Geologic Hazards in Navarin Basin Province, Northern Bering Sea

Abstract

Abstract Navarin Basin, scheduled for leasing in 1984 (OCS sale 83), may contain vast accumulations of oil and gas. Several geologic and oceanographic processes that may be active in and around Navarin Basin province could be hazardous to commercial development. These potential hazards include submarine slides; sea-floor instability resulting from disturbance of gas-charged sediment; sediment transport and erosion caused by storm waves, tsunamis, internal waves, or bottom currents; pack ice; and active faults and ground motion. Introduction The quest for energy independence by the United States includes exploration of new segments of the outer continental shelf. The Navarin Basin lease sale (OCS sale 83) is scheduled for the spring of 1984. The study area, hereafter referred to as the "Navarin Basin province," is located on the outer continental shelf and upper slope in the northern Bering Sea (Fig. 1). The area is bounded on the northwest by the U.S.U. S.S.R. convention line of 1867 and on the southwest by the base of the contingent slope; it extends to within 100 km of st. Matthew Island to the northeast and of St. Paul Island to the southeast. This region potentially contains commercially exploitable accumulations of oil and gas, and it is likely to be the subject of intensive exploration. The purpose of this paper is to delineate, describe, and assess potential geologic hazards _on the sea floor in the Navarin Basin province that must be considered in the design of offshore facilities. Data Collection The principal sources of data for this study have been seismic-reflection profiles and sediment samples collected in 1980 and 1981 on the R/V Discoverer (Carlson and Karl, 1981). The seismic-reflection systems used included two 40-in3 air guns, an 800-J minis parker, and a 3.5-kHz transducer as acoustic sources. Spacing between geophysical track lines over this immense area averages about 15 km; sea-floor geological samples were taken at intersections of track lines and at selected geologically significant sites. Navigational control was LORAN C updated with satellite positioning. Shear-strength measurements were made on selected cores by means of a motorized Wykeham-Farrance* miniature-vane shear device. Tests were made at 20-cm intervals on core segments that had been split longitudinally. Immediately following strength testing, water-content and bulk-density sub samples were obtained at the locations of the vane tests. Consolidation analyses were performed on selected cores. Additional data collected in 1980 from the USCG Polar Star and the R/V S.P. LEE were incorporated into our data base as were seismic-reflection records collected over the past 15 years by the U.S Geological Survey for resource evaluation (Marlow and others, 1981). Other sources of data include studies by scientists from the universities of Washington and Alaska, and from Russia, and Japan (e.g. Kneel, 1972; Sharma, 1979; Lisitsyn, 1966; Takenouti and Ohtani, 1974). Morphology Of Navarin Basin Province Three physiographic provinces comprise the Navarin study area. These are the flat, wide, continental shelf; the steep, rugged continental slope, and the continental rise that extends from the base of the slope to the 3600-m isobathic. Three large submarine canyons deeply dissect the outer shelf and slope (Fig. 2).