﻿166 
  DK. 
  C. 
  DAVISON" 
  ON 
  THE 
  PEMBROKE 
  EARTHQUAKES 
  [May 
  1897, 
  

  

  (iii) 
  After- 
  Shocks, 
  

   d. 
  August 
  18th 
  : 
  0.37 
  a.m. 
  

  

  Intensity, 
  about 
  4. 
  — 
  Number 
  of 
  records, 
  23 
  ; 
  from 
  23 
  different 
  

   places. 
  

  

  The 
  disturbed 
  area 
  includes 
  the 
  whole 
  of 
  Pembrokeshire 
  and 
  

   parts 
  of 
  Caerdiganshire, 
  Caermarthenshire, 
  and 
  North 
  Devon. 
  Its 
  

   boundary 
  is 
  indicated 
  on 
  the 
  map 
  (PI. 
  XI) 
  by 
  a 
  dotted 
  and 
  broken 
  

   line 
  ( 
  — 
  — 
  .), 
  and, 
  though 
  somewhat 
  uncertain 
  on 
  account 
  of 
  the 
  

   small 
  number 
  of 
  determining 
  stations, 
  it 
  is 
  clear 
  that 
  its 
  centre 
  

   must 
  lie 
  under 
  the 
  sea, 
  and 
  several 
  miles 
  south 
  of 
  that 
  of 
  the 
  

   principal 
  earthquake. 
  

  

  The 
  shock 
  consisted 
  of 
  one 
  series 
  of 
  very 
  slight 
  vibrations, 
  the 
  

   accompanying 
  sound 
  being 
  a 
  low 
  rumble, 
  like 
  a 
  distant 
  thunder- 
  

   peal. 
  

  

  e. 
  August 
  18t7i 
  : 
  about 
  1.5 
  a.m. 
  

  

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

  

  A 
  very 
  slight 
  shock, 
  felt 
  at 
  Dale 
  and 
  Pembroke 
  Dock, 
  at 
  the 
  

   latter 
  accompanied 
  by 
  a 
  subdued 
  rumbling 
  sound. 
  The 
  epicentre 
  

   was 
  probably 
  not 
  far 
  distant 
  from 
  either 
  of 
  these 
  places. 
  

  

  f 
  . 
  August 
  18t7i 
  : 
  about 
  1.40 
  a.m. 
  

  

  Intensity, 
  about 
  5. 
  — 
  Number 
  of 
  records, 
  114; 
  from 
  111 
  different 
  

   places. 
  

  

  Disturbed 
  Area 
  and 
  Sound-Area. 
  — 
  This 
  was 
  the 
  strongest 
  of 
  all 
  

   the 
  after-shocks, 
  and, 
  owing 
  to 
  the 
  fact 
  that 
  many 
  observers 
  

   remained 
  awake 
  and 
  on 
  the 
  watch, 
  it 
  was 
  felt 
  over 
  a 
  comparatively 
  

   wide 
  area. 
  

  

  The 
  isoseismal 
  4 
  (see 
  map, 
  p. 
  158) 
  can 
  be 
  traced 
  with 
  some 
  

   accuracy. 
  Except 
  that 
  it 
  extends 
  a 
  little 
  farther 
  westward, 
  it 
  coin- 
  

   cides 
  nearly 
  with 
  the 
  isoseismal 
  7 
  of 
  the 
  principal 
  earthquake. 
  The 
  

   shorter 
  axis 
  of 
  the 
  curve 
  is 
  24 
  miles 
  in 
  length, 
  the 
  longer 
  axis 
  is 
  

   directed 
  approximately 
  north 
  and 
  south, 
  and 
  the 
  land-area 
  enclosed 
  

   by 
  it 
  contains 
  about 
  510 
  square 
  miles. 
  The 
  centre 
  is 
  probably 
  

   close 
  to 
  the 
  coast 
  almost 
  due 
  south 
  of 
  Pembroke, 
  but 
  whether 
  it 
  

   lies 
  beneath 
  the 
  land 
  or 
  the 
  sea 
  is 
  uncertain. 
  

  

  Outside 
  this 
  isoseismal, 
  the 
  places 
  at 
  which 
  the 
  earthquake 
  was 
  

   observed 
  are 
  far 
  apart, 
  and 
  it 
  is 
  impossible 
  to 
  draw 
  the 
  boundary 
  

   of 
  the 
  disturbed 
  area 
  or 
  any 
  other 
  isoseismal. 
  The 
  most 
  distant 
  

   places 
  at 
  which 
  the 
  shock 
  was 
  felt 
  are 
  Knighton 
  and 
  Glasbury 
  

   (Badnorshire), 
  Cantref 
  and 
  Aberclydach 
  (Breconshire), 
  Exmouth, 
  

   St. 
  Austell, 
  and 
  Kyle 
  and 
  Wexford 
  (Co. 
  Wexford). 
  All 
  of 
  these 
  lie 
  

   outside 
  the 
  isoseismal 
  5 
  of 
  the 
  principal 
  earthquake, 
  and 
  one 
  of 
  

   them, 
  Knighton, 
  is 
  26 
  miles 
  beyond 
  it. 
  

  

  The 
  sound 
  was 
  everywhere 
  much 
  less 
  intense 
  than 
  that 
  which 
  

   accompanied 
  the 
  principal 
  shock. 
  With 
  two 
  exceptions 
  (Llany- 
  

   byther 
  in 
  Caermarthenshire, 
  and 
  Treneglos 
  near 
  Launceston), 
  it 
  

   was 
  not 
  heard 
  beyond 
  the 
  isoseismal 
  6 
  of 
  that 
  earthquake. 
  

  

  