This is a yellow alert bulletin from our watch team. If you have friends travelling to the region or friends who live there, it is time to at least give them a heads up. The magnitude and frequency of the earthquake swarms has increased in the last 24 hours prompting this alert. The region also has a recent history of creating tsunamis and the area of quake activity is on a plate fault line that has had significant movements with previous great quakes. This is complicated by deep water graduating to very shallow water quickly which can amplify tsunami wave heights very quickly and without much time to react.
Virgin Islands region has had:
- 14 earthquakes today
- 118 earthquakes in the past 7 days
- 141 earthquakes in the past month
The 1867 Virgin Island Tsunami
On the afternoon of November 18, 1867, a magnitude 7.5 earthquake occurred in the Anegada trough, located between the US Virgin Islands of St. Croix, and St. Thomas. The earthquake actually consisted of two shocks, separated by ten minutes. These shocks generated two tsunami waves that were recorded at several Island locations across the eastern Caribbean region, most notably on the Islands of St. Thomas and St. Croix.
The first tsunami wave struck the town of Charlotte Amalie, on the island of St. Thomas, approximately 10 minutes after the first shock, and the second wave approximately 10 minutes after the second shock. Both waves struck the harbor at Charlotte Amalie first as a large recession of water, followed by a bore, which eyewitness accounts describe as a 4.5 to 6.1 meter wall of water. At the southern point of Water Island, located approximately four kilometers from Charlotte Amalie, the bore was reportedly 12.1 meters high! The waves destroyed many small boats anchored in the harbor, leveled the town’s iron wharf, and either flooded out or destroyed all buildings located along the waterfront area. The waves also damaged a United States Navy ship De Soto, that happened to be anchored in the harbor at the time of the event. The tsunami produced an estimated 2.4 meters of runup at Charlotte Amalie, and a maximum 75 meter inland inundation.
Fredriksted St. Croix was struck by two large tsunami waves, each approximately 7.6 meters high, according to eyewitness accounts. These waves caused severe damage along the waterfront, washing several wooden houses and other structures a considerable distance inland. The waves destroyed many of the smaller boats anchored in the harbor, and beached a large United States Navy ship, the Monongahela (see photo below). A total of five people died as a result of the tsunami. Eyewitness accounts from Frederiksted indicate that the water withdrew from the harbor almost immediately after the earthquake, which suggests that the first wave to strike here might have been a local tsunami produced by a submarine landslide. Reports from Christiansted, St. Croix, indicate that the tsunami inundated an area up to 91 meters inland. The greatest damage here occurred at Gallows Bay, where the waves destroyed 20 houses and beached many boats.
The 1967 Virgin Island Tsunami
The 1967 Virgin Island tsunami was recorded at several other islands in the eastern Caribbean region. The tsunami produced 1.2 to 1.5 meters of runup, and washed away most of the smaller buildings on the island of Tortola in the British Virgin Islands. At St. John’s on the Island of Antigua, the tsunami produced a 2.4 to 2 meter runup. At St. Rose on the island of Guadeloupe, the tsunami reportedly struck as a 18.3 meter wave, flooding houses and damaging boats. This extreme value however, is most likely an exaggeration, as it exceed the maximum wave heights reported at the locations closest to the earthquake’s epicenter, and the tsunami waves reported at nearby Basse-Terre where only 2 meters high. At Bequia Island the tsunami washed in as a 1.8 meter wave. At St. George, on the island of Grenada, 1.5 meter tsunami waves damaged boats and buildings. The tsunami was also observed at several locations on the eastern shore of Puerto Rico. At all location the tsunami was marked by an initial recession of water from the shore.