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DEPARTMi,NT OF THE INTERIOR TO ACCOMPANY MF-620

- UEITED STATES GEOLOGICA1. SURVEYg

SEISM 0 TECTONIC MAP OF THE EASTERN UNITED STATES *"

By Jarvis B. Hadley and James F. Devine

INTRODUCTION used in present study (Coffman and von H.ke, 1972,p. 5-57) occurred during this period. For New England

The purpose of a seismotectonic map is to describe and New York this figure is about 66 percent; for thethe distribution of historic seismic activity in re- southern 'Appalachiac and coast al areas it is 70 percent;lation to geologic st ructures and tectonic provinces and for the region extending from the Appalachianand to identify structures or regions that are Mountains to and including the Mississippi River valley

,g''" it 'is about 80 pucent. Because of the relativelycharacterited by consistent relations betweene seismic activity and structural features. An exper- ' low f requency of occurrence of eastern earthquakes

imental study to test the feasibility of preparing (abcm.J>.2 earthquakes of MM IV-V or greater per yearsuch a map and its usefulness in evaluating earth- during 1900-1970), it was considered desirable toquake hazards was initiated jointly by the U.S. include data f rom the earlier period of less completeGeological Survey and the former Seismology Division records in order to obtain as long a record of seismic

*of the National Oceanic and Atmospheric Administration; activity as possible. This means that probably 85financial support was provided by the U.S. Atomic percent of the epicenter locations used are based onEnergy Commission. It was hoped that the study would macroseismic rather than instrumental ebservations anddevelop evidence for the existence of tectonic regions are limited correspondingly in accuracy,or structural provinces that are useful in defining The epicenter data used for this study were extractedparameters of seismic hazard in relation to engineered from the current working file of the National Earthquakestructures. As with many experiments, this one did Information Service and do not represent a final editednot produce the results envisioned at the outset, but compilation of eastern United States seismicity.it did result, we think, in assembling seismic and However, subsequent refinement and improvement of lo-structural data useful in evaluating the distribution cations or maximum intensities are expected to resultand origin of earthquakes in the eastern part of in only minor changes in the seismic-frequency contoursthe United States and in delimiting areas of relative developed for this study. The locations and maximumseismic activity. epicentral intensities of earthquakes were recorded onThe tectonic provinces of the eastern United Statea, ma6netic tape and plotted from the tape. Locations

as outlined and described by King (19 51), are as were fixed to the nearest 0.1 degree of latitude andfollows: longitude; the symbol used represents the highest

I. Central stable region epicentral intensity located at the plotted pcint.a) Laurentian shield (part of Precambrian The contours shown on the epicenter plot were

Canadian shield) developed by counting the number of epicenters, in-b) Interior lowlands (bordering platf orms cluding repeated events at the yamt; plotted location,

covered by younger rocks) within a circle representing 10'km" at the original11. Appalachian (orogenic) system or tectonic map compilation scale of 1:2,500,000. They were

province generated by tracing in a somewhat generalized fashiona) Fold belt (roughly the Valley and Ridge the position of the center of the counting circle

physiographic province) while moving it so as to include up to but not moreb) Blue Ridge belt (Blue Ridge physiographic than ti.e 4, 8, 16, 32, and 64 epicenters sela ted as

province) contour intervals. Because we wished to emphasizec) Piedmont belt (Piedment physiographic the areal distribution of seismic activity which might

prevince and part of Blue Ridge be related to geologic structure, rather thac the totalphysiographic province) seismic energy released, the intensities of individual

d) Sew England-Maritime belt (extension earthquakes were ignored in contc,uring seismicof belts 11 a, b, and c north of New frequency.Jersey and Pennsylvania) We wish to acknowledge here the indispensible contri-

III. Coastal Plains (postorogenic deposits overlapping bution of D. W. Garden and Carl Stover, then of thethe Appalachian system; of subordinate tectonic Seismology Division of the National Oceanic andsignificance except in Mississippi embayment). Atmospheric Administration and now of the Geological

It is clear f rom existing structural data, es well as Survey, in extracting the earthquake data and preparingf rom the distribution of earthquakes, that historic the computer plot. We also acknowledge the work ofearthquake activity bears no consistent relation to D. W. Gordon in preparing an earlier version of thethe provinces and subprovinces defined above. Parts seismic-frequency contours,of the provinces differ from one another in structure The accompanying tectonic map shows the majorand tectonic history, especially of Mesozoic and structural features and tectonic provinces of theCenozoic age, and in seismic history during the past eastern United States as currentif understood, with200 years. Seismically active renes locally cut emphasis on features that seem to be involved inacross tectonic provinces as, for ex eple, the New historic seismic ac tivity (map A). The features shownMadrid meismic zone and the transverse seismic area are abstracted primarily f rom the Tectonic map of thein central Virginia. Only the southwestern faulted United States (Cohee, 1962) and the Basement rock mappart of the Appalachlan fold belt is identified as of the United States (Bayley and Muehlberger, 1968),a tectonic prosince with fairly uniform structural with minor revisions and additions based on informationcharacteristics and seismicity, published or obtained since those maps were compiled.

The bagic method of this study has been to compare For New England and adjacent parts of Canada, additionalseismicity, as shown by the location of epicenters of geologic information was obtained from a recentlyrecorded earthquakes (map B), with lithologic, published tectonic map of the Appalachian regionstructural, and geophysical features (map A) that (Rodgers, 1970, pl. 1), from geologic maps of Newmay have served to generate or control the release of Hampshire and Verment (Billings, 1956; Doll, 1961),seismic energy. Results of the study, depicted as and from unpublished data for southern Naw Englandareas of varying amounts of seismic activity and (Barosh, P. J., written commun., 1973). Aeromagneticvarying degrees of inferred structural control, are maps of many areas and from various seurces were used,shown on the seismetectonic map (map C). especially for infermation en the structure of the

The epicenter plot of map B shows computer plotted Precambrian basement west of the Appalachian tectoniclocations of epicenters of earthquakes of Modified system, on the pre-Cretaceous basement beneath theMercalli (MM) 1I1 or greater intensity which occurred Atlantic Coastal Plain, and on the rocks beneath theduring the period 1800-1972. Reasonably complete and Gulf of Maine. For similar purpeses, as well as toaccurate data on earthquakes in the eastern United obtain informatten about the deeper structure in theStates have been kept since about 1900, and about 75 Appalachian tectonic belts, the Bouger gravity anomalypercent of the earthquakes of MM IV-V and greater map of the United States (Woollard and Joesting, 1964)

* Prepared in cooperation with the U.S. Atomic Energy Commission

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was used, which the characteristic Appalachian folds die out in theIn addition to assembling and analyzing the seismic relatively undelormed rocks of the Appalachian Plateaes

#and structural data, descriptions of about 60 earth- of the continental interior. Norta of New York the *quakes that had been investigated in the field or other- st ructural province adjoining the f old belt on the westwise described in more than cursory fashion were is the Canadian shield and its outlier in the Adirondackexamined for evidence indicating structural cont rol. Mountains of New York state. This part of the boundary

