(from Summer 1986 Ohio Geology)

On January 31, 1986, many northeastern Ohio residents were startled into the realization that this area is seismically active; historically, the region has the second highest frequency of earthquake activity of any area of the state. Only Shelby County and vicinity in western Ohio have experienced more earthquakes in historic times. The 1986 northeastern Ohio earthquake has the distinction of being the most intensively studied Ohio earthquake, the first earth quake in the state for which injuries were recorded, and the nearest earthquake to a nuclear power plant in the United States. The 1986 event ranks as probably the third largest earthquake in Ohio.

The January 31st earthquake struck just before 11:47 a.m. Eastern Standard Time. Although early media speculation had the epicenter located from Columbus to southern Canada, the U.S. Geological Survey quickly determined that the epicenter was east of Cleveland, and within a few hours the epicenter had been accurately located in southern Lake County just north of the Geauga-Lake County line. This Richter magnitude 4.96 (commonly rounded to 5.0) event was felt in parts of 11 states, the District of Columbia, and southern Ontario. Most of Ohio and western Pennsylvania experienced particularly strong vibrations that were noted by numerous individuals. The Division of Geological Survey received hundreds of telephone calls in the hours after the earthquake as did numerous federal, state, and local agencies.

Early rumors of mass destruction, injury, and death turned out to be false. Although newspapers reported 17 people being treated for injuries in the epicentral area, only two injuries were a direct result of the earthquake. A woman received minor cuts from falling ceiling tile in a Mentor shopping mall and a child received a minor cut from broken window glass at Lake Erie College in Painesville. The remainder of the reported injuries turned out to be people treated for anxiety and effects of cold weather after they were evacuated from buildings suspected of being damaged by the quake.

Destruction in the epicentral area was mostly minor. Merchandise fell from store shelves in Mentor, Painesville, and Chardon and buildings in these communities experienced varying degrees of cracked plaster and cracked or broken windows. Chimneys are particularly susceptible to damage or destruction from ground motion associated with moderate to strong earthquakes. There was, however, only one confirmed report of a chimney being toppled. Local newspapers reported several other chimneys that sustained cracks or that were pulled away from a home or building in the epicentral area. Many schools in Lake and Geauga Counties were evacuated after the earthquake and inspected for structural damage. None were reported to have sustained significant structural damage, although cracks in walls were reported at several schools.

There were numerous reports from Lake and Geauga Counties of changes in water wells. The most common effect was a change in color or taste of the well water. There were several reports of wells going dry and a few even increased their flow by a considerable rate.

Many people in northeastern Ohio initially interpreted the earthquake as an exploding furnace or a truck striking the building. Less mundane interpretations included a nuclear attack on New York City or the aftershock of the explosion of the space shuttle Challenger on January 28, 1986.

Perhaps the greatest concern--and controversy--was directed toward the Perry Nuclear Power Plant in northern Lake County. The plant was not operating at the time of the earthquake but was scheduled to load fuel rods on the next day. Officials at the Perry plant, which is located about 11 miles north of the epicenter, declared a precautionary site area emergency immediately after the earthquake but downgraded this to alert status within a short time. Accelerometers on site at the Perry plant recorded accelerations as high as 0.19 to 0.23 g; the plant is designed to withstand 0.15 g. These higher values, however, were at high frequencies and represented only momentary peak accelerations not capable of causing significant damages. Inspections of the Perry plant after the earthquake disclosed only minor cracks in concrete and small leaks in noncritical water pipes. Both conditions may have existed before the earthquake, according to newspaper reports.

Because of an increased interest in earthquakes in the eastern United States, the comparatively large magnitude of the event, the potential for aftershock activity, and the proximity of the epicenter to a nuclear power plant, approximately 30 seismologists representing Lamont-Doherty Geological Observatory (Palisades, New York), University of Michigan, St. Louis University, Tennessee Earthquake Information Center, U.S. Geological Survey (Reston, Virginia; Denver, Colorado; Menlo Park, California), Weston Geophysical (Westboro, Massachusetts), University of Wisconsin, and Woodward-Clyde Consultants arrived at the epicentral area on the day after the earthquake. The primary objective of these seismologists was to place portable seismographs in the epicentral area in order to record aftershocks.

Although aftershocks are commonly considerably smaller in magnitude that the main event, the proximity of portable instruments deployed around the perimeter of an epicenter permits precise locations of focal depths for the aftershocks. Such numerous detailed seismic records can then be used to located the zone of rupture and define the direction of movement along the fault plane.

