ML19309C560

App 2D to TMI-1 PSAR, Geologic Investigation of TMI & Vicinity. Prepared for Gilbert Associates,Inc

ML19309C560
Person / Time
Site:	Three Mile Island
Issue date:	01/14/1967
From:	Kauffman M FRANKLIN & MARSHALL COLLEGE, LANCASTER, PA, JERSEY CENTRAL POWER & LIGHT CO., METROPOLITAN EDISON CO.
To:
References
NUDOCS 8004080782
Download: ML19309C560 (38)

Text

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APPENDIZ 2D GE0I4GY O l 8004080 0002 316

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O GE0 LOGIC INVESTIGATION OF THaSS MILE ISLAND AND VICINITY O <te=via x utr===

Geolo61st January 14, 1967 O

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0002 317

FR.ANKIJN and MARSHALL COLLEGE

!.ANCASTER, PENNSYLVANIA DEPARTMENT rJ GIOLOGY January 14, 1967 Gilbert Associates, Inc.

Att: hr. ?. 3. dright 525 Lancaster Avenue deading, Penna.

4 lentlecen:

The attached recort is a sun =ation of the regional structural, geologic, and tectonic asnects of the region in the vicinity of Three (111e Island. I trust that this comolies fully with your reonest f or such a study, as indicated in telechone conversations and confirmed by your letter of Dec. 21, 1966.

Very truly yours,

))k t. m S --

Harvin,d. Kauffman, Ph.D.

Associate Professor of Geology 0

0002 618

O LIST OF ILLUSTRATIONS Figure Page 1 hajor Tectonic Features - South Central Pennsylvania 2 2 Origin of Triassic basins and border fault 5 3 Triassic Diabase sills, dikes, and sedi-mentary rockr 7 4 Various hypothetical relationshics among Glenarm series 10 5 Location of Yellow dreeches Thrust Fault 14 6 Location of Sweet Arrow Fault 16 O

7 Oream Valley Fault in map and cross-section 20 8 Kelvin Seamount trend (Kelvin-Cornwall zone) 23 9 Suicenters of earthquakes of the United States 28 Geologic Map of Proposed Site (western half Middletown 15' quadrangle; and eastern half New Cumberland 15' quadrangle) - folded at end of report l

1 04)02 319

O GEOLCGIC SETTING OF THE PROPOSED SITE The geology of the proposed site was examined in a wide variety of ways. A survey of the literature has been =ade in order to determine those aspects of the geology which were considered to play a role in the overall geologic setting of the proposed site and its immediate environs. Field checking of such of the area adjacent to the site was conducted to fir:

establish the accuracy of the geologic contacts. Air photo geologic investigations were combined with topographic map interpretations and with aerocagnetic studies of the area to provide as exhaustive a study as possible in this region.

In addition, the earthquake history of Pennsylvania was reviet to determine the seismicity pattern of the state.

The results of this examination of all the information  !

available are given in this report and are summarized in the small scale map showing the general region (Fig. 1) and in th-large map showing the geology of the four 7-1/2 minute map areas immediate'ly adjacent to the site.

MAJOR TECTONIC ELEMENTS J

The major structural features and principal tectonic -

elements are indicated on the sketch map for central Penn-sylvania (Fig. 1). Each of these features will be discussed separately and an attempt will be made to indicate what effec

(]) if any, each f eature might be expected to have on the proposes site.

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O These tectonic elements include:

1. Triassic border fault, dikes, sills and fractures

2. Martic line

3. Chickies Thrust

4. Stoner Thrust

5. Yellow 3reeches Thrust i

6. Sweet Arrow Fault

7. Cream Valley Fault-Peach dottom S7ncline-Serpentine Zone

8. Kelvin-Cornwall Zone j 1

9. Seismicity pattern in Pennsylvania  ;

10. Susquehanna diver terraces

11. Minor structural features (such as fault splays f in Northern Blue Ridge; da==er Creek nappe zor  !

allochthonous Heading Pron 6; allochthonous

=aterial in Martinsburg; Donegal Springs brecc zone; Tucquan-Mine Ridge Anticline; South Mountain Anticlinoriu=; etc.)

l Triassic border f ault l

The proposed site is situated within the Triasaic belt I of rocks which extends in broken patches from Connecticut to

