Wednesday, October 1, 2014

Earth-Shaking Mystery


Was a sizeable earthquake that rocked Knoxville, Tennessee, on March 28, 1913—just when the massive floodwaters were receding from Ohio and Indiana—somehow related to or even triggered by the Great Easter Flood?

BOOM! 

At the loud shock of what sounds like the building’s boiler exploding, reporters at The Journal and Tribune in Knoxville, Tennessee, rush to the windows. On the sidewalks below, people are pouring out of office buildings, factories, and stores into the streets.
Front page story of the Knoxville Journal and Tribune for Saturday, March 29, 1913, about the earthquake shaking the city the afternoon before.

Simultaneously, every phone in the newspaper offices starts ringing, anxious residents demanding answers to the same questions the reporters themselves are wondering: “Was that an explosion?” “The marble courthouse shook like a leaf for half a minute!” “It woke me from sound sleep!” “Pictures fell from the walls, the clocks stopped, and the brick chimney of my neighbor’s house fell into my yard!” “Did a meteor hit us?” “The asphalt paving in the street literally cracked!” “The earth literally jumped! It made me feel queasy, physically ill.”

…BOOM!

A second loud shock with a whip-like motion of the earth, maybe three minutes after the first one around 4:55 PM Friday, March 28, 1913, set off a fire alarm near the Southern Railway depot. Dinging fire trucks race through the streets to the scene, fearing a locomotive had exploded… but there is no fire. Phone calls to the newspaper offices become even more frantic, reporting wild rumors: the Knoxville Banking & Trust Co. building collapsing, an oil truck exploding, gunpowder at the Hand Powder Co. igniting, or a magazine at zinc mines at Mascot blowing up—all of which the reporters verify to be false.

“Get close to the walls!” shouts a man at the weekly planning meeting of the directors of the National Conservation Exposition. “The building is falling in. Maybe the walls will hold.” In instants, the dozen men are hugging walls as the building sways. 

That warning may have been shouted by geology professor C. H. Gordon of the University of Tennessee, who is attending the meeting, and who instantly knows exactly what was happening: an earthquake. Indeed, the fact that objects in the room were being thrown up and down instead of side to side suggests to Gordon that Knoxville itself was right over the center of the earthquake.

That earthquake realization dawns also on the reporters, after they start receiving calls from towns miles outside of Knoxville—Newport, Sevierville, Morristown, Maryville, Jellico. Clearly, this phenomenon was so widespread it could be no mere explosion: it had to be an earthquake—indeed, the most severe the city had experienced since the Big One of 1865. 

At "ground zero" Dayton, Ohio, of the 1913 flood, homes were
inundated up to their eaves. Credit: Dayton Metro Library
But Knoxville residents are jumpy. As one reporter at The Journal-and Tribune rather breathlessly observed in a long article on March 30, “There have been so many appalling floods and disasters of late that they have preyed upon the minds of people, and the disposition of the public just at this time is very excitable, everybody’s nerves at high tension, and most anybody is prepared to believe that almost anything bad may happen.” 

Map in Bulletin Z
documented flood down
the Mississippi River.
In fact, on Friday, March 28, just as the earthquake struck Knoxville, the massive, multistate Great Easter Flood precipitated by unprecedented rains beginning Sunday, March 23, was still well in progress—although the floodwaters were just receding from the streets of “ground zero” Dayton, Ohio, where entire houses had been inundated to their eaves (see “Like a War Zone”). The flood crest cascading down the Ohio River had not yet reached Paducah, Kentucky.

The public nervousness was not helped when an aftershock struck Knoxville less than three weeks later, on April 17 (at which time the devastating floodwaters had poured out of the Ohio River and the flood crest was bursting levees halfway down the Mississippi River. 

Mid-continent active seismic zone

Earthquakes in Knoxville, Tennessee??

Yes, indeedy. In fact, just this year (July 2014) the U.S. Geological Survey released new maps upgrading the seismic risk of living in eastern Tennessee.

How extensive was the March 28, 1913 earthquake and the April 17 aftershock? Fortunately for researchers today, University of Tennessee geologist Gordon immediately began scouring Knoxville and the surrounding areas, surveying damage and interviewing residents. His field work and map, published in the December 1913 Bulletin of the Seismological Society of America, revealed that the quakes had been felt over a 7,000-square-mile area. 

Cover of July 2014 USGS report.
I added an arrow pointing to
Knoxville in a seismic zone.
How strong was the March 28, 1913 earthquake? 

In 1913, the familiar Richter scale that measured the magnitude of earthquakes—that is, the amount of energy the earthquake released—had not yet been invented (it was introduced by Caltech seismologist Charles Richter in 1935. And FYI: since the late twentieth century, the Richter scale has now been supplanted by the moment magnitude scale, because the monumental Chilean earthquake of 1960 and the Alaska earthquake of 1964 revealed the inadequacy of the Richter scale in measuring truly powerful earthquakes.) So in 1913, the scale then in use was the Mercalli scale, adopted in 1902. 
This scale comparing the Modified
Mercalli Scale with the Richter
scale is on the website of the
Missouri Department of Natural Resources.

The Mercalli scale measures the local intensity of an earthquake by the shaking of the earth’s surface, as indicated by damage observed: chimneys falling, pavement ruptured, people running outdoors. Based on the Mercalli scale, the USGS rates the intensity of the March 28, 1913 Knoxville earthquake as VII on the Mercalli scale, although perhaps the cracked pavement might indicate it was higher—up to a IX—in some locations. 