Data for the Main Event and Aftershocks of the January 31, 1986, Northeastern Ohio Earthquake

Date	Origin Time(UTC)*					Location		Magnitude	Depth	Event
Yr	Mo	Day	Hr	Min	Sec	Lat. °N	Long. °W	Richter	(Km)	Type
1986	01	31	16	46	42.3	41.65	81.16	4.96	8.00	main
1986	02	01	18	54	49.2	41.65	81.16	1.4	4.97	aftershock
1986	02	02	3	22	48.5	41.65	81.16	0.8	4.99	aftershock
1986	02	03	19	47	19.6	41.65	81.16	1.8	6.93	aftershock
1986	02	06	6	34	2.4	41.65	81.16	-0.3	2.07	aftershock
1986	02	06	18	36	22.2	41.64	81.16	2.4	5.89	aftershock
1986	02	07	16	20	20.2	41.65	81.15	1.0	4.64	aftershock
1986	02	10	20	6	13.5	41.65	81.16	0.9	4.97	aftershock
1986	02	23	03	29	48.5	41.65	81.16	-0.3	4.77	aftershock
1986	02	24	16	66	6.4	41.65	81.16	0.1	3.72	aftershock
1986	02	28	1	39	34.1	41.65	81.16	0.1	4.31	aftershock
1986	03	08	20	42	49.5	41.65	81.16	-0.5	4.42	aftershock
1986	03	12	8	55	26.7	41.73	81.17	-0.2	2.01	aftershock
1986	03	24	13	42	41.2	41.63	81.17	1.3	4.92	aftershock

Source: Rob Wesson, U.S. Geological Survey

*UTC, Universal Coordinated Time, is equal to Greenwich Mean Time (GMT) and is used to standardize all earthquakes. To convert to local time (Eastern Standard Time) subtract 5 hours (4 hours for Daylight Savings Time)from UTC. Note that events that occur in early morning hours on UTC are listed a day later than local time.

---

At least 13 aftershocks (see accompanying table) occurred after the January 31st main event and were monitored by the network of portable seismographs. It is probable that additional aftershocks occurred in the hours immediately after the main shock; however, these were not recorded because it took more than 15 hours for portable instruments to reach the epicentral area from the institutions noted above. Unfortunately, no institution currently has the instrumentation or a program to quickly respond to such events. The monitored aftershocks had Richter magnitudes of 0.5 to 2.4. The latter event was felt by some individuals in the epicentral area. Studies of the aftershock data by seismologists at Lamont-Doherty Geological Observatory indicate a zone of rupture about 1 km wide, centered at a depth of about 6 km, and striking north-northeast. Faultplane solutions based on these aftershock data indicate right-lateral strike-slip displacement on the fault. This orientation of the fault plane is consistent with the northeasterly directed axis of maximum horizontal compression that is characteristic of the regional stress field. The aftershocks tended to cluster in a pattern reminiscent of a vertical cylinder and were probably concentrated in the periphery of the main rupture.

Relatively few aftershocks were associated with the January 31st earthquake, perhaps because of a significant drop in stress after the main event. Seismologist Leonardo Seeber of Lamont-Doherty Geological Observatory suggests that faults in the eastern United States can produce larger earthquakes than similar-sized faults in the western United States. Although most of the aftershocks occurred within a few days of the main event, monitoring will continue on a reduced scale for at least two more years through a program funded by the Cleveland Electric Illuminating Company and carried out under the direction of Rev. William Ott of John Carroll University in Cleveland.

An initial concern of several geologists immediately after the January 31st event was that it may have been induced by a Calhio deep-disposal well located near the town of Perry, approximately 8 miles north of the epicenter. This we II has been injecting liquid wastes from agricultural manufacturing into the Mt. Simon Sandstone at a depth of about 6,000 feet since the early 1970's. Since that time more than 300 million gallons of liquid have been injected into the Mt. Simon and Kerbel (Maynardsville), units of Cambrian age that overly the Precambrian crystalline rocks of the basement.

There are several documented cases of seismic activity being induced by injection of liquids, including the famous Denver, Colorado, series of earthquakes in the late 1960's. Geologists from the U.S. Geological Survey and several other organizations examined available data pertaining to the injection well and the earthquake but no definite correlation could be made between them. Although the involvement of the injection well in the seismic activity could not be totally ruled out, most geologists who studied the available data concluded that there was a low probability for a case of induced seismicity. The historic seismic activity in northeastern Ohio, which long predates the Calhio injection well and indeed any drilling or deep mining activity in this part of the state, suggests that seismic activity in this area is not a result of human activities.

INTENSITIES AND FELT AREA

As is common and might be expected, the highest intensities for the January 31st earthquake were in the epicentral area. An onsite canvass of damages in the epicentral area by a geologist from the National Earthquake Information Center (U.S. Geological Survey, Denver) determined that the highest intensities were in the VI range on the Modified Mercalli Intensity Scale.

It is apparent from damage and felt reports that there was variation of intensities in the epicentral area. Damages in Mentor and other lakeshore communities can probably be attributed to the effect of amplification of ground vibrations by relatively thick sequences of lake clays and glacial sediments. Although it is not well documented through detailed studies, newspaper accounts and eyewitness reports to the Survey indicate that structures located above deeply buried preglacial valleys experienced higher ground motions than did similar nearby structures situated on bedrock. Such phenomena are typical of many earthquakes.

The irregularities of the isoseismal lines on the isoseismal map are not well understood at present. The northeastward elongation of these contours into Ontario coincides with the orientation of the earthquake-generating fault and may represent a focusing of seismic energy in this direction. Various isolated pockets of higher or lower intensities at some distance from the epicentral area are poorly understood at present but are probably related to local geologic conditions.

