Earthquake Risk and the New OhioSeis Network
Mike
Hansen (Ohio Geological Survey, Columbus, Ohio, USA)
Ohio State University, Columbus, Ohio, USA
8 April 1999
OhioSeis
earthquake detection network - geosurvey.ohiodnr.gov/earthquakes-ohioseis/ohioseis-home
[Note: this link will not work in Safari,
apparently. It will work with Google Chrome and likely other browsers.]
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.