io8 STEPHEN TABER 



Several severe earthquakes have originated in the Anegada 

 Trough and many Hght shocks are recorded by the seismographs on 

 the Island of Vieques. A severe earthquake was felt in Antigua, 

 St. Christopher, and Tortola July ii, 1785. Since the shock was 

 strongly felt on all three islands its epicenter was probably between 

 them; and the report that cracks were formed in the ground in 

 Tortola suggests an origin in the vicinity of that island. 



A severe shock was felt in St. Thomas, April 20, 1824. The 

 precise location of the epicenter cannot be determined from the 

 data available but is not far from St. Thomas, probably in the 

 Anegada Trough, though possibly on the opposite side of the island 

 along the southern scarp of the Brownson Trough. The strong 

 shock reported from St. Thomas September 19, 1853, ^^^ the two 

 felt on May 12, 1865, appear also to have originated near that 

 island. 



The great earthquakes of November 18, 1867, originated along 

 the northern scarp of the trough 15 to 20 km. south of St. Thomas. 

 , There were two strong shocks separated by an interval of about 

 10 minutes, both being followed by sea-waves. Aftershocks 

 continued for several months, the strongest occurring December 

 I and 12, 1867; January 5 and March 17, 1868, and September 

 17, 1869. The shock on March 17, 1868, was accompanied by a 

 small sea-wave and seems to have had its epicenter a little farther 

 west than the others, though all originated along the same scarp. 



On July 24, 1913, a severe earthquake was felt in the Virgin 

 Islands and throughout Porto Rico except along the west coast. 

 The epicenter was apparently in the Anegada Trough near lati- 

 tude 18° 30' N., longitude 64° W. 



THE NORTHERN ESCARPMENT OF THE CARIBBEAN BASIN 



The Caribbean Basin is bounded on the north by an escarpment 

 that descends steeply from Porto Rico and Haiti to a depth of 

 4,572 m. within 90 km. of the islands. This is the only important 

 scarp in the region that does not form one side of a relatively narrow 

 trench. It gives the Porto Rico-Virgin Islands ridge, extending 

 eastward from Haiti, the topographic characteristics of a great 

 horst. 



