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Earthquakes in and near the northeastern United States, 1638-1998 --
Construction of the earthquake catalog for an outreach map (on-line
edition)

*by* Russell L. Wheeler^1^

Open-File Report 00-0316

2000

This report is preliminary and has not been reviewed for conformity with
U.S. Geological Survey editorial standards or with the North American
Stratigraphic Code. Any use of trade, firm, or product names is for
descriptive purposes only and does not imply endorsement by the U.S.
Government.

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

^1^Golden, Colorado

Earthquakes in and near

the northeastern United States, 1638-1998 --

Construction of the earthquake catalog

for an outreach map

by

Russell L. Wheeler

ABSTRACT

This report provides documentation for a large-format map that is aimed
at the lay public. The map shows epicenters of known earthquakes of
magnitude 3 and larger over the northeastern United States and adjacent
parts of Canada and the Atlantic Ocean. The map area covers more than
1.3 million square kilometers, and part or all of 14 States and four
Canadian Provinces. No existing earthquake catalog provided current,
uniform coverage down to magnitude 3, so a catalog had to be made for
the map. Because the map is an outreach product, in each State or
Province it had to match the way earthquakes are represented by whatever
source is regarded as authoritative by the citizens and agencies of that
State or Province. This report outlines procedures that produced the
catalog for the map.

INTRODUCTION

The goal of this effort was to make a map for the lay public. The
purposes of the map are to inform the audience and to provide a useful
outreach tool for the hazards community in the map area. The map shows
three and a half centuries of earthquakes across a large area down to
magnitude 3 (Wheeler and others, 2001). (Throughout this report,
"magnitude" without a specified scale refers to m~b~ or an estimate of
it.) Magnitude 3 was chosen because it approximates the threshold above
which shocks would be felt within the map area. The area spans long.
66°-81° W. and lat. 38°-48° N., a polygon more than 1,100 km on a side.
It covers all of ten States and parts of another four States and four
Canadian Provinces. No existing earthquake catalog provided current,
roughly uniform coverage of the area. Instead, parts of the area are
covered by two regional seismograph networks and the Canadian national
network, and several States maintain or are compiling their own lists of
earthquakes from various sources. Accordingly, making the map required
compilation of a catalog.

RATIONALE

Catalog construction was guided by the principle that the map should
show each State's earthquakes in a manner consistent with the way that
State's authoritative persons or organizations show them. This principle
of consistency with authoritative sources in each State was urged by one
State geologist within the map area, and it was welcomed by members of
other State geological surveys who were contacted during catalog
construction. Accordingly, I contacted each State geological survey and
the Geological Survey of Canada to determine to which person, catalog,
list of earthquakes, or other authority they directed inquiries about
earthquakes. In some States, the authoritative source is the operator of
a local or regional network. In others, a geologist had been tasked with
compiling a list of the State's earthquakes. In some of these latter
instances, World Wide Web-based regional catalogs or published catalogs
could be used, in collaboration with the compiling geologist, to enhance
the State's existing compilation. In each State and Canada, the result
of these contacts and collaborations is that the map shows the same or
virtually the same earthquakes as does the source or sources that are
regarded as locally authoritative, down to magnitude 3.0.

The resulting catalog is based on approximately the same primary and
secondary sources that would have been used had a single seismologist
compiled the catalog as a research task. However, probably there are two
main differences between this catalog and one that would result from a
seismologist's research. First, I have not examined the original
seismographic or intensity data. Second, the combination of sources used
and the relative preference given to each source changed from State to
State, and from Canada to the United States. However, the map still
shows accurately the relative differences of seismicity between States
and large parts of States. The larger damaging earthquakes have been
vetted individually by local seismologists.

