﻿162 
  DR. 
  C. 
  DAVISON 
  ON 
  THE 
  PEMBROKE 
  EARTHQUAKES 
  [May 
  1897, 
  

  

  liminary 
  sound, 
  and 
  thus 
  the 
  earlier 
  phenomena 
  were 
  lost 
  to 
  them. 
  

   But 
  there 
  remain 
  a 
  large 
  number 
  of 
  careful 
  accounts 
  written 
  by 
  

   those 
  who 
  were 
  awake 
  at 
  the 
  time, 
  and 
  from 
  these 
  I 
  select 
  the 
  

   following 
  as 
  generally 
  descriptive 
  of 
  the 
  shock 
  in 
  different 
  parts 
  of 
  

   the 
  disturbed 
  area 
  : 
  — 
  

  

  Haverfordwest. 
  — 
  The 
  shock 
  began 
  violently, 
  gradually 
  weakened, 
  

   then 
  became 
  stronger 
  than 
  at 
  first 
  ; 
  it 
  lasted 
  about 
  14 
  seconds. 
  

  

  Cresselly. 
  — 
  Four 
  sets 
  of 
  vibrations 
  — 
  weak, 
  medium, 
  strong, 
  weak; 
  

   the 
  second 
  and 
  third 
  sets 
  separated 
  by 
  a 
  few 
  seconds, 
  during 
  which 
  

   a 
  tremulous 
  motion 
  was 
  felt. 
  Duration, 
  about 
  20 
  seconds. 
  

  

  At 
  several 
  other 
  places 
  in 
  Pembrokeshire 
  (especially 
  Cheriton, 
  

   Cosheston, 
  Manorbier, 
  Eedberth, 
  and 
  St. 
  .Florence), 
  the 
  nature 
  of 
  

   the 
  shock 
  closely 
  resembled 
  that 
  felt 
  at 
  Cresselly. 
  

  

  From 
  these 
  and 
  many 
  other 
  accounts 
  it 
  is 
  clear 
  that 
  near 
  the 
  

   epicentre 
  the 
  shock, 
  though 
  continuous, 
  contained 
  two 
  maxima 
  of 
  

   intensity, 
  the 
  second 
  of 
  which 
  was 
  stronger 
  than 
  the 
  first. 
  Farther 
  

   away, 
  the 
  tremulous 
  motion 
  felt 
  between 
  the 
  two 
  maxima 
  was 
  

   imperceptible, 
  and 
  the 
  shock 
  then 
  consisted 
  of 
  two 
  detached 
  series 
  of 
  

   vibrations 
  separated 
  by 
  an 
  interval 
  of 
  a 
  few 
  seconds 
  of 
  rest. 
  The 
  

   following 
  may 
  be 
  mentioned 
  as 
  examples 
  : 
  — 
  

  

  Clynderwen 
  (Caermarthenshire) 
  : 
  sharp 
  vibrations 
  increasing 
  in 
  

   intensity 
  for 
  about 
  5 
  or 
  6 
  seconds, 
  ceasing 
  for 
  2 
  or 
  3 
  seconds, 
  and 
  

   renewed 
  with 
  greater 
  violence 
  for 
  about 
  10 
  to 
  15 
  seconds. 
  

  

  Port 
  Eynon 
  (Glamorganshire) 
  : 
  two 
  series 
  of 
  vibrations, 
  with 
  an 
  

   interval 
  of 
  about 
  10 
  seconds 
  between 
  them. 
  

  

  Cleavehouses 
  (near 
  Bideford) 
  : 
  two 
  distinct 
  shocks, 
  the 
  first 
  a 
  

   tremor 
  like 
  that 
  produced 
  by 
  a 
  clap 
  of 
  thunder, 
  the 
  second 
  more 
  

   pronounced. 
  

  

  Ballywalter 
  (near 
  Gorey, 
  Co. 
  Wexford) 
  : 
  two 
  series 
  of 
  vibrations^ 
  

   the 
  second 
  more 
  intense 
  ; 
  an 
  interval 
  of 
  about 
  2 
  seconds 
  between 
  

   them. 
  

  

  The 
  double 
  series 
  of 
  vibrations 
  was 
  observed 
  practically 
  all 
  over 
  

   the 
  disturbed 
  area, 
  at 
  Khyl 
  in 
  the 
  north, 
  Tresco 
  Abbey 
  (in 
  theScilly 
  

   Isles 
  to 
  the 
  south), 
  at 
  Worcester 
  on 
  the 
  east, 
  and 
  at 
  Tullow 
  (Co. 
  

   Carlow) 
  on 
  the 
  west. 
  Excluding 
  some 
  rather 
  doubtful 
  cases, 
  it 
  was 
  

   noticed 
  by 
  42 
  observers, 
  30 
  of 
  whom 
  record 
  the 
  relative 
  intensity 
  

   of 
  the 
  vibrations. 
  The 
  second 
  is 
  said 
  to 
  have 
  been 
  the 
  stronger 
  at 
  

   22, 
  and 
  the 
  first 
  at 
  2, 
  of 
  these 
  places, 
  while 
  at 
  the 
  remaining 
  6 
  places 
  

   the 
  two 
  series 
  are 
  described 
  as 
  of 
  approximately 
  the 
  same 
  intensity. 
  

   The 
  two 
  places 
  at 
  which 
  the 
  first 
  series 
  was 
  regarded 
  as 
  the 
  stronger 
  

   are 
  Martletwy, 
  in 
  Pembrokeshire, 
  and 
  Treorchy, 
  in 
  Glamorgan- 
  

   shire 
  ; 
  but 
  there 
  can 
  be, 
  I 
  think, 
  little 
  doubt 
  that 
  these 
  observations 
  

   are 
  incorrect. 
  When 
  we 
  remember 
  that 
  most 
  of 
  the 
  accounts 
  were 
  

   written 
  after 
  the 
  lapse 
  of 
  several 
  days 
  or 
  weeks, 
  it 
  is 
  obvious 
  that 
  

   some 
  allowance 
  must 
  be 
  made 
  for 
  defects 
  of 
  memory. 
  It 
  is 
  

   probable 
  that 
  the 
  difference 
  in 
  intensity 
  was 
  not 
  very 
  great, 
  but 
  that 
  

   all 
  over 
  the 
  disturbed 
  area 
  the 
  second 
  maximum 
  w|as 
  

   stronger 
  than 
  the 
  first. 
  The 
  significance 
  of 
  this 
  conclusion 
  

   will 
  be 
  considered 
  in 
  a 
  later 
  section 
  dealing 
  with 
  the 
  origin 
  of 
  the 
  

   shock. 
  

  

  