ML19309E068
| ML19309E068 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 03/31/1980 |
| From: | WESTON GEOPHYSICAL CORP. |
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| ML19309E067 | List: |
| References | |
| NUDOCS 8004180348 | |
| Download: ML19309E068 (18) | |
Text
- - _ _ _ _ _
O NRC INFORMATION REQUEST ON GEOLOGY AND SEISMOLOGY HADDAM NECK SITE t
prepared for l
NORTHEAST UTILITIES SERVICE COMPANY t
i March 1980 t
I I
L sg Weston GeophyCORPORATION sical a004180 M 3
e -
U Weston Geo hysical conpoa m on March 27, 1980 Northeast Utilities Service Company Post Office Box 270 Hartford, Connecticut 06101 Attention:
Mr. J.
Clint Gladding Generation Engineering Department
Subject:
NRC Information Request on Geology and Seismology Haddam Neck Site Gentlemen:
Enclosed is a summary of our responses to the Nuclear Regulatory Commission's request for additional information on Geology and Seismology on the Haddam Neck site.
These requests resulted from a meeting between the NRC and Connecticut Yankee Atomic Power Company in Bethesda, Maryland, on May 16, 1979.
The NRC's request concerning geology can be divided into 2 areas of concern:
the geology and tectonics of the central Connecticut area (requests 2, 3, 4, and 5), and consideration of bedrock stresses (requests 1 and 6).
Accordingly, the enclosed summary of our investigations is divided into 3 sections:
geology; stress; and seismology.
This summary and our complete formal report, currently in preparation, address all of the NRC's requests with one ex-ception, that of the gravity data for the site area.
As you are aware, we have recently obtained, after considerable delay, the original gravity data acquired for the New England Seismotectonic Study sponsored by the NRC.
We are currently processing the gravity data and when completed, will submit the required gravity information in the form of an amendment to our report.
Please contact us should you have any questions or desire additional information.
Sincerely, 9
(-
e W
L w-Edward N.
Levine ENL:jb Enclosure Post Office Box 550. Westboro, Massachusetts 01581. (617) 366-9191
f TABLE OF CONTENTS Page 1
I.
GEOLOGY AND TECTONICS 1
1.1 Introduction 1
1.2 Regional Structural Setting 2
1.3 Site Area Geology 3
1.4 Site Area Structural Geology 4
1.4.1 Bonemill Brook Fault 5
1.4.2 Honey Hill Fault 6
1.4.3 Pre-Triassic-Jurassic Structure 7
1.4.4 Brittle Structures 8
1.5 Summary of Geologic Data 9
II.
STRESS CONSIDERATIONS 11 III.
SEISMOLOGY 12 IV.
CONCLUSIONS 13 FIGURES T
I i
l h Geophysed L
I.
GEOLOGY AND TECTONICS 1.1-Introduction Background data for the Haddam site area geology I
includes the following 7.5 minute quadrangle geologic reports; Middle Haddam (Eaton and Rosenfeld, 1972), Haddam (Lundgren, 1979), Moodus (Lundgren, et al.,
1971), and Deep River (Lundgren, 1963).
In the immediate vicinity of the Haddam Station, preliminary mapping by London, et al.
(1980) was available.
Regional geologic data was derived from Pease (1979),
Lundgren and Ebblin (1972), Dixon and Lundgren (1968), and Wintsch (1979) among others.
Additional bedrock geologic information was obtained by detailed and reconnaissance mapping of areas critical to existing geologic interpretations and field studies of previously unreported structural elements.
A complete geologic map will be submitted at a later date.
In addi-tion to the field mapping, available Landsat and U-2 imagery were examined and geophysical data utilized, included current U.S.G.S.
7.5 minute quadrangle aeromagnetic maps, as well as regional compilations by Harwood and Zietz (1976) and Zietz et al. (1974).
Detailed site area gravity data by Kick (1978) were not available and the final compilation of geologic studies awaits the incorporation of this gravity data.
Petrologic studies of critical rocks and mineral assemblages were undertaken.
Weston Geophysical
. The following is a brief synthesis of the existing geologic and geophysical data base (with the previous ex-coption noted) of the Haddam Station site area.
1.2 Regional Structural Setting Eastern Connecticut is underlain by a sequence of sedimentary, volcanic, and plutonic rocks of Precambrian (?)
to middle Paleozoic in age.
This sequence of eugeosynclina.
rocks have been metamorphosed to amphibolite grade by re-peated dynamo-thermal orogenesis of the Appalachian /
Caledonian Orogen.
Avalonian, Taconian (?), Acadian, and Alleghenian compression, translation, and accretion have contributed to the structural and stratigraphic succession now observed in this amphibolite grade metamorphic terrain.
Repeated orogenesis of Avalonian, Taconian (?), Acadian, and Pennsylvanian ages has resulted in the metamorphic fabric now observed.
