NEFEMA (Scenario Catalog)

ShakeMap Scenario Catalog for Selected Historical New England Earthquakes

Contact

Email

Thomas Pratt (USGS) <tpratt@usgs.gov>

Authors: Thomas Pratt (USGS), John Ebel (Boston College, john.ebel@bc.edu)

Description

Event Selection

These are maps of ground shaking from five scenario earthquakes that could affect the New England region based on known historical earthquakes, plus an additional scenario for a hypothetical earthquake directly beneath the city of Boston. Input parameters are based on what is known about these historical earthquakes, based largely on the work of John Ebel at Boston College (Ebel, 2019).

Historical earthquakes included in the scenarios are:

June 1, 1638, central New Hampshire, USA, M6.5. The 1638 earthquake is described in Ebel and Starr (2018). The earthquake is known from strong shaking described by colonists in eastern Massachusetts and Trois-Rivieres, Quebec, although damage apparently was minimal (Stevens, 1991). It is estimated to have occurred in central New Hampshire, so modern seismicity and focal mechanisms were used to infer that the earthquake was on a reverse (thrust) fault between 3 and 10 km depth. The thrust fault is inferred to project to the surface near the Pemigewasset and Merrimack Rivers, and the hypocentral depth in the scenario was placed at 7.5 km depth.

February 5, 1663, St. Lawrence River Valley, Charlevoix, Quebec, Canada, M7.7. This earthquake is described in Ebel (2011), with a magnitude of at least 6.9 and possibly as large as 7.7, with the best estimate being 7.5. Damage primarily consisted of fallen chimneys at Trois-Rivieres, Quebec, and minor damage at Quebec City (Stevens, 1991), with some chimney and wall damage in Boston (Ebel, 2011). We chose the upper end of the magnitude range to examine the worst-case scenario, with the hypocenter placed at 26 km depth.

September 16, 1732, Montreal, Quebec, Canada, M6.2. This earthquake is described in Leblanc (1981), who estimated the magnitude to be in the body wave magnitude range of 5.6 to 6.0. Leblanc (1981) concludes that a location near Montreal is consistent with the intensity data. Damage in the earthquake was primarily in Montreal and consisted of three seriously damaged buildings and damage to several houses (Stevens, 1991). In the scenario, we use the upper end of the magnitude range to see what its effects would be in New England.

November 18, 1755, Cape Ann, offshore Massachusetts, USA, M6.6. This earthquake caused significant damage in eastern Massachusetts, eastern New Hampshire, and southern Maine, and is the largest earthquake known to have occurred in the New England region. Based on analyses of intensities, the location is estimated to have been about 40 km ENE of Cape Ann, Massachusetts (Ebel, 2001; Backun et al, 2003). The moment magnitude is uncertain. A range of 5.6 to 6.6 is suggested depending on location (Backun et al., 2003), with Ebel (2001) favoring a moment magnitude of 5.9. We use the upper end of the magnitude range to examine the worst-case scenario.

October 29, 1727, Newburyport, Massachusetts, USA, M5.9. This earthquake is known from felt reports from throughout eastern New England, consisting of a mainshock followed by numerous aftershocks that may be still continuing (Ebel, 2000). Its epicenter based on felt reports and ongoing seismicity is thought to be shallow and northwest of Newbury, MA. The earthquake caused liquefaction in the Newbury area (Tuttle and Seeber, 1991). It is estimated to have had a body wave magnitude of about 5.6, but we use a moment magnitude of 5.9 to model the worst-case scenario in case the historical estimate is low.

Boston, Massachusetts, USA, scenario M5.9. We add an additional scenario to the historical earthquakes with a M5.9 earthquake directly beneath Boston, Massachusetts. There has not been a recorded earthquake of this magnitude in this location, but such an earthquake is plausible. The purpose of this scenario, therefore, is to estimate damages from a moderate earthquake directly beneath the largest city in the region. We used nearly the same parameters as those used in the 1727 Newburyport earthquake scenario, shifting the location to be directly beneath downtown Boston, MA, with a deeper hypocenter.

Earthquake Parameters

The fault parameters are summarized in Table 1.

Table 1
Scenario Name Length (km) Hypocenter Latitude Hypocenter Longitude Moment Magnitude Depth (km) Slip Sense Reference
Cape Ann 25 42.793 -70.123 6.6 7.5 reverse Ebel et al. 2000, Ebel 2006
Central New Hampshire 23 43.425 -71.640 6.5 7.5 reverse Ebel et al. 2000, Ebel and Starr 2018
Charlevoix 135 47.645 -70.135 7.7 26.0 reverse Ebel et al. 2000, Ebel 2011, Lamontagne and Ranalli 1997
Montreal 15 45.770 -73.545 6.2 8.0 reverse Ebel et al. 2000, Leblanc 1981
Newburyport 8 42.795 -70.898 5.9 7.0 reverse Ebel et al. 2000, Ebel 2000
Boston 8 42.400 -71.043 5.9 10.0 reverse Ebel et al. 2000, Pratt

Ground Motion Models

The ground motion models used for the scenarios are a weighted combination of models for reference rock conditions that is consistent with the 2023 version of the USGS National Seismic Hazard Model. Details about the ground motion models are provided in Petersen et al. (2024).

The ground motion parameters in ShakeMap are converted from the average horizontal component, which is given by most ground motion models, to the peak horizontal component. This is necessary for consistency with real-time ShakeMaps. Additional details are discussed in this section of the ShakeMap manual (Worden et al., 2020).

References