But the Mercalli scale is not an absolute measure of the power of the earthquake itself, as the Richter and moment magnitude scales are: after all, the intensity of local shaking falls off with distance from the epicenter, and the damage observed to manmade structures depends on the soundness or flimsiness of their construction as well as on local geology. And if the quake’s epicenter is deeply buried, a stronger quake might produce less shaking at the surface than a shallower quake of lesser magnitude.

Thus, although there are scales that make rough comparisons of the Mercalli scale and the Richter scale (see the green rulers above), there actually is no one-to-one conversion between the scales because they measure entirely different things (surface shaking versus total energy released). Indeed, the Mercalli scale can be useful even today for categorizing damage to manmade structures. 

All disclaimers notwithstanding, the USGS puts the strongest earthquake in Tennessee—the big one of 1865—at a magnitude of 5.00. It also rates the 1865 quake’s Mercalli intensity as VII—yes, the same as the rating given for Knoxville in 1913. So by Midwest standards, it was an unusual and significant earthquake that would have inspired apprehension and respect even in California.

Could the Easter flood have triggered the earthquake?

To borrow the title of the 1950s TV game show, the $64,000 question is: Could the Knoxville earthquake of March 28, 1913 (if not the aftershock of April 17) have been triggered by the massive multistate Great Easter 1913 flooding of that entire week?

C.H. Gordon's map of the areas of shaking of the March 28, 1913 earthquake and its April 17 aftershock, published in the December 1913 issue of the Bulletin of the Seismological Society of America.
A flood trigger an earthquake?? Remember, this was no ordinary flood, as this entire research blog has been documenting for nearly two years. The geological stresses and strains of a sudden megatonnage of turbulent water over multiple states first deluging then receding had to be monumental for the underlying rocks. Knoxville lies in an active seismic zone. And the sheer timing gives pause: to paraphrase Rick’s famous line in Casablanca, of all the earthquakes in all the regions in all the world, this one had to occur in the Midwest as the Noachian waters were shifting…

For decades, geologists have documented that earthquakes have been triggered in active seismic zones when the reservoirs behind new dams have been filled for the first time (see “Selected references” below). That possibility concerns engineers, who want to ensure their dams are designed to withstand any likely earthquake.
Knoxville was spared the brunt of the flooding, as it received "only"
about 3 inches of rain that week. But much of its geology is
porous karst (hence its many caverns) and it is at the northern
edge of an active seismic zone. 1913 disasters plotted by Trudy E. Bell
on a base outline map of the U.S.

Natural floods have also been implicated in the triggering of other California earthquakes. And in 2011, geophysicists at two Florida universities presented a research paper before the American Geophysical Union called “Disaster triggers disasterthat showed strong statistical correlation between unusually heavy, wet tropical cyclones and subsequent earthquakes. 

I’m not a geologist or geophysicist—my background is in physics and astrophysics, with a good smattering of engineering, planetary sciences, meteorology, and history of science—nor am I familiar with the geologies of Ohio, Indiana, Kentucky, or Tennessee. So this post ends with the same open question with which it begins: Was a sizeable earthquake that rocked Knoxville, Tennessee, on March 28, 1913—just when the massive floodwaters were receding from Ohio and Indiana—somehow related to or even triggered by the Great Easter Flood?

I would very much welcome hearing from geologists and geophysicists, including exploring the possibility of collaborating on a potential research article (my historical data and your geophysical expertise). Please contact me at t.e.bell@ieee.org.

Next month:Advertising Disaster

Selected references

Bulletin Z. The Floods of 1913 in the Rivers of the Ohio and Lower Mississippi Valleys. U.S. Department of Agriculture. Weather Bureau. Washington, Government Printing Office, 1913. Principal author was Alfred J. Henry, but additional reports were contributed by five other authors.
 
Gordon, C. H., “Earthquakes in East Tennessee,” Bulletin of the Seismological Society of America 3: 191-194, December 1913.A longer version of the same article under the same title was published in The Resources of Tennessee (the journal of the State Geological Survey) 4(1): 15–23, January 1914. 


“How was the Richter scale for measuring earthquakes developed?” Scientific American. The USGS provides a somewhat technical description of the Richter scale and the moment magnitude scale. Actually, if you really want to dive deep into the weeds, there are half a dozen scales for measuring aspects of earthquakes, as described on this page of an education module developed by the Southern California Earthquake Data Center.

For more about the statistical evidence that extremely heavy, wet tropical cyclone seasons have triggered large earthquakes, see this press release from the University of Miami describing the work of Shimon Wdowinski.

There is a large body literature on reservoir-induced earthquakes. See, for example, “On the Nature of Reservoir-Induced Seismicity” by Pradeep Talwani, Pure and Applied Geophysics 150 (1997): 473–492 and “A review of recent studies of triggered earthquakes by artificial water reservoirs…” by Harsh K. Gupta, Earth Science Reviews 58 (202): 279–310. Moreover, the 2012 report Did the Zipingpu Dam Trigger China’s 2008 Earthquake? The Scientific Case by Fan Xiao of the Sichuan Geology and Mineral Bureau documents the mounting body of evidence that the 2008 magnitude-8 Sichuan earthquake that killed 80,000 people in China had been triggered by the filling of the Zipingpu reservoir.

Bell, Trudy E., The Great Dayton Flood of 1913, Arcadia Publishing, 2008. Picture book of nearly 200 images of the flood in Dayton, rescue efforts, recovery, and the construction of the Miami Conservancy District dry dams for flood control, including several pictures of Cox. (Author’s shameless marketing plug: Copies are available directly from me for the cover price of $21.99 plus $4.00 shipping, complete with inscription of your choice; for details, e-mail me), or order from the publisher.


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