Preliminary results of geomagnetic surveys off northwest Kyushu during cruises GS23 and GB23

Geomagnetic surveys were undertaken to compile marine geophysical maps of the area off northwest Kyushu.A total magnetic anomaly map was created based on observations of the total magnetic field.The survey area contains a complex distribution of magnetic anomalies ranging from short to long wavelengths.The area west of the Goto Islands and east of Ikishima Island is marked by complex shortwavelength magnetic anomalies.In contrast, the area from west of the Goto Islands to south of Tsushima Island is characterized by a long-wavelength positive anomaly that trends northeast-southwest.Given the shallow water depth over most of the survey area, bathymetric data are insufficient to assess the seafloor topography.The short-wavelength magnetic anomalies likely reflect the occurrence of igneous rocks on the seafloor, as also observed on nearby islands.The northeast-southwest trending positive magnetic anomaly is presumed to correspond to the northern end of the belt of positive magnetic anomalies that extends from near the Senkaku Islands to the Goto Islands.