With the exception of the New Madrid earthquakes of 1811- is not only sharper but presents a much strongtr tectonic12, none of these reports contained evidence of surf ace- contrast than the farther southwest.breaking faults. For only a few earthquakes whieh have The Blue Ridge belt, bordering the fold belt on theoccurred since 1960 did such descriptions indicate southeast, is characterized by many f olds and f aults and,evidence of structural control. more importantly, by major deformation involving not

To review the tectonic and structural features of the only the Precambrian basement rocks but also severaleastern United States and to provide background for kilometers of upper Precambrian sedimentary and volcanictheir relation to historic seismic activity, as presented recks, which are mostly absent from the fold belt. Thein the accompanying seismotectonic map, a brief Blue Ridge belt is also characterized by higher gradesstructural summary follows. of regional metamorphismi hence its rocks a;e relatively a

strong crystalline rocks, as distinguished f rom the lessSUMMARY OF STRUCTURAL FEATURES cryst lline and generally weaker sedimentary rocks of

the fold belt. In many places the northwestern boundaryPrecambrian structures of the Blue Ridge belt and its northern extension, the

'Creen Mountains of western New England, is marked by low-Precambrian rocks underlying a relatively thin cover angle faults on which the rocks of the Blue ILidge and

of Paleozoic recks are the dominant supracrustal rocks Green Mountain belts have been carried westward over thethroughout the interior of the 1*ntted States and Canada. rocks of the fold belt. This is especially true in the

Although largely concealed within the United States, southwestern part of the system, where the Blue Ridgethe lithology, age, and distribution of the Precambrian rocks have been thrust many kilometers over the rocksrocks are at least partly known from exposures, drill of the fold belt.records, and aeromagnetic and gravity surveys. The Appalachian Piedmont belt adjoining the Blue RidgeStructures thus recognized include both local trends belt on the southeast is as wide as or wider than theand regional features, such as the Lake Superior Blue Ridge and is at least as c omplex st ructurally. Itsyncline in Wisconsin, Minnesota, and lowa and the so- is less well known geologically and consists largely ofcalled Grenville metaaerphic or orogenic f ront that has unfossiliferous sedimentary and volcanic rocksbeen traced from easte.n Canada southward into Michigan moderately to strongly recrystallized and invaded byand Ohio. many different kinds of f elsic and mafic intrusive rocks.

For the most part, major Precambrian structures of The metamorphosed volcanic and sedimentary rocks arethe continental interior are not specifically associated probably mostly of early Paleozoic age but may includewith current or historic seismicity. It is not knewn rocks of late Precambrian age, as well as isolatedwhether carthquakes have resulted from movements on bodies of older Precambrian rocks. Deformation.F recambrian f aults or other st ructural discontinuities, metamorphism, and intrusion are believed to have takenespecially in the central l'nited States where scattered place at several times during the Paleozoic. Rocks insmaller earthquakes commenly cannot be related to known the northeastward continuation ot the Piedmont belt infeatures in the Paleezoic or younger rocks. It is New England range in age from early through middle and

late Paleczoic, and their structural history has beennotable, however, that such structures seem to nave

played only a reinor or local role in determining the at least as complex as that of the Piedmont rocks.release of seismic energy (Kiss 11nger and Nuttli, The geologic boundary between the Blue Ridge and1965). Green Mountain belts and the Piedmont belt to the south-Rocks similar in age and Precambrian structural his- east is not well def ined. In the southern Appalachians

tory to those in the eastern part of the continental the geologic boundary has been interpreted as a zone efinterior occur also within the Appalachian system f rom combined rec un. bent folding, ove r t h ru s t faulting, and pre-M w England to Georgia. Their structural trends have, Triassic high-angle or strike-slip shearing known as thehoweser, been so strongly overprinted in most places Brevard f ault zone (Reed and Bryant, 1964; Burchfiel andby Paleozoic deformation that no distinctively Lisingston, 1967; Hatcher, 1971; Roper and Justus, 1973).Precambrian structures can be related to regional Farther northeast in the central and northern Appalachians,

seismic activity. the boundary is even lesa well defined. For the purposesof this report, the Blue Ridge and Piedmont belts and

Paleozoic structures their equivalents in New England are considered as asingle tectonic province.

Appalachian system Rock types and structures characteristic of theAppalachian Pied mnt disappear eastward beneath the

Paleozoic structures include structures that have deposits of the Atlantic Coastal Plain so that noaffected the Paleozoic rocks and can reasonably be re- structurally significant castern boundary is known ingarded as having f ormed bef ore Mesozoic time. They are the castern United States. Fvidence from drill holesconcent rat ed in the Appalachian and Ouachita t ec t onic and aeronagnetic surveys, however, suggests that thesystems, where their characteristic features are those rocks of the Florida platform buried beneath theof sup rac tustal compression and shortening ac ross the Coastal Plain are significantly different from those of

belts, resulting in folds and faults, regional dynamo- the Pied:ent in central Georgia, and therefore a major

thermal met amorphiru, and enplacement cf various intru- tectonic province boundary may exist between them.sive rocks. Since most ef the Ouachita system lies out-side Lt.e area of the present study, the subsequent Central stable region

discussion deals mainly with the Appalachian system.The Appalachian system dcminates the eastern part of Distinctive P.zleozoic structures of the continental

the continent, especially within the United States. It interior are principally broad upwarps such as theconsistg ef several structural belts which can be traced Cincinnati, Findlay, and Kankakee arches, the Ozark up-t h rou ghod the length of the system. The northwestern lift, and the Nashville dome, bordered by moderatelyor Appalachian fold belt consists of strongly folded deep depesitional basins of Paleozoic rocks, includingPaleozoic sedimentary rocks 3 to 10 km thick, broken by the Michigan and Illinois basins. Exceptionally deep

low-angle thrust faults thit are largely confined to the depositional troughs border the Appalachian and Ouachitasedimentary rocks above a deeply buried but little de- tectonic systems. These uplifts and the complementarfformed basement surface. The fold belt is 32 to 96 km basins developed gradually throughout most of Paleozoicwide in most places but increases to nearly 200 km in time. In plaecs the uplift or subsidence was accompaniedPennsylvania and West Virginia. Re- ,M low-angle by high-angle faulting and mild folding, the effects offaults daplicating parts of the s.ifmente y sequence are which are included among the Paleozoic structures on theprominent throughout the southwestern part of this belt, actempanying tcctonic map.

but they are much less abundant in the central part.The equivalent structural belt ncrth of New York City ismuch narrower and is characterized by both folds and

low-angle faults. The western boundary of the fold beltsouthwest of New York City is a transitional zone in

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e * Structures of late Paleozoic (?) and Mesozoic age faults of the St. Genevieve system in southern Illinois*