. North Carolina. That portion in Pennsylvania has been studied by Stose & Stose (1944), Stose (1949), Sanders (1963) and most recently by Glaeser (1966). The conclusion of all these worke is that the sediments all dip in a more-or-less unifor= patter with gentle tilting toward the north and northwest (averaging

() about 25 to 35 degrees). This dip is due partially to the l initial slope of sedimentation but erincipally to downdropping 0002 322 I

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4-Q of the northwestern border by nor=al or block-faulting. Thus the sediments thicken from a depositional feather edge on the i

south to the deepest portion of the Triassic basin close to the northwestern edge. The deenest portion is probably a short distance from the edge. Stose (1949) points out that "the floor of the Triassic basin in southern Pennsylvania is exposed in several places close to the (north) western =argin of the basin where the thickest sediments would be expected. To explain this anomaly, a fault is postulated within the basin at the (north) west edge of the deeper part. A line of stocks, repre-senting =agma that rose from a deep source, is believed to

= ark the line of the postulated fault." (See figure 2 on the following page.)

The border fault itself is probably a series of normal g

faults which are more-or-less continuous along the present margin of Triassic sediments. The pattern of the faults suggest that the border fault (or faults) is offset by other normal faults nearly at right angles to the border (for instance see the fault trace southeast of Harrisburgl Stose & Stose (1944) call this a rhombic fault pattern and suggesd it is due to the intersection of several transverse faults trending about N30 0 W with the nor=al strike faults trending N50-60E. The age of these faults may be " partly, or wholly Triassic" (Stose &

S to s e , 1944 ) . "It~is probable that the faulting and adjusting l of blocks took place under conditions of tension at the beginning of the Triabdic period,during the formation of the. basin in which the Triassic sediments were later deposited. Many places

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along the northwest border of the Triassic rocks show evidence of such early Triassic faulting during the formation of this basin and its progressive sinking."

"The diabase sills, with which many of the dikes connect at their northwestern ends, ccalesce to for: extensive intrusive bodies in the northwestern part of the friassic area of Penn-sylvania... They parallel the strike of the sedi=entary rocks for long distances, and then 'i'e intrusive body cuts across the strike at right angles. host of these crosscutting bodies extend to the northwestern edge of the Triassic basin where the3 terminate against the f aults that f orm the boundary of the basin. Each of these intrusive bodies, therefore, has the form of a great tilted trough bounded on the southeast side by the west-dipping sills and at the ends by the cross-cutting bodies and open at the west."

"The fissures through which the diabase entered the Triassic rocks are believed to lie near the northwest edge of the basin where the greatest amount of progressive sinking and faulting occurred during Triassic decosition. The rising sagma broke through the Triassic beds near the vents in the f orm of cross-cutting bodies, and injected the beds to the southeast in the form of sills. The magna extended still farther southeastward as dikes that followed vertical fractures in the Triassic sedimentary rocks and continued into the older underlying rocks southeast of the limits of the basin of Triassic sedimentation. So=e of these dikes in the area k southeast of the Triassic outcrops say have been feeders of 4 'i ' W01 0002 326

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The zones of weakness within the Triassic belt appear to have " healed" soon af ter intrusion by diabasic material (in the case of the dike-and sill-injected faults) or at least by Cretaceous or earliest Tertiary time. The coastal plain sedi-ments do not appear to have undergone renewed movement along the projection of these dikes.

There is no evidence to suggest that the border fault or the magma-injected zones will be positions of future movement.

D1e fault across Three-Mile Island (see geologic map) is extremely tentative and is based on Stose and Jonas' (1933) mapping in the Middletown quadrangle. It is thought that the data upon i ggg which they based their inferred fault is supported only by offsets of the Triassic diabase dikes and sills several miles distant from the island. Examination of the Triassic' sedimentary rocks along the east bank of the Susquehanna aiver fails to support the existenc of such a fault.

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hartic Line .

Knopf and Jonas (1929) described the Martic overthrust fault in southeastern Pennsylvania. It has been extended northward to New Jersey and south as far as Virginia by Jonas (1927). The fault was supposed to have thrust the Wissahickon schist and related quartzites, marbles, and slates ,

of the Precambrian Glenarm series over rocks of lower Paleozoic age. The distance of thrust move =ent was thought to be about 20 mil hackin (1935) questioned such large amounts of move =ent and presented evidence to support the hypothesis that the Glenarm series is Paleozoic rather than of Precambrian age.

