Wednesday, June 16, 2010

Cleveland Earthquake History - F.A.Q.

Just last Thursday, we received calls in the newsroom about an earthquake out in Lake County.  Each time an earthquake happens, it never ceases to amaze me how many people are shocked that they actually occur here in Northeastern Ohio.  The prevailing thought is that earthquakes in the Cleveland area are a relatively new phenomena.  In reality, quakes have been a regular occurrence in northeastern Ohio since the last glacial period 15,000 years with the root, quake-driving structures beneath the surface present for undoubtedly millions of years or longer.

In order to better document and understand the small quakes throughout the state, the Ohio Seismic Network was formed in 1999 to better track these tremors.  25 stations are distributed across the state, more in earthquake prone areas, to accurately detect and measure the quakes.

Rather than continue siting trivia about earthquakes, I've compiled a list of frequently asked questions from the Ohio Seismic Website that mirrors the requests we receive via email and phone calls each time an earthquake occurs.

Q:  What is the largest earthquake recorded in the Cleveland area?

The largest earthquake since 1700 was in 1986, January 31st pictured below.  This was the first earthquake where injuries were reported.  Prior to this quake, most people in Northeastern Ohio were unaware of how strong earthquakes can get in this area of the state.  It ranks third all-time in the state behind the 1937 quake in Shelby county.  

Q:  How many quakes have caused minor to moderate damage?

Only 15 quakes have caused this level of damage--a very low number.  Below is a map of the earthquakes across the state.  Notice the higher concentrations in our area (Cleveland) and in western Ohio.

Q:  Can we be affected by distant quakes like the ones in California and Alaska?

Absolutely.  Seismographs around the world can detect the waves from these massive earthquakes.  The 7.9-magnitude Denali, Alaska earthquake on November 3, 2002 caused water-level changes in some Ohio wells.

Q:  What causes the Ohio earthquakes?

In our area, extremely small fault lines--compared to the ones in California--are the focus of our seismic activity.  Studies have suggested that these fault lines might be remnants of an ancient fault line from a billion years ago.  Yes, BILLION.  See the known faults below followed by a map of faults around Cleveland, Ohio.

Q:  Since our ground in northern Ohio is more sediment, gravel and sand in nature, an earthquake is more apt to be weakened and absorbed causing less damage than if we lived on more rocky ground.  True or False?

The answer is false.

Q:  How many fault lines are there in the Cleveland area?  Can we see them?

There are many fault lines across the region.  A large number exist that are not mapped.  The map above
shows the mapped fault lines and other deep structures that cause earthquakes.

There are studies currently underway that aim to map the deep structures that cause the earthquakes
around the state. Since we do not have large earthquakes (magnitude 5 or greater) the data needed from earthquakes to map these small fault lines is incomplete.

Q:  Do earthquakes occur more often now than in the past?

Examining this list, you could easily conclude that this is the case.  But the list is misleading.  Most
earthquakes less than a 3 on the scale were not reported as they are today.  So the list is more detailed
now with better instruments to detect them.

The list can be found HERE.

Since 1776,  more than 160 earthquakes have been documented with more than 70 quakes since 2000. Only 3 quakes greater than 3 on the Richter Scale and one quake greater than a 4.  That was in 2001 east of Edgewood in Ashtabula county.  Contrast that with more than 138 earthquakes reported in Alaska from June 12th through early June 15th.

Q:  Since the tsunami in the Pacific back in 2004, people have wondered if such an event could occur over Lake Erie.  Is this possible?

According to the Ohio Seismic Network, the chances are almost zero.  Why?, an earthquake of at least a 7.0 or greater would be needed over the lake.  The fault line would need to move vertically displacing the rock and sediment.  All of the faults in Ohio are horizontal.  Many scientists believe that the vertical displacement would need to occur in very deep water.  Lake Erie is very shallow--average depth of 62 feet and relatively flat on the bottom.  The depth of the ocean near the location of the tsunami in 2004 is more than 12,000 feet!

Q:  How do I report an earthquake?

Call the Ohio Seismic Network at 614-325-1051

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