Quake!

Earthquake, Arkansas, July 27, 2016

Quite a non-event, really.

Yesterday evening, we felt, and heard a bump – or thump – or muffled boom – that was noticeable, but not lasting.  My initial impression was  that it was a sonic boom.

It turns out that what we actually experienced was a small earthquake, with an epicenter 2.45 miles 3.9 (km) north of us and, according to the US Geological Survey Earthquake Hazards Program, was a magnitude 2.8 at a depth of 4.3 miles (7 km) .

Tiny – no big deal.

Of course, now it begs the question, what about all those others in the past that we attributed to sonic booms?  Scientists speculate that some ‘booms’ are probably small shallow earthquakes that are too small to be recorded, but large enough to be felt by people nearby1.

The following trace was recorded at Cathedral Cave in the Onondaga Cave State Park in Missouri.  Time 0:00:00 is the time of the event.  The colored marks are the times that various seismic waves reached the seismic monitoring equipment there. The location of an earthquake – and its depth are determined by comparing the times with other seismic stations.

Earthquake, Arkansas, July 27, 2016, seismograph trace from Cathedral Cavern, Missouri

The following map shows 3526 magnitude 1.0 or higher earthquakes in a square centered on Arkansas  recorded since we moved here in August, 1980. There were only 632 at or above magnitude 2.5, 57 at or above 3.5, and 1 at or above magnitude 4.5.   In the same period, USGS only has 53 quakes recorded of a magnitude less than 1.0 in the same region.

3526 magnitude 1.0 or higher earthquakes in a square centered on Arkansas  since August 1980

During the same period, the following map shows 6338 earthquakes in the region of the New Madrid fault.

8338 magnitude 0.0 or higher earthquakes in a square centered on the New Madrid Fault since August 1980

In this part of the country, earthquakes are more of a curiosity than a real danger.


1. Earthquake Booms, Seneca Guns, and Other Sounds (USGS)

arkansas, life, now that's cool!, science and nature
4 comments… add one
  • Hilary Jul 29, 2016

    Hi Mike – fascinating to read … and I’m sure there are lots of quakes happening that don’t really register … the earth continues to move – cheers Hilary
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    • Mike Jul 29, 2016

      We sure won’t take it for granted that any “booms” like that are sonic booms from jets. 😉
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  • Rummuser Jul 29, 2016

    I am glad that you are safe and that it was no big deal!
    Rummuser recently posted…Talking About My Generation.My Profile

    • Mike Jul 29, 2016

      Thanks. If we ever have anything severe, it’ll probably be from an event further away from us. The nearest significant area for significant earthquakes is in eastern Arkansas and Missouri, called the New Madrid Seismic Zone. It ranges from about 140 miles (225 km) away (Marked Tree, Arkansas) from us to over 200 mile (321 km). Historically, the zone has seen quakes with as high as a magnitude as the 7.5 to 8.0 quake that occurred on February 7, 1812, near New Madrid, Missouri, a frontier town in the southeast “corner” of Missouri. New Madrid was destroyed. In St. Louis, Missouri, 140 miles (225 km) away, many houses were severely damaged, and their chimneys were toppled.
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