﻿170 
  DR. 
  C. 
  DAVISON 
  ON 
  THE 
  PEMBROKE 
  EARTHQUAKES 
  [May 
  1 
  897, 
  

  

  the 
  fault 
  hades 
  towards 
  the 
  south. 
  But 
  the 
  inference 
  is 
  

   far 
  from 
  certain, 
  and, 
  the 
  isoseismal 
  lines 
  being 
  incomplete 
  near 
  the 
  

   epicentre, 
  no 
  additional 
  evidence 
  is 
  furnished 
  by 
  their 
  relative 
  

   position. 
  If 
  it 
  be 
  correct, 
  however, 
  the 
  fault-line 
  must 
  be 
  situated 
  

   a 
  short 
  distance 
  to 
  the 
  north 
  of 
  the 
  centre 
  of 
  isoseismal 
  6. 
  

  

  Nature 
  of 
  the 
  Shock. 
  — 
  The 
  following 
  accounts 
  are 
  given 
  to 
  illus- 
  

   trate 
  the 
  nature 
  of 
  the 
  shock 
  : 
  — 
  

  

  White 
  Lays 
  (Pembrokeshire) 
  : 
  a 
  rather 
  severe 
  swaying 
  motion, 
  

   in 
  two 
  series 
  of 
  vibrations, 
  the 
  second 
  the 
  stronger 
  ; 
  durations 
  of 
  

   the 
  first 
  series, 
  interval, 
  and 
  second 
  series 
  about 
  3, 
  4, 
  and 
  5 
  seconds 
  

   respectively 
  : 
  slight 
  trembling 
  and 
  rumbling 
  souud 
  between 
  the 
  

   two 
  series 
  ; 
  the 
  rumbling 
  sound 
  preceded 
  the 
  sensible 
  movement 
  

   by 
  about 
  3 
  seconds, 
  and 
  followed 
  it 
  by 
  the 
  same 
  interval. 
  

  

  Ballyhealy 
  (Co. 
  Wexford) 
  : 
  two 
  series 
  of 
  vibrations, 
  the 
  first 
  the 
  

   stronger 
  ; 
  durations 
  of 
  the 
  first 
  series, 
  interval, 
  and 
  second 
  series 
  

   about 
  6, 
  1, 
  and 
  4 
  seconds, 
  respectively 
  ; 
  slight 
  tremulous 
  motion 
  

   and 
  rumbling 
  sound 
  before 
  the 
  first 
  series, 
  in 
  the 
  interval 
  between, 
  

   and 
  after 
  the 
  second 
  series. 
  

  

  At 
  some 
  distance 
  from 
  the 
  epicentre, 
  the 
  tremulous 
  motion 
  

   between 
  the 
  series 
  was 
  of 
  course 
  imperceptible, 
  and 
  the 
  shock 
  con- 
  

   sisted 
  of 
  two 
  detached 
  series 
  of 
  vibrations, 
  generally 
  of 
  unequal 
  

   strength. 
  At 
  a 
  very 
  large 
  number 
  of 
  places, 
  one 
  of 
  the 
  two 
  series 
  

   passed 
  unnoticed 
  or 
  unrecorded, 
  but 
  as 
  observations 
  of 
  the 
  double 
  

   series 
  come 
  from 
  nearly 
  all 
  parts 
  of 
  the 
  disturbed 
  area, 
  even 
  from 
  

   places 
  so 
  near 
  the 
  boundary 
  as 
  Bournemouth, 
  Ashley, 
  and 
  Derby, 
  

   the 
  number 
  of 
  such 
  records 
  is 
  49. 
  In 
  18 
  of 
  these 
  the 
  first 
  series 
  

   is 
  described 
  as 
  the 
  stronger, 
  and 
  in 
  14 
  others 
  the 
  second. 
  Within 
  

   and 
  near 
  the 
  isoseismal 
  6, 
  the 
  second 
  series 
  is 
  invariably 
  estimated 
  

   as 
  the 
  stronger 
  ; 
  and 
  at 
  a 
  considerable 
  distance, 
  generally, 
  but 
  not 
  

   always, 
  the 
  first. 
  The 
  observations 
  from 
  neighbouring 
  places 
  are 
  

   not, 
  however, 
  always 
  concordant, 
  and 
  this 
  prevents 
  the 
  statement 
  

   of 
  any 
  general 
  law. 
  

  

  Near 
  the 
  epicentre 
  the 
  shock 
  consisted 
  of 
  rapid 
  vibrations, 
  but 
  

   at 
  some 
  distance 
  from 
  it 
  the 
  period 
  seems 
  to 
  have 
  lengthened 
  out, 
  

   and 
  the 
  shock 
  is 
  described 
  as 
  a 
  'swaying 
  motion.' 
  The 
  fifteen 
  

   places 
  from 
  which 
  such 
  records 
  come 
  lie 
  within 
  an 
  oval 
  area 
  ex- 
  

   tending 
  from 
  Whitchurch 
  (Salop) 
  on 
  the 
  north 
  to 
  Wells 
  on 
  the 
  

   south, 
  and 
  from 
  Llangammarch 
  (Brecon) 
  on 
  the 
  west 
  to 
  Hereford 
  

   on 
  the 
  east. 
  

  

  Sound-Area. 
  — 
  Records 
  of 
  the 
  earthquake-sounds 
  come 
  from 
  253 
  

   places, 
  while 
  at 
  95 
  others 
  it 
  is 
  stated 
  that 
  no 
  sound 
  was 
  heard. 
  In 
  

   this 
  case, 
  the 
  boundary 
  of 
  the 
  sound-area 
  (shown 
  by 
  a 
  broken 
  line 
  on 
  

   the 
  map, 
  PI. 
  XI) 
  can 
  be 
  drawn 
  with 
  considerable 
  accuracy. 
  Its 
  

   length 
  is 
  231 
  miles, 
  breadth 
  210 
  miles, 
  and 
  the 
  contained 
  area 
  

   about 
  37,700 
  square 
  miles. 
  Its 
  form 
  and 
  size 
  are 
  thus 
  approxi- 
  

   mately 
  the 
  same 
  as 
  those 
  of 
  the 
  isoseismal 
  4; 
  indeed, 
  if 
  the 
  

   isoseismal 
  were 
  shifted 
  about 
  10 
  or 
  12 
  miles 
  north-eastward, 
  it 
  

   would 
  coincide 
  roughly 
  with 
  the 
  boundary 
  of 
  the 
  sound-area. 
  

  

  