ML19260C178
| ML19260C178 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 09/30/1976 |
| From: | Fogle G LAW ENGINEERING TESTING CO. |
| To: | |
| References | |
| NUDOCS 7912180929 | |
| Download: ML19260C178 (50) | |
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@n LAW ENGINEERING TESTING COMPANY Enwronmental Sciences. Geotechnwat and construction Servoces 2749 DELK ROAD. S E. / M ARIETTA, GEORGIA 30067 (404) 971-9005 September 30, 1976 Mr. L. C. Dail Civil / Environmental Division Duke Power Company Post Office Box 2178 Charlotte, North Carolina 28242
Subject:
Jocassee Hydro-Station Seismic Studies Summary Report LETCo Job Number SA-1297
Dear Mr. Dail:
As authorized on February 25, 1976 by Mr. R. S. Bhatnagar, Law Engineering has completed an analyses and report of the seismic activity in the vicinity of the Jocassee Hydro-Station. This report summarizes geologic studies made at Jocassee since 1966 and the seismic investigation made between October 1975 and the present.
From data collected from the Jocassee microcarthquake recording network, earthquakes have been cataloged, hypo-centers have been determined, fault plane solutions made and the maximum earthquake pertinent to the site calculated.
Regional and local geology and seismicity pertinent to the Jocassee area are discussed. Recommendations for further monitoring are made.
We believe you will find this report complete, but.
please let us know if you require additional information.
Yours very truly,
, LAW ENGINEERING TE TING COMPANY s '
Gd ald I. Fogle f
Chief Geologist Assistant Vice President GIIF:pbb 1697 162 7912180 D 7
TABLE OF CONTENTS Section Page Introduction 1 Report Summary 1 1.0 Reservoir Filling History and Statistics 3 2.0 Local Earthquake History 3 2.1 Seismic Events Prior to Reservoir 3 Filling 2.2 Seismic Events Following Reservoir Filling 4 3.0 Regional and Local Geology 5 3.1 Regional Geolo9Y 5 3.2 Local Geology 7 4.0 History of Instrumentation 9 5.0 Data Reduction and Analysis 11 5.1 "a" Values and "b" Values 11 5.2 Hypocenter Computations 12 5.3 Magnitude Computations 12 6.0 Discussion of Events Recorded 13 6.1 Number and Size of Events 13 6.2 Hypocenter Locations 13 6.3 Lake Levels, "a" Values and "b" Values 14 7.0 Fault Plane Solutions 15 7.1 Techniques Used for Fault Plane Solutions 15 7.2 Fault Plane Solutions and Stress la Field Results 7.3 Comparison of Results with Other Local and 19 Regional Stress Field Measurements 1697 163
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TABLE OF CONTENTS CONT'D Section Page 8.0 Site Geologic Reconnaissance 20 9.0 Maximum Earthquake Calculation 21 10.0 Continuing Monitoring Program 22 References
_ Figures Tables 1697 164 m.........1m.co....g
Introduction This report is a summary of an investigation into earthquake activity in the vicinity of Lake Jocassee South Carolina under the supervision of Duke Power Company.
The following summarizes the roles played by the con-tributors to this report.
George F. Sowers Senior Geotechnical Consultant Law Engineering Gerald H. Fogle Project Manager Law Engineering Leland T. Long Seismology Consultant Law Engineering and Georgia Institute of Technology Robert D. Hatcher Structural Geology Consultant Clemson University Robert M. White Project Senior Author Law Engineering Arthur F. Benson Data reduction and analysis Law Engineering and author of part of the report Stephen L. Wampler Data reduction and analysis Law Engineering and author of part of the report Richard J. Lance Field geologic work and Law Engineering author of part of the report Report Summary A network of between 4 and 6 microearthquake recorders was in operation in the Lake Jocassee area from November 16, 1975 to June 30, 1976. An additional recorder has been in operation approximately 6 miles to the north since March 4, 1976 at the site of the planned Bad Creek Pumped Storage Project. Four strong motion acceleographs were i.n operation during most of the above period.
