Earthquake Intensity Database 1638–1985

The U.S. Earthquake Intensity Database (1638–1985) is a collection of damage and felt reports for more than 23,000 U.S. earthquakes. The database contains information regarding epicentral coordinates, magnitudes, focal depths, names, and coordinates of reporting cities/ localities, reported intensities, and the distances to the epicenter. Earthquakes listed in the file date from 1638 to 1985. The majority of the felt reports are in the U.S. States and Territories (155,301). Other reporting countries include: Antigua and Barbuda (2), Canada (1,364), Mexico (54), Panama (285), and the Philippines (9).

Product Overview

The U.S. Earthquake Intensity Database (1638–1985) includes the maximum intensity for each city (or locality) that felt a particular earthquake. For later years, the USGS National Earthquake Information Center provides maximum intensities for each event.

Download the NCEI Earthquake Strong Motion Database

(MS Excel format; 15 MB). The file contains more than 157,000 records. NOTE: This database is static and is no longer being updated.

Data are also available on the Seismicity Catalog CD Rom 1996 for more than four million earthquakes from 2100 B.C. to 1995 A.D.

Database Description

The Earthquake Intensity File contains more than 157,000 reports on over 20,000 earthquakes that affected the United States from 1638 through 1985. The principal data included for each earthquake are the names and geographic coordinates of the cities/localities that reported effects from earthquakes, (hereafter called "reporting cities") and the intensities assigned to those effects. Each intensity has been assigned using the Modified Mercalli Intensity Scale of 1931 (Wood and Neumann, 1931). Other information given for each earthquake includes: distance of each reporting city from the epicenter of the earthquake; number of hours to subtract from Universal Time (UT) to obtain origin time in local standard time; reference (authority) codes for reporting cities and intensity values, and state codes. In addition, the date, origin time, epicenter, magnitude, and depth (where available) are given for all earthquakes.

Although the Earthquake Intensity File represents an important contribution to seismology research, it has several limitations that should be mentioned:

About 25 percent of the 2,500 earthquakes reported from 1638-1928 and 10 percent of the 18,500 events from 1928-1980 do not have instrumental epicenters; this omission is mainly due to the fact that seismological instruments were not developed until the late 1800s, and further that the instruments were not widely distributed for many years later.
Several of the reporting cities listed in the file have not been assigned geographic coordinates.
The file contains data primarily for those earthquakes that have epicenters in the United States, nearby U.S. territories, and areas of Canada and Mexico that border the United States. Data for a few events in the Philippines (from the late 1930s through 1941) is also included.

Year Mo Da Hr Mn Sec

The Date and Time are listed in Universal Coordinated Time and are Year, Month (Mo), Day (Da), Hour (Hr), Minute (Mn), Second (Sec)

UTC Conv

Number of hours to subtract from the Date and Time given in Universal Coordinated Time to get local standard time for the epicenter. In general:

4 = 60 degree meridian (Atlantic Standard Time)
5 = 75 degree meridian (Eastern Standard Time)
6 = 90 degree meridian (Central Standard Time)
7 = 105 degree meridian (Mountain Standard Time)
8 = 120 degree meridian (Pacific Standard Time)
9 = 135 degree meridian (Alaska Standard Time)
10 = 150 degree meridian (Hawaii-Aleutian Standard Time)

Use care when converting Universal Coordinated Time to local standard time. It is uncertain how some of the conversion factors in this database were determined; for example, whether Daylight Saving Time or Standard Time was used. Many, but not all, areas represented in this database observe Daylight Saving Time during the summer.

Prior to 1966, states and communities that observed Daylight Saving Time used whatever beginning and ending dates they chose. The Uniform Time Act of 1966 provided that any area that observes Daylight Saving Time must begin and end on specified federal dates.

