Gravity and magnetic measurements over Bowers Ridge and Shirshov Ridge, Bering Sea

Abstract

Bowers ridge, which is submerged in the deep-water part of the Bering Sea, has the geophysical and structural characteristics of an island arc-trench system. Three crustal structure sections of the strongly curved aseismic Bowers ridge based on seismic, magnetic, and gravity data, indicate that Bowers ridge is a volcanic ridge characterized by large-amplitude, short-wavelength magnetic anomalies and bordered on its convex side by a sediment-filled trench. Positive gravity anomalies greater than 200 mgal are associated with Bowers ridge; negative anomalies with amplitudes greater than 100 mgal are associated with the bordering trench. The geophysical and structural characteristics of the linear, also entirely submerged, Shirshov ridge in the Bering Sea differ significantly from the characteristics of Bowers ridge. Over Shirshov ridge the gravity anomalies are of small amplitude and there is no geophysical evidence of a buried trench. A straight NE-SW trending chain of elongated seamounts, possibly located on an old transform fault zone, connects Bowers ridge and Shirshov ridge and may indicate the direction of late Mesozoic-earliest Tertiary subduction from the northeast, which would have led to the construction of the Bowers arc-trench system.