Abstract：There is a large-scale land subsidence due to withdrawal of water-soluble natural gas and medicine iodine in Boso Peninsula，Japan. Land subsidence surveying started in 1969. Till 2002，the accumulated maximum subsidence was 0.85 m. In order to alleviate subsidence， extractable volume of groundwater should be forecasted. A 3D finite element model was established based on the structure of Kanto Groundwater Basin. This model can calculate groundwater seepage and land subsidence in one process. The parameters used in the model are determined from consolidation test under high pressure on the samples of outcropped soft rock at the south part of the peninsula. Calculation results indicate that from 1956 to 2002 the groundwater head dropped to 190 m in the center of groundwater withdrawal area. The results also indicate that at the beginning (in 1957) groundwater flows from elevated mountain area to sea，however，in 2002，groundwater flew from sea to the withdrawal area. This result is coincident with the structure of Kanto groundwater basin with syncline aquifer overlain/underlain by aquitards. Therefore，the land subsidence can be alleviated by limiting the withdrawal volume even if groundwater withdrawal is not stopped. The calculation value of land subsidence from 1969 to present agrees the measured value well.