(Heyl and ot*ers, 1965, pl. 2). Although some of thee Appalachian system northeast-trending f aults have been described as con-

tinuous and contemporary with the east-west faults.The orogenic events that formed the Appalachian system detailed investigation has shown that they are somewhat

in the eastern l'nited States were succeeded by a new younger and more continuous than the east-west faultstectonic regime both in the Appalachian orogenic belt where the two sets intersect in the Illinois fluoriteand in the central stable region to the west. This district (Weller, Grogan, and Tippie, 1952). Fromregime was at least partly extensional and, caused high- evidence (partly seismic) that seme of the northeast-angle faulting of near-surface rocks, in contrast to trending f aults continue southwestward beneath thethe compressional and deep-seated ef f ects of the earlier seismically active part of the embayment, Heyl andtectonism. These later features are divided into two others (1965, p. B-5) have applied the name New Madridbroad groups, a series of fault-block basins of Triassic fault zone to them.age entirely within the Appalachian orogenic system. Data on the pre-Cretaceous subsurface geology of theand a group of riftlike fault zones within the central Mississippi embayment show that the Paleozoic rocks are

,stable region. arched over and eroded f rom a northwest-t rending up-

Structures known to be Triassic are confined essen- lift (Pascola arch) between the Nashville dome andtially to the Appalachian Piedmont and its New England the Ozark uplift and that they may be considerablycounterpart. They consist of block-faulted basins in faulted as well (Freeman, 1945; 1953, pl. 5) . Thewhich continental sediments were deposited, in part locations, trends, and displacements on these faultscontemporaneously with the faulting. The deformation are not well known, but it is possible that both north-*

was primarily extensional, resulting in tilted and down- east-trending faults of the New Madrid system anddropped basins bordered by high-angle faults. Invasions northwest-trending faults related to the St. Genevieveby basaltic rocks are associated with these movements fault and to the f aults exposed in the Ozark uplif tthroughout the Piedmont belt. Neither the sedimentary are present.nor the igneous rocks have been extensively determed The northeast-trending faults, like some of the east-or metamorphosed, as they were formed after Paleozoic west faults, are overlapped by the Coastal Plaindeforzation and regional metamorphism had ceased deposits of the embayment, but recent work has showncompletely. that movements on them continued well into Late

In New England a chain of shallow intrusive and Cretaceous and prc bably into Tertiary time (Ross, 1963).associated volc anic rocks known as the White Mountain Thus, although the faults were well established byplutonic-volcanic series extends northward f rom central Late Cretaceous time, they appear to have been

to northern New Hampshire. They include stocks, arcuate tectonically active during subsidence of the embaymentdikes, and related intrusive rocks of Jurassic age which, syncline which began in the Late Cretaceous and contin-like the Triassic rocks, are younger than the Appalachlan ued into Eocene time. Topographic features and localtectonic belts. They are well represented in the structural evidence within the emhayment suggest post-

seismically active part of central New Hat 4 shire, and Pliocene movement on f aults of this trend possibly asa recent earthquake has been ascribed to displacement f ar south as the vicinity of Memphis, Tenn.

along the border of one of the intrusives (Leet and The other major region of high-angle faulting liesLinehan, 1942). along the southeastern edge of the Canadian shield in

the vicinity of the Adirondack Mountains and the OttawaCentral stable region and St. Lawrence lowlands. Lower Paleozoic rocks on

the margin of the shield appear in tilted f ault blocksThe fault zones in the central stable region include on the east flank of the Adirondacks and in the St.

a series of east-trending f ault zones extending through Lawrence lowland east of Montreal. They also occur in

Kentucky, across southern Illinois, and into south- a west-trending fault and graben zone 96 km wide thatcastern Missouri. They are known in eastern Kentucky penetrates the shield and separates the Adirondack up-

zone and in western lift from the main part of the shield to the northas the Kentucky River faultEentucky as the Rough Creek fault zone, which continues Middle Ordovician rocks are preserved en the dewn-into southern Illinois as the Shawneetcwn and Cottage dropped blocks, but the age cf the subsidence is notGreve fault zones. A western continuation includes the well established. Dikes and stocks in and near thewell known St. Genevieve fault zone and several other faulted areas range in age from early Paleozoic to Earlyfaults in southeastern Missouri. The f aults are record- Cre t ac eous , based on K-Ar dates (Doig and Barton, 1968).ed in nearly horizontal Paleozoic rocks so that, The development of topographic lowlanas en the down-alth, ugh they may have significant st rik e-slip d is- dropped blocks has resulted f rom dif f erential erosionplacements, such displacements are difficult to detect. of the less resistant Paleozoic roc ks and not fromThe presence of high-angle reverse faults and evidence recent fault movements. The faults trend east-west orof right-lateral movement in parts of the Rough Creek, west-northwest and in places north-south, but they areShawneetown, and Cottage Crove fault systems have been generally markedly discerdant to structural trends ininterpreted as evidence of wrenth f aulting (heyl and the adjacent Frecambrian rocks. King (1951, p. 22-23)

Brock, 1961). concludes that they were formed subsequent to PaleozoicThe fault zones include many normal or gravity f aults, time and correlates them with post-Early Cretaceous

some with displacements of several hundred meters, as faultirs in the shield.well as reverse f ault s. Large displacements are foundin rocks as young as Fennsylvanian, and associated Coastal Plain sub sident edoming and mafic and alkalic intrusive rocks of HicksDome in southeastern Illinois are regarded as Permian A group of Mesozoic and Tertiary structures is(Heyl and others, 1965, p. Bil). At the northern edge associated with subsidence of the continental bordersof the Mississippi embayment, some of these faults are alcng the Atlantic and Gulf coasts. For the most part,

covered by L'prer Cretaceous sedimentary rocks of the subsidence began in Cretaceous tire and persistedCoastal Plain shewing that most of the displacements throughout most of the Tertiary although the rate andhad taken place before they were laid down. The fault amount of subsiu mce varied considerably in locationzones seem to bear little tectonic relationship to the and time during this period. The basement surface isearlier Paleozoic arches and danes previously described; relatively high and the Coastal Plain deposits thinnerf or example, the Kentucky kiver, Roagh Creek, and Cottage along the northwest-trending Cape Fear arch than in theCrove zones t rend perpendicula rly ac ross the Cincinnati- bordering Coastal Plain embayments to the nerth andNashville arch and extend well into the sedimentary south. The sedimentary record indicates that the Capebasins on either side. They r'epresent quite a different Fear arch was tectenically positive during the Earlytectonic pro (ess which probably occurred in the interval Cretaceous and again during the Eocene, but that it

between Pennsylvanian and Late Cretaceous time. has been esu ntially neutral relative to adjoinin3A third set of high-angle faults crosses the trend of areas during the late Cenozoic. A similar uplift

the Rough Creek and Cottage Grose fault zones in south- prebably exists in the Norfolk, Va., region borderingeastern Illinois and extreme western Kentucky. These the deep Salisbury embayment in Maryland and Delaware.northeast-trending faults, known in southeastern Illinois Although this structure is smaller and less well knownas the Wabash Valley faults, form a zone about 60 km than the Cape Fear arch, Eocene faulting along it haswide which is parallel to the axis of the Mississippi been suggested on meager evidence (Cederstrom, 1945).embavment syncline and is sharply defined against the Aside from this, the Atlantic Coastal Plain arches andeast-west faults in western Kentucky and against the embayments are not knewn to be separated f rom one another

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* *by sharp structural or stratigraphic discontinuities line extending roughly f rom central Minnesota south-that would indicate faulting, eastward through Milwaukee, Det roit , New Yerk , and .

