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罗马尼亚语
罗马尼亚语Earthquakes and Maryland
Earthquakes and Maryland
Maryland's earthquake monitoring network is online. Visit the
for more information, and see live seismic displays.
of this brochure, suitable for printing.
By James P. Reger
INTRODUCTION
Earthquakes can be among the most devastating and terrifying of natural hazards.
Although floods, tornadoes and hurricanes account for much greater annual loss
in the United States, severe earthquakes pose the largest risk in terms of
sudden loss of life and property. There are many interrelated factors that
determine the extent of loss of property and life from an earthquake. Each
of the following should be prefaced with &other factors being equal .
Amount of seismic energy released: The greater the vibrational energy,
the greater the chance for destruction.
Duration of shaking: This is one of the most important parameters of ground
motion for causing damage.
Depth of focus, or hypocenter: The shallower the focus (the point of an
earthquake's origin within the earth), usually the greater the potential
for destructive shock waves reaching the earth's surface. Even stronger events
of much greater depth typically produce only moderate shaking at ground level.
Distance from epicenter: The potential for damage tends to be greatest
near the epicenter (the point on the ground directly above the focus), and
decreases away from it.
Geologic setting: A wide range of foundation materials exhibits a similarly
wide range of responses to seismic vibrations. For example, in soft unconsolidated
material, earthquake vibrations last longer and develop greater amplitudes,
which produce more ground shaking, than in areas underlain by hard bedrock.
Likewise, areas having active faults are at greater risk.
Geographic and topographic setting: This characteristic relates more to
secondary effects of earthquakes than to primary effects such as ground shaking,
ground rupture, and local uplift and subsidence. Secondary effects include
landslides (generally in hilly or mountainous areas), seismic sea waves,
or tsunamis (pretty much restricted to oceans and coastal areas), and fires
(from ruptured gas lines and downed utility lines).
Population and building density: In general, risk increases as population
and building density increase. Types of buildings: Wooden frame structures
tend to respond to earthquakes better than do more rigid brick or masonry
buildings. Taller buildings are more vulnerable than one- or two-story buildings
when located on soft, unconsolidated sediments, but taller buildings tend
to be the more stable when on a hard bedrock foundation.
Time of day: Experience shows there are fewer casualties if an earthquake
occurs in late evening or early morning because most people are at home and
awakeand thus in a good position to respond properly.
Although earthquakes have been the object of study and superstition for many
centuries, the modern science of seismology really gained impetus after the
famous San Francisco earthquake of 1906. Since then, geologists have learned
much more about the structure and composition of the earth's interior and,
more recently, have made progress in earthquake forecasting and in hazard and
risk mitigation.
ORIGIN OF EARTHQUAKES
Most earthquakes occur when great stresses building up within the earth are
suddenly released This sudden release of this stored energy causes movement
of the earth's crust along fractures, called faults, and generates shock waves.
These shock waves, or seismic waves, radiate in all directions from the focus,
much as ripples radiate outward in two dimensions when a pebble is dropped
into a pond.
FIGURE 1. Highly generalized cross section of earth's crust and upper mantle depicting seismic waves, earthquake focus and an epicenter.
The two basic types of seismic waves are body waves, or primary waves, which
travel through the interior of the earth, and surface waves, which travel along
the earth's surface and are believed to be responsible for most earthquake damage
There are two types of body waves: P waves, or primary waves, and S waves,
or secondary waves. The faster moving P waves are compressional waves, and
the slower S waves are shear waves. Compressional waves involve a &push-pull& vibration
of earth material in the same direction as the P waves are moving. In contrast,
shear waves &shake& material at right angles to their path. Differences
in P- and S-wave characteristics have provided much information about the structure
and composition of the earth's interior.
Although most earthquakes are associated with movement along faults, they
can also be triggered by volcanic activity, by large landslides, and by some
types of human activity. However, in areas not known for frequent earthquakes,
pinpointing the cause of the rare tremor can be very difficult.