SOURCE CATALOGS USED IN VARIOUS PARTS OF MAP AREA

[Emb.cc:]{.underline} This catalog was compiled for use in making the
1996 USGS national seismic hazard maps (Frankel and others, 1997;
Mueller, Hopper and Frankel, 1997). Within the map area emb.cc extends
through June 16, 1995, and is dominated by contributions from the
NCEER-91 catalog (Seeber and Armbruster, 1991) through February, 1985
and from the USGS PDE afterward. Emb.cc uses the m~b~ scale and extends
down to m~b~ 3.0. I obtained a digital version of the part of emb.cc
that covers the map area (C. Mueller, written commun., September 24,
1998), and added records from the USGS PDE through 1998 (URL
http://wwwneic.cr.usgs.gov/neis/epic/epic.html).

[LCSN:]{.underline} The Lamont Cooperative Seismic Network has been
operated since 1990 by the Lamont-Doherty Earth Observatory and
cooperating institutions in New York, New Jersey, Vermont, and Delaware.
The LCSN and NESN are the successors to the NEUSN. Records include one
or more of M~c~, m~b~, and M~N~. I obtained a digital catalog covering
1991 through 1998 (W.-Y. Kim, oral and written communs., May 14 and 20,
1999).

[NCEER-91:]{.underline} The National (now Multidisciplinary) Center for
Earthquake Engineering and Research funded L. Seeber and J. Armbruster
of the Lamont-Doherty Earth Observatory at Columbia University to
compile existing catalogs for the central and eastern U.S., and to find
and incorporate a wealth of archival intensity reports of historic and
early instrumental earthquakes. Results improved locations, magnitude
estimates, and completeness (Seeber and Armbruster, 1991). The catalog
extends through 1985 and down to magnitude 3. The magnitude scale used
is m~b~ (Sibol, Bollinger and Birch, 1987). NCEER-91 is represented on
the map by having been incorporated into emb.cc, and through comparison
of numerous records of individual earthquakes to entries in NCEER-91
(URL http://elwe.ceri.memphis.edu/\~seisadm/cat_nceer.html).

[NESN:]{.underline} The New England Seismic Network has been operated
jointly by Weston Observatory of Boston College and the Massachusetts
Institute of Technology since 1990. The LCSN and NESN are the successors
to the NEUSN. Weston and MIT each compiled their own digital catalogs
from 1991 through 1997. Since then, Weston and MIT have produced a joint
digital catalog. Records include one or more of M~c~, m~b~, and M~N~. I
obtained the Weston, MIT, and joint digital catalogs (J. Ebel, C. Doll,
oral and written communs., May 14 and 19, 1999).

[NEUSN:]{.underline} The catalog of the Northeastern U.S. Seismic
Network covered most of the map area through 1990, with contributions
dominantly from Weston Observatory of Boston College, the Massachusetts
Institute of Technology, and the Lamont-Doherty Earth Observatory.
Funding cuts forced the breakup of the network at the end of 1990. The
NEUSN was succeeded by the LCSN and the NESN. NEUSN records include one
or more of M~c~, m~b~, and M~N~. I obtained the digital version of the
catalog (J. Ebel, written and oral communs., May 14, 1999).

[NOTTIS:]{.underline} Nottis (1983) critically evaluated, edited, and
corrected a previous unpublished catalog of E. F. Chiburis and others.
Nottis's catalog covers most of the map area and adjoining parts of
Canada to the north and east. It includes earthquakes through 1980. Most
magnitudes are m~bLg~ but some are M~L~. There is no lower magnitude
limit.

[SEUSSN:]{.underline} The catalog of the Southeastern U.S. Seismic
Network is compiled at Virginia Tech from data supplied by network
members throughout the region. Magnitudes reported for the map area are
mostly M~c~ and M~N~. I obtained a digital version of the SEUSSN catalog
for Virginia and West Virginia (M. Chapman, oral and written communs.,
March 3 and May 12, 1999, respectively).

[SHEEF:]{.underline} The Seismic Hazard Earthquake Epicentre File of the
Geological Survey of Canada was compiled for use in making the 1995
national seismic hazard maps of Canada (Adams, et al., 1996). Magnitudes
are M~N~. The portion of SHEEF that I used spans the map area, extends
through 1994 and down to M~N~ 3.0, and was obtained in digital form from
the Geological Survey of Canada after earthquakes from 1995 through 1998
were added from another Canadian catalog (S. Halchuk, written commun.,
February 26, 1999).