*High-anale faults that displace Coastal Plain strata Long Island, and northeastward to Nova Scotia. The

have been ebserved in the Gulf Coastal Plain, where central part of this region, in the Hudson Bay area,they are largely strike f aults bounding depressed blocks. appears to be still rising relative to sea level atSubsurface evidence commonly indicates that these faults about 7 mm/yr. Isobases of equal uplift during the

flatten with depth and have resulted f rora basinward past 13,000 years and hinge lines marking succetsivesliding within the sedimentary pile. Because few if northward shifts of the limit of warping trend approx-

any earthquakes are associated with these faults, most imately parallel to the outer glacial limit andare not shown on the ae ompanying tectonic map. Linear concentric to the former ice cap.

topographic depressions, displaced flood plains, and Similar crustal warpind, apparently unrelated toeven fault scarps have been reported along the Baton glacial unloading, is suggested by recently completedRc>uge fault zone (Durham and Peeples, 1956). leveling traverses throughout the eastern 1;nited St ates,

Known f aults are much less common in t he Atlantic as reported by Meade (1971). These results indicateCoastal Plain. Those that have been reported were crustal updoming during the period 1930-1970 at aobserved very locally in artificial excavations or rate of 7 mm/yr centered in northwestern Georgia, as -

interpreted from local subsurface data. They are well as subsidence along the Atlantic coast north ofknown to displace Coastal Plain strata from Late Cape Hatteras reachind 5 to 6 mm/yr in New Er. gland.Cretaceous to Eocene or younger age, and some displace Elsewhere in the easte rn l' nit ed States, including

the basement rocks as well (Jacobeen, 1972, Glaser. Florida, changes of elevation oppear to be minimal.1971; Bruce O'Connor, eral commun., 1974). Linear Regional t ilt s indicated by the level measurements showsurf ace f eatures seen on aerial photegraphs er satellite a maximum of 6 mm/yr/100 km 'n New England and 3.5imagery bave been interpreted as representing fault mm/yr/100 km in northern Georgia and the Carolinas. In

traces in the Atlantic Coastal Plain, but evidence comparison, current tilt rates due to glacial reboundrelating these features to observable displ cements in the Great Lakes region are estimated at only 1.5 mm/is mostly lacking. yr/100 kn (Flint, 1947, p. 425).The most significant of the Coastal Plain structures, Very different evidence of Quaternary deformatien is

from the standpoint of seism;c activity, is related to found in faults that offset surficial materials ofthe Mississippi embayment t rough north ef the Monroe up- late Cenoroic age. These include many examples of

lift and Jackson dome The record of the sediments f ault s displacing geologically young f eatures, such asdepeelted in the embayment shows that subsidence was alluvial deposits, till, leess, glaciated bedrock sur-

relatively short lived, beginning in Late Cretaceous faces, and river terraces. Although such f eat ures havetime and ending by Oligocene time; since then only been widely repcrted from localities in the Appalachianabout a hundred meters of Pleistocene and Holc cene Piedmont and Coastal Plain, most have been ebservedalluvial deposite have accumulated. The trend and only in limited exposares such as road cut s and riverextent of the basin deep into the cent ral stable reglen banks in unconsolidated materials which are subject to

indicate tectonic control rather dif f erent from that rapid creslor and overgrowth of vegetation. Littlegoverning the broader, l es ., linear basins in other parts informatien has been available as to their regional

of the Atlantic and Gulf Coastai Plains. The timing extent er tectonic significance. A reported exception

of the tectonic events involved suggests a connection is that of the glaciated bedrock surfaces in the

with the Laramide orogeny of the Rocky Mountain region. Champlain-Hudson valley region; these surfaces showAn apparent tectonic relatienship exists between this systematic reverse-fault diaplacements of a millimeter

pat tern of crust al subsidence and the nor theast-t re nd- or more on southeast-dipping regional cleavage (Oliver,ing Wabash Valley faults dirntly along strike in south- Johnson, and Derman, 1970).eastern Illinois. As mentioned previousiv, these faults In the Mississippi embayment region, faults areappea r t o repres,'nt a somewhat younger, through-geing known in rocks of Plioc ene-Pleistocene age (Finch,

system that transects the Rough Creek and St. Genevieve 1966; Olive, 1963, 1965). Faults in loess and alluviumfault zones near the head of embayment. The northeast- of Pleistocene age have been interpreted as oc curring

trending faults are overlapped by the Coastal Plain along topographic lineament s whish may represent moredeposit s ef the embayment , but retent werk has shown extensive faults and fractures in the Coast al plain

that movement s en the faults continued well inta sediments (Krinitzsky, 1950). For the most part.

Cretaceous and probably into Tertiary time (Ross, 1963). however, direct evidence indicating that faults are

Thus, altheugh the faults were established by Late coincident with these features is la(k in ;. With the

Cretace>us t !w , they appear to have been active exception of the vicinity of New Madrid, Mo., andtectonitally during subsidence of the embayment svncline Reelfoot Lake. Tenn., no faults or other indications

th4t began in Late Cretaceous and tentinued into M ene of recent faultirg are known to be associated with

time, any histeric earthquake.For an evaluation of reglenal seismicity, it is im-

portant to know what st ruc tural boundary if any exists SEISMIC AREASbetween the Mississippi eribayment and the seismicallyless active Gulf Coastal " lain to the south. This A study of the carthquake epicenter map B shows thatboundary seems to be marked by a series of transverse large areas of background er minimal seinic activity

uplifts and mafic intrusive bodies in the embayment are distin;;uished f rom epicentral concentrations repre-

deposits in northern Louisiana, southeastern Arkansas, senting areas that are seinrically more active. The

and adiacent parts cf Mississippi. These features upper limit of astivity in the t ickground areas is' 2formed in Middle and Late Cretaceous time and served arbitrarily taken as less than 8 epicenters per 10*kmta restrict the embaynent t rough to the narth, where (in most places less than 4) and the absence of eart h-deposition virtually ceased after early Tertiary time quakes with epit entral intensities greater than VI.These features i nd i c a t e. the existence of a tectonic Nat all such areas are wholly ase}sq c, although someboun.tary between the embavment trough and the region of areas tensiderably larger than 10*km' have generated noontinued deepening of the Gulf Coast geosyncline. If recorded earthquases. In f act , areas with no epicenters