If this is the case, it is not necessary to have them thrust such a distance. Rather, only slight movement, if any, need be implied for the Martic line. Indeed, there may be only local movement along minor faults paralleling this line.

Eardley (1951) reviewed the possible interpretations of I the Glenarm relationships ( see summary diagram, figure 4, next page). The present writer similarly reviewed this problem l (Kauffman,1960) and concluded that the Glenarm series was most probably lower Paleozoic in age and therefore there was i

no need for great distances of overthrusting along this Martic line. South of the line, however, there are definite zones of thrusting (Eardley, 1951).

Chickies Thrust "The Chickies overthrust enters the (Middletown) quadrangl O east of Chickies and lies in the river beyond its sharp bend...

(north of) Chickies Rock.

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i trend, which is diagonal to the trend of the folds, so that beds in the Chickies Rock, Accccac, and Trout Hun anticlines are truncated by the fault. This diagonal movement is in part a thrusc and in part a horizontal shear across the bedding.

At Accomac the trend of the Acco=ac anticline is much more diagonr1 to the thrust fault than that of the folds farther east. West of Dugan Run many minor overturned and recumbent folds of the massive quartzite beds of the Chickies on the nor limb of the Trout Run anticline are exposed in the river bluff Each fold is broken and overthrust, forming slices of the main overthrust mass, and these minor thrust planes pass diagonally into the Chickies thrust plane below.

"The Chickies overthrust is obscured by normal faulting near the mouth of Codorus Creek and apparently lies in the.

Harpers phyllite south of Saginaw. Westward it lies along the northern edge of the block of Chickies quartzite and Harpers phyllite northwest of Starview and apparently passes under Triassic rocks one mile south of MCunt Wolf." (Stose &

Jonas, 1933).

Immediately north of Chickies acek the thrust has brought the Chickies Formation in contact with the'Conococheague Formation, cutting out several thousand feet of section. The Chickies Thrust zone apparently marks a major line of demarcat

'oetween facies of sedimentary rocks to the south from those to the north. There are no exposures of the Conestoga Limestone

() north of this zone. Likewise there is no Kinzers shale to the 1 -

0002 131

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Ih north of the Chickies Ihrust zone. This zone =ay continue across the Lancaster valley and tie in with the thrust fault on the north side of the Welsh Mountains (see Fig. 1). It appears to bear no direct relationship to the proposed site.

Stoner enrust "The Stoner overthrust fault lies on the south side of the

?ork Valley, but the fault is not clearly evident in (all places East of Strickler station, however, this fault cuts off the Strickler anticline, which enters the (iIiddletown) quadrangle fron the Lancaster quadrangle, where its east end plunges under Conestosa limestone south of Mountv111e. In the river gorge the lower beds of the Chickies in the Mount Pisgah anticline of the Stoner overthrust mass are thrust against the Conestoga lll limestone in the compressed syncline on the south side of the Strickler anticline, and therefore it is evident that this f ault represents considerable horizontal shortening. The Stoner overthrust extends southwestward across the York and danover quadrangles and passes under Triassic rocks southwest of Hanover." (Stose & Jonas, 1933).

Stose & Stose (1944) report curther that "all the rocks of the Stoner overthrust block are closely fcided, and the axial planes of the folds dip southeastward... The sinuous outline of the Stoner overthrust... indicate a low angle of dip for the thrust plane, uhich was gently folded during or after thrusting.

The folding and P.he thrust faulting in the district involved O

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all the Paleozoic rocks, the youngest of which are probably of Crdovician age. The magnitude of these folds and over-thrusts and their general parallelism with those of the Great Valley lead to the conclusion that they were formed at the sam time as the major folds and overthrusts throughout the Appalachian province."

Yellow 3reeches Thrust The Yellow Breeches Thrust truncates the plunging nose of the South Mountain anticlinorium and separates exposures of  !

the lithologies and structures of the Cumberland Valley from I those of the Lebanon Valley farther east. Maclachlan and Root l (1966) describe vast differences in facies across the thrust

( but only minor diff erences within each equence. "This leads to the inference that thrusting has juxtaposed distant segment of the depositional basin. . . The considerable irregularity of the thrust front is an erosional effect which shows that the thrust is quite flat and locally even north dipping. . ."