The theory of plate tectonics explains most earthquake occurrences. Ninety
percent or more of all earthquakes occur along boundaries between large, slowly
moving slabs, or plates, of the earth's crust and upper mantle, collectively
called the lithosphere. (For more background on plate tectonics, the reader
is encouraged to refer to a recent introductory geology text or a good encyclopedia.)
Most earthquakes are shallow (0-40 miles to the focus), occurring in the lithosphere.
The mechanism for most very shallow earthquakes probably involves fracturing
of brittle rock in the crust or relief of internal stresses due to frictional
resistance locking opposite sides of a fault.
Very little is known about the causes of earthquakes in the eastern United
States. In general, there is no clear association among seismicity, geologic
structure, and surface displacement, in contrast to a common association in
the western U.S.
The mid-Atlantic and central Appalachian region, including Maryland, is characterized
by a moderate amount of low-level earthquake activity, but their cause or causes
are largely a matter of speculation. In Maryland, for example, there are numerous
faults, but none is known or suspected to be active. Because of the relatively
low seismic energy release, this region has received relatively little attention
from earthquake seismologists (Bollinger, 1969).
In the Atlantic Coastal Plain, it is now thought that earthquakes may be associated
with nearly vertical faults that formed during the opening of the present Atlantic
Ocean during the Triassic period about 220 million years ago (Hanks, 1985).
Such faults would occur in the &basement& bedrock, and not in the
overlying, younger Coastal Plain sediments themselves.
Recent evidence suggests that earthquakes in the Valley and Ridge Province
and in the Piedmont Province occur at shallow depths (usually less than 15
miles) in the Precambrian crystalline basement rocks (Wheeler and Bollinger,
1984). The geologic structure that may be responsible for earthquake activity
in these areas is a nearly horizontal fault that formed during continental
collision and closing of a proto-Atlantic Ocean during late Paleozoic time
approximately 300 million years ago. It is also possible that some earthquakes
in the Piedmont are in some way related to igneous dikes that were intruded
into surrounding bedrock during the Triassic and Jurassic periods (roughly
200-175 million years ago).
MEASURING EARTHQUAKE
The vibrations produced by earthquakes are detected and recorded by instruments
called seismographs. The time of occurrence, the duration of shaking, the locations
of the epicenter and focus, and estimates of the energy released can be obtained
from data from seismographs set up around the world.
TABLE 1. The Modified Mercalli Intensity Scale of 1931 (abridged). I Not felt
except by very few people under especially favorable conditions. II Felt by
a few people, especially those on upper floors of buildings. Suspended objects
may swing. III Felt quite noticeably indoors. Many do not recognize it as an
earthquake. Standing motorcars may rock slightly. IV Felt by
felt by a few outdoors. At night, some awakened. Dishes, windows and doors
rattle. V Fel many awakened. Some dishe
unstable objects overturned. VI F many
frightened and run outdoors. Some h some fallen plaster
or damaged chimneys. VII Most people alarmed and run outside. Damage negligible
in well c considerable damage in poorly constructed buildings.
VIII Damage slight in speciall considerable in ordinary
great in poorly built structures. Heavy furniture overturned. Chimneys,
monuments, etc. may topple. IX Damage considerable in specially designed structures.
Buildings shift from foundations and collapse. Ground cracked. Underground
pipes broken. X Some well-built wooden structures destroyed. Most masonry structures
destroyed. Ground badly cracked. Landslides on steep slopes. XI Few, if any,
masonry structures remain standing. R bridges destroyed.
Broad fissure in ground. XII Virtually total destruction. Wobjects
thrown into the air. In 2002, a seismograph station was established at Soldiers
Delight in Baltimore County. A live link to the station is at .
The station is a cooperating partner in the Lamont Doherty Earth Observatory
Seismic Network of Columbia University, along with stations in Delaware and
Pennsylvania. Other regional seismograph stations are in State College, P
Morgantown, West V and Blacksburg, Virginia.
TABLE 2. Approximate relationships among earthquake magnitude,
intensity, worldwide occurrence, and area affected (after U.S. Geological
Survey, ).
