Density Distribution in Sakurajima Volcano by High Density Gravity Measurement

我们对樱岛火山进行了地质和重力调查，以揭示详细的重力异常分布，并估计了11,000年前产生最大喷发的火山口的位置。在地质调查中，研究了萨摩火山喷发的火舌分布，揭示了火山喷发的详细地层、变化和特征。从基底涌浪的分布和基底涌浪中埋有树木的方向推测，该火山口可能存在于樱岛西部。由346个重力点组成的重力测量显示了樱岛地区重力异常的详细分布。总体上，重力异常由南部的正异常（+12mgal）逐渐转变为北部的负异常（-18mgal）。在樱岛西部的大正湖地区也有一个局部的负异常（-4mgal）。从简单的数值实验结果来看，这一负异常表明浅层存在低密度体。最后，我们得出结论，这个负异常对应于产生萨摩陨石坑的位置。

We carried out geological and gravity surveys in Sakurajima Volcano in order to reveal the detailed gravity anomaly distribution and estimate a location of a crater which produced the biggest eruption 11,000 years ago.In the geological survey, we investigated a distribution of the Satsuma tephra released from the crater, revealed the detailed stratigraphy, a change and characteristic of the eruptions. We also estimate d that the crater may exists in the western part of Sakurajima from a distribution of the base surge and a direction of trees buried in the base surge.The gravity survey, which was composed of 346 gravity points, showed the detailed gravity anomaly distribution in Sakurajima. In general, the gravity anomaly gradually changed from the positive anomaly (+12mgal) in the southern area to the negative anomaly (-18mgal) in the northern area. It is also revealed that there is an local area with a negative anomaly (-4mgal) in the Taisho lave area in the western part of Sakurajima. This negative anomaly suggested a low density body in the shallow area from results of a simple numerical experiment. Finally we concluded that this negative anomaly would correspond to a location of the crater which produced the Satsuma tephra.