(See figure 5 on the next page.)

"On the basis of structural and stratigraphic relationship

...there were relatively small movements on steep thrusts in the Cumberland Valley. . . Minor steep faults may be related to this movement. Relatively late normal faults apparently relat to development of the Triassic basin are the youngest f eature l

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recognized, with the possible exception of the ' Triassic dikes l

() which may be Jurassio. Later Mesozoic and Cenozoic broad vertical movements undoubtedly affected this area."

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This interpretation is the most recent in a long series of debates over the meaning of the irregularities in the cut-crop pattern of Martinsburg Shale and the earlier carbonate units exposed between Middletown and Harrisburg on the north side of the Susquehanna River (see geologic map). These irregularities may merely be complications in the unconformab2 relationship of the Martinsburg on the Crdovician limestones, rather than thrusting, which requires superimposing younger units onto older in a rather awkward series of fault inter-pretations.

Sweet Arrow Fault the Sweet Arrow Fault is an 80-mile long south-dipping

() thrust fault, described by Wood and Kehn (1961)(see figure 6 next tage). " Geologically, the Sweet Arrow fault is divisible into three segments: (1) a western segment from the Susquehar River to Swatara Gap; (2) a central segment from Swatara Gap to New dingold; and (3) an eastern segment from New Ringold tc Bowmanstown". The writers believe that the fault is a south-dipping thrust and that the upper plate moved north relative to the lower plate.

"In the western segment, evidenca for the existence of tt Sweet Arrow fault is based largely on the local absence of formations from the stratigraphic succession and on the westws thinning of formations. Through the segment the stratigraphic sequence is slightly overturned to the north; thus, a thrust O f ault dipping south less steeply than the bedding would thin I

the sequence t'oward the north by structural overlap.h002 335

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0002 ~36 l 1 Figure 6.

"Between Indiantown Gap and Manada Gap, red shale units in the middle part of the Catskill formation are in contact with strata of the underlying Trimmers acek sandstone at

several localities. The sequence of alternating marine gray i beds and continental redbeds in the basal part of the Catskil2 is missing and is presumed to have been cut out by a fault.

"The Trimmers Rock sandstone is missing for about 4 miles north and west of Piketown. West of this area, the upper bedt of ths Trimmers Rock reappear and are apparently in fault contact with the older part of the Mahantango formation. The j area where the Trimmers acck is absent and the area where it is thinner than normal and in apparent fault contact with the ,

I Mahantango is covered by heavy talus and a dense forest, whict l

( makes the identification r f poorly exposed rocks difficult. . .'

...The writers believe that the Sweet Arrow fault has  !

cut out part of the stratigraphic section at the Susquehanna River, and that elsewhere in this segment it thrusts the  !

! Trimmers Rock sandstone and the Mahantango formation over the '

Catskill formation."

This fault is sufficiently far removed from the proposed l site so as to have no presumed affect on the stability of that I i

region.

Cream Valley Pault - Peach Bottom Zone - Serventine Belt A complex region of inter-related structural elements occurs from Chester County along a WSW trend through Lancaste.

County and crosses the Susquehanna River in the vicinity of t'.

Peagh Bottom atomic power site.

t' / ' 0002 337

l l

I 1

Armstrong (1941) summarized the tectonics asscciated with the Cream Valley fault. "A fault, described by Bascom (1909) as the Cream Valley f ault, bounds the gneiss on the north in l the western half of the area, crosses it just east of Wissahicko Creek, and continues on the south side of :he gneiss in the eastern part of the region where it is called the Huntingdon Valley fault (Bascom, 1909). A second fault bounds the gneiss on the south in the western part of the region and joins the Huntingdon Valley fault just east of Wissahickon Creek. In this paper this southern fault will be called the Rosemont fault, from the town of dosemont which is situated on the fault line. It is a branch of the Cream Valley-Huntingdon Valley fault. Both are steep faults. Small overturned folds along the Huntingdon Valley fault and along the Rosemont fault indi-cate movement downward on the south. Those along the Cream Valley fault show movement in both directions, probably indicating that there has been more than one period of slipping along this fault and that the downthrow side has not always been the same. The Cream Valley fault is mapped as bifurcating again at the western boundary of the region."

