Several volcano-tectonic earthquakes were recorded during the period under review. Two of these types of earthquake were large enough to be located. The first occurred at 04:45 (magnitude 2.0) and the second at 11:27 (about magnitude 1.2) on 18 February. Both were located at depths of about 2 to 2.5 km beneath the volcano. The broadband tremor, which has been observed intermittently on the seismograph station at Gages, increased in amplitude at about 17:30 on 17 February and continued at this increased level for approximately 5 hours. Other seismic signatures, associated with small rockfalls and eruptions, were detected throughout the period under review. The largest of these rockfalls occurred at 15:41 on 18 February. The seismic network also recorded two regional earthquakes at 16:56 on 17 February and 08:34 on 18 February with locations approximately 9 and 12 km northeast of the island, respectively. Depths of approximately 14 km and magnitudes of 2.8 were obtained for both of these earthquakes. A further regional earthquake, with al location 40 km northeast of the island, occurred at 15:11 on 18 February; this had a magnitude of about 3.0.
EDM measurements were made on the eastern triangle to Castle Peak today. The Whites Yard-Castle Peak line shortened by 8 mm while the Long Ground-Castle Peak line shortened by 1 cm since their previous occupation on 14 February. The recent changes in line length are a continuation of the long-term trend of shortening which have been occurring since 5 December 1996. The rate of change over this period has been approximately 0.6 mm per day.
Low cloud cover and mist obscured the top of the volcano for the entire day and did not permit any views of conditions at English's Crater.