0 2so, the boundary is censiderably south of and seemingly within 10 km could be outlined, but this d ist inc t ion

independent of the buried Quac hita tet tonic front, which is believed to be tectonically uninterpretable from a

passes beneath the deepest , art of the trough, regional point of view.For meaningf ul t ec tonic interpretation one must turn

Quaternary structures to the twre seismic areas and these, c lassif ied accord-

ing to level cf seis=le activity and degree of knownThe most recent structures, those ef Quaternary age or st ruc tural cont rol, are shown on map C. They are

younger, are of course particularly important in a study described in seme detail in the following pages.

of the causes of historical scismicity. Several lines In establishing the dif f erent areas of earthquake

cf evidence attest to crustal movements during the attivity shown on the seismetectonic map, use is made

Quaternary, although quantitative data are scat tered o' three parameters. One is the areal density (seismicand incomplete. One of the best documented crustal fre,uency) of epicenters, including separate events

movements is the record of upwarping threughout the at the same location. A second is the maximum ept-

northeastern part of the continent as a result of central intensity, according to the Modified Mercallideglaciation and unloading of the crust during and scale (Wood and Neumann, 1931), ef any earthquake knownafter removal of the Lab r ado r ice sheet. These move- to have occurred in the given area. Although magnitudements were apparentiv Itmited to the reglun north of a determinations are given for many earthquakes that have

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occurted since 1960, they are generally not available been produced on a branching f ault or f aults on the -

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for earlier events. Moreover, since it is expected southwest flank of the Illinois basin. There seems toL'h a t a principal use of the map will be to estim4 e be, however, no geologic record of a major fault with,

potential earthquake damage, intensity values are this location and orientation.considered to be more useful. The third parameter is Evidence from fault plane solutions of 25 earthquakesthe evidence of structural control on epicenter distri- recorded since 1962 in the Mississippi embayment andbution as determined by the tectonic study. From these adjoining areas (Stauder and Nuttli, 1970; Street andparamete rs f ive levels of seismic activity and three Herrmann, 1974) indicates that northwest directed

categories of structural control were selected (see map compressional fault movements dominate in the embay-C explanation). ment north of the crest of the Pascola arch and also

The seismic areas described herein are intended to in southeastern Illinois. Earthquakes in the embay-represent areas designated by notable seismicity and, ment south of the crest, however, indicate normal fault

in sa far as possible, the structural features believed movements on north-trending faults. Strike-slip fault-to be casually related to the seismicity. In some ing was found in only two earthquakes, both along theareas notable seismic activity is not associated with northwestern edge of the New Madrid fault zone north-

. any known structural feature, but is distributed so as northwest of New Madrid, Mo. This vidence, ifto indicate rather clearly that the activity is localized confirmed, would indicate that earthquakes near andalong concealed or unidentified faults or other struc- northeast of New Madrid arise from tectonic mechanismstures. Seismicity, usually of low level, is scattered different f rom those controlling f aulting f arther south-

in many areas so that no localizing fault or other west.

structure is indicated. In a few places, such as Several much less seismic areas within the central*

central Virginia, central New England, and the vicinity stable region deserve mention. The largest of these isof Charleston, S.C., seismic activity of intermediate in northwestern Ohio, where a northeast-trending cluster

or even high levels cannot, in the light of present of epicenters includes those of the earthquakes nearinformation, be cansidered localized along known struc- Anna, Ohio, and others of MM VII or higher. Thistures. In the southern Appalachian fold belt referred seismic area lies a little west of the crestline of theto above, the level of seismicity is mere uniform, but Findlay and Cincinnati arches in an area where theit is nowhere well enough defined to indicate individ- arches broaden and merge westward with the less wellually active structures. defined Kankakee arch. The seismic plot shows that theIt should be emphasized that tb rdN mm en a epicenters are crowded, reaching 32 per 10'* km2, in

c r. !b of - rc b v preisc S R!crid 's hm brks. contrast to the broad and poorly defined PaleozoicFew earthquakes in the eastern United States can be structure at this point. The local concentration ofshown to be related to spesific faults, as are many epicenters and the marked northeast trend, which isearthquakes in the west. Moreover scatter of epicenters about parallel to that of the Wabash River faults ofand lack of correlaticn with geologic structure may be southeastern Illinois, suggest control by a basementdue in part to the scarcity of instrumental data and the fault or faults related to but not necessarily contin-

resulting inacct racy in locating epicenters. Where a uous with the New Madrid fault system.good correlation seems to exist between seismic activity Two still smaller clusters of epicenters, involvingand known structures, or where the distribution of epi- much less seismic frequency and no earthquakes greatercenters seems to outline a localizing fault zone or than MM VI, appear in northeastern Ohio east of Clevelandother structure, the seismotectonic map boundaries are and in south-central Ohio. No specific structural

drawn to conform rather ciosely to the geologic or control is indicated but the weak alinements suggest

seismological information available. Elsewhere bvund- that they may have resulted from movements on minoraries are nore generalized and essentially indicate areas faults.

where more information is needed to deteririne the rela- An area of low regional seismic activity, which in-

tions between seismic activity and structure. cludes epicenters of two earthquakes of intensity VII,is located in western illinois and southern Michigan.

Seismic areas in the central stable region This is unusual in that earthquakes of this intensitygenerally have not occurred in areas whose seismic

Two areas in the central stable region of the continent frequency is less than 8. The area is one of slightly

that have been subject to unusual deformation in deformed Paleozoic rocks, although its northern end,

Paleozoic or later time are also areas of more than which is the locus of one of the larger earthquakes,

average historic seismicity. The more important ef is in a region of subsurface folds and high-angle faults

these two is centered in the Mississippi emhayment trough in the Paleozoic rocks near the western end of the poor-

and includes parts of western Tennessee, western Kentucky, ly defined Kankakee arch. Recorded earthquake epicenters,

southern Illinois, southeastern Missouri, and eastern however, are too few to define what the structural

Arkansas. Earthquakes in the southeastern part of this control may be.seismic area are believed to have been caused by move- A small sels=ic area in western New York and adjoin-

ments en members of the northeast-trending New Madrid ing Ontario suggests centrol by an unidentified west-

and Wabash River fault systems described previously, ward-trending structure about parallel to the strike

Such earthquakes include the New Madrid series of 1811- of the south-dipping Paleozoic rocks of the region.