Description
Microearthquake
Perceptible
Felt generally
Large (Strong)
Major (Severe)
Measurement of the severity of an earthquake can be expressed in several ways,
the two most common being intensity and magnitude. The intensity, reported
on the Modified Mercalli Intensity (MMI) Scale, is a subjective measure in
terms of eyewitness accounts (Table 1). Intensities are ranked on a 12-level
scale and range from barely perceptible (I) to total destruction (XII). The
lower intensities are described in terms of people's reactions and sensations,
whereas the higher intensities relate chiefly to observable structural damage.
Magnitude is an objective measure of earthquake severity and is closely related
to the amount of seismic energy released at the focus of an earthquake. It
is based on the amplitude of seismic waves as recorded on standardized seismographs.
The standard for magnitude measures is the Richter Scale, an open-ended scale
expressed in whole numbers and decimal fractions. The Richter Scale is logarithmic,
meaning that an earthquake of magnitude 5.0 has 10 times the wave amplitude
of a magnitude 4.0 and 100 times the ground vibration amplitude of a magnitude
3.0 event. As a first approximation, each whole number increment on the Richter
Scale corresponds to a release of about 31 times more seismic, or vibrational,
energy. Actually, there are several different methods of determining Richter
magnitude. One uses surface waves, another body waves, and so on. However,
the differences in results are slight.
Although the Richter scale has no upper limit, the greatest magnitude on record
is 8.9 for earthquakes that occurred off the northwest coast of South America
in 1906 (magnitude estimated) and off the east coast of Honshu, Japan in 1933.
By comparison, the famous San Francisco earthquake of 1906 had an estimated
magnitude of about 8.3 and an MMI of X.
A comparison of the Modified Mercalli and the Richter Scales is shown in Table
2. It is important to realize that these relationships are only generalizations
and can vary for any given earthquake depending upon local geologic conditions.
As a general rule of thumb, damage is slight at the magnitude 4.5 level, becomes
moderate at about 5.5, and above 6.5 or so can range from considerable to nearly
total (Bollinger et al., 1989). This rela tion may not apply to earthquakes
in Maryland, if recent events are any indication. A small tremor in January,
1990, west of Baltimore was assigned an Modified Mercalli Intensity V near
the epicenter, but registered only a 2.5 to 2.6 magnitude on the Richter scale.
EARTHQUAKES IN AND AROUND MARYLAND
To most people in the United States, damaging earthquakes are a California
phenomon, but this is misleading. Even though the greatest seismicity in the
United States occurs along the Pacific Coast (especially Alaska and Southern
California), major earthquakes have also occurred in the central and eastern
FIGURE 2. Earthquake epicenters in the eastern United States,
(from Foley et al., 1985; Sibol et al., 1985; and Stover et al., 1984).
The last earthquake to cause appreciable damage in the eastern United States
occurred in 1886 near Charleston, South Carolina. It had an estimated magnitude
of 6.5-7, an intensity of X, and was felt over an area of two million square
miles. Even in Maryland, the felt intensity from this earthquake was IV to
Perhaps the greatest seismic event ever to occur in North America in historic
times was a series of earthquakes that shook the mid-continent around New Madrid,
Missouri in the winter of . Estimates of the magnitude range as high
as 8.7; estimated maximum intensity was XII; and the felt area, which included
Maryland, was 2 million square miles.
Other damaging earthquakes in the eastern U.S. include an intensity VIII event
near Boston in 1755 and intensity VI events near New York City in 1737 and
Figure 2 shows earthquake epicenters in the eastern United States and eastern
Canada for a 10-year period, . Although numerous, these earthquakes
were all low-intensity, low-magnitude events. Most had a magnitude less than
2.0. It is definitely worth noting that Maryland seems to be part of a seismically
quiet zone.
