Abstract

The occurrence of the 1982 Miramichi earthquake sequence in central New Brunswick brought into focus the need to improve our knowledge of historical seismicity in the Northeastern Appalachians. By combining the results of recent archival research in the Maritime provinces of Canada and in the New England states, substantially enlarged sets of felt reports become the basis for re-evaluating the epicentres and magnitude estimates of four historical earthquakes that occurred in the Maine-New Brunswick region.

For the March 21st, 1904 earthquake, estimated Modified Mercalli intensities were obtained at 237 locations from 114 references. Using the Street and Turcotte [1977] relationship between the Area IV and magnitude, a 5.9 mbLg was calculated for the 318,000 km2 area. Reid’s original location, near Passamaquoddy Bay, is confirmed. The epicentral intensity suggested is VI - VII [MM]. The October 22nd, 1869 event appears to have its epicentre in the same area as the 1904 event instead of in the Bay of Fundy as previously listed. On the basis of 85 reporting locations, an epicentral intensity VI [MM] and a felt Area IV of 228,000 km2 corresponding to mbLg = 5.7 are found. The February 8th, 1855 earthquake epicentre is located in the Moncton - Dorchester, New Brunswick area; an estimated mbLg = 5.2 is obtained from an Area IV of 80,000 km2, based on 41 locations. An I0 = V - VI is suggested. Finally, the May 22nd, 1817 earthquake, previously mislocated in central Maine, is now associated with the Passamaquoddy Bay area, on the basis of 23 reporting locations. A poorly defined Area IV gives a mbLg in the 4 1/2 to 5 range.

From this review, it is concluded that earthquakes similar in size [5 1/2 to 6] to that of January 1982 have occurred in the Maine-New Brunswick border region and that the Dorchester, New Brunswick area has experienced activity in the magnitude 5 to 5 1/4 range. Low level seismicity has also been recently detected in these same areas, suggesting the presence of seismotectonic structures.

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