﻿Vol. 
  53.] 
  THE 
  PEMBROKE 
  EARTHQUAKES 
  OE 
  1892 
  & 
  1893. 
  159 
  

  

  I. 
  — 
  Earthquakes 
  oe 
  August 
  17th-23rd, 
  1892. 
  

  

  The 
  following 
  is 
  a 
  list 
  of 
  the 
  earthquakes 
  of 
  this 
  series, 
  the 
  

   principal 
  shock 
  being 
  denoted 
  by 
  a 
  capital 
  letter 
  : 
  — 
  

  

  a. 
  August 
  17th 
  : 
  about 
  11.30 
  p.m. 
  

  

  b. 
  August 
  ISth 
  : 
  0,22 
  a.m. 
  

   C. 
  „ 
  0.24 
  am. 
  

  

  d. 
  „ 
  0.37 
  a.m. 
  

  

  e. 
  ,, 
  about 
  1.5 
  a.m. 
  

  

  f. 
  ., 
  about 
  1.40 
  a.m. 
  

  

  g. 
  August 
  10th 
  : 
  2.50 
  a.m. 
  

   h. 
  „ 
  about 
  4 
  a.m. 
  

  

  i. 
  August 
  19th 
  : 
  9.30 
  a.m. 
  

   k. 
  August 
  22nd 
  : 
  about 
  11.55 
  a.m. 
  

   1. 
  August 
  23rd 
  : 
  4.30 
  a.m. 
  

  

  It 
  should 
  be 
  remarked 
  that 
  the 
  earthquake 
  denoted 
  by 
  the 
  letter 
  

   i 
  depends 
  on 
  the 
  evidence 
  of 
  one 
  witness 
  only. 
  But, 
  as 
  it 
  is 
  recorded 
  

   by 
  a 
  most 
  careful 
  observer, 
  the 
  usual 
  rule 
  of 
  regarding 
  such 
  an 
  

   earthquake 
  as 
  doubtful 
  should, 
  I 
  think, 
  be 
  suspended 
  in 
  this 
  case. 
  

  

  (i) 
  Preparatory 
  Earthquakes. 
  

  

  a. 
  August 
  17th 
  : 
  about 
  11.30 
  p.m. 
  

  

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

  

  The 
  shock 
  was 
  felt 
  at 
  Haverfordwest 
  and 
  Rudbaxton, 
  3 
  miles 
  

   farther 
  north. 
  At 
  the 
  same 
  time, 
  two 
  rumbling 
  noises 
  were 
  heard 
  

   at 
  Pembroke. 
  

  

  b. 
  August 
  18th: 
  0.22 
  a.m. 
  

  

  Number 
  of 
  records, 
  7 
  ; 
  from 
  7 
  different 
  places. 
  

  

  Two 
  minutes 
  before 
  the 
  principal 
  shock, 
  a 
  distant 
  sound, 
  as 
  of 
  

   thunder, 
  was 
  heard, 
  without 
  any 
  accompanying 
  tremor. 
  The 
  places 
  

   of 
  observation 
  are 
  situated 
  within 
  a 
  small 
  area 
  in 
  the 
  extreme 
  south 
  of 
  

   the 
  county 
  (see 
  map, 
  p. 
  158). 
  The 
  longer 
  axis 
  of 
  the 
  area 
  is 
  directed 
  

   approximately 
  north 
  and 
  south, 
  and 
  its 
  centre 
  is 
  either 
  close 
  to 
  the 
  

   coast 
  (about 
  1| 
  mile 
  west 
  of 
  Manorbier) 
  or 
  else 
  beneath 
  the 
  sea. 
  

   The 
  land-area 
  over 
  which 
  the 
  sound 
  was 
  heard 
  contains 
  about 
  33 
  

   square 
  miles. 
  Five 
  minutes 
  before 
  the 
  great 
  shock, 
  Dr. 
  Propert, 
  at 
  

   St. 
  David's, 
  heard 
  a 
  noise 
  as 
  of 
  a 
  cart 
  passing. 
  It 
  is 
  uncertain 
  

   whether 
  this 
  observation 
  refers 
  to 
  the 
  same 
  earth-sound 
  as 
  ihe 
  

   others. 
  

  

  (ii) 
  Principal 
  Earthquake. 
  C 
  : 
  0.24 
  a.m. 
  

  

  Intensity, 
  7. 
  — 
  Number 
  of 
  records, 
  712, 
  from 
  555 
  different 
  places 
  ; 
  

   also 
  114 
  records 
  from 
  111 
  different 
  places 
  at 
  which, 
  so 
  far 
  as 
  known, 
  

   the 
  earthquake 
  was 
  not 
  observed. 
  

  

  Disturbed 
  Area 
  and 
  Isoseismal 
  Lines. 
  — 
  On 
  the 
  map 
  illustrating 
  this 
  

   earthquake 
  (PI. 
  XI) 
  are 
  shown 
  the 
  isoseismal 
  lines 
  corresponding 
  

   to 
  intensities 
  4 
  and 
  5 
  of 
  the 
  Rossi-Porel 
  scale. 
  Portions 
  of 
  those 
  

   corresponding 
  to 
  intensities 
  6 
  and 
  7 
  are 
  also 
  given, 
  but 
  the 
  land- 
  

   areas 
  traversed 
  by 
  these 
  lines 
  are 
  not 
  great 
  enough 
  to 
  allow 
  of 
  the 
  

   remaining 
  parts 
  being 
  drawn. 
  On 
  this 
  account 
  it 
  is 
  not 
  possible 
  to 
  

   determine 
  the 
  position 
  of 
  the 
  epicentre 
  with 
  great 
  exactness. 
  

  

  