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Japan: The earthquake/groundwater connection

What happens above the Earth’s surface was dramatically apparent in the recent earthquake devastating Japan. What’s not obvious to the public are impacts beneath the surface to groundwater.

While it’s too early to assess, the Japanese can expect fluctuations in groundwater levels and damage to water wells systems. Japan has the additional concern of groundwater contamination by radioactive, and other, constituents.

Since aquifers are water-bearing subsurface formations, it makes sense that water levels and wells would be affected. For example, one well driller after a California quake cited a well that produced 60 gallons per minute prior to a moderate earthquake slowing down to “practically nothing” after.

Sometimes the reason for such impacts is obvious. In bedrock formations, for instance, the well will be drilled until it hits a fracture or crevice that holds water. As one well driller says, “It wouldn’t take much to mess up that well if you had a good earthquake.”

Aquifers consisting of unconsolidated materials can compact, or become unstructured, as a result of the seismic energy moving though them during the earthquake in a process called liquefaction. This results in a loss of storage for groundwater and subsidence of the ground’s surface. Some coastal areas of Japan still remain under water even after the tsunami, which may be the result of compaction and subsequent subsidence.

While surface structures are often designed to be earthquake resistant, the same cannot be said of water well construction. The result is that often wells are destroyed.

Water quality can be affected as well. Turbidity is common and if there is associated flooding caused by a tsunami, as in Japan, bacterial and chemical contamination are common. In addition, the tsunami wave drives ocean saltwater over coastal areas, which can lead to saltwater contamination of wells located near the shore.

There is one other earthquake/groundwater connection less well known. Water wells can actually function as seismometers of sorts.

In a sense, water wells can reflect the Earth tide, which is a separate, but related, phenomenon to the ocean tides. The Earth is “pulled” by the Moon much in the same way the ocean is. This “surface tide” can cause the water in a well to go up and down in the hole, referred to as oscillation. This oscillation can occur in the aftermath of an earthquake.

There is one case of a well in Florida that oscillated up and down 17 feet following a 1964 earthquake in Alaska. A well in Christianburg, Virginia, has become renown, picking up 200 large earthquakes around the world since real-time monitoring began in 2004.

Check out some groundwater information resources related to the natural disasters in Japan and Haiti at NGWA’s Web site. | Impressum