Several earthquakes in adjacent states have been felt in Maryland. Marylanders
are more likely to feel one of these out-of-state earthquakes than one within
Maryland. As shown by Figure 2, Southwestern Virginia, central Virginia, and
the Atlantic seaboard northward from Wilmington, Delaware have significantly
more seismic activity than does Maryland. One out-of-state earthquake that
was felt in much of Maryland occurred Easter Sunday, April 22, 1984. In fact,
it was reported felt in eight states and the District of Columbia, over an
area of approximately 19,000 square miles. Centered about 12 miles south of
Lancaster, Pennsylvania, this earthquake registered 4.1 on the Richter Scale
and had an epicentral intensity of V to VI. Most notable effects in Maryland
were in the northeastern part of the state, which generally experienced Modified
Mercalli Intensity V effects for example, hanging pictures fell in C
windows cracked in Elkton and J and standing vehicles rocked slightly
in Union Bridge (Stover, 1988). A 3.0-magnitude tremor four days earlier is
considered to have been a foreshock. Ten aftershocks registering 2 to 2.5 Richter
magnitude occurred over a four-day period after the April 22 event. The Lancaster
earthquake is likely related to Triassic-age structures in the area.
As of late 1993, 47 earthquakes had been reported within Maryland’s
borders (Table 3 and Fig. 3). Over the next ten years, that total reached 61.
(For a frequently updated list and map of Maryland earthquakes, go to the Maryland
Geological Survey’s . The accuracy
and precision of these epicenter determinations is such that a few of the closer
out-of-state earthquakes could have occurred within Maryland and some of those
near the state’s boundaries may actually have occurred in adjacent states.
For example, not included in the list was a moderate shock that occurred on
January 2, 1885 in an area near the Frederick County, Maryland-Loudon County,
Virginia border. The maximum intensity was V, with the total felt area covering
more than 3,500 square miles. Of the Maryland earthquakes, 2 occurred in the
Valley and Ridge Province, 36 were in the Piedmont Province, and 10 were in
the Coastal Plain Province.
FIGURE 3. Map showing approximate epicenters of historic earthquakes in and near Maryland
The first reported earthquake to have actually had its epicenter in Maryland
occurred south of Annapolis on April 25, 1758, but no record of its strength
is known to exist. The shock lasted 30 seconds and was preceded by subterranean
noises. Additional felt reports were received from a few points in Pennsylvania
(U.S. Geological Survey, 1973). Maryland's strongest confirmed tremor was a
3.1-magnitude event near Hancock, Washington County, in 1978. That perhaps
was rivaled by an intensity V event (unknown magnitude) near Phoenix, Baltimore
County, in 1939. Earthquakes of such magnitudes or intensities are still considered
to be minor, and very seldom result in significant damage or injury.
Table 3:& Earthquake chronology of Maryland, .
The numbers 1-61 refer to those on the map in Figure 3. (Data for
compiled primarily by the U.S. Geological Survey (USGS); data
from Delaware Geological Survey (DGS), Lamont-Doherty Earth Observatory
(LDEO), and USGS; 1996 to 2002 data from DGS, LDEO, Virginia Polytechnic
Institute (VPI)., and Maryland Geological Survey.
Date (UTC)
Year& Mo. Day
(hh:mm:ss)
General Location
Depth (km)
Magnitude&
N Lat (deg.)
W Lon (deg.)
(3.5, 3.7)
Prince Frederick
Brandywine
Westminster
(3.1, 3.3)
(2.7, 2.9)
Union Bridge
Union Bridge
Union Bridge
Union Bridge
Catonsville
Westminster
Catonsville
Ocean City
(2.7, 3.3)
Round Bay - Severna Park
(3.1, 3.3)
Round Bay - Severna Park
(3.5, 3.7)
Accoceek - Piscataway
Randallstown (V), Eldersburg (IV), Ellicott City (IV), Granite
(IV), Owings Mills (III)
Granite - Randallstown - Baltimore
Granite - Randallstown
Columbia (IV) - Ellicott City (II) - Fulton (II)
Columbia - Allview Estates
Columbia - Allview Estates - Laurel
Columbia - Allview Estates
Columbia - Allview Estates
Columbia - Allview Estates
Columbia - Allview Estates
Columbia - Allview Estates
Aberdeen - Bel Air
Columbia - Allview Estates
Ellicott City near jct US40 & 29
&1.5 (est.)