The Uniform Time Act of 1966, P.L. 89-387, section 4(c), also established four time zones in Alaska:

Pacific Standard Time (120th meridian--southeastern Alaska--8 hours behind UTC)
Yukon Standard Time (135th meridian--Yakutat--9 hours behind UTC)
Alaska-Hawaii Standard Time (150th meridian--most of Alaska, from west of Yakutat to just east of Cold Bay, and northward--10 hours behind UTC)
Bering Standard Time (165th meridian--westward from just east of Cold Bay, at the western end of the Alaska Peninsula--11 hours behind UTC)

On October 30, 1983, the number of time zones in Alaska was reduced from four to two, which placed 90 percent of Alaska on the same time, just one hour behind the U.S. West Coast; the boundary between the two zones is just west of Umnak Island in the Aleutian chain:

Alaska Standard Time (9 hours behind UTC)
Hawaii-Aleutian Standard Time (10 hours behind UTC)

U/G Unpublished or grouped intensity

U = Intensity (MMI) assigned that was not listed in the source document
G = Intensity grouped I-III in the source document was reassigned intensity III

EQ Lat / EQ Long

This is the geographic latitude and longitude of the epicenter expressed as decimal numbers. The units are degrees. The latitude range is +4.0 to +69.0, where "+" designates North latitude; note there are no South latitudes in the database. The longitude range is -179.0 to +180.0, where "-" designates West longitude and "+" designates East longitude. Most of the epicenters are West longitude (from -56 to -179), but a few epicenters in the Philippines and Aleutian Islands are East longitude (from +120 to +180).

Mag

These are magnitudes as listed in United States Earthquakes, Earthquake History of the United States (either MB, MS, or ML), or the equivalent derived from intensities for pre-instrumental events. The magnitude is a measure of seismic energy. The magnitude scale is logarithmic. An increase of one in magnitude represents a tenfold increase in the recorded wave amplitude. However, the energy release associated with an increase of one in magnitude is not tenfold, but thirtyfold. For example, approximately 900 times more energy is released in an earthquake of magnitude 7 than in an earthquake of magnitude 5. Each increase in magnitude of one unit is equivalent to an increase of seismic energy of about 1,600,000,000,000 ergs.

Depth (km)

Hypocentral Depth (positive downward) in kilometers from the surface.

Epi Dis

Epicentral Distance in km that the reporting city (or locality) is located from the epicenter of the earthquake.

City Lat/City Long

This is the geographic latitude and longitude of the city (or locality) where the Modified Mercalli Intensity was observed, expressed as decimal numbers. The units are degrees. The latitude range is +6.0 to +72.0, where "+" designates North latitude (there are no South latitudes in the database). The longitude range is -177.0 to +180.0, where "-" designates West longitude and "+" designates East longitude. Most of the reporting cities are West longitude (from -29 to -177), but a few reporting cities in the Philippines and Aleutian Islands are East longitude (from +119 to +180).

MMI Modified Mercalli Scale Intensity

(MMI) is given in Roman Numerals. Values range from I to XII (Roman Numerals were converted to numbers in the digital database. Values range from 1 to 12). Macroseismic information is compiled from various sources including newspaper articles, foreign broadcasts, U.S. Geological Survey Earthquake reports and seismological station reports.

State Code

Numerical identifier for state, province, or country in which the earthquake was reported (felt) by residents:

01 Alabama
02 Alaska
03 Arizona
04 Arkansas
05 California
07 Colorado
08 Connecticut
09 Delaware
10 District of Columbia
11 Florida
12 Georgia

14 Hawaii
15 Idaho
16 Illinois
17 Indiana
18 Iowa
19 Kansas
20 Kentucky
21 Louisiana
22 Maine
23 Maryland

24 Massachusetts
25 Michigan
26 Minnesota
27 Mississippi
28 Missouri
29 Montana
30 Nebraska
31 Nevada
32 New Hampshire

33 New Jersey
34 New Mexico
35 New York
36 North Carolina
37 North Dakota
38 Ohio
39 Oklahoma
40 Oregon
41 Pennsylvania
42 Puerto Rico

43 Rhode Island
45 South Carolina
46 South Dakota
47 Tennessee
48 Texas
49 Utah
50 Vermont
51 Virginia
52 Virgin Islands
54 Washington

55 West Virginia
56 Wisconsin
57 Wyoming
58 West Indies
74 Panama
75 Philippine Is.
80 Mexico
81 Baja California
90 Canada
91 Alberta

92 Manitoba
93 Saskatchewan
94 British Columbia
95 Ontario
96 New Brunswick
97 Quebec
98 Nova Scotia
99 Yukon Territory

City Name

City (or locality) in which the earthquake was reported /felt by residents.

Data Source

This is a code referring to the source of one or more of the reported parameters (e.g., epicenter, city and intensity).

