Rare East Coast earthquake might have caused changes in local groundwater
What happens above the Earth’s surface was dramatically apparent this week in places from Mineral, Va., to Washington, D.C., but what’s not so obvious are impacts beneath the surface to groundwater, said the National Ground Water Assn. (NGWA).
While it’s too early to assess in Virginia and surrounding areas, earthquakes commonly cause fluctuations in groundwater levels and damage to water wells systems, said NGWA Public Awareness Director Cliff Treyens.
“Since aquifers are water-bearing subsurface formations, it makes sense that water levels and wells would be affected,” Treyens said. “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, the well will be drilled until it hits a fracture or crevice that holds water. A moderate earthquake could easily alter that configuration, Treyens said.
Aquifers consisting of unconsolidated materials can compact, or become unstructured as a result of seismic energy moving though during the earthquake, in a process called “liquefaction.” This results in a loss of storage for groundwater and subsidence on the ground’s surface.
While surface structures are often designed to resist earthquakes, the same cannot be said of water well construction, and as a result wells are often destroyed. Earthquakes also can affect groundwater quality, sometimes causing turbid well water.
In addition, water wells can actually function as seismometers. In a sense, water wells can reflect the Earth tide, which is a separate—but related—phenomenon from 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 can occur in the aftermath of an earthquake. A water well in Christianburg, Va., has become renown, picking up 200 large earthquakes around the world since real-time monitoring began in 2004.