 
  longitude, 
  

   then 
  the 
  number 
  of 
  epicentres 
  within 
  this 
  rectangle 
  is 
  at 
  the 
  rate 
  

   of 
  100 
  for 
  the 
  time 
  considered. 
  

  

  If 
  all 
  of 
  the 
  Mino-Owari 
  after-shocks 
  had 
  been 
  exceedingly 
  weak, 
  

   so 
  that 
  each 
  was 
  felt 
  at 
  one 
  station 
  only, 
  that 
  place 
  might 
  be 
  

   regarded 
  as 
  the 
  centre 
  of 
  the 
  shock, 
  and 
  the 
  two 
  methods 
  would 
  be 
  

   the 
  same, 
  except 
  in 
  one 
  slight 
  detail. 
  Some 
  shocks, 
  however, 
  were 
  

   strong 
  or 
  violent, 
  1 
  and 
  must 
  have 
  been 
  felt 
  at 
  a 
  large 
  number 
  of 
  

   stations, 
  and 
  in 
  these 
  cases 
  Prof. 
  Omori's 
  method 
  of 
  counting 
  the 
  

   shock 
  at 
  each 
  station 
  is 
  equivalent 
  to 
  drawing 
  the 
  disturbed 
  area 
  of 
  

   that 
  shock. 
  Thus, 
  the 
  difference 
  in 
  principle 
  between 
  the 
  two 
  

   methods 
  is 
  nearly 
  the 
  same 
  as 
  that 
  between 
  Mallet's 
  map 
  of 
  the 
  

   world, 
  in 
  which 
  the 
  disturbed 
  areas 
  are 
  coloured, 
  and 
  Milne's 
  map 
  of 
  

   Japan, 
  in 
  which 
  the 
  epicentres 
  only 
  are 
  marked. 
  But, 
  as 
  a 
  matter 
  

   of 
  fact, 
  so 
  large 
  a 
  number 
  of 
  the 
  Mino-Owari 
  after-shocks 
  were 
  weak 
  

   or 
  feeble 
  that 
  the 
  two 
  series 
  of 
  maps 
  bear 
  a 
  certain 
  resemblance 
  one 
  

   to 
  another. 
  The 
  features 
  in 
  which 
  they 
  differ 
  are 
  due 
  mainly, 
  

   I 
  believe, 
  to 
  the 
  difference 
  in 
  principle 
  noticed 
  above 
  and 
  to 
  the 
  

   shorter 
  intervals 
  of 
  time 
  adopted 
  in 
  this 
  paper. 
  

  

  5. 
  It 
  is 
  important 
  to 
  point 
  out 
  a 
  source 
  of 
  possible 
  error 
  in 
  the 
  

   maps, 
  due, 
  however, 
  not 
  to 
  defects 
  in 
  the 
  method 
  so 
  much 
  as 
  to 
  

   the 
  approximate 
  character 
  of 
  the 
  available 
  data. 
  In 
  a 
  map 
  of 
  all 
  

   Japan 
  which 
  I 
  have 
  prepared, 
  the 
  number 
  of 
  rectangles 
  is 
  so 
  great, 
  

   and 
  their 
  size 
  is 
  so 
  small 
  compared 
  with 
  that 
  of 
  the 
  whole 
  country, 
  

   that 
  the 
  errors 
  may 
  he 
  neglected 
  except 
  in 
  minute 
  details. 
  But 
  in 
  

   the 
  present 
  case 
  the 
  number 
  of 
  rectangles 
  in 
  each 
  map 
  is 
  only 
  

   100, 
  and 
  the 
  number 
  to 
  which 
  the 
  epicentres 
  are 
  principally 
  

   confined 
  is 
  very 
  much 
  smaller, 
  and 
  therefore 
  the 
  errors 
  may 
  be 
  of 
  

   greater 
  consequence. 
  If 
  the 
  epicentres 
  are 
  connected 
  with 
  lines 
  of 
  

   fault, 
  it 
  is 
  unlikely 
  that 
  they 
  should 
  be 
  distributed 
  evenly 
  between 
  

   the 
  centres 
  of 
  adjacent 
  rectangles. 
  Thus, 
  some 
  error 
  is 
  un- 
  

   avoidably 
  introduced 
  into 
  the 
  curves 
  by 
  regarding 
  the 
  epicentres 
  as 
  

  

  1 
  ' 
  Of 
  the 
  3365 
  after-shocks 
  recorded 
  at 
  Gifu 
  during 
  the 
  first 
  two 
  years, 
  

   10 
  were 
  'violent,' 
  97 
  'strong,' 
  1808 
  'weak,' 
  and 
  1041 
  'feeble,' 
  while 
  in 
  the 
  

   remaining 
  409 
  only 
  sounds 
  were 
  heard 
  without 
  shocks.' 
  — 
  Oinori, 
  op. 
  jam 
  cit. 
  

   p. 
  113. 
  

  

  b2 
  

  

  