[STOVER AND COFFMAN:]{.underline} Stover and Coffman (1993) compiled
damaging earthquakes of the U.S. They defined "damaging" as at least MMI
VI or magnitude 4.5 for the States of the map area. These authors
reexamined and reassigned intensities according to uniform criteria,
which led to revision of some locations. The catalog extends through
1989. Magnitude scales used for earthquakes within the map area are
mostly m~b~, M~N~, and M.

CATALOG CONSTRUCTION FOR VARIOUS PARTS OF MAP AREA

[CANADA:]{.underline} Earthquake hazards in Canada are addressed by the
national geological survey (Franklin, 1999). Accordingly, earthquakes in
the Canadian portion of the map are represented almost entirely by
SHEEF. The few exceptions occurred during 1995-1998 after SHEEF was
completed, and were obtained from another Canadian catalog. Canadian
earthquakes before 1930 that are listed in both emb.cc and SHEEF have
magnitudes that average 0.4 units higher in SHEEF (Wheeler, unpub.
results). The cause of the difference is unknown. Comparison of the
current map with an early draft that used emb.cc instead of SHEEF for
Canadian earthquakes showed that the current map shows more Canadian
earthquakes with magnitudes of 3.0 or slightly larger than it would if
the map had been compiled strictly from U.S. sources. For the 1925
Charlevoix, Quebec earthquake, the map uses m~b~ 6.5 (Bent, 1992)
instead of the 6.7 listed in SHEEF. Bent's analysis used previously
unstudied seismograms that were unavailable to previous workers.

[DELAWARE:]{.underline} The Delaware Geological Survey maintains its own
list of earthquakes (S. Baxter, oral and written communs., March 26-July
15, 1999). The Delaware survey operates its own seismograph network as
part of the LCSN. The survey has critically evaluated seismological data
and intensity reports of events within and near Delaware. Results
include some revisions of epicenters and magnitudes that are listed in
standard sources. I used the survey's catalog for earthquakes within the
boundaries of the State.

[MARYLAND:]{.underline} The map shows mainly earthquakes from the
catalog emb.cc and from the SEUSSN catalog (M. Chapman, written commun.,
May 12, 1999). The Maryland Geological Survey maintains its own list of
earthquakes (J. Reger, oral and written communs., May 11-13, 1999).
Comparison of emb.cc, the SEUSSN catalog, Gordon and Dewey (1999), and
the list from the Maryland survey resulted in several improvements and
additions to this map and the Maryland list.

[NEW ENGLAND:]{.underline} The State geological surveys of Maine, New
Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut all use
Weston Observatory of Boston College as their authoritative source for
earthquake matters. None of these surveys maintains their own lists of
earthquakes. Accordingly, the map shows only the NEUSN and NESN catalogs
for New England.

Ebel (2000) revised the location and magnitude of the damaging Newbury,
Massachusetts earthquake of 1727. Previously the earthquake had been
assigned a location 18 km offshore from northeastern Massachusetts. From
a new compilation of aftershocks and analysis of a sequence of small
earthquakes that occurred near Newbury in 1999, Ebel (2000) increased
the 1727 magnitude from the previous estimate of m~bLg~ 5.0 to m~b~ 5.6,
and moved the estimated epicenter onshore to approximately 10 km north
of Newbury.

The location of the 1755 Cape Ann, Massachusetts earthquake is
uncertain. Hitherto the earthquake had been assigned a location offshore
from Cape Ann. However, Ellis and de Alba (1999) performed geotechnical
analyses of sites at which liquefaction was reported in 1755, and
suggested an onshore epicenter west of Boston. In contrast, the
geographic distribution of intensity reports from the Cape Ann mainshock
and the paucity of aftershock reports favor an offshore location.
Pending resolution of this discrepancy, the map shows the standard
offshore location.