" . . .The occurrence of the muscovite mylonites along the Rosemont and Cream Valley faults suggests that the development l

of the muscovite is associated with the faulting, possibly resulting from the rise of hydrothermal solutions along the fault planes." g q,. g 0002 338

O "Along the Cream Valley fault south and southwest of Conshohocken a schistose zone 20 or 30 feet thick crops out..

The schist here is a suscovite-chlorite schist containing garnet and blue-green tour = aline. The micas were deformed after crystallization."

McKinstry (1961) redescribed some of the structural relationships of this fault (see map and section, figure 7, next page).

The Peach Bottom syncline and slate district was describ by Agron (1950). His mapping showed the Cardiff conglomerate to be missing along the northern edge of the syncline. He inferred a fault to have cut out part of the stratigraphic column.

( "The major fault in the Peach Bottom syncline cuts out the conglomerate and cart of the slate for about 9 siles alon, the north side of the syncline. The fault zone is sarked by deep weathering. There are no outcrops along its extent. On the east bank of the Susquehanna River, in the vicinity of th fault, there is a gap of about 60 feet between the north end of the exposed e'ste and the south end of the schist.

"The displacement along the fault is estimated to be at least 450 feet. The fault plane may dip southeast and parall the arial plane of the overturned Peach Bottom syncline, or i may dip steeply to the northwest" (as does a small parallel fault a few hundred feet to the southeast). "The omission of

(} beds along the fault suggests that the relative movement was j down on the southeast side."

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. , 0002 339 l

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Map showiny relationship of Coatenille West Chester dhtrict to Philadciphis ares. After Bascom (1909), modined by daia trom .\rmstrong (1941), Postc! (1940), Weiss (1949), and others O

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ized attitudes of cleavsp. Wg. Wbuhickon fornution gneissN facies; CDs.

Shenandinh timestones; Cc. Chickies quartzite; bg Baitimore gneiss n n . 2.

O m: G... 0002 340

i O

This region also is marked by injection of serpentine, )

i presumably along fractures or faults which the serpentine bod:

l parallel. Lapham & McKague (1964) state 'the initial emplace-ment of ultramafic material seems to have been controlled by a structural lineament other than one within the deformations: ,

l systems presently recognized. Such a lineament might well be l 1

the Appalachian geosyncline and/or basement configuration....

Or the locus of intrusion may have been controlled by a major 1 l

basecent fault system, possibly coinciding with the offshore '

wrench fault noted by Drake (1963) at about latitude N 40 l (but tentatively located in the Triassic to the north by  !

Woodward, 1963)."

{} Kelvin-Cornwall Zone

" Accumulating evidence suggests that the arcuate Appalaci i rolds of central Pennsylvaniaere related to a major.basinal displacement in the nature of a concealed transcurrent wrench fault effecting a dextral dislc;ation of the entire Appalachis system near 40 N. latitude. The relative amount of movement may approach 85 miles. The age of this fault is believed to be late Devonian, although an older basement pattern may have sited the pre-Pocono movement and later produced Triassic adjustments. The east-west Triassic belt between the Delawari

, and Susquehanna rivers is believed to follow the course of th:

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fault, for which the name Cornwall displacemeht is proposed.

Woodward and Drake have elsewhere related this fault to the subsea Kelvin displacement similarly offsetting the continental shelf as far east as the Kelvin Seamount group 400 miles at sea As a connection is also postulated with the basinal declivity lately described in eastern Kentucky, the likelihood is strengthened that Appalachian tectonics involve a fragmented basement below a superficially folded sedimentary carpet" (Woodward, 1963).

Drake and Woodward (1961) attribute the arcuate pattern of Appalachian structures in Pennsylvania to northwestward movement of a crystalline block located near the present position of Baltimore. A result of this movement was that the llh Appalachian structures should have been bent into their present pattern with a major right-lateral strike-slip fault developing This fault would strike nearly east-west, passing approximately along the northern edge of the Triassic basin.

Paleomagnetic studies (Beck,1965), while not necessarily completely validating these hypotheses, do substantiate them in a preliminary way.