Columbia - Allview Estates
Columbia - Allview Estates
1993&04&& 08
Columbia - Allview Estates
Columbia - Allview Estates
0.5 (est.)
Columbia - Allview Estates
0.5 (est.)
Ilchester - Ellicott City
Ilchester - Ellicott City
Columbia - Allview Estates
0.5 (est.)
1.7 (est.)
Columbia - Allview Estates
&1.5 (est.)
Columbia - Allview Estates
about 1.5 (est.)
Glen Burnie - Pasadena -Gambrills -Millersville
Perryville
Rising Sun (epicenter may be in Pennsylvania)
3 very small events in 35 min.
Columbia - Allview Estates
&1.5 (est.)
3 very small events in 75 min.
Columbia - Allview Estates
&1.5 (est.)
1996& 12&& 16
Ilchester - Ellicott City
about 1 (est.)
1996& 12&& 22
Columbia - Allview Estates
Columbia nr US29-Md32
1.5-2.0 (est)
Columbia nr US29-Md32
1-2 (est.)
28 miles west of the Richmond in rural Powhatan County, VA
SE Baltimore near Fort McHenry, Dundalk, Glen Burnie, Pasadena, Gambrills
9 km (6 miles) W of Lancaster, PA.
Southwestern New Jersey
7 km (4 miles) NNE (15&) from Bel Air North, MD
Potomac-Shenandoah Region, MD
8 km (5 miles) SSW (195&) from Mineral, VA
* Probable, but not confirmed by seismographs in the region. Magnitude
estimated from other events in the series.
Time (UTC): Coordinated Universal Time.& For the Eastern time
zone, subtract 5 hours from UTC time for Eastern Standard Time, 4 hours
for Eastern Daylight Saving Time.& For example:& 1200 UTC
(noon) = 0800, or 8:00 am EDT = 0700, or 7 am EST.& Note that
00:00-04:59 UTC converts to
of the previous day.
Epicenter, as calculated from seismograph stations =data and/or
estimated by the Maryland Geological Survey on the b
1962 marked the first instrumentally determined epicenter.
Except for event #6 in 1881 (see note 5 below), pre-instrumental
(pre-1962) intensity estimates are earthquake catalogs published by
various seismograph networks.
Except for event #6 in 1881 (see note 5 below) pre-instrumental magnitude
estimates (shown in parentheses) by L. Seeber and J. Armbruster (Lamont
Doherty Earth Observatory of Columbia University) and/or M. Chapman
(Virginia Tech Seismological Observatory); magnitude estimates for
a large number of pre‑instrumental earthquakes in the region
were derived using the region-specific relationships between felt area,
maximum intensity and mb(Lg) magnitude developed by Sibol et al. (1987).& Subsequent
magnitudes are from instrumental measurements.
Event #6 has not been listed in any previously published earthquake
list.& A rather detailed account of this event appeared in the
January 8, 1881 edition of the American Sentinel newspaper.& Estimates
of the epicenter and intensity have been made on the basis of the newspaper
magnitude estimates based on Sibol et al. (1987).
The Delaware Geological Survey states that this event may have been
a sonic boom instead of an earthquake (S. Baxter, oral commun., Aug.
16, 2001). &
Recent confirmed earthquakes in Maryland were both felt in roughly the same
location and, therefore, may possibly be related. The first of these occurred
on January 13, 1990 at about 3:48 p.m. local time (EST). According to reports
from nine seismograph stations, the shock's magnitude registered 2.5 to 2.6
on the Richter scale. Depth to focus was approximately 2 miles, which indicates
a very shallow earthquake. Intensities ranged from MMI V in the Randallstown
to IV at Eldersburg, Ellicott City, Granite and W and III at
Owings Mills. Several first-hand accounts of the event from the Granite-Hernwood
area reported that houses shook or windows rattled, both indicative of an intensity
IV. No damage was reported.
On April 4, 1990, reports of another small earthquake came from the Randallstown-Granite-Hernwood
area. However, seismic stations in Delaware and Virginia place the epicenter
in western Carroll County (Fig. 4), approximately 20 miles west of the Randallstown
area. By all accounts, this event was smaller than the January tremor. Preliminary
analysis of seismic records indicated a magnitude of about 1.6 or 1.7, and
first-hand accounts of a few local residents suggested a Mercalli intensity
of about II or III. One eyewitness described the event as starting with the
sound of distant thunder, getting louder for about 25 seconds, then followed
by 5 to 7 seconds of minor rumbling or shaking. Another resident of this area
has reported nearly two dozen similar events, although not confirmed as earthquakes,
between October, 1987 and May, 1990.