The 1638 earthquake is the oldest shown on this map. Its location is
uncertain by 100-200 km or more. From intensity data Ebel (1996)
estimated a location on the Vermont-New Hampshire border but possibly
ranging from northeastern New York State to central Maine. Ebel (2000)
noted that more recent epicenters of smaller earthquakes in central New
Hampshire form two diffuse alignments that trend north and northeast.
Ebel (2000) speculated that either alignment might represent aftershocks
of the 1638 mainshock. Ebel (1999) suggested that the 1638 epicenter
might have been near Northfield, New Hampshire, and the map shows the
earthquake at Northfield.

[NEW JERSEY:]{.underline} The New Jersey Geological Survey maintains its
own list of earthquakes in and near the State (D. Dombroski, oral and
written communs., May 12 -- June 15, 1999). The list was compiled from
numerous sources, chief among them the NEUSN bulletins, the USGS PDE,
and USGS monthly and annual publications. I obtained a digital copy of
the State survey's earthquake list (D. Dombroski, written commun., June
10, 1999). NCEER-91 provided some missing magnitudes and improved
locations, and the LCSN catalog provided records of recent earthquakes.
J.G. Armbruster provided an improved location for the magnitude 5.2
earthquake of October 10, 1884, outside New York harbor (written
commun., January 9, 1999). The new location moved the estimated
epicenter across the New York boundary, slightly into New Jersey. By
informal agreement with the New Jersey Geological Survey, for the 1884
shock I used the magnitude estimate of 5.2 from NCEER-91 instead of the
estimate of 5.5 from Stover and Coffman (1993), because NCEER-91 was
produced by seismologists of the Lamont-Doherty Earth Observatory.
Within New Jersey, Lamont is likely to be the chief seismological
authority.

[NEW YORK STATE:]{.underline} New York has three organizations that
members of the public in different parts of the State might regard as
authoritative sources of earthquake information. (1) The New York State
Geological Survey has headquarters in Albany in the east-central part of
New York. The survey generally consults two published earthquake
catalogs by Nottis (1983) and Stover and Coffman (1993). (2) The
Multidisciplinary Center for Earthquake Engineering Research (MCEER) is
in Buffalo in western New York. The center funded production of the
NCEER-91 catalog (Seeber and Armbruster, 1991). (3) The Lamont
Cooperative Seismic Network is operated from the Lamont-Doherty Earth
Observatory in Palisades in southeastern New York. The network
contributed results to the NEUSN catalog through 1990 and to the LCSN
catalog since then. Accordingly, the list of earthquakes to be shown on
the map includes contributions from each of these authoritative sources
within New York State. The core of the list is New York earthquakes
listed in the NEUSN and LCSN catalogs, because these catalogs are
primary sources of instrumental epicenters and magnitudes. To this core
were added earthquakes, mostly pre-network, from Nottis (1983) and the
catalog emb.cc; the emb.cc additions are nearly all from NCEER-91.
Finally, the few locations or magnitudes of damaging earthquakes that
did not match the values of Stover and Coffman (1993) were changed to
match. The resulting catalog of New York State earthquakes is dominated
by NCEER-91 before approximately 1940, then by NEUSN, and after 1990 by
LCSN.

[FAR OFFSHORE:]{.underline} Several sources listed differing numbers of
earthquakes 100-300 kilometers offshore in the New York Bight, east of
New Jersey and south of New England. Most were smaller than magnitude
3.0. The eight shown on the map were derived from the NEUSN and Weston
catalogs, except one in 1847 of magnitude 3.5 that was attributed to
Canadian sources by the New Jersey Geological Survey.

[OHIO:]{.underline} The Ohio Geological Survey maintains its own list of
earthquakes (M. Hansen, oral and written communs., May 6 and 10, 1999).
The map shows three small earthquakes in the northeasternmost county of
Ohio. Their records were obtained from the Ohio survey, Seeber and
Armbruster (1993), and Gordon and Dewey (1999).

