A preliminary study on paleomagnetic field intensity variation forthe past 6000 years

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During this funding period, a high-sensitivity magnetic balance for measuring a Curietemperature of rocks was purchased and the calibration and adjustment were completed.Using this system, a rock sample which is suitable for paleointensity measurement canbe recognized in the future paleointensity studies. Paleomagnetic sample was collectedat 13 sites of the Kuju volcanic field, and paleomagnetic directions with relatively highreliability were obtained from eight sites. In the Kuju volcanic field, the ages of lavaswere reported based on the relation with volcanic ash layers, and therefore the formationages of lava were not precisely determined. We recognized that these inaccuracies of theages of the lavas were not suitable for recovering the paleointenisty variation for thepast several thousand years. We noticed that we should not limit our sampling to the Kujuvolcanic field, but we should change the plan to collect samples from lavas andpyroclastic-flows for which carbon-14 ages have been reported. Paleointensitymeasurements are being conducted on these lavas and pyroclastic-flows.