Post metamorphic deformation of Permian, Triassic, and Jurassic periods has resulted in the dominant brittle fabric of the site area.
This fabric.is expressed by joints and high-angle, gouge-filled, and mineralized faults.
Five major structural units characterize eastern Connecticut.
These units or domains are the Triassic-Jurassic Rift Valley, the Bronson Hill Anticlinorium, the Lyme Dome, the Merrimack Synclinorium, and the Willimantic Dome (Figure 1).
These are fault bounded units across which stratigraphic correlation is not poisible.
Except for the Weslon Geophysical
- Triassic-Jurassic sequences, these faults represent accre-tion onto Avalonian Basement (Frecambrian Z) during the structural / tectonic development of the Appalachian /Caledonian Orogen from Cambrian to Carboniferous.
1.3 Gite Area Geology The Haddam Neck Nuclear Station site area (5 mile radius) is underlain by a sequence of amphibolite grade rocks of sedimentary, volcanic, and plutonic origin.
These amphibolite grade rocks can be divided into three dissimilar structural / stratigraphic blocks that are separated by deep seated, Paleozoic, ductile fault zones.
The ductile fault zones conceptually represent the locus of sequential accre-tion / welding and translation of these structural blocks on to the Avalonian Craton and finally to the present day North American Craton.
Precambrian to Silurian (?) in age these structural blocks consist of eugeosynclinal deposits and Pennsylvanian intrusives now at amphibolite grade.
Site area strata have undergone three possible periods of orogenesis, i.e.,
Taconic (?), Acadian, and Alleghenian.
Polydeformational overprint has resulted in the complex structural and strati-graphic relationships now observed.
Available U.S.G.S.
aero-magnetic data correlates well with mapped geology.
In the site area the structural blocks are the Bronson Hill Anticlinorium Sequence, the Willimantic Dome Sequence, and a Basement Complex (Figure 1).
Stratigraphic correlation Weston Geophyscal
i
- between these fault bounded blocks is not possible.
The site proper is founded on rocks of the Bronson Hill Anti-clinorium Sequence.
Subsequent to Pennsylvanian thermal activity the site area was affected by Permian-Triassic doming / extension (emplacement of nonfoliated pegmatites) and Jurassic high-angle faulting and dyke emplacement (Higganum Dyke).
Unsuccessful Mesozoic continental rifting of the Connecticut Valley produced the dominant brittle fabric in the site area.
This fabric is characterized by predominately-northeast-trending faults although north, northeast-and northwest-trending faults are also recognized.
Three types of fault mineralization are recognized:
- 1) quartz mineralized;
- 2) zeolite mineralized; and 3) gouge-filled faults.
Neither gouge, zeolite, or quartz mineralized faults show any macro-scopic reorientation, crushing, or fracturing of the fault infilling material which would indicate movemeat subsequent to the development of the fault infilling.
1.4 Site Area Structural Geology Two deformation styles characterize the Haddam Station site area.
An initial pre-Premian in age amphibolite (silli-manite-muscovite) grade of deformation is documented by tight isoclinal folding, drag folding, ductile faulting, boudinage, migmatization, and mylonite development.
The second and younger' deformation is brittle and manifested by joints,. retrograde mineralization (chlorite), quartz and l
zeolite mineralized faults, and gouge-filled faults.
t weson c,eonnym
. The major structural domains of the site area are:
the Bronson Hill Anticlinorium with north-south trending sub-elements; the Killingworth Dome, the Ivoryton Synform, and the Monson Anticline; the Hopyard Basin; and the Lyme/Seldon Neck Dome (Figure 2).
Pre-Permian in age these domains are separated by deep-seated ductile fault zones that demon-strate complex and, at least initially, synchronous structural histories.
1.4.1 Bonemill Brook Fault In the site area, a north-south trending zone of ductile, structural discontinuity separates the Bronson Hill domain from the Hopyard Basin (Figure 1).
This zone shows similar structural style, stratigraphic juxtaposition, and charac-teristic textures to the Bonemill Brook Fault mapped in north central Connecticut and south central Massachusetts and described by Peper (1976), Fahey and Pease (1977), Peper (1977), and Peper, et al. (1975).
However, the continuity of this fault into the Haddam area is not yet unequivocally proven.
Geologic mapping (London, et al.,
1980; Peper, et al.,
1975; and Peper, 1977; among others) geochronology (Wintsch, 1980), and indirect paleomagnetic correlations (Van der Voo, et al., 1979; Kent and Opdyke, 1978; and Kent and Opdyke, 1979) indicate the so called Bonemill Brook Fault has l
undergone left-lateral, right-lateral, and reverse movements prior to the injection of Permian nonfoliated pegmatites.
l Weston Geophysical
. 1.4.2 Honey Hill Fault Lundgren and Ebblin (1972) describe the Honey Hill Fault as a thick slab of cataclastic rock at amphibolite grade separating quartz feldspar rocks (Basement Sequence) from generally more micaceous rock (Willimantic Dome Seg-uence) (Figure 1).