Over 2000 earthquakes of local magnitude between -2 and 3.2 were recorded during the seven and a half month period
- the network was in operation. Twenty of these had local mag-nitudes equal to or greater than 1.5; they possibly could have been felt by a person resting indoors. The hypocentern of 176 events were located using a computer program at the Georgia Institute of Technology. The epicenters are located in a crude circle, 10 km in diameter, centered on the lake.
1697 165 m . ..... u... m 1 . _ .. ,
Mr. L. C. Dail september 30, 1976 Page Two Several parameters which have been used to predict earth-quakes in cases of reservoir-induced seismicity were calculated and tabulated. Among these were "a" values (the number of earthquakes per day), "b" values (a parameter related to the
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inverse of the average earthquake magnitude for a period of time) and lake levels. All of these are shown on Figure 8.
No reliable earthquake predictor was found. Lake levels did not show an obvious correlation with activity or the occurrence of events with M 2 1 There has been a gradual decline in seismic activity 3 ( " a values)
". 5 . since its peak in mid-January, as illustrated in Figure 8.
As a tool to study the earthquake mechanisms, composite fault plane solutions were made for six areas and periods of time. From this it was learned that the stress field changes both spatially and temporally; however, the stress field can be generalized to be extensional below 1 km below msl and both extensional and compressional above 1 km. These results are in agreement with a report submitted by Professor Robert D. Hatcher of Clemson University to Law Engineering Testing Company which concludes that an extensional stress field is to be expected in the Southern Appalachians.
The maximum possible earthquake was calculated fcr the site by estimating the largest reasonabic fault plane and the maximum expected stress drop for the hypothetical maximum earthquake on that fault plane. The maximum hypothetical earthquake has a magnitude of 5.6.
A geologic reconnaissance was made at the site to determine if any surface manifestations of the recent seismic activity were present. A few faults were found in partially weathered rock and saprolite; however, Dr. Hatcher and we conclude from inspection that these are very sid (older than .5 to 1 million years and probably late Paleozoic, about 300 million years) and not related to the current seismicity of the site.
The purpose of the seismic network at Jocassee was to monitor seismic activity, noting the number of events and their size, and to determine the maximum possible earthquake for the site. This was accomplished. If activity levels and event magnitudes remain at current levels or continue their present slow decline, continued monitoring of the number and size of events by means of one or two microcarthquake recorders will continue. If, on the other hand, activity or event magnitudes increase, or if the area of activity noticibly changes, a microearthquake recording network will be reinstalled 1697 166
Mr. L. C. Dail September 30, 1976 Page Three to allow precisc location of events and further mechanism studies.
An event of local magnitude greater than or equal to 3, or more than 100 events in a week would constitute a significant increase, and carrant reinstallation of the network.
1.0 Reservoir Fillina History and Statistics
. Reservoir impoundment began in mid April of 1971 and the full pool elevation of 1110 feet above ms1 was reached at the end of April 1974. Figure 1 is a filling curve showing the increasing pool elevation with time.
When full the reservoir has a storage capacity of 1,160,298 acre feet (3.78 x 1011 gallons or 1.43 x 10 9 cubic meters) with a surface area of 7,565 acres (3.06 x 108 square meters). The maximum water depth is 107 meters (350 feet) at the dam.
Under normal operating conditions the maximum 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> draw down condition is 3.3 feet, (1.006 meters) and the. maximum 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> rising condition is 4.3 feet. (1.31 meters).
2.0 Local Earthquake History 2.1 Seismic Events Prior to Reservoir Filling Prior to the filling of the Jocassee Reservoir, 32 earthquakes were observed within a radius of 95 km (60 miles) of the reservoir.
These occurred between the year 1776 and 1973, about 200 years.
Table 1 lists these events, first in decreasing intensity and then chronologically. Figure 2 illustrates the proximity of these events to the site area. The minimum intensity observed was III, corresponding to a magnitude of approximately 3. It is likely that others of smaller or comparable magnitudes were not noted because of small size and the scattered habitation.