A = Source unknown; 1925 earthquake in Boston area (reports not listed in source H).
B = Report by Bollinger and Stover, 1976.
C = Quarterly Seismological Reports, 1925-27.
D = Source unknown; 1937-1977 earthquakes in Hawaii, California, and eastern U.S.
H = Earthquake History of the United States (Coffman and others, 1982).
K = Report by Carnegie Institution, 1908, 1910.
M = Source unknown; 1899-1912 Earthquakes in Alaska.
N = Report by Nuttli, 1973.
Q = Abstracts of Earthquake Reports for the United States, 1933-70.
S = Unpublished report by Nina Scott, 1965.
T = Source unknown; 1872-1904 earthquakes along U.S. west coast.
U = United States Earthquakes, 1928-85.
W = Monthly Weather Service Seismological Reports, 1914-24.

Earthquake Intensity Values

Earthquake intensities are numerical values assigned to the effects of earthquakes on people, property, and on the natural environment. Intensities are evaluated using the Modified Mercalli Intensity Scale of 1931, which contains levels of effects ranging from intensity I, barely perceptible, to intensity XII, total damage.

Although the development of seismological instruments and instrumental techniques the past 80 years has been impressive, earthquake intensity remains among the most acceptable criteria on which to base earthquake risk factors and to project future seismic activity. (Brazee, 1976) This is due in part to the extensive availability of earthquake intensity data from the mid-1600s compared to the availability of earthquake instrumental data from approximately 1897.

Earthquake intensity information is a unique and valuable data source for the research seismologist, the structural engineer, the actuary, and the earth science instructor. Although published information on earthquake effects has been available for many years, compiling comprehensive lists of earthquakes and the intensities that were experienced requires a lot of time and effort.

In the early 1960s, however, preparing lists of historical earthquakes became less laborious and time consuming after the U.S. Coast and Geodetic Survey compiled a computerized data file of worldwide earthquakes. The file not only contained epicenters of earthquakes, but also held other valuable information on each event, including the maximum reported intensity. The new file still had limitations, however, because the names of cities experiencing the earthquakes and the intensities at these cities were not included in the database. The next logical step, therefore, was to compile an Earthquake Intensity File. This would include instrumental earthquake data, but would also contain the important ancillary data on earthquake effects.

Although the history of the development of earthquake intensity scales is long and interesting, only a brief summary will be presented here. Poarid, an Italian scientist, made the first known attempt to classify earthquakes by intensity in 1627. He used a scale of four levels of intensity to describe effects of earthquakes experienced at different towns. Although many additional attempts were made in the 18th and 19th centuries to develop comprehensive scales for measuring earthquake intensity, none was more widely used than that formulated in 1873 by M. S. de Rossi of Italy and F. A. Forel of Switzerland. But this scale also had severe limitations, and therefore was superseded in the early 1900s by Mercalli's revised intensity scale which contained 12 levels of intensity.

In 1931, a modified version of Mercalli's scale was published by H. O. Wood and Frank Neumann. Known as the Modified Mercalli Intensity Scale of 1931, it became the standard used by the United States engineering seismology community, which includes the National Geophysical Data Center and the U.S. Geological Survey. An interpretation of the values is listed in Table 1.

Table 1.--Modified Mercalli Intensity Scale of 1931
Intensity	Description/Damage
I	Not felt except by a very few under especially favorable conditions.
II	Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
III	Felt quite noticeably by persons indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to a passing truck. Duration estimated.
IV	During the day felt indoors by many, outdoors by few. At night, some awakened. Dishes, windows, and doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
V	Felt by nearly everyone; many awakened. Some dishes, windows etc., broken, a few instances of cracked plaster, unstable objects overturned. Disturbance of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.
VI	Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight.
VII	Everyone runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures. Some chimneys broken. Noticed by persons driving motor cars.
VIII	Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motor cars disturbed.
IX	Damage considerable in specially designed structures; well-designed frame structures thrown out of plum; damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken.
X	Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed over banks.
XI	Few, if any (masonry), structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipe lines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII	Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.

