Results of Magnetic-Variation Sounding of the Tatar Strait at Two Points on Its Opposite Shores

Abstract

Abstract —Results of magnetic-variation sounding on the opposite shores of the Tatar Strait are presented. The resulting frequency dependences of tippers serve as a basis for 3D inversion carried out using the ModEM software. The inversion yields horizontal and vertical sections of the Tatar Strait in a 400×400×400 km area along the x, y, and z axes, respectively. A conductive zone is revealed near the continental shore, and its central part has an electric resistivity of 0.5 Ohm∙m at a depth of 5–7 km. The zone reaches 20–40 km across and vanishes in the lower crust. Along the shore, an anomaly begins north of the Datta Village and extends to the area south of the town of Sovetskaya Gavan. There is a similar anomaly that is isometric in the horizontal plane and less contrasting, which exists near Sakhalin Island at depths of 8–12 km, where the crust resistivity is 15 Ohm∙m. The position of the anomaly matches the nearby zone of local М = 4–6 earthquakes in the upper crust. At depths greater than 10 km beneath the strait, these anomalies merge and the electrical resistivity increases. In the lower crust and in the upper mantle beneath the strait, the section is characterized by a resistivity of 30–60 Ohm∙m. At depths greater than 100 km, there is a conductive layer submerging beneath the Tatar Strait from the Sea of Okhotsk, with conductive branches running from it beneath the Tatar Strait south and north of the Datta Village. The possible causes of near-shore conductive anomalies are discussed.