﻿^°1- 
  53«] 
  0F 
  ATJGIJST 
  1 
  ^9 
  2 
  a:n 
  " 
  d 
  November 
  1893. 
  167 
  

  

  Nature 
  of 
  the 
  Shock 
  and 
  Sound. 
  — 
  Detailed 
  accounts 
  of 
  this 
  earth- 
  

   quake 
  are 
  rather 
  rare, 
  but 
  they 
  all 
  agree 
  in 
  representing 
  it 
  as 
  much 
  

   simpler 
  in 
  character 
  than 
  the 
  principal 
  earthquake. 
  The 
  following 
  

   may 
  be 
  given 
  as 
  examples 
  : 
  — 
  

  

  Tenby 
  : 
  tremulous 
  motion 
  for 
  a 
  few 
  seconds, 
  ending 
  in 
  a 
  sharp 
  

   shake 
  ; 
  a 
  low 
  rumbling 
  sound, 
  becoming 
  gradually 
  louder 
  until 
  the 
  

   shake 
  occurred, 
  and 
  then 
  suddenly 
  ceasing. 
  

  

  Maenclochog 
  : 
  a 
  thud 
  accompanied 
  by 
  a 
  little 
  swaying 
  motion 
  of 
  

   the 
  ground 
  and 
  tremulous 
  motion. 
  

  

  At 
  most 
  of 
  the 
  places, 
  however, 
  the 
  tremulous 
  motion 
  and 
  low 
  

   rumbling 
  sound 
  were 
  not 
  observed 
  ; 
  the 
  shock 
  is 
  described 
  simply 
  

   as 
  a 
  jolt 
  or 
  thud 
  ; 
  the 
  sound 
  as 
  a 
  cannon 
  boom, 
  beginning 
  and 
  

   ending 
  abruptly, 
  and 
  coinciding 
  with 
  the 
  shock. 
  

  

  The 
  shock 
  was 
  felt 
  on 
  the 
  river 
  opposite 
  Langwm, 
  and 
  was 
  

   accompanied 
  by 
  a 
  wave, 
  but 
  not 
  nearly 
  so 
  marked 
  as 
  those 
  seen 
  at 
  

   the 
  time 
  of 
  the 
  principal 
  shock. 
  

  

  g. 
  August 
  18th 
  : 
  2.50 
  a.m. 
  

  

  Intensity 
  3. 
  — 
  Number 
  of 
  records, 
  69 
  ; 
  from 
  67 
  different 
  places. 
  

  

  The 
  disturbed 
  area 
  includes 
  the 
  whole 
  of 
  Pembrokeshire, 
  most 
  

   of 
  Caermarthenshire, 
  and 
  parts 
  of 
  the 
  counties 
  of 
  Caerdigan 
  and 
  

   Glamorgan 
  ; 
  in 
  all, 
  a 
  land-area 
  of 
  about 
  1680 
  square 
  miles. 
  The 
  

   boundary 
  of 
  the 
  area, 
  so 
  far 
  as 
  it 
  can 
  be 
  traced, 
  is 
  shown 
  by 
  a 
  dotted 
  

   and 
  broken 
  line 
  on 
  the 
  map 
  of 
  the 
  principal 
  earthquake 
  (PI. 
  XI). 
  

   Its 
  position 
  can 
  be 
  regarded 
  as 
  only 
  approximately 
  correct, 
  on 
  account 
  

   of 
  the 
  small 
  number 
  of 
  observations 
  made 
  at 
  a 
  distance 
  from 
  the 
  epi- 
  

   centre. 
  The 
  centre 
  of 
  the 
  area 
  obviously 
  lies 
  under 
  land, 
  and 
  some 
  

   miles 
  farther 
  north 
  than 
  that 
  of 
  the 
  principal 
  earthquake. 
  

  

  The 
  shock 
  is 
  everywhere 
  described 
  as 
  a 
  slight, 
  tremulous 
  motion. 
  

  

  The 
  accompanying 
  sound 
  was 
  heard 
  at 
  only 
  17 
  places, 
  and 
  is 
  

   always 
  described 
  as 
  a 
  distant, 
  faint 
  sound, 
  or 
  compared 
  to 
  very 
  

   distant 
  thunder. 
  At 
  39 
  other 
  places 
  it 
  is 
  expressly 
  stated 
  that 
  no 
  

   sound 
  was 
  heard. 
  

  

  The 
  sound-area 
  is 
  elliptical 
  inform, 
  16 
  miles 
  long, 
  13 
  miles 
  broad, 
  

   and 
  containing 
  about 
  175 
  square 
  miles. 
  The 
  centre 
  coincides 
  

   almost 
  exactly 
  with 
  the 
  town 
  of 
  Haverfordwest. 
  It 
  will 
  be 
  

   observed 
  that 
  the 
  axis 
  of 
  the 
  sound-area 
  is 
  situated 
  3| 
  miles 
  

   west 
  of 
  that 
  of 
  the 
  isoseismal 
  7 
  of 
  the 
  principal 
  earthquake, 
  to 
  which 
  

   it 
  is 
  nearly 
  parallel, 
  and 
  6 
  miles 
  west 
  of 
  that 
  of 
  the 
  preliminary 
  

   earth-sound 
  b. 
  (See 
  map, 
  p. 
  158.) 
  

  

  h. 
  August 
  18th 
  : 
  about 
  4 
  a.m. 
  

  

  Intensity, 
  2 
  or 
  3. 
  — 
  Number 
  of 
  records, 
  10 
  ; 
  from 
  10 
  different 
  

   places. 
  

  

  Part 
  of 
  the 
  boundary 
  of 
  the 
  disturbed 
  area 
  is 
  shown 
  in 
  the 
  map, 
  

   p. 
  158. 
  Only 
  the 
  eastern 
  half 
  of 
  it 
  can 
  be 
  drawn, 
  but 
  this 
  is 
  sufficient 
  

   to 
  show 
  that 
  the 
  longer 
  axis 
  of 
  the 
  curve 
  runs 
  approximately 
  east 
  

   and 
  west, 
  coinciding 
  roughly 
  with 
  the 
  axis 
  of 
  Milford 
  Haven. 
  The 
  

   shorter 
  axis 
  is 
  9 
  miles 
  in 
  length. 
  ^.The 
  shock 
  is 
  everywhere 
  described 
  

  

  