Drake, et al (1963) reported that magnetic profiles also suggest a =ajor transcurrent fault near latitude 40 N off the eastern North America coast. Geophysical and geological observations indicate a right lateral displacement of the fault of about 100 miles and a total length in excess of 600 miles. &

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0002 342

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Figure 8.

g "The need for- a fault near 40 N Cwas expressed by Woodward (1961) on the argument that since the Connecticut Triassic is bounded by high angle faults the New Jersey Triassic--should be bounded in the same manner. This predicated a fault along the Hudson River at the base of the Palisades, for which there is no evidence (Worzel and Drake, 1959), as well as one to truncate the south-pointing structures of Connecticut. Norton (1960) postulated a transcurrent fault at the same latitude on the basis of a stress analysis of the Appalachian region but required that the movement be sinistral rather than dextral as established by the data given previously (in this paper)...

"Some limits can be placed on the age of the faulting and of the associated seamonts. Tolstoy and Ewing (1949), Northrop.

I et al (1959), and D. B. Ericson (personal cocmunication) note the occurrence of Eocene sediments on the tops of some of the seamounts in the Kelvin chain, and Nor throp et al (1962) suggest a Late Cretaceous age for the volcanic activity. The lack of any evidence. of transcurrent faulting in the coastal plain sediments on shore can be taken as an indication that the movement was pre-Raritan (Upper Cretaceous) in age. It is l

difficult to establish mazimum possible age of the faulting i

without evidence from land geology. The subordinate shears l

j of Sanders (1962) suggest that movement continued until post-1 Late Triassic time, but there is no assurance that a major part of the movement may not have occurred earlier. A dis-placement of the magnitude indicated by the data would be lll l expected to have had a greater effect on the folded rocks of i

is-

! 0002 344

l i

() Pennsylvania than a broad overall change in the strike of the f olds, if it occurred af ter consolidation and f olding of these rocks. Thus it is conceivable that considerable displacement took place before the end of Paleozoic time."

Minor Tectonic Elements A number of lesser tectonic features has been reported and will: be incorporated in the Tectonic Map of Pennsylvania (Gwinn, in preparation). Wise (in press) has described many of these features for the Piedmont area of the state. Taken i in their broadest sense, several of these features play a role in determining the overall structural development of this general region. In a strictest interpretation, they probably bear no direct relationship to the proposed site and have there fore been cuitted in this treatment.

A few of these elements are included on the sketch map showing the tectonic features of south central Pennsylvania (Fig. 1). Uplif ts affecting the general area include the South Mountain Anticlinorium with its fault splays along the northern Blue aidge Province along the western edge of.the map the Tucquan-Mine Ridge Anticlinal upwarp, the allochthonous Heading Prong of the New England Province and its associated South Mountain just west of the Schuylkill River in the north-eastern part of the map. Kittatinny Ridge marks the beginning of-the. aidge and Valley Province of the Folded Appalachian.

Mountains. .The Honeybrook uplif t along the eastern edge

) represents an upwarped portion of the Precambrian crystalline basement co= plex.

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.sithin the general map area are zones of tectonic movement, not previously described in the literature but observed repeat-edly by students mapping in the Lancaster region. These are being described by Wise (in press) as cart of the description of the tectonic map of Pennsylvania. Included here are the dammer Creek nappe zone, a zone of overturning and overthrusting in the Manheim-Ephrata-Mt. Joy area, and the Donegal Springs breccia zone, a northwest trending occurrence of brecciation within the Lancaster valley carbonate units.

ZAliTHQUAKES IN PSNNSYLVAsiIA Considering the seismic activity of the continent as a whole, Pennsylvania is notably free bf shocks (Neumann,1941) . lll ;

Wine recorded earthquakes occurred within Pennsylvania between 1638 and 1938. The dates for these occurrences are:

March 17, 1800 March 8, 1839 November 29, 1800 May 31, 1908 November 11, 1840 October 29, 1934 November 14, 1340 July 15, 1938 May 31, 1884 Several earthquakes of light to moderate intensity have occurred since 1938.

The earthquake of November 34, 1951 in A:.lentown, Lehigh County, was light with little damage. The earthquakes at dinking Springs, Berks County, on January 7, 23, August 10 and September 24, 1954, were light, only one having an intensity of VI. Wilkes-Barre, Luzerne County, experiences two earthquake g l W I one on February 21, 1954 and another February 23, 1954, one with

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. 0002 346

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intensity VII. Another quake occurred in Berks County on January 19, 1955 with reported intensity of IV, and was felt from West Reading to Vernersville and from West Leesport to Gouglersville. Another quake was reported September 14, 1961.