[PENNSYLVANIA:]{.underline} The Pennsylvania Bureau of Topographic and
Geologic Survey maintains its own list of earthquakes (R. Faill, oral
and written communs., December 2, 1998 to March 9, 1999). The list was
compiled from numerous sources, chief among them the bulletins of the
NEUSN and LCSN, Gordon and Dewey (1999), the USGS PDE (Preliminary
Determination of Epicenters) and related USGS digital catalogs and paper
publications, and publications on specific areas or groups of
earthquakes in the State. Faill and I consulted extensively with the aim
of insuring that our catalogs for Pennsylvania matched. We discussed
each earthquake individually, but some general guidelines emerged from
frequent use. First, C. K. Scharnberger summarized evidence indicating
that several events might be mine blasts instead of earthquakes (oral
and written communs., January 7 to 18, 1999). To be conservative we
retained most of these events in the State compilation and on this map,
pending Scharnberger's planned publication of the evidence that some are
blasts. Therefore, some blasts might remain on the map. Second, we
preferred primary sources over secondary ones, and instrumental results
over macroseismic locations or magnitudes. Third, we preferred results
of Gordon and Dewey (1999) over those of the NCEER-91 catalog for early
instrumental earthquakes, because Gordon and Dewey (1999) is more likely
to be regarded as authoritative by the lay audience in Pennsylvania.

[VIRGINIA:]{.underline} The State survey deferred to the Seismological
Observatory at Virginia Tech. Accordingly, the map shows earthquakes
from the SEUSSN catalog (M. Chapman, oral and written communs., March 30
and May 12, 1999), with a few small changes derived from comparison with
emb.cc.

[WEST VIRGINIA:]{.underline} The State survey deferred to the USGS.
Accordingly, the map shows earthquakes from the SEUSSN catalog (M.
Chapman, oral and written communs., with a few small earthquakes added
as a result of comparison with emb.cc.

DEPENDENT EARTHQUAKES

Aftershocks and foreshocks were detected and eliminated by inspection of
each State's earthquake list. Criteria were subjective and some
dependent earthquakes probably remain on the U.S. portion of the map.
More than three fifths of the mapped earthquakes occurred in Canada.
Thus, Canadian earthquakes are too numerous to attempt subjective
detection of aftershocks or foreshocks. However, nearly all dependent
earthquakes in the U.S. part of the map area occurred at locations that
are indistinguishable from the mainshock epicenter at the scale of the
map. Therefore, retaining dependent U.S. earthquakes would not have
materially changed the appearance of the map, and the same is presumed
to be true of Canadian shocks. If this presumption is valid, the only
Canadian aftershocks or foreshocks that are likely to affect the
appearance of the map are those of magnitude 5.0 or larger. These larger
earthquakes are identified on the map by their years of occurrence.
Accordingly, inclusion of dependent earthquakes larger than magnitude
5.0 would cause a visible excess of year labels on the map. Therefore, I
examined each earthquake of magnitude 5.0 or larger for proximity in
time or space to a larger shock. In this manner, seven aftershocks and
one foreshock larger than 5.0 were detected and deleted, all of them in
Canada.

ACKNOWLEDGMENTS

The preceding descriptions make it clear that the map would not exist
without generous contributions from many people at various stages. The
idea of making such a map originated with S. Nishenko several years ago,
and R. G. Updike suggested reviving the idea now. J. Adams, J.E. Ebel,
K.H. Jacob, and C.S. Mueller advised on early designs of the map and
catalog. J.G. Armbruster, C.G. Doll, Jr., Ebel, R.T. Faill, R.H.
Fakundiny, E.S. Fratto, Jacob, A.L. Kafka, C.A. Langston, C.K.
Scharnberger, L. Seeber, and M.N. Toksöz examined early drafts of the
map and parts of its catalog and suggested numerous improvements. M.C.
Chapman, Doll, Ebel, W.-Y. Kim, S. Halchuk, and Mueller graciously
supplied digital data sets. Adams, S. Baxter, Chapman, D.R. Dombroski,
Faill, M.C. Hansen, G.N. Nottis, J.P. Reger, and Scharnberger discussed
the earthquakes of individual States and Canada, sometimes at a length
and with a frequency that must have appalled them. The manuscript of
this report was improved by suggestions from J.W. Dewey. Errors and
omissions are mine alone.

