Seismic investigation of geological structure bordering the Caribbean Island arc, part I
Miller, Dale Everett
Officer, Charles B.
Master of Arts
In recent years the seismic refraction technique has been used extensively to study the crustal structure of the earth beneath the great oceanic areas. These studies have led to the recognition of a characteristic oceanic crustal structure quite distinct from that characteristic of continental areas. This distinction has naturally led to investigations of the transition region between oceanic and continental structure. As part of an extensive deep-sea refraction program in 1951 members of Lamont Geological Observatory, Columbia university, made a series of eight profiles across the eastern Caribbean, which, except for a single profile by Hersey in 1949, represent the first refraction work in the area. The interpretations of these profiles were made by G. H. Sutton and preliminary calculations reportedly indicated the typical ocean basin structure beneath the Caribbean with a definite thickening of lighter material in the Puerto Rico trench. Hersey's single profile and six of Sutton's profiles were used by Ewing and Worzel along with the gravity measurements of Hess (1938, see map) in an attempt to present a consistent picture of the structure of the West Indies. This data, however, was too sparse to allow more than a calculated guess to be made. Interest in the Caribbean island-arc area continued with the 1955 investigation by Officer, et al., who made 47 seismic refraction profiles covering the exterior Atlantic basin, the interior Venezuelan basin, the Puerto Rico trench, and the island arc of the Lesser Antilles and Puerto Rico. The results of this investigation indicated a Caribbean crustal structure suggestive of a slightly altered standard oceanic structure and led to the consideration of a complementary relation between the origin of an island-arc and deep-sea trench and the origin of the altered interior basin. Officer, et al. concluded from the 1955 data that the island-arcs and deep-sea trenches are the result of horizontal compression at the border between the altered Caribbean basin structure and the normal Atlantic basin structure. In the summer of 1956 this work was continued on the Atlantis-224 and Bear-141 cruises in which the author took part. Thirty profiles, covering the same general areas as the 1955 profiles, were positioned to complete and reinforce the 1955 data. This paper is concerned only with the 1956 profiles located outside the island arc, in particular, profiles 2, 4, 6, 17, and 20. The 1956 profiles 1, 3, 18, and 29, located in the same area, were computed by D. G. Harkrider, the author of Part II of this work. Whereas previous seismic work in the area was confined to the refraction technique, provisions were made on both the '55 and '56 cruises for recording data suitable for reflection studies on the shorter range shots. The results of all '55 and ‘56 profiles outside the island arc are discussed later in this paper.