Earthquake in Japan Affects Groundwater Worldwide

Posted: May 15, 2011 in Uncategorized
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From the American Geological Institute

The Earthquake-Groundwater Connection

Cliff Treyens, National Ground Water Association

What happens above the earth’s surface was dramatically apparent in the March 11, 2011 earthquake that devastated parts of northern Japan. What’s not obvious are the likely 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 well 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. One well driller after a California quake cited a well that produced 60 gallons per minute (gpm) 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 said, “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 on 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, such as happened in Japan, bacterial and chemical contamination of groundwater wells 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.

Water wells can reflect the earth tide, which is separate but related 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. These effects can occur far from the source earthquake. A several inch rise in the water table was noted in a major Florida aquifer within 34 minutes after the Japan earthquake. A well in Christianburg, Virginia, has become renowned, picking up 200 large earthquakes around the world since real time monitoring began in 2004.

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