Of the 32 events, 3 were of epicentral intensity VI MM, 9 of epicentral intensity V Foi and 20 were of less than epicentral intensity V MM. The epicentral 12. tensity VI MM event nearest the site occurred on November 24, 1957 approximately 52 km (33 miles) to the west (see Figure 2) . Based on the isoseismal map contained in United States Earthquakes, 19571, the Jocassee area was included in the I-IV Foi intensity zone. The other two intensity VI MM cvents occurred approximately 70 km (44 miles) to the northeast of the reservoir.
Two of the 32 events were reported to have occurred within 11 miles of the Jocassee Reservoir. The first occurred on December 13, 1969, approximately 17.5 km (11 miles) to the north northwest of the site and had an epicentral intensity of V MM. This event should have been felt in the Jocassee uw suciarenino restino company 3 1697 if7
Mr. L. C. Dail September 30, 1976 Page Four area; however, due to the sparse population in the area, this is not confirmed. The local intensity might have been IV MM, because intensity IV MM effects were felt in Greenville, S.C. located approximataly 40.5 km (25 miles) further from the event than Jocassee. The second event cccurred on July 13, 1971 near Seneca S.C. approximately 16.2 km (10 miles) to the south of 'the site. An intensity survey by Sowers and Fogle (1971)2, indicated an epicentral intensity of IV MM.
This event was reported not felt at the Jccassce Reservoir.
Following the initiation of reservoir filling in April of 1971, several events were reported in the local area. The Seneca event of July 13 , 1971, see Table 1, located to the south of Jocassee (see Figure 2), is most likely not associated with the Jocassee impoundment. This is based on the fact that the reservoir was only partially full and that the event occurred approximately 16 km (10 miles) south of Jocassee.
A very small event occurred on August 12, 1973, approximately 9 months before the reservoir reached full pool. This event is not plotted on Figure 2 due to uncertain location, but was reported to have been felt to the northeast of the reservoir area. Its intensity and relation to the present activity are also uncertain.
2.2 Seismic Events Following Reservoir Filling The earliest confirmed earthquakes near the dam following filling were felt in mid October 1975, 17 months after the reservoir reached full pool. The first event occurred on October 18, 1975 and was noticibly felt in the Jocassee area.
The epicentral intensity was approximately III-IV MM. Imme-diately following this event an aftershock-microearthquake investigation was initiated jointly by the University of South Carolina and Georgia Institute of Technology. This investigation revealed the presence of numerous small events in the immediate area. Because these small events are undetectable in the absence of recording instrumentation, it is unknown how long they had been occurring prior to the event of October 18, 1975.
Additional " felt events" were reported on November 6, 21 and 22, 1975. These events were apparently a foreshock sequence for a Mn =3.2 earthquake that occurred on November 25, 1975.
Since the event of November 25, 1975, approximately 2000 events have been recorded in the Jocassee area. Twenty of these uw suomerma resima comw 1697 168
Mr. L. C. Dail September 30, 1976 Page Five have had local magnitudes equal to or greater than 1.5 and several were reported to have been felt in the immediate area.
3.0 Regional and Local Geology Jocassee Dam is located on the Keowee River in northwestern South Carolina near the intersection of the Toxaway and White This corresponds to about latitude 34 057' 3 d' north and
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Rivers.
longitude 820 55' west. The dam is near the northwestern border of the Piedmont physiographic province. The impoundment backs water across the Brevard Zone and a short distance into the Blue Ridge physiographic province (see Figure 3). Figure 5 is a regional geologic section through the Lake Jocassee area. An introduction to these physiographic provinces with additional -
detail for the immediate Jocassee Reservoir area follows.
3.1 Regional Geology The Blue Ridge physiographic province is about 15 to 70 miles wide and 600 miles long, extending from Pennsylvania to Georgia. The province encompasses the most rugged terrain and the highest elevations in the eastern United States. Surface elevations are generally 1500 to 5000 feet with the highest elevation being 6684 feet at Mount Mitchell, North Carolina.