Comparison of Modified Mercalli (MM) and Other Intensity Scales
Modified Mercalli	Rossi-Forel	Japanese	European
I	I	0	I
II	I–II	I	II
III	III	II	III
IV	IV–V	II–III	IV
V	V–VI	III	V
VI	VI–VII	IV	VI
VII	VII–VIII	IV–V	VII
VIII	VIII+ to IX-	V	VIII
IX	IX+	V–VI	IX
X	X	VI	X
XI		VII	XI
XII			XII

Collecting Data on Earthquake Intensity

The U.S. Geological Survey (USGS) is the Federal agency responsible for collecting earthquake intensity data. The USGS carries out this responsibility using a questionnaire called, "Earthquake Report," and also sends field investigators to the scene of destructive earthquakes to analyze the resulting damage. Different versions of the questionnaire have been used since the mid-1920s by several groups who were responsible for collecting intensity data. The present questionnaire contains pertinent questions about earthquake effects that enable a seismologist to evaluate the intensity of the earthquake in all parts of the shaken area; it is designed specifically for computer processing.

In the past, the USGS sent questionnaires immediately after each U.S. earthquake to postmasters, National Weather Service offices, military installations, and others, requesting that they report all effects of the earthquake in their area. If the earthquake was damaging, expert observers traveled to the field to investigate and photograph the damage incurred. This data-collection program was supplemented by newspaper accounts of earthquake effects, published scientific reports, and reports provided by seismology collaborators.

After the completed earthquake questionnaires were returned to USGS, a seismologist analyzed each report and assigned intensities on the basis of the effects at each town; intensity ”Isoseismal” maps were then constructed for earthquakes felt over large areas. Descriptions and maps of these events were published annually in the United States Earthquakes series, and a summary of the stronger earthquakes (MM intensity >= V) was published periodically in Earthquake History of the United States.

The USGS now only canvasses selected earthquakes. If you want to report an earthquake, use the National Earthquake Information Center's Did You Feel it? page.

Earthquake History of the United States

This publication is a summary of all earthquakes (intensity V and above) that have occurred in the United States and its territories from earliest recorded history (about 1638 in the New England region) through 1980. The 1982 edition of this publication (Coffman and others, 1982) contains revised epicenters and intensities for several earthquakes. This source, therefore, is the authority for epicenters of significant earthquakes in the file and also for most intensities of MM intensity >= V. In addition, pages xi-xii of "Earthquake History" contain several addenda and corrigenda, which have been used to update information in the Intensity File.

United States Earthquakes

Much of the intensity data in the Earthquake Intensity Database from the years 1928-1985 was taken from this annual report. Its publication in 1928 began a continuing program of collecting comprehensive effect reports on all earthquakes in the United States and its territories. This publication not only contains brief descriptions of all earthquakes that were felt or damaging, but also includes MM intensities for most of the cities (or localities) in which the tremors were observed. For earthquakes from 1928-1931, however, published intensities were assigned using the Rossi-Forel (RF) intensity scale. When included in the Intensity File, these intensities are converted to values on the MM scale. In addition, some descriptions of earthquake effects in United States Earthquakes were not assigned an intensity because the effect information was insufficiently detailed (e.g., "slight," "feeble," "felt"). To make the computerized file as complete as possible, NCEI assigned an intensity of II to earthquake reports that had only the slightest of details, and an intensity of III to earthquake reports that were grouped as intensity I-III.

Quarterly Seismological Report

This publication, which was published by the U.S. Coast and Geodetic Survey, was a source of information on reporting cities and intensities for the years 1925-1927. All Rossi-Forel intensities assigned to earthquake reports during this period have been converted to the MM Intensity Scale. Where omitted, intensities have been assigned according to the method described in the preceding paragraph.

Abstracts of Earthquake Reports for the United States

This quarterly publication includes all the effect data collected for earthquakes in the United States and its territories during the 1933-1970 period. Because the quarterly "Abstracts" report contains only preliminary earthquake data, information in United States Earthquakes, "Annual Reports," and in "Earthquake History of the United States," is preferred, for they contain additional reporting cities and revised intensity information.

Monthly Weather Service Seismological Reports

These reports represent a main source for information on earthquake effects in the United States and nearby territories for December 1914 through June 1924. As in other pre-1931 publications all intensities were assigned according to the Rossi-Forel scale; however, minimal reported effects (e.g., slightly felt) were not assigned intensities. NCEI, therefore, has assigned intensities to all effects and, in addition, has converted Rossi-Forel intensities to the MM scale.