ASSESSING THE RISK
The earthquake hazard in the United States has been estimated in a variety
of ways. Chief among them is the production of &risk maps.& Such
maps prove useful in establishing building codes, engineering design standards,
and insurance rates in areas of high risk. Seismic risk maps are based either
on relative risk or on the probability of a certain seismic event at a particular
time and place.
FIGURE 4. Earthquake risk maps of the United States: (a) Relative risk of damage, based to a large extent on known earthquake history (Algermissen, 1969). (b) Probabilistic risk map showing maximum horizontal ground acceleration with a 90-percent probability of not being exceeded in 50 years (Algermissen et al., 1982).
Two examples of risk maps are shown in Figure 4. Figure 4a shows four zones
that are assigned risk on a relative scale. This map is based on the known
occurrence of damaging earthquakes in the past, evidence of strain release,
and consideration of major geologic structures and provinces believed to be
associated with earthquake activity.
For years, this map was widely used, because it was the best risk map available.
However, this type of risk map has several drawbacks. For one thing, it does
not consider frequency of occurrence. Furthermore, there is no justification
for assuming that events larger than those observed historically, especially
in the East, will not occur in the future. It is also known that ground-motion
attenuation (&dying out& of the shock waves) with distance is far
less in the eastern U.S. than in the western states. Felt areas are, in general,
one order of magnitude greater in the East than for similar earthquakes in
the West (Bollinger, 1973). Nonetheless, according to this map, Maryland is
appropriately placed into a zone of minor expected damage, corresponding to
Mercalli intensity V to VI.
A more recent development that is still being improved upon is the probabilistic
map. One example is illustrated in Figure 4b. This particular map shows the
expected maximum horizontal ground acceleration (as a percentage of g, the
acceleration due to gravity, 32.2 ft/sec2) on rock sites. These ground accelerations,
which are one measure of ground shaking, have a 90-percent probability of not
being exceeded in 50 years. This is equivalent to a recurrence interval, or
return period, of 475 years (Hays, 1980).
Damage begins to occur at about 10-15% g. Below 4% g, which is the lowest
contour on this map, shaking effects are controlled by earthquakes of magnitude
4.0 or less in other words, minor earthquakes. An acceleration of 0.1% g or
more is perceptible to people (Algermissen and Perkins, 1976). According to
Figure 4b, Maryland has a very low chance of experiencing a damaging earthquake
in a 50-year period. For moderate exposure times (10-100 years), the expected
ground motion associated with earthquakes in this region would be of marginal
interest (Algermissen et al., 1982). As a rough estimate, Maryland's falling
in the 4-10% g category on the map in Figure 4b might translate into a maximum
expected magnitude of 4.0-4.5. It is important to emphasize that these figures
are only rough estimates. The difficulty in assigning maximum magnitudes is
most acute where no faults are known, where seismicity is low, and where near-maximum
earthquakes may not have occurred in historical times. This is true for most
of the eastern United States (Algermissen and Perkins, 1976).
Downloads and Links
Educational Series 9:
(pdf, 1.1 MB)
Fact Sheet 13:
(pdf, 334 kB)
Open File Report 99-03-1:
REFERENCES CITED
Algermissen, S. T., 1969, Seismic risk studies in the United States:
Proc., 4th World Conference on Earthquake Engineering, Santiago, Chile,
v. 2, p. 14-27.
Algermissen, S. T. and Perkins, D. M., 1976, Probabilistic estimate
of maximimum acceleration in rock in the contiguous United States: U.S.