The state of Pennsylvania as a whole is therefore conside to be an area with only few weak earthquakes expected. This 1

suggests that move =ents along any of the existing faults have been extremely minor in the past and there is no indication th future movements.are very likely. The accompanying map of l i

earthquake epicenters shows none near the proposed site in  !

central Pennsylvania. (See figure 9 on the next page.)

Terrace Decosits

{} Terrace gravel deposits have been examined along the Susquehanna Elver by a number of workers, including Peltier (1949) and by the writer (Kauffman, 1957). No evidence is apparent for any displacements or offsets in these deposits, suggesting that there was no significant movements within this general region cf a magnitude sufficient to cause these relatively unconsolidated materials to shift. Certainly if there had been earth tremors of any measureable amount, these gravels and sands would have shown evidence of such movements.

The youngest terrace gravel deposits are at least 10,000 years old, the oldest being of even greater antiquity. This line of evidence, therefore, suggests little or no earth movements in quite some time in this vicinity.

H. u. . 0002 347

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This lack of shifting or offset'in the deposits along the Susquehanna River terraces =ight be considered to be the most telling evidence for the relatively stable condition of the earth's crust in the south-central Pennsylvania region.

GEOLOGIC HAP OF PROPOSED SITE AND VICINITY The Geologic Map represents a compilation from published reports including Stose & Jonas,1933, The Pennsylvania Geolof Map, 1960, and Maclachlan,1966, plus minor revisions by this author where field checks showed changes to be required. The base map is from the series of aero=agne. tic maps and shows high =agnetic readings associated with the ferromagnesian-ricl

() Triassic diabase as well as anomalous eadings near industria:

complexes in Steelton and Harrisburg.

1 l

l l

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l 1

O VLX 0002 349 1

1

-3 -

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SUMMA.RY AND CONCLUSIONS l

l The proposed site is in an area ~which has undergone a rather high degree of tectonic and igneous activity. This i

l activity has been concluded f or such a long period of time,

• i t

however, that today this caa be described as a very stable region. Seismic activity has been of such minor importance in l

historic times in all of the state, and especially in the central and south-central parts. Any earthquakes would most likely be l

detected from seismic and geologic history of this area.

l Faults and fractures with minor amounts of movement are f airly l

widespread within the Piedmont and Triassic belts. Studies at Three-Mile Island do not definitely establish the existence of such minor structures. In the event that such inconspicuous lll 3 features do exist, the probability of future movement along such zones is so small as to be negligible. The movements which did l occur were at times of major crustal adjustments during late Paleozoic times (225-300 million years ago), during Triassic time (180-225 m.y.) and during late Cretaceous and Tertiary time (approximately 50-100 m.y.). Several of the high terraces along the Susquehanna River have been offset by post-Cretaceous and are-Pleistocene faulting along the old Triassic border fault northwest 1

of Middletown (Stose, 1927). The younger Pleistocene terraces, l

however, have not undergone such =ovements, suggesting that this l

region has been extremely stable for at least the last 10,000 years and perhaps as much as the last million years.

9e c .i...

1 0002 350

REFERENCES O Agron, S.L., 1950, Structure and petrology of the Peach Bottom-slate, Pennsylvania and Maryland, and its environment; 1

l GSA Bull v.61, p.1265-1306 l Armstrong, E., 1941, Mylonization of hybrid rocks near Philadelp  :

Pennsylvania; GSA Bull v.52, p.667-694 Bascom, F., et al, 1909, Description of the Philadelphia distric U . S .G eol . Sury. Geol. Atlas, folio 162.

Beck, M.E., 1965, BLeomagnetic and geological implications of magnetic properties of the Triassic diabase of southeas Pennsylvania; Jour. Geophys. Research, 7.70, p.2845-28 Bromery, a.W., et al, 1961, Geochysical Investigations, Aeromagn Maps; Map GP-269 Mdtown Quadrangle; Map GP-275 New Cumberland Quadrangle.

Drake, C.L. and Woodward, H.P., 1963, Appalachian curvature, wre faulting and offshore structures; Trans. N.Y. Acad. S

v. 26, p,48-63 Drake, C.L. , Heirtzler, J. and Hirshcan, J. ,1963, Magnetic anomalies off eastern North America; Jour. Geophys.