Bibliography

Bollinger, G.A. and Carl W. Stover, 1976: List of Intensities for the 1886 Charleston, South Carolina, Earthquake, U.S. Geological Survey Open-File Report 76-66, 31 p.
Brazee, Rutlage J., August 1976: Final Report: An Analysis of Earthquake Intensities with Respect to Attenuation, Magnitude, and Rate of Recurrence (Revised Edition), NOAA Tech. Memorandum EDS NGSDC-2, NOAA/National Geophysical Data Center, Boulder, Colorado, 53 p. (plus appendices).
Carnegie Institution of Washington, vols. 1-2, 1908, 1910: California Earthquake of April 18, 1906, Report of the State Earthquake Investigation Commission, v.1 (by Andrew C. Lawson); v. 2 (by Harry F. Reid), Washington, D.C., 623 p. (plus Atlas).
Coffman, Jerry L., Carl A. von Hake, and Carl W. Stover, 1982: Earthquake History of the United States, Publication 41-1, Revised Edition (with Supplement Through 1980), National Oceanic and Atmospheric Administration and U.S. Geological Survey, Boulder, Colorado, 258 p.
Dutton, Clarence E., 1889: "The Charleston Earthquake of August 31,1886," Ninth Annual Report, 1887-88, U.S. Geological Survey, Washington D.C., p. 203-528.
Meyers, Herbert, April 1976: A Historical Summary of Earthquake Epicenters in and Near Alaska, NOAA Tech. Memorandum EDS NGDC-1, NOAA/National Geophysical Data Center, Boulder, Colorado, 57 p. (plus appendices).
Meyers, Herbert and Carl A. von Hake, 1976: Earthquake Data File Summary, Key to Geophysical Records Documentation No. 5, NOAA/National Geophysical Data Center, Boulder, Colorado, 32 p. (plus appendices).
Meyers, Herbert, R.J. Brazee, J.L. Coffman, and S.R. Lessig, 1976: An Analysis of Earthquake Intensities and Recurrence Rates in and Near Alaska, NOAA Technical Memorandum EDS NGSDC-3, NOAA/National Geophysical Data Center, Boulder, Colorado, 101 p.
Murphy, Leonard M. (Scientific Coordinator), 1973: San Fernando, California, Earthquake of February 9, 1971, vols. 1-3, NOAA/Environmental Research Laboratories, Washington D.C.
Nuttli, Otto W., 1973: "The Mississippi Valley Earthquakes of 1811 and 1812; Intensities, Ground Motion, and Magnitudes," Bulletin of the Seismological Society of America, v. 63, No.1, p. 227-248.
Scott, Nina, 1965: List of Modified Mercalli intensities for the April 8, 1906, San Francisco, California, Earthquake, Prepared under contract for U.S. Geological Survey, unpublished manuscript.
Tarr, Ralph S. and Lawrence Martin, 1912: "The Earthquakes at Yakutat Bay, Alaska, in September 1899," U.S Geological Survey Professional Paper 69, U.S. Department of the Interior, Geological Survey, Washington D.C., 135 p.
U.S. Department of Commerce, Coast and Geodetic Survey, Quarterly Seismological Report, 1925-27, Washington D.C.
U.S. Department of Commerce, Environmental Science Services Administration, vols. 1-3, 1966, 1967, 1969: The Prince William Sound, Alaska, Earthquake of 1964 and Aftershocks, Publication 10-3 (in three volumes), Washington, D.C.
U.S. Department of Commerce, National Oceanic and Atmospheric Administration (and predecessor agencies), Abstracts of Earthquake Reports for the United States, quarterly issues 1933-70. (Earlier title: Abstracts of Earthquake Reports for the Pacific Coast and the Western Mountain Region).
U.S. Department of Commerce, National Weather Service, Monthly Weather Review, December 1914-June 1924 (Seismological reports are usually described in the issues for the month in which the earthquakes occurred), Washington D.C.
U.S. Geological Survey, United States Earthquakes, published annually by: Coast and Geodetic Survey from 1928-68; National Oceanic and Atmospheric Administration (NOAA) from 1969-72; NOAA/U.S. Geological Survey from 1973-80; and U.S. Geological Survey from 1981-1986.
Wood, Harry O. and Frank Neumann, Dec. 1931: "Modified Mercalli Intensity Scale of 1931," Bulletin of the Seismological Society of America, v. 21, No. 4, p. 277-283.

Earthquake Intensity Database 1638–1985

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