REFERENCES CITED

Adams, J., Weichert, D.H., Halchuk, S., and Basham, P.W., 1996, Trial
seismic hazard maps of Canada - 1995 \-- Final values for selected
Canadian cities: Geological Survey of Canada Open File 3283, 97 p.

Bent, A.L., 1992, A re-examination of the 1925 Charlevoix, Québec
earthquake: Bulletin of the Seismological Society of America, v. 82, p.
2097-2113.

Ebel, J.E., 1996, The seventeenth century seismicity of northeastern
North America: Seismological Research Letters, v. 67, no. 3, p. 51-68.

\-\-\-\--1999, Speculations on the source parameters of the 1638
earthquake in the northeastern United States using inferences from
modern seismicity \[abs.\]: Seismological Research Letters, v. 70, no.
1, p. 114.

\-\-\-\--2000, A reanalysis of the 1727 earthquake at Newbury,
Massachusetts: Seismological Research Letters, v. 71, no. 3, p. 364-374.

Ebel, J.E., Bonjer, K.-P., and Oncescu, M.C., 2000,
Paleoseismicity---Seismicity evidence for past large earthquakes:
Seismological Research Letters, v. 71, no. 2, p. 383-294.

Ellis, C., and de Alba, P., 1999, Acceleration distribution and
epicentral location of the 1755 "Cape Ann" earthquake from case
histories of ground failure: Seismological Research Letters, v. 70, no.
6, p. 758-773.

Frankel, A., Mueller, C., Barnhard, T., Perkins, D., Leyendecker, E.V.,
Dickman, N., Hanson, S., and Hopper, M., 1997, Seismic-hazard maps for
the conterminous United States: U. S. Geological Survey Open- File
Report 97-131, 12 colored sheets, scale 1:7,000,000.

Franklin, J.M., 1999, Rebuilding geoscience in Canada: Geotimes, v. 44,
no. 4, p. 14-19.

Gordon, D.W., and Dewey, J.W., 1999, Earthquakes, *in* Shultz, C.H.,
ed., The geology of Pennsylvania: Pennsylvania Geological Survey Special
Publication 1, p. 762-769.

Mueller, C., Hopper, M., and Frankel, A., 1997, Preparation of
earthquake catalogs for the national seismic-hazard maps \-- Contiguous
48 States: U. S. Geological Survey Open- File Report 97-464, 36 p.

Nottis, G.N., ed., 1983, Epicenters of northeastern United States and
southeastern Canada, onshore and offshore; time period 1534-1980: New
York State Museum Map and Chart Series, v. 38, 39 p., 2 folded maps,
scale 1:1,000,000.

Seeber, L., and Armbruster, J.G., 1991, NCEER-91 earthquake catalog:
Buffalo, New York, National Center for Earthquake Engineering Research,
p. 110.

\-\-\-\--1993, Natural and induced seismicity in the Lake Erie - Lake
Ontario region \-- Reactivation of ancient faults with little
neotectonic displacement: Geographie physique et Quaternaire, v. 47, no.
3, p. 363-378.

Sibol, M.S., Bollinger, G.A., and Birch, J.B., 1987, Estimation of
magnitudes in central and eastern North America using intensity and felt
area: Bulletin of the Seismological Society of America, v. 77, p.
1635-1654.

Stover, C.W., and Coffman, J.L., 1993, Seismicity of the United States,
1568-1989 (revised): U. S. Geological Survey Professional Paper 1527,
418 p.

Wheeler, R.L., Trevor, N.K., Tarr, A.C., and Crone, A.C., 2001,
Earthquakes in and near the northeastern United States, 1638-1998: U.S.
Geological Survey Geologic Investigations Map I-2737, 1 sheet, scale
1:1,500,000 (Also available on the Web at
http://greenwood.cr.usgs.gov/pub/i-maps/i-2737/).