In the site area, the Honey Hill Fault Zone is characterized by blastomylonite, ultramylonite, and rare mylonite.
The entire cataclastic sequence is at i
sillimanite-muscovite metamorphic grade with negligible retrograde (chlorite) mineral assemblages present (Lundgren and Ebblin, 1972).
Like the Bonemill Brook Fault, the Honey Hill Fault exhibits a complex movement history which can be deciphered by small-scaled folding events.
Sequentially, these events in the Haddam area are:
D-1, north over south thrusting; D-2, development of Z (dextral) folds with gently northwest plunging fold axes that are contemporaneous with blasto-mylonite and intrusive ultramylonite (Lundgren and Ebblin, 1972); and D-3, development of S (sinistral) folds which fold cataclastic units and is younger than D-2.
The final motion along the Honey Hill, D-4 (post metamorphic thrusting), truncates both the Bonemill Brook Fault and the small-scaled reverse faults associated with D-3.
l t
h Geophysicd t
. 1.4.3 Pre-Triassic-Jurassic Structure Numerous other structures, faults, and folds are mapped separate from the Bonemill Brook and Honey Hill Faults.
Although they are most probably related to these two major structures, no direct field correlation can be demonstrated.
These structures are pre-Triassic-Jurassic as they do not offset the Higganum Dyke and are associated with nonfoliated Permian pegmatites.
Two to three miles southwest of the Haddam plant, Lundgren (1979) recognized an east northeast-trending north over south thrust fault which results in an inlier of Middletown Formation surrounded by Monson gneiss.
Aero-magnetic data indicates this thrust turns to the southeast and is offset by inferred, northeast-trending, strike-slip faults.
Several reverse faults similar to those east of the Bonemill Brook Fault are also recognized.
These faults are associated with small-scaled thrusts and are pre-Permian in age based on the folding of syntectonic pegmatites and are cross cut by nonfoliated pegmatites.
London, et al. (1980) in the immediate vicinity of the Haddam Station map a series of north-northeast-to northeast-trending high-angle faults.
These faults are associated with nonfoliated pegmatites, chlorite mineralization, and nonbrittle dragged foliations and are presumably Permian in age.
i
. 1.4.4 Brittle Structures Numerous northwest, north, north-northeast, and' northeast-trending brittle faults are recognized primarily in recent road cuts in the Haddam site area.
These faults can be characterized by the material infilling or mineralizing the faults (quartz, zeolite, or gouge).
Although well exposed, no cross-cutting relationships between these faults and the Higganum Dyke nor each other were seen or reported by various workers in the area.
In all cases the infilling material indicates no move-ment subsequent to the emplacement of. quartz or zeolite or the production of gouge.
No post-Pleistocene movement is recognized or reported by others (Barosh, 1980).
Northeast-and northwest-trending quartz-filled faults are recognized near Mount Tom and along Route 9.
De Boer and Snider (1979) indicate quartz veining is representative of the hydro-thermal phase of early Triassic thermal activity.
Zeolite mineralized faults trend northwest with pre-dominent left-lateral strike-slip motion.
These faults are recognized in the East Haddam area and were apparently mineralized during the burial metamorphism reported in the Triassic-Jurassic Rift Valley (Rodgers, 1968 and Osberg, 1978).
De Boer and Snider (1979) suggest a Late Jurassic age for a low-grade regional metamorphism.
The gouge-filled faults contain a green (chloritic) and light brown soft clayey gouge and trend north, northwest, Weston Geophysical
. and northeast.
Preliminary x-ray analysis indicate the gouge are predominately chlorite and smectite.
K-Ar radio-metric studies on gouge-filled faults at Millstone, Connecticut, and in other similar terrains in New England yield ages of 160-198 mya (NNECO, 1975, 1976, and Lyons and Snellenburg, 1971).
The nature and composition of these fault gouges indicates that these faults developed at relatively shallow depths and at temperatures lower than 250 C.
The lack of post-Pleistocene offset and coherent nature of the gouge preclude recent re-activation; however, the minimum age is somewhat in doubt and the faults are inferred to be middle to Late Jurassic in age.
1.5 Summary of Geologic Data A.
The Bonemill Brook Fault is a north trending, Paleozoic, ductile fault zone which is located approximately 1,000 feet east of the Haddam Neck site.
Three distinct movements are recognized, a left-lateral, a right-lateral, and a reverse motion (east side up).
B.
The Honey Hill Fault is a thick slab of east-west-trending cataclastic rock now at amphibolite grade separating two distinctive lithologic sequences.
