Earthquakes sometimes affect the earth's surface by uplifting, downwarping, or tilting large areas; during some large earthquakes surface fault rupture occurs. Liquefaction (when surface materials behave as a liquid as a result of ground shaking) occurs during moderate to large earthquakes, and may affect large areas. Sand boils and sand fissures sometimes occur during moderate to large earthquakes. Landslides and/or lateral spreading may occur on slopes of as little as 1 to 2 degrees.
Surface water courses and groundwater levels may be changed. Water quality may also be affected: sometimes it degrades and sometimes it improves. Areas that are well drained before an earthquake may become flooded and areas that were wetlands or shallow water bodies may dry out after an earthquake. The courses of some natural drainage, especially those near local base level, may change. The apparent depth of the water table may change because of the raising or lowering of the land surface. Lateral groundwater flow may be affected by fault gouge, sand fissures or areas of liquefaction.
One impact is that man-made, gravity-flow systems, e.g., canals, ditches and sewers, may be disrupted or the designed drainage profile changed. This may result in those systems not working properly. In some areas flow may be reduced to zero or backflow may result and deposition may occur. In other areas, flow may be increased, which may cause scour, erosion, or bank failure.
Structures, including buildings, levees, roadways, transmission lines and towers, can be directly affected by fault rupture, sand boils and fissures, liquefaction, landslides and lateral spreading, and other earthquake-induced landform changes.
There is high risk for changes to natural and man-made drainage systems due to wide spread uplift, downward, tilting and local settling in the lowlands of southeast Missouri which includes the most likely epicentral areas for large earthquakes on the New Madrid fault system. This area is extremely flat-lying, sometimes having less than one foot of relief over several miles. During the 1811-1812 series of earthquakes, uplift, downwarping, and tilting of up to 10 feet or more occurred over hundreds of square miles.
Southeast Missouri, including all or parts of Dunklin, Pemiscot, New Madrid, Mississippi, Stoddard, Scott, Butler, Bollinger, and Cape Girardeau counties, is highly developed agriculturally and includes some of the most productive agricultural land in Missouri and the nation.
The agricultural development has only been possible within the last century because of the installation of a series of man-made drainage systems. Prior to this, the area was often saturated to the point of having standing water at the surface. These man-made drainage systems, including some in northeast Arkansas, have been developed and administered by several private drainage districts. All have been "cooperatively engineered" --- that is, the channels and ditches have been designed and installed to most effectively drain excess water from the land and deliver it ultimately to the Mississippi and St. Francis Rivers. The channels cross drainage district borders as well as state boundaries.
On a smaller scale, there are hundreds of municipal water distribution and wastewater collection systems in southeast Missouri that may also be adversely affected by earthquake-induced uplift, downwarp, or tilting.
The geoscience response team would document all observable landform change and damage, such as landslides, liquefaction features, sand blows, fissures, water course changes and flooding, and other earthquake-induced effects. The report generated by the team will present essential information for emergency response and post-earthquake recovery work, and for short- and long-term preparedness and mitigation planning.
No training or team mobilization trial runs for a geoscience response team have been implemented in Missouri although the DGLS has developed an operational plan, including designated geologists, needed equipment, mobilization and other immediate-response activities. Lack of funding and scheduling has prevented training implementation. Sufficient numbers of people must be trained because not all team members will be available and because the smallest team size is three persons for safety reasons. While one team may suffice for a small event, several teams may be required for even a moderate earthquake. Funding and experienced USGS direct staff support are essential requirements for training. The teams should consist of geoscience, geotechnical, lifeline and highway professionals.