High‐resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku‐oki earthquake rupture zone

Abstract

AbstractUsing high‐resolution paleomagnetic data, we examined the potential for obtaining precise ages from sediment core samples recovered from deep‐sea basins close to rupture zones of the 2011 and earlier earthquakes off Tohoku, Japan. Obtaining detailed stratigraphic ages from deep‐sea sediments below the calcium compensation depth (CCD) is difficult, but we found that the samples contain excellent paleomagnetic secular variation records to constrain age models. Variations in paleomagnetic directions obtained from the sediments reveal systematic changes in the cores. A stacked paleomagnetic profile closely matches the Lake Biwa data sets in southwest Japan for the past 7000 years, one can establish age models based on secular variations of the geomagnetic field on sediments recovered uniquely below the CCD. Comparison of paleomagnetic directions near a tephra and a paleomagnetic direction of contemporaneous pyroclastic flow deposits acquired by different magnetization processes shows precise depositional ages reflecting the magnetization delay of the marine sediment record.