1812 and the subsequent shocks in the Mississippi embay- Earthquake intensities are low except for an earth-

ment, the 1968 carthquake in southern Illinois, and quake of MM VIII near Attica, N.Y., at the eastern end

others in the area northeast of the embayment. There of the area. This earthquake and some lesser ones near-

is little evidence that historic movement has occurred by may be related to a buried north-trending faulton the faults of the east-trending Rough Creek fault that displaces the lower part of the Paleozoic sequence

zone in adjacent parts of Kentucky and Illinois. and prebably the underlying basenent; it is represented

The lateral boundaries of the New Madrid seismic zone by a west-dipping monocline in the surface rocks known

are determined by geologic evidence of consistent fault as the Clarendon-Linden structure (Chadwick, 1920,

trends, including the through-going northeast-trending 1932). This structure trends north-south, and its re-

faults in southern Illinois, and by surf ace evidence lation to the east-west seismic trend is not clear,

of recent (post-Pliocene) faulting. The northeastern The other principal region of historic earthquakes

limit of the zone daes not appear to be structurally in the central stable region is located in ncrtheastern

centrolled and is arbitrarily placed where the seismic New Yerk and adjc ning parts of Quebec; it extends

frequency drops to 8. The maximum seismic activity northwestward beyond Ottawa and northeastward beyondcoincides approximately with the crestal part of the Quebec City. The region has an exceptionally longPascola arch and also with a possible extension history of recorded earthquakes, beginning in the 17thbeneath the embayment of a group of northwest-trending centry, and several of these have been rated as inten-

faults west of the seismic zone. Scattered surface sity IX or higher on the basis of contemporary but

evidence of northwest-trending post-Eocene faults with- ebviously rather limited accounts. The continued oc-in the embavment (Farrar and McManamy,1937) suggests currence of earthquakes, however, and the high seismic

that part of the seismic activity in the New Madrid frequency--more than 64 in the Montreal area and thearea has resulted from movements on northwest-trending area northeast of Quebec City--attest to unusual seismic

structures. activity in the region.Although the St. Genevieve fault, as mapped, seems to The region is characterized by high-angle faults

have been largely inactive according to the seismic belonging to an east-west or west-northwest-trending

record, a group of epicenters including two of MM V11 set that extends well into the I.aurentian shield andin southwestern Illinois suggests that earthquakes have a northeast-trending set limited mainly to the east-

s, s

1568 066gg-

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ern border of the shield along its boundary with the earthquakes except one ,f intensity VII near the head of , ,

Appalachian tectonic system. Epicenter elinements Delaware Bay. A cluster of epicenters in the entern

indicate control by faults belonging to each of these part of the Gettysburg Triassic basin suggests, but does ,

sets of faults, although specific faults cannot be not strengly indicate, mevement on faults within oridentified, and in the area of highest earthquake inci- bordering the basin. Elsewhere in the Appalachian

dence, epicenters are so numerous that individaal trends Piedmont and Blue Ridge regions, earthquake frequencycannot even be detected. The distribution does show, is less than 8, and in central and nerthern Georgia it

however, that most of the earthquakes have occurred in is less than 2. An exception to this may be developing

the reglen of high-angle faults associated with rela- in central South Carolina, where several minor earth-

tively late disruption of the shield. There is little quakes have occurred recently (Bollinger, 1972).evidence that distinctively Precambrian structures are The st ructural geology of the Sew ngland-Maritimee

involved. region is dominated by north- and northeast-trending f olds,f ault s, elongated int rusive bodies, and metamcrphic

Seismic areas in the Appalachian tectonic province features These trends are reflected also in extensiveand detailed aeromagnetic data of the region and to

Historic earthquakes have occurred throughout much of some extent in gravity data. Special significance is

the Appalachian tectenic province in the eastern United attached to a series of northeast-trending faults in,

States, ar.d. in general, this province has been consid- central and southwestern Connecticut; these faults cut

etably more active than adjoining parts of the central Triassic rocks and appear in a zone of prominent mag-stable region and the Coastal Plain. netic lineaments extending northeastward into

Seismic activity in the faulted part of the Appalachian Massachusetts and southeastern New Hampshire (P.J. Baresh,fold belt is characteristically higher than in the less w r i t t e n commun . , 1973). While displacements on thesefaulted central part, and epicenter alinement s in f aults took place before Triassic time, they appearseveral places sug;;est that one or more of the faults to have remained active during the Triassic, and ept-

may have been factors in releasing seismic energy. Most central alinements suggest that they may have been aof the known faults are believed to extend to relative- source of earthquakes in historic time. Minor earth-

ly shallow depths, probably 1 css than 7 km, and two quakes recently recorded by the Lamont seismographrecent earthquakes in the belt are esti.nated to have network have been interpreted as originating along theoriginated within this limit (Bollinger, 1968; Ramapo f ault, which marks the northwestern edge of theBollinger and Hopper, 1970). In addition to having Newark Triassic basin (Page, Molnar, and Oliver, 1968).higher average seismic frequency, four of the five Seismic activity of more than background f requency andearthquakes of intensity VII that have occurred in the intensity is confined to the southeastern part of thesouthern part of the Appalachian tectonic province reglen in Connecticut, eastern Massachusetts, southernoriginated in this faulted part of the fold belt. New Hampshire, and southern Maine. Seismic f requency is

In contrast, the less faulted central part has shown unusually high as compared with the rest of therelatively little seismic activity. Seismic frequency Appale.hian system, although this may have resulted inis less than 4 in most of it, and lagge areas have part from the lenger period during which earthquakeshad less than 2 epicenters per 10'kmt The few earth- have been recorded. The lack of resolution in lx ating

quakes known provide no indication of tectonic control. and plotting epicenters, combined with relatively highFor seismotectonic purposes the Blue Ridge and seismic frequency, makes it especially dif ficult to

Piedmont form a single unit with complex and inconplete- correlate earthquakes with specific structures in thisly known tectonic features. Within it there is much part cf the Appalachian region, despite the availabili-diversity of structure and of seismi- activity but ty of bet ter st ructural data. The nost likely correlation

relatively little information on structural control. seems to be between faulted terranes and northeast-The most concentrated activity occurs in an east-trend- trending epicentral alinements, although a small areaing area in central Virginia, within which the seismic of epicenters along the international boundary in south-frequency is 16 to 32 or higher. Most of the earth- eastern Maine fits known f aults of northwest trend.quakes in this area have been of intensity VI or less, Otherwise, much of the seismic activity is classedalthough one near Richmond, Va., is reported to have withcut correlation to known structures.been MM VI-VII (Bollinger and Hopper, 1971). The areaconsists largely of crystalline rocks with northeast- Seismic areas in the Atlantic C astal Plaintrending structures and includes parts of the JamesRiver and Arvonia synclinoria. It also spans three Although rocks and structures typical of the Bluenorth-trending f aulted basins of Triassic sedimentary Ridge and Piedmont provinces extend beneath the Atlanticrocks. Epicentral trends are not well defined, but and Gulf Coastal Plains, seismic frequency in the

their distribution indicates that mos! of the earth- Coastal Plains is much lower than in the Appalachian

quakes originated in the crystalline rocks rather than belt s to the west , except locally in areas adjacent toin the Triassic basins or their bordering faults. The seismically active parts of those belts. Low seismicseismic area terminates near the edge of the Coastal activity is also charac teristic of more distant parts ofPlain, which is puzzling since one wauld expect greater the Coastal Plain, such as those on the Florida plat-

macroseismic effects in the Coastal Plain sediments than f o rm . This is true even where the Coastal Plainin the crystalline rocks of the Piedmont. The overall sequence is considorably f aulted, as in the Gulf Coastaltrend of the seismic area crosses the regional st ruc- Plain of southern Arkansas, Mississippi, and southwesternture of the near-surface rocks; perhaps it represents Alabama. Most of these faults are thought to have been

a deeper c rustal st ruc ture of east-west trend, but such caused by seaward sliding within the stdimentary sequence;a structure is not shown by most geophysical data. whene rock s are not streng enough to accumulate largeAnother area of more than average seismicity in the strains and thus generate o.11y minor earthquakes. This

