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| | Abstract | | In limestone area, finding out about underground caves to avoid collapse is important to maintain water resources being used. We applied microgravity survey to find underground caves in Shirakawata water resources area, miyakojima city. On three survey lines (340, 160 and 144 m length) including 176 gravity points, gravity was measured by using Lacoste and Romberg D type gravimeter (D68). We conducted duplicate measurements at 54 points for quality control and consequently got the averaged measurement variation of 0.004 mgal (SD). Three profiles of local Bouguer anomaly were calculated with accuracy using the terrain correction calculated from 1m DEM within 350 m range. Usually, a negative gravity anomaly is expected for underground cave, however positive signals with approximately 100 m width are found around the water resource. This positive signals infer an absence of underground cave. On the other side, this signals are consistent with the presence of recrystallized limestone zone which was find in borehole cores around the water resource. |
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