Preliminary report on the so-called pulse of the ground observed in the Niigata plain.

1. Since 1955, rapid land subsidence occurred in and around Niigata City by withdrawal of natural gas bearing water. As a result of several control for water extraction, rate of subsidence has become rapidity decrease as shown in Fig, 5. After the sixth countermeasures of water injection in 1942, the ground surface of the Niigata plain has shown vertical fluctuation which is called as “pulse of the ground” as shown in Figs, 2 and 5. 2. Similar phenomena can be recognized in the other land subsidence areas such as Tokyo, Saga in Japan during the decreasing period of subsidence rate. MIYABE (1966) considered that the fluctuation of the ground in central part of Tokyo (Fig, 9) might be caused by the seasonal change of the tidal loading of sea water of Tokyo Bay. 3. In Niigata plain, the pulse of the ground has close relation with the vertical movement of the deeper layer as shown in Fig, 6 on the basis of record of observation wells. Therefore, the pulse phenomena may have been caused by a kind of natural movement of the deeper layer, but the amount of displacement of ground surface is larger than that of the so-called natural crustal movement