Earthquakes in the United States? California is probably the first state that comes to mind. The largest earthquake with an estimated 8.7-9.2 magnitude in the contiguous US was a megathrust earthquake off the coast of Washington state on 26 January 1700. Because of Conevery Bolton Valencius, we know that the 1811-1812 earthquakes in today’s Missouri, which reached magnitudes of between 7 and 8, were felt over large parts of the Central and Eastern United States. The East Coast has experienced some strong earthquakes in the past—most recently on the 23 August 2011, when an earthquake in Virginia with a magnitude of 5.8 and a maximum perceived intensity of VII (very strong) damaged the Washington monument and the National Cathedral in Washington, D.C., among other buildings.
In May 2018, I spent a month in the US visiting several archives to study the weather in the 1780s to see what sort of impact, real or imagined, the Laki Fissure eruption in Iceland, the topic of my dissertation, might have had on North America. In Europe, it caused a sulfuric-smelling dry fog that lasted for about two months, and it was associated with several other extraordinary natural phenomena at the time. In the US, I studied mostly meteorological records, diaries, correspondence, and annotated almanacks. The latter turned out to be a very fruitful source for reconstructing historical weather. Almanacks were printed the year before, but they contained (sometimes individually added) blank pages next to the printed page about every month of the year, which were used to describe the local weather of the respective month. Usually the blank page was a list, numbered 1 through 31 for the days of the month, with additional information on the weather of the day, information on farming or harvest, personal events, as well as mentions of anything extraordinary. An earthquake on the East Coast would certainly fall into the latter category. Not expecting to learn about earthquakes in North America, I was fascinated to find a description such as this:
“29 [November] Sat[urday]. Clear. Mr. Philip Derheimer spend [sic] the evening at my home. At about twenty minutes after 10 o’clock at night I felt an Earthquake walking through the room upstairs by the Rattling of the Windows which lasted about a half a minute.“
I found this mention in the diary of Jacob Hiltzheimer, a German immigrant, who emigrated from Mannheim to Philadelphia in 1748. He was a farmer in Philadelphia at the time.
Many of the diaries I studied in the American archives mentioned this earthquake—in Philadelphia, New Haven, Boston, and Worcester. Most of these entries are really brief, usually only consisting of a few words, such as the line “Between 10 & 11 [pm] a small shock of an Earthquake” from Cotton Tufts’ diary on 29 November 1783. He lived in Weymouth, Massachusetts. The fact that diarists from several different states reported on the earthquake, means the earthquake must have been felt over a large area and must in fact have been quite strong, but not strong enough to cause widespread destruction.
Several contemporary newspapers also featured reports about this earthquake, such as this one in the Pennsylvania Packet and General Advertiser, published in Philadelphia, from 2 December 1783:
“On Saturday night last, about a quarter after ten o’clock, a smart shock of an earthquake was felt in and about this city; and about one o’clock on Sunday morning another, less violent, was felt by many people in the city and suburbs. Most of the houses were very sensibly shaken so that in many the china and pewter, &c. were thrown off the shelves, and several persons were waked [sic] from their sleep. We hope that the country has sustained no damage by this convulsion of nature, which brings fresh to our memory the late calamities of Italy, &c, &c.”
Indeed, the earthquake(s) seemed to have awoken many people along the East Coast, famously, however, George Washington was not one of them. According to Ron Chernow’s Washington: A Life, Washington was staying at the Fraunces Tavern in Lower Manhattan, New York, at the time, and Chernow argues, a man who has been through war isn’t unsettled easily.
Today we know that this earthquake on 29 November 1783 originated in New Jersey, probably in the Reading prong on the 12 km wide Ramapo Fault, but the location has an uncertainty of 100 km (according to Sykes et al. 2008). The USGS states that it reached a magnitude of 5.3 and an intensity of VI (strong) on the Modified Mercalli Intensity Scale, which is a category of an earthquake “felt by all; many frightened and run outdoors, some heavy furniture moved; a few instances of fallen plaster or damaged chimneys; damages slight” and therefore is in accordance with the description in the newspaper. The earthquake was preceded by a magnitude 4.65 foreshock at around 9 pm local time (according to Sykes et al. 2008) and a less severe aftershock at around 2 am, both were only felt in New York and Philadelphia.