Geol. Survey Open-File Report 76-416, 45 p.
Algermissen, S. T., Perkins, D. M., Thenhaus, P. C., Hanson, S. L.
and Bender, B. L., 1982, Probabilistic estimates of maximum acceleration
and velocity in rock in the contiguous United States: U. S. Geol. Survey
Open-File Report 82-1033, 99 p.
Bollinger, G. A., 1969, Seismicity of the Central Appalachian states
of Virginia, West Virginia, and Maryland: Seismol. Soc. America
Bull., v. 59, no. 5, p. .
_______, 1973, Seismicity of the southeastern United States: Seismol.
Soc. America Bull., v. 63, no. 5. p. .
Bollinger, G. A., Snoke, J. A., Chapman, M. C., and Sibol, M. S.,
1989, Estimates of the occurrence and resulting effects of damaging earthquakes
in Virginia: Virginia Minerals, v. 35, no. 3, p. 17-22.
Foley, J. E., Doll, C., Filipkkowski, F., and Lorsbach, G. (eds.),
1985, Seismicity of the Northeastern United States, April 1-June 30, 1984:
Weston Observatory, Boston College, Northeastern U.S. Seismic Network Bull.
Hanks, T. C., 1985, The National Earthquake Hazards Reduction ProgramScientific
Status: U.S. Geol. Survey Bull. 1059, 40 p.
Hays, W. W., 1980, Procedures for estimating earthquake ground motions:
U.S. Geol. Survey Prof. Paper 1114, 77p.
Sibol, M. S., Bollinger, G. A., and Mathena, E. C. (eds.), 1985,
Seismicity of the Southeastern United States, January 1-January 30, 1985:
Seismological Observatory, Virginia Polytechnic Institute and State University,
Southeastern U.S. Seismic Network Bull. 16, 70 p.
Spence, W., Sipkin, S. A., and Choy, G. L., 1989, Measuring the size
of an earthquake: Earthquakes and Volcanoes, U.S. Geological Survey, v.
21, no. 1, p. 58-63.
Stover, C. W., 1988, United States Earthquakes, 1984: U.S. Geological
Survey Bulletin
Stover, C. W., Reagor, B. G., and Algermissen, S. T., 1984, United
States Earthquake Data File: U.S. Geological Survey Open-File Report 84-225,
U.S. Geological Survey, 1973, Earthquake history of Maryland: Earthquake
Information Bulletin, v. 5, no. 4, p. 22-23.
_______, 1981, Questions and answers: Earthquake Information Bulletin,
v. 13, no. 4, p. 153-154.
_______, 1990, Preliminary Determination of Epicenters, Weekly Listing:
National Earthquake Info. Center, Denver, No. 2-90, Feb. 1, 1990.
Wheeler, R. L. and Bollinger, G. A., 1984, Seismicity and suspect
terranes in the Southeastern United States: Geology, v. 12, no. 6, p. 323-326.
SUGGESTED READINGS FOR THE NON-GEOLOGIST
Bolt, B. A., 1978, Earthquakes, a primer: W. H. Freeman and Co., San
Francisco, 241 p.
Gere, J. M. and Shah, H. C., 1984, Terra non firma: W. H. Freeman
and Co., San Francisco, 203 p.
Halacy, D. S., Jr., 1974, Earthquake A natural history: Bobbs-Merrill
Co., New York, 162 p.
Hodgson, J. H., 1964, Earthquakes and earth structure: Prentice-Hall,
Inc., Englewood Cliffs, N.J., 166 p.
Pakiser, L. C., 1988, Earthquakes: U.S. Geological Survey, Denver,
Colo., 20p.
This pamphlet was prepared by James P. Reger.
Compiled by the , 2300 St. Paul Street, Baltimore, MD 21218
This electronic version of &Earthquakes and Maryland
& was prepared by Bob Conkwright, Division of Coastal and Estuarine Geology, Maryland Geological Survey.
Richard A. Ortt, Jr., Director2300 St. Paul Street, Baltimore, MD 21218
& 2017 Maryland Geological Survey