FAULTS

In the days after the January 31st earthquake there was considerable public interest in the location of faults in the epicentral area and in northeastern Ohio in general. Many people were surprised to learn that few faults are known from surface exposures in Ohio and none are known to be exposed at the surface in northeastern Ohio. There are several reasons for this circumstance. It is probable that most significant faults in the state, and certainly the earthquake generating ones, originate in the crystalline basement rocks that underlie Ohio. Many of these faults are thought to be ancient ones that were initially formed hundreds of millions of years ago.. They are zones of weakness that periodically experience failure in the current stress field. It is probable that many of these basement faults do not reach the surface because they die out within the sedimentary rock sequence that overlies the basement rocks. Faults that may extend to the surface are difficult to detect because in many areas of the state outcrops of rock are limited owing to lack of relief of the land surface, a thick vegetational or soil cover, and a mantling of glacial sediment over the bedrock. In addition, many areas of the state have not been mapped, geologically, in detail, although the Survey's statewide county geologic mapping program will eventually remedy this situation.

Several faults have been mapped in northeastern Ohio on the basis of oil and gas well data. No faults were detected in the epicentral area of the earthquake in this mapping study; however, there is an insufficient number of oil and gas wells in the area from which structural determinations can be made.

There was considerable publicity in some northeastern Ohio newspapers about a supposed earthquake-related geologic structure exposed along Bates Creek in Lake County. A photograph of this structure (see Ohio Geology, Winter 1985) was featured in Charles S. Prosser's Devonian and Mississippian formations of northeastern Ohio, published in 1912 (Ohio Geological Survey Bulletin 15). Recent field investigations by Weston Geophysical geologists of this and similar structures revealed the presence of more than 75 similar features in a two-quadrangle area near the epicenter of the 1986 earthquake. No ne of these features could be traced at depth. They are interpreted to be either stream anticlines (see Ohio Geology, Winter 1985), or soft-sediment deformational features formed soon after deposition of the sediments, or they possibly may be related to disturbance by glaciers of the Pleistocene ice age. These structures clearly do not have any apparent relationship to deep faults or seismic activity.

PREVIOUS EARTHQUAKE ACTIVITY IN NORTHEASTERN OHIO

At least 19 earthquakes are known to have occurred in the northeastern Ohio counties of Ashtabula (1), Cuyahoga (7), Lake (4), Lorain (1), Portage (3), and Summit (3) prior to the 1986 Lake County event. Most of these earthquakes, the earliest of which occurred in 1836, predate the availability of seismographs and are therefore located and rated as to intensity on the basis of newspaper and other historic accounts. These data have recently been researched and evaluated in detail by personnel from Weston Geophysical.

These accounts suggest that most of the previous seismic activity in northeastern Ohio was of relatively low intensity and associated with only minor and isolated damages such as a few broken windows and items falling off shelves. One earthquake, which occurred on March 9, 1943, had a Richter magnitude of 4.7 and an epicentral intensity of V. No significant damages were reported from this quake, which had a felt area of 220,000 square kilometers (85,000 square miles). This event was originally assigned a location beneath Lake Erie, offshore from Ashtabula County; however, recent reevaluation of the seismic records of this event by seismologists from the U.S. Geological Survey placed the epicenter on the Lake-Geauga County line, near the epicenter of the 1986 event.

It should be kept in mind that the epicentral locations of all of these historic, noninstrumentally located earthquakes in northeastern Ohio are subject to some error, perhaps as great as 10 or 20 miles. A margin of error in location also applies to instrumentally located events prior to the 1986 earthquake because of the small nature of most of them and the poor distribution of seismographs. It is prudent, therefore, to avoid inferring apparent alignments of epicenters as indicating fault trends. If the January 31, 1986, event were located solely on the basis of newspaper accounts of damages, the epicenter probably would have been placed between Painesville and Mentor, two communities that reported damages. The precise location of the event was primarily the result of monitoring the location of aftershock activity with portable seismographs that were placed in the epicentral area.

Although the January 31, 1986, Lake County earthquake and its aftershocks qualify as the best documented and most thoroughly studied seismic event in Ohio, there is still little understanding of the source mechanism for this and other earthquakes in various parts of the state. Such uncertainty applies, in general, to earthquakes throughout the eastern United States.

ACKNOWLEDGMENT

We thank Carl Stover and Robert L. Wesson, U.S. Geological Survey; John Armbruster and Leonardo Seeber, Lamont-Doherty Geological Observatory; Preston Turner, Weston Geophysical; and Rev. William Ott, John Carroll University, for providing information used in this article. --Michael Hansen

FURTHER READING

Hansen, M. C., 1986, Earthquakes in Ohio: Ohio Division of Geological Survey Educational Leaflet No. 9. [619 KB pdf]

Wesson, R. L., and Nicholson, Craig, eds., 1986, Studies of the January 31, 1986, northeastern Ohio earthquake: U.S. Geological Survey Open-File Report 86331, 131 p.

---

Last update March 04, 2003