Research, v. 68, p. 5259-5275 Eardley, A.J., 1951, . STHUCTURAL GEOLOGY OF NORTH AMERICA; Harper & Bros.

Eppley, R.A., 1965, (revised edition) Earthquake history of the United States; part 1: Continental U.S. and Alaska; (originally published as U.S. Coast and Geod. Survey, series 609 by Heck, H.H.) series 41-1 Glaeser, J.D. ,1966, Triassic sediments in the Newark-Gettysburg basin; Penna Geol. Sury. Bull. G-43 G ray , C . , et al, 1961, Geologic Map of Pennsylvania; Penn. Geol Survey Gwinn, V.E., (in press) Tectonic Map of Pennsylvania; Penna.

Geol. Survey Jonas, A.I. ,1927, Geologic reconnaisance in the Piedmont of Virginia; GSA Bull v. 38, p. 837-846 Kauff5an, M.E.,1957, Statistical analysis of certain characteri of the Susquehanna River terrace deporuas; M.S. thesis Northwestern Univ.

Kauffman, M.E. ,1960, Stratigraphic relations of the Glenarm Ser s- Guidebook, Penna. Field Conf.

l Knopf,, E.3. and Jonas, A.I., 1929, Geology of the McCalls Ferry-l Quarryville District, Penna; US Geol. Sury. Bull. 799

( .- - '

(i 'i n ') 7g) i _. . -- .

REFERENCES (Cont.)

Lapham, D.M. and McKague, H.L., 1964, Structural patterns O

associated with the serpentinites of southeastern Pennsylvania; Bull. GSA v. 75, p.639-660 Mackin, J.H., 1935, The problem of the Martic overthrust and age of the Glenarm Series in southeastern Pennsylvania; Jour. Geol. v. 43, p. 356-380 Maclachlan, D.B. and Root, S.I., 1966, Comparative tectonics and stratigraphy of the Cumberland and Lebanon Val 1Q s; Penna. Field Conf. Guidebook.

McKinstry, H. ,1961, Structure of the Glenar= Series in Chester County, Pa. ; GSA Byll. v. 72, p. 557-578 Neumann, F., 1942, United States earthquakes 1940, Dauphin County; U.S. Coast and Geod. Survey serial 647 Peltier, L.C., 1949, Pleistocene terraces of the Susquehanna River, Penna; Penna. Geol. Sury. Bull, G-23 Sanders, J.E., 1963, r. ate Triassic tectonic history of northeaste2 U.S.; Amcr. Jour. Scil, v. 261, p. 501-524 l Stose, G.W., 1927, Possible post-Cretaceous faulting in the Appal-achians; GSA Bull., v. 38, p. 493-504 l

Stose, G.W., 1928, High gravels of the Susquehanna River above O

Columbia, Pennsylvania; GSA Bull., v. 39, p. 1073-1086 Stose, G.W., 1949, The fault at the west edge of the Triassic in southern Pennsylvania;' Am. Jour. Sci., v.247, p.531-f Stose, G.W. and Bascom, F., 1929, Description of the Fairfield and Gettysburg quadrangles; U.S. Geol. Sur7., Geol.

Atlas of U.S. folio 225 Stose, G.W. and Jonas, A.I., 1933, Geology and mineral resources of the Middletown quadrangle, Pa.; U.S. Geol. Surv. Bull.

Stose, G.W. and Stose, A.I. ,19W, Geology of the Hanover-York district, Pennsylvania; U.S. Geol. Sur7 Prof. Paper 201 Wise, D.U. and Kauffman, M.E., 1960, Some tectonic and structural problems of the Appalachian Piedmont along the Susquehanna River; Penna. Field Conference Guidebook.

Wise, D.U.,(in press) Tectonics of southeastern Pennsylvania; text accompanyin6 Tectonic map of Pennsylvania, edit.

by V.E. Gwinn Wood, and Kehn, 1961, Sweet Arrow fault, east-central Pennsylvania AAPG Bull. v.45, p. 256-263 h

Woodward, H.P., 1963, Cor$ m il displacement, an Appalachian basinal dislocation; GSA abstracts, p.181-A m

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