Fracture zones and magnetic anomalies south of the Aleutian Trench

Magnetic anomalies south of the Aleutian trench between 164° and 180°W trend east-west. The magnetic pattern is disrupted at 173°W and 177°30'W by north-south-trending fracture zones named Amlia and Adak fracture zones, respectively. Correlation of magnetic anomaly profiles shows apparent left-lateral offsets of 220 km across the Amlia fracture zone and 30 km across the Adak fracture zone. The amplitudes of the anomalies are sharply reduced where they intersect the trench, resulting in a magnetically `quiet zone' over most of the Aleutian trench and terrace. Although there are suggestions that the fracture zones extend north of the trench, the evidence is inconclusive.