Blue Ridge-Piedmont province covers parts of western situation p robably explains why f ew eart hquakes strongNorth Carolina and northwestern South Carolina. enough to be locally reported or teleseismically located

Structurally the area includes part of the Murphy syn- have occurred in large parts of the Coastal Plain,cline, much of the great allochthonous terrane of Blue A highly anomalous exception to the characteristicRidge rocks with its large negative gravity anomaly, seismic inactivity of most of the Coastal Plain is the

and segm nts of the Brevard fault zone. Weak epicentral well knewn record of earthquakes in the vicinity ofalinements suggest that longitudinal f ault s within the Charlesten, S.C. This record includes several unusualMurphy svncline may have controlled a few earthquakes; features that distinguish it from seismic activity else-

other alinements may be related to east-west transverse where in the eastern Cnited States. The intensity IX-X

displacements that have been ebserved in the Blue Ridge earthquake of 18% seems to have occurred af ter a centrypart ef the seismic area. A few epicenters are lecated or more of little seis ic activity in the regian, and the

close to the Brevard fault zone, which may have had a many subsequent shocks that occurred within a 20- to 30-local influence on the distribution of macroseismic year period all took place in the area of the originaleffects of nearby earthquakes, but over most of its earthquake; thus, they have been referred to as a lengextent the fault zone has been notably lacking in sequence of aftershocks of the 1886 event. No other part

seismic activity. There is also no evidence that the of the Coastal Plain or other locality in the eastern

Triassic (?) fault-breccia zones in Folk County, N.C., Cntted States shows a similar record,

and in Greeneville and Spartanburg Counties, S.C., The wide extent of high-intensity ef fects of the 1886

have been seurces of historic carthquakes. earthquake, as well as the large region in which it wasNortheast of central Virginia, the Piedment belt is felt, indicate that it originated at considerable depth

an area of low-level seismic activity with no strong in the crustal rocks below the Coastal Plain sedimentary

~d h ' 4c c 1568 067 9n, nu,a

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,

cover. The lithologic character and structure of the its relation to mineral deposits: l' . S . Geo l . /-, ,

basement rocks in the region are, however, poorly Survey Prof. Paper 424-D, p. D3-D6.

knean, and there ? s very lit tle evidence to indic at e Hey l , A.V. , J r . , Brock, M.R., Jolly, J.L., and Wells,g ,

what kind of structure was involved. The seismic C.E., 1965, Regional structure ef the southeast

area shown on the map is therefore merely a representation Missouri and Illinois-Kentusky mineral districts:

of the areal frequency of many imprecisely located U.S. Geol . Survey Bull . 1202-B, p. BI-B20.

epicenters reported in the Charleston area. The computer Jaccheen, F.H. , Jr. ,1972, seismic evidence f or high-plot of epicenters indicates a weak northwest trend angle reverse faulting in the coastal plain ofthat may or may not reflect real structural conditions. Prince Georges and Charles Counties, Maryland:

Maryland Geol. Survey Inf. Cire. No. 13, 21 p.FEFERENCES King, P.B., 1951. The tectonics of middle North

America: Princeton, N.J., Princeton Univ. Press,

American Geophysical Union, Special Committee for the 203 p.

Geophysical and Geological Study of the Continents, Kisslinger, Carl, and Nuttli, 0.W., 1965, The earth-

1964 Bouguer gravity anomaly map of the United quake of October 21, 1965 and Precambrian structureStates, exclusive of Alaska and !iawa11: Washington, in Missouri: Earthquake Setes, v. 36, p. 32-36.

,

D.C., U.S. Geol. Survey, 2 sheets, scale 1:2,500,000. Krinitzsky, E.L., 1950, Geologic investigation of

Bayley, R.W., and Muehlberge r, W.R. , comp ile rs , 1968, faulting in the lower Mississippi Valley: U.S.Basement rock map of the United States, exclusive Waterways Expt. Sta. Tech. Mem. no. 3-311.of Alaska and Hawa11: Washington, D.C., U.S. Geol. Leet, L.D., and Linehan, Daniel, 1942, Instrumental

Survey, 2 sheets, scale 1:2,500,000. study of the New Hampshire earthquakes of%

Billings, M.P., 1956. The geology of New Hampshire. December 1940: Seismol. Soc. America Bull., v. 32

Pt. 2, Bedrock geology: Concord, N.H., New Maepshire p. 75-82.State Plan. Devel. Comm., 203 p. Meade, B.K., 1971, Report of the subcommission on

14111nger, G.A., !963, The Narrows, Virginia, earthquake recent crustal movements in North America: Natl.

of March 8, 1968: Earthquake Notes, v. H , p. 35-47. Ocean Survey Tech. Paper, 19 p.1972, Histerical and recent seismic activity in Murray, G.E., 1961, Geology of the Atlantic and GulfSouth Carolina: Seismol. Soc. America Bull., v. 62, coastal province of North America: New York,p. 651-864. Harper and Brothers, 692 p.

Bollinger, G.A., and Hopper, M.G., 1970, The Elgood, Olive, W.h 196 3, Geology of the Flva quadrangle,,

West Virginia, earthquake of Neverber 20, 1969: Kentucky: U.S. Geol. Survey Geol. Quad. Map

Earthquake Notes, v . 41, p . 19-30. GQ-230.1971, Virginia's two largest earthquakes--December 1965 Geology of the liico qudrangle, Kentucky:22, 1875, and May 31, 1897: Seismol. ,o c . America U.S. Geol . Survey Geol . Quad . Np GQ-3 32.Bull., v. 61, p . 1033-1039. Oliver, Jack , Johnson, T rac y, Do rma n , J ane s , 1970,

Bu rc h f ie l , B.C., and Livingston, J.L., 1967, Erevard Postglacial f aulting and seist.icity in Nu Yorkzone compared to Alpine root zones: Am. Jour. and Quebec, Symposium on recent crustal move-Sci., v. 265, p. 241-256. ments. Ottawa, Canada, 1969, Papers: Canadian

Cederstrom, D.J., 1945. St rt.c tural geology of south- Jour. Earth Sci., v. 7, no. 2, pt. 2, p . 579-590.

