Earthquake Risk and the New OhioSeis Network
Mike Hansen (Ohio Geological Survey, Columbus, Ohio, USA)
Ohio State University, Columbus, Ohio, USA
8 April 1999
It has been determined that 6 to 6.5 magnitude earthquakes are due ~ every 100 years in the New Madrid fault zone. >8 magnitude earthquakes in the New Madrid FZ have an unknown frequency - estimates range from 500 years to 20,000 years. The 1811-1812 earthquakes have little recorded effects in Ohio, but Ohio was sparsely populated then.
On 27 July 1980, there was a 5.3 magnitude earthquake in north-central Kentucky. On 25 September 1998, there was a 5.2 magnitude earthquake (the Pymatuning eq.) near the Ohio-Pennsylvania border. There is a concentration of earthquakes in western Ohio and northeastern Ohio. The southern half of Ohio has scattered earthquakes. Central Ohio appears aseismic. These earthquakes are occurring deep (~5 km), in Precambrian basement rocks. Earlier literature attributed midwestern USA earthquakes to glacial rebound, which doesn't wash well because non-glaciated areas are also affected.
In the mid-1980s, much more detailed deep geology of Ohio was gathered, including the magnetic signature of Ohio's basement, which shows lots of complexity, lots of rock types, lots of structures, etc. In the late 1980s, the COCORP line came through Ohio, which imaged crustal structures down to 30 miles or so. The COCORP line shows lots of deep faults in the basement.
Ohio's Grenville Front zone shows up well, as do lots of rift basins to the west of the GF (such as the Ft. Wayne Rift, the East Continent Rift Basin, etc.). The Coshocton Zone is considered to be the root of the old Grenville Mountains (800 my to 1 by). Reactivation of ancient structures in the basement causes these earthquakes. Structures in Ohio are few at the surface, but are plenty in the subsurface. The Bowling Green Fault is the best exposed in Ohio (in a quarry). Ohio is under a regional compressive stress oriented approximately ENE. The Indiana map doesn't show much earthquake activity. But, a 7 magnitude earthquake occurred in Indiana about 4000 years ago, according to recent research.
The western Ohio seismic zone is most active around Anna, Ohio (Shelby County). Anna experienced two ~5.5 magnitude earthquakes on 7 March 1937 and 9 March 1937. Anna is approximately located at the intersection of several faults, including the SE-NW trending Anna-Champaign Fault, the trace of which the buried Teays River Valley follows. The area around Anna was relatively quiet since 1937, until a July 12, 1986 earthquake near St. Marys.
Northeastern Ohio is the 2nd most active zone in Ohio. Most earthquakes in northeastern Ohio occur in the Cleveland area. In 1943, a 4.5 magnitude earthquake hit eastern Cleveland. On 31 January 1986, a 5 magnitude earthquake hit in the eastern Cleveland area (Lake County), and did damage. This earthquake caused a lot of concern about the nearby Perry Nuclear Power Plant. The Calhio injection well is nearby the epicenter of the 1/31/86 quake, and several people proposed blaming the injection well (fluids are pumped down into the Mt. Simon Sandstone). The causality has been rejected by many, though, due to presence of historic seismicity in area.
On 25 September, 1998, an earthquake hit near Pymatuning, Pennsylvania, near the Ohio border. This earthquake is still being studied, but we do know that it occurred on a NW-SE fault. It casued some damage, but in a very small area.
Seismic risk areas in the eastern USA include: 1) New Madrid, Missouri area; 2) Charleston, South Carolina area; 3) St. Lawrence Seaway; 4) Ohio - western Ohio, northeastern Ohio, and a nebulous southeastern Ohio zone; 5) other areas as well.
A >6 magnitude earthquake tends to result in liquified sediments. Can potentially use liquefaction features in glacial cover to determine paleoseismicity records/trends. There is no clear evidence of such features in Ohio. A clastic dike-like feature has been found in Marion County, Ohio, but this is probably a glacial feature, though. Radiocarbon dates can give us ages of such features, and one can potentially determine paleo-epicenters.