In the Haddam area four distinct motions are recognized t
along the Honey Hill Fault.
Both the Honey Hill and the Bonemill Brook Fault initially developed contemporan-eously.
Late Pennsylvanian to Permian post metamorphic thrusting along the Honey Hill Fault offsets the Bonemill Weston Geophysical
. Brook Fault.
No subsequent tectonic motion along either fault is recognized.
C.
Northeast-trending, high-angle faults in the immediate vicinity of Haddam Neck Station are considered Permian in age based on structural style and associated nonfoliated pegmatites.
These faults are younger than the Bonemill Brook Fault based on mapped and inferred cross-cutting relationships.
D.
Numerous high-angle mineralized faults (quartz and zeolite) are recognized throughout the Haddam site area.
The nondisturbed nature of these cementing minerals indicate that no relative motion along these northwest-and northeast-trending faults has taken place since the emplacement of these minerals.
Based on regional correlations, these faults are inferred to be Triassic-Jurassic in age.
E.
Soft gouge-filled faults of northwest and northeast trends are also recognized.
The gouge in these faults shows no evidence of movement subsequent to the pro-duction of gouge.
Preliminary x-ray data indicates the gouge material is not suitable for K-Ar studies.
Radiometric studies on gouge-filled faults elsewhere in eastern Connecticut results in a Triassic-Jurassic ege of faulting.
Consequently, these faults are considered as Late Jurassic but could be younger.
WeWon Geophysicol
. F.
No post-Pleistocene movement is recognized or demon-strated by others (Barosh, 1980) and no evidence of capable faulting has been documented.
II.
STRESS CONSIDERATIONS Offset drill holes in a road cut in the Salem, Connecticut area were first observed in 1970 as reported by Block, et al. (1979).
Recent data indicates there has been no measureable movement since 1976 and that the strain is now released (Dr. J. de Boer, personal communication, 1980).
The drill hole offsets do not appear to be tectonic as they are of a decreasing, nonrecurring nature and are not indicative of a t--riocent southward thrusting along the Honey Hill Fault Zone.
Joints and vertical fractures in the artificially isolated hogback display the same magnitude and offset direction as the drill holes thereby precluding episodic motion.
To the immediate south, gouge-filled vertical faults do not show any disruption.
Drill hole offsets appear to be related to residual stress released by excavation of a very large mass of mylonitic rock.
Reported rock squeeze phenomena at Portland and Millstone Point, Connecticut, and elsewhere in Southern New England indicate this is not an isolated occurrence of residual stress release.
WeWon Geophysicd
. III.
SEISMOLOGY The seismicity of the immediate site region can be characterized as low to moderate.
The majority of the events are in the III-IV(MM) intensity range with several earthquakes of Intensity V (MM), and one, that of May 16, 1791, with an Intensity VI-VII(MM).
This earthquake centered in the East fladdam-Moodus area of Connecticut, was originally categorized as an Intensity VIII(MM), but was re-evaluated as an Intensity V-VI(MM) by Reverend Daniel Linehan, S.J.
(1964).
For purposes of conservatism, it is currently retained in our data base as an Intensity VI-VII(MM).
Approximately 75% of the events in the site region are historical with epicentral locations estimated from felt reports, resulting in a large location uncertainty.
The epicentral coordinates of the May 16, 1791, event ( 41. 5 N,
72.5 W) have also been determined in this manner.
Because it is the largest event in the site area and one of the earliest, its coordinates have been assigned to numerous subsequent events reported in the East Haddam-Moodus area.
In a similar manner, coordinates of reporting towns have been assigned as the epicentral locations of other earth-quake tremors which were not widely felt.
Assuming 1935 as a starting point for the instrumental era in New England, numerous events located instrumentally by NESA were reexamined, in order to estimate their epicentral Weston Geophysical
. uncertainty.
Instrumental data were also compared with available felt reports.
In general, there is agreement between the two data sets, but the location uncertainty is still variable, between 5 and 25 km.
The epicentral locations obtained for small events after 1968 show some activity in 0
the area centered around 41.5 N and 72.5 W.
Between 1682 and 1977, 81 events have been catalogued 0
for the area between 72 W and 73 W, 41 W and 42 N.
These events constitute a diffuse cluster of small activity around a single larger event (1791).
Due to poor resolution of all locations, one to one correlation of any events with particular geologic structures, is not advisable.
This seismicity pattern is typical of New England.
IV.
CONCLUSIONS Recent geologic mapping and conclusions with respect to regional and subregional geology have no impact on previous seismological determinations of the design earthquake for the Haddam site.
Although there is an apparent clustering of seismic events in the site region, it is not adviseable because of epicentral location uncertainty to attempt a one to one correlation with the numerous faults that have been revealed through intensive mapping.
No Pleistocene movements can be demonstrated in the Haddam site area and no evidence of capable faults exists.
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