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PRELIMINARY ANALYSIS REPORT, ALEUTIAN ISLAND EXPERIMENT OCEAN-BOTTOM SEISMOGRAPHIC EXPERIMENTS
TEXAS INSTRUMENTS INC DALLAS SCIENCE SERVICE DIV
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A preliminary model of the crustal structure across the Aleutian Ridge in the vicinity of Amchitka is presented. Data from two inline-reversed refraction profiles utilizing shot and Ocean-Bottom Seismograph OBS arrays along a northeast-southwest line through Amchitka were used to determine the structure. The analysis was limited to first-arrival data, most of which was Moho-refracted however, some upper-crust refractors were identified immediately beneath Amchitka. Observed traveltimes were corrected to a reference plane 4.5 km below sea level to minimize lateral velocity variations associated with the large changes in water depth and the changes in subwater crustal velocities along the profiles. Moho velocity of 8.0 to 8.1 kmsec was obtained for the area. Also, 4.9- and 6.2-kmsec refractors at depths of about 1 and 10 km were identified beneath Amchitka. Shot depths were determined from hydroacoustic data by using the bubble-pulse method and converting traveltime data to depths. A detailed discussion of these methods, including an error analysis, is presented. A total of 2734 station events was observed, 306 of which were associated with the 35 explosions and 198 associated with earthquakes having known epicenters.
APPROVED FOR PUBLIC RELEASE