An Enigmatic Report

When a felt report is found for the New Madrid earthquakes the hope is that it will be informative with specifics like date, time and effect of the earthquake at that location.  Many times the report will only have one or two of those pieces of information that are needed to make it a totally useful felt report.

Here is an example that informs and mystifies at the same time;

This is one of the northernmost felt reports for the New Madrid earthquakes from Prairie Du Chein in Wisconsin.  At the time of the earthquakes is was an isolated trading post and on the far edge of American occupation of the Louisiana Territory.  The report lacks some crucial information.  For instance it does not give the date the earthquake was felt. One is left guessing which one of the three main earthquakes the author is talking about.  The other information is on effect and leaves the researcher wanting more information.  It relates that the earthquake was "severely felt" without defining what that would be.  No information on the specific effects is given meaning little can be done to quantify the report. It also mentions that the earthquake is noted in "several letters" holding hope that they might survive in some archival collection and provide more information.  Somtimes a hint like this can provide clues on finding more information on the earthquakes.  It give the researcher more incentive to dig for information.
(Source New Madrid Compendium, Far Field Catalog, Article "We Have Learned..." Worthington, Ohio, Western Intelligencer, March 27, 1812, Item Number 1205. ( Original Source St. Louis, Louisiana Gazette date unknown.

More on Felt Reports

In the previous post I mentioned the esoteric art of felt reports and tried to define what they were and how they were used.  In this post I will give an example of  New Madrid felt report and what can be learned from it.

Here is a brief example

New Madrid item 18121228_nmad_2_27

Our correspondent at Cape Girardeau has [unreadable] us with the following notice on the Earthquake.

Dec. [unreadable], 1811.

The concussions of the Earthquake which commenced at two o'clock on Monday morning still continue. We have experienced five severe shocks which split brick houses and damaged five brick chimneys in this place."

J.M.F.

The first thing you will notice is that the account in the original image is very hard to read.  It the reason the Compendium has transcripts of the felt reports to make them easy to read .Next you will notice that the account notes  the time that the first earthquake occurred on December 16, 1811.  Time in 1812 was not standard and so there is a variance in the stated times when earthquakes occurred.  Local time at each location can vary by 30 minutes or more depending on location.  Time was set at each location probably by noting when the sun reached noon then setting a clock accordingly.  The account goes on to note that there were five severe shocks but does not say if they were aftershocks or during the original earthquake on December 16.  And finally the account notes that the damage as being houses split and damage to chimneys.  This damage can be quantified  using a measurement called the Mercali Scale.  This scale will be the subject of another post.

A Close One

Sometimes earthquakes happen very close to Memphis. During the Labor Day weekend a small earthquake occured near Marion Arkansas which is north of West Memphis Arkansas.  The distance from Memphis was 14 miles northwest of the city.  It has been a while since we have had one this close to CERI as they are usually further north along the New Madrid Seismic Zone.
For more information: Marion Arkansas Earthquake

The Esoteric Art of Felt Reports

In the era before seismic instrumentation became available and reliable the only source of information on earthquakes were the written accounts left by eyewitnesses to the event.  In the modern short hand of seismology they are referred to as felt reports.  These reports  reflected the education and interests of the observers who recorded their observations.  To modern researchers these accounts are a gold mine of information if used properly. The sources of these reports are as varied as the persons who recorded them  They can be in diaries, letters, legal documents, and in almost any written record contemporary with the earthquakes.  One of the most prolific sources of felt reports are contemporary newspapers.  With the effort to catalog and preserve early newspapers came the preservation of vast amounts of written felt reports.  The problem is finding them in the ocean of the surviving printed words.  Many of the accounts that you have seen on the blog are from the effort to find New Madrid felt reports to help better understand the earthquakes.