John E. Ebel

A detailed record of New England earthquakes – or at least earthquakes that were felt in New England – by John Ebel, Boston College geologist. After an introductory chapter on seismology, Ebel goes over historical earthquakes in the region. For most of the time – the 17th, 18th, and 19th centuries – there were no seismographs, so Ebel has to estimate earthquake location and intensity based on historical reports – for example, did people feel the earthquake outdoors? Were there any chimneys damaged? (Earthquake magnitude is measured by seismographs; earthquake intensity is what people feel and see).

The first recorded earthquake is from 1638; based on reports from New England and Quebec, Ebel puts it at magnitude 6.5 with an epicenter somewhere in central New Hampshire. There was a major earthquake in Quebec in 1663, felt as far away as New York (then New Amsterdam). Ebel and coauthor Emanuela Guidoboni used this earthquake as an example in their book on historical earthquake research, Earthquakes and Tsunamis in the Past, to illustrate calendar comparisons. The earthquake occurred on February 5, 1663 in Quebec – which was using the Gregorian calendar with the year starting on January 1 – and on January 26, 1662 in New England, which was using the Julian calendar with the year starting on March 25.

Ebel mentions other earthquakes in 1727, 1744, 1755, 1791, 1884, 1904, 1929, 1940, 1944, 1982 and 1988. The 1929 earthquake occurred off the coast and caused a destructive tsunami, with 27 lives lost in Newfoundland; it also broke a number of transatlantic cables. The timing and location of the cable breaks lead to the concept of turbidity currents, a subject of considerable importance in sedimentology.

Ebel doesn’t speculate too much on the large-scale tectonic causes for New England earthquakes – because there isn’t much to go on. The Atlantic coast hasn’t been an active plate margin for hundreds of millions of years. Some earthquakes might be caused by isostatic adjustment after glaciations – “glacial rebound”, there was a suggestion that some might have to do with cooling of deep plutons, and it’s been theorized that the St. Lawrence River is in a “failed rift” – but none of these are heavily supported by actual observations.

Lots of relevant illustrations, and isoseismic maps for most of the earthquakes mentioned. No footnotes, and no bibliography; however some sources are mentioned in the index.… (meer)