eastern Virginia: Am. Assoc. Petroleum Geologists ovens, J.P. 1972. Post-Triassic tectenic movements inBull., v. 29, p. 71-95. the central and southern Atlantic Coastal Plain,

Ch adwic k , C.H., 1920, A large fault in western Sew York: it: Fisher, G.W., Pettijohm, F. J . , Reed , J .C . , J r . ,Geol. Soc. America Bull., v. 31, p. 117-120. and Weaver. K.S., eds., Studies of Appalachian19 32, Linden monocline, a correction / bs.7: Geol. geology--central and southern: New York, Intersc i .Soc. America Bull., v. 4 3, p. 14 3; Pan-Am. Ge.1 gl s t , Publishers, p. 417-427.v. 57, p. 69. Page, R.A., Molnar, P.H., and Oliver, Jack, 1968,

Coffman, I.L., and von Hake, C.A., 1972. EarLhquake Seismicity in the vicinity of the Ramapo fault,history of the United a ates: U.S. Natl. Oceanic New Jersey-Stw York: Seismol. Soc. Ar er ic a Bula ,

Atmospheric Admin. , Environmental Data Service, v. 58, p . 681-687.Pub. 41-1, 208 p. Reed, J .C. , J r. , and Bryant , Bruce, 19 % Evidence

ting alorg the Erevard zoneDoll , C.G. , Cady . W.M. , Thompson , J . B. , J r. , Billings, fer strike-slip faulM.P., 1961, Centennial geologic m ,) of Vermont: in North Carolina: Geol. St- America Bull.,

Burlington, Vt., Verment Geol. Survey, scale v. 75, p. 1177-1196.1:250,000. Rodgers, Jonn, 1970, The tectenics of the Appalachians

Doig, Ronald, and Barton, J .M. , J r. , 1968, Age of New York, Intersci. Publishers, 271 p.

carbonatites and other alkaline rocks in Quebec: Ecper, P.J., and Justus, P.S., 197 3, Polytec tonic

Canada Jour. Earth Sci., v. 5, p. 1401-1407. evolution of tne Brevard zone: Am. Jeur. Sci.,

l'u r h am , C.O., Jr., and Feeples, E.M., III, 1956, v. 273-A (Ceoper Volume), p. 105-132.Pleistocene fault zone in southeastern Louisiana Ross, C.A., 1963, Structural fraaework cf seutherne.ost

[a t> s . 7 : Gulf Coast Assec. Geel. Socs. Trans., Illinois: Illinois State Geol. Survey Circ. 351,

v. 6, p. 65-66. p. 1-27.Farrar, Willard, and McManamy, Lyle, 19 37. The geology of Staude r, William, .ad Nuttli, 0.W., 1970, Seismic

Stoddard County, Missouri: Missouri Geol. Survey, studies--South central Illinois earthquake of

59th Bienn. Rept., 1935-1936, App. 6, 92 p. November 9, 1968: Seismol. Set America Bull.,

Fenneman, N.M., 19 38, Physiography of eastern United v. 63, no. 3, p. 973-931.States: New York, McGraw Hill Book Co., 714 p. Street, R.L., and Herrmann, R.B., 1974 Earthquake

Finch, W.I., 1966, Geologic map of the Paducah West mechanics in southeast Missouri and adjacent areas

and part of the Metropolis quadrangles, Kentucky- Obsy: Geol. Soc. America, Abs. with Frogram::,

Illinois: U.S. Geol. Survey Geol. Qaad. Map GQ- v. 6, no. 3, p. 312-313.551. Street, R.L., Herrmann, R.B., and Nuttli, 0.W 1974,,

Flint, R.F., 1947, Glacial geology and the Pleistocene Earthquake mechanics in the central United States:epoch: New York, John Wiley and Sons, 589 p. Science, v. 184, no. 4143, p. 1285-1287.

Freeman, L.B., 1945, Paleozoic structure and stratigraphy Taber, S.W 1914, Seismic activity in the Atlantic,

(of the Jackson Purchase region, Kentucky): Coastal Plain near Charleston, South Carolina:

Kentucky Dept. Mines and Minerals, Geol. Div. Bull., seismol. Soc. A erica Bull., v. 4, p. 108-160.ser. 8, p. 12-43. Taylor, P.T., Zietz, Isidore, and Dennis, L.S., 1968,

_195 3. Regional subsurf ace stratigraphy of the Geolontic implications of aeromagnetic data forCambrian and Ordovician in Kentucky and vicinity: the eastern continental cargin of the United States:

: Kent *cky. Geol. Survey, ser. 9 Bull, no. 12, 352 p. Geophysics, v. 3 3, p. 755-780.Gl'astr, J.D., 1971, Geology and min ral resources cf Thomas, W.A., 1973, Southwestern Appalachian structural

southern Maryland: Maryland Geol. Survey Rept. system beneath the Gulf Coastal Plain: Am. Jour.

Inv. no. 15, 84 p. Sci., v. 2 7 3-A (Cooper Volume), p. 372-393.Hatche r, R.D. , J r. , 1971, Stratigraph R , petrolegic, 17.S. Geolegical Sur.-y and American Association of

and structural evidence favoring a thrust solution Petroleum Geologists, 1962. Tectonic map of the

to the Brevard problem: Am. Jour. Sci., v. 270, United States, exclusive of Alaska and hawaii:

r. 177-202. Washington, D.C., 2 sheets, scale 1:2,500,000.

Hey l, A.V. , J r. , and B roc k , M.R. , 1961, structural frame- Weller, J.M., Gregan, R.M., and Tipple. F.E., 1952, Geol-

work of the Illinois-Kentucky mining district and egy cf the fluorspar deposits of Illinois: Illinois

VIH NH ,

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.- i

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AllyJ ( s s,

**

State Geol. Survey Bull. 76, 147 p. , ,

White, W.A., 1952. Post-Cretaceous faults in Virginia*

ant North Carolina: Geol. Soc. America Bull., e p

v. 6 3, p. 74 5-7 48.Wood, H.O., and Neumann, frank, 1931. Modified Merc4111

intensity scale of 193. Seismol. Soc AmericaBull., v. 21, p. 277-233.

Zartman, R.E., Brock, H.R., Heyl, A.V., and Thomas, H.H.,

1967, K-Ar aad Rb-Sr ages of some alkalic intru-sive rocks f rom central and eastern United States:Am. Jour. Sct., v.265, p. 848-870.

Zietz. Isidore, and Kirby, J.R., 1968. Transcentinentalgeophysical survey (lat. 350-39 N.), magnetic mapfrom 87* to 100 W. longitude: U.S. Geol. SurveyMisc. Geol. Inv. Map 1-5 34- A.

Zietz, Isidore, 5tockard, H.P., and Kirby , J . R. , -

1968. Transcontinental geophysical survey (350-390N.), magnetic and bathymetric map from 74 to 87

W. longitude: U.S. Geol. Survey Misc. Geol. Inv.Map 1-535-A. o

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