13 research outputs found
Groundwater management based on monitoring of land subsidence and groundwater levels in the Kanto Groundwater Basin, Central Japan
Over 40 million people live on and exploit the groundwater resources of the
Kanto Plain. The Plain encompasses metropolitan Tokyo and much of Chiba
Prefecture. Useable groundwater extends to the base of the Kanto Plain, some
2500 to 3000 m below sea level. Much of the Kanto Plain surface is at sea
level. By the early 1970s, with increasing urbanization and industrial
expansion, local overdraft of groundwater resources caused major ground
subsidence and damage to commercial and residential structures as well as to
local and regional infrastructure. Parts of the lowlands around Tokyo
subsided to 4.0 m below sea level; particularly affected were the suburbs of
Funabashi and Gyotoku in western Chiba. In the southern Kanto Plain,
regulations, mainly by local government and later by regional agencies, led
to installation of about 500 monitoring wells and almost 5000 bench marks by
the 1990's. Many of them are still working with new monitoring system.
Long-term monitoring is important. The monitoring systems are costly, but the
resulting data provide continuous measurement of the "health" of the Kanto
Groundwater Basin, and thus permit sustainable use of the groundwater
resource
Liquefaction-fluidization induced land subsidence: impact of the 2011 Tohoku earthquake on reclaimed land around Tokyo bay area, Japan
The 2011 Tohoku earthquake caused major liquefaction-induced, ground
deformation of the reclaimed land surrounding Tokyo Bay. In this area,
liquefaction was visibly manifest by sand boils, ejection of sandy water,
land subsidence and floating underground tanks. The level measurements show
a correspondence between the degree of liquefaction-fluidization and the
amount of subsidence. The strata most susceptible to liquefaction are
hydraulically emplaced dredged fill and artificial strata on thick
uncompacted Holocene deposits. On the other hand, the phenomena of seismic
isolation coursed by liquefaction had saved the single-family houses from
collapse
Subsidence by liquefaction-fluidization in man-made strata around Tokyo bay, Japan: from geological survey on damaged part at the 2011 off the Pacific Coast of Tohoku Earthquake
Geological disaster by liquefaction-fluidization happened on southern part
of the Quaternary Paleo-Kanto submarine basin at the 2011 Earthquake off the
Pacific Coast of Tohoku. Liquefaction-fluidization phenomena occurred mainly
in man-made strata over shaking 5+ intensity of Japan Meteorological
Agency scale. Many subsided spots, 10–50 m width, 20–100 m length and
less than 1 m depth, by liquefaction-fluidization distributed on reclaimed
land around northern Tokyo bay. Large amount of sand and groundwater spouted
out in the terrible subsided parts. But there are little subsidence and no
jetted sand outside the terrible subsided part. Liquefaction-fluidization
damaged part at the 1987 earthquake east off Chiba prefecture re-liquefied
and fluidized in these parts at the 2011 great earthquake. The damaged area
were more wide on the 2011 earthquake than the 1987 quake. Detailed
classification maps of subsidence by liquefaction-fluidization on the 2011
grate earthquake were made by fieldwork in Chiba city around Tokyo bay. A
mechanism of subsidence by liquefaction-fluidization in man-made strata was
solved by geological survey with continuous large box cores on the ACE Liner
and large relief peals of the cores at a typical subsided part