THE GREAT FAULT TROUGHS OF THE ANTILLES 91 



the Owens Valley earthquake of 1872;^ and there are many 

 examples along the line of the San Andreas fault zone of Cali- 

 fornia. 



Seismologic evidence, when available, is especially valuable in 

 locating active faults which are not exposed to direct observation. 

 Ma.ny earthquakes have been recorded in the Greater Antilles 

 and Virgin Islands during the last four centuries, and, while the 

 pubHshed catalogues of these earthquakes are far from complete, 

 it seems probable that few, if any, of the very destructive shocks 

 have been omitted. Most of the weak shocks of a district originate 

 in the same locahties as the stronger ones, and therefore in this 

 investigation attention has been focused on the destructive earth- 

 quakes, In the region of the Greater Antilles the epicenters of 

 destructive earthquakes, instead of being scattered at random, are 

 almost entirely limited to a few well-defined belts, which also possess 

 the topographic characteristics of fault zones. 



Most of the earthquakes occurred before seismographs were 

 developed, and, therefore, in determining the location of their 

 epicenters, it has been necessary to rely chiefly on the distribution 

 of intensities and the evidence derived from a study of accompany- 

 ing sea waves. Fortunately, for present purposes an approximate 

 location of an epicenter is, in most cases, sufficient. The seismo- 

 logic data are only briefly summarized here as they are discussed 

 in more detail in another paper which will be pubhshed shortly 

 in the Bulletin of the Seismological Society of America. 



DESCRIPTION OF FAULT ZONES AND FAULT TROUGHS 



The principal troughs of the Antillean region are: the Bartlett 

 Trough, which lies between Cuba and Jamaica and extends from 

 the Island of Haiti westward into the Gulf of Honduras; the 

 Brownson Trough, lying immediately north of Porto Rico and the 

 Virgin Islands; and the Anegada Trough, which separates Porto 

 Rico and the Virgin Islands Bank from St. Croix and the Lesser 

 Antilles. In addition to these there are some minor troughs and 

 probably one fault zone that is not associated with any trough. 



^ G. K. Gilbert, "Lake Bonneville," U.S. Geol. Surv. Monograph I (1890), 

 p. 361. 