This province is characterized by closely spaced ridges trending in a northeasterly direction.
Rock units underlying the Blue Ridge province consist of slate, phyllite, schist, gneiss, granite, pegmatite, and quartzite.
These units are metamorphic rocks of Precambrian and lower Paleozoic age, generally of amphibolite grade, with local intrusions.
The schist and gneiss are considered the oldest rocks in the Icgion. Recent radiometric dating places the peak of the Paleozcic metamorphism at a minimum of 430 million years ago. Pegmatite is younger, with measured ages of 380 million years.' The Blue Ridge physiographic province is highly deformed with the meta-morphic grade increasing from west to east. The northwestern boundary of this province generally coincides with major faults, along which metamorphic rocks have been thrust to the northwest over younger unmetamorphosed sedimentary rocks of the Valley and Ridge province. The southeastern boundary is primarily a topographic change, known as the Blue Ridge Front, where the steep slopes of the Blue Ridge join the 2 TG rolling hills of the Piedmont. In South Carolina this '- .icadary subparallels but does not coincide with the outcrop pmtc n 61 the Brevard Zone.
1697 169
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Mr. L. C. Dail September 30, 1976 Page Six Some have interpreted the front as a fault scarp :24 however, direct evidehee of fault ng coincident with the front is lacking.19 The Brevard Zone is part of the Chauga Belt. This zone contains highly brecciated rocks that stretch from Ala: una to Virginia and is thought to be the trace of a major strike-slip or thrust fault which was active during the Paleozoic Era.
Mica schist and phyllite, locally containing biotite and graphite gneiss, are the predominent rock types found in this zone; although, other persistent rock units have also been identified.
South of the Blue Ridge Front and Brevard Zone lies the Piedmont physiographic province.
The Piedmont physiographic province is about 40 to 125 miles wide and about 1000 miles long, extending from Alabama to New York. The province is bounded on the northwest by the Blue Ridge Front and to the southeast by the Fall Line. The Fall Line is the surface expression of the erosional unconformity between the Piedmont metamorphic rocks to the north and overlying Cretaceous and younger sediments of the Costal Plain province to the south. In the southern section, surface elevations are about 1000 feet near the Blue Ridge physiographic province and decrease to about 500 feet near the Fall Line. Elevations gradually decrease northward and range between about 100 to 500 feet near the northern terminus of the province.
The Piedmont rocks of the Jocassee Reservoir region are a complex series thought to hava formed during the late Precambrian to early Paleozoic Eras (600 to 400 million years ago). These rocks have been subjected to several periods of deformation and intrusion by younger granitic rocks. This metamorph.ic series appears to directly overlie a sequence of older, basement gneisses of the Precambrian Era (comparable to rocks underlying the Blue Ridge province) which may also overlie upper Cambrian carbonates or a thrust sheet of Blue Ridge crystalline rocks.5 Geologists generally believe that the major deformations -
and metamorphism in the Piedmont accurred near the close of the Paleozoic Era (about 250 million years ago). Intense folding and faulting has resulted in a general regional structure having a nor.heasterly strike and a southeasterly dip. Figure 5 is a generalized regional cross section illustrating the structures and relationships between geologic units of the Blue Ridge, Chauga Belt, and the Inner Piedmont. This regional structure is locally reflected by the orientation of rock foliation, fold axes, and strike of major thrust faults.
1697 170 mm--- mm _,,,
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Mr. L. C. Dail September 30, 1976 Page Seven During periods of deformation, and possibly for sometime afterward, the Piedmont rocks were intruded by several types of igneous bodies. Displacements caused by these injections
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disturbed the original structure of the adjacent rocks. Thus, rock structures - joints, foliation, and folds - may have locally divergent characteristics. Latest instrusions are
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diabase dikes and sills traditionally assigned to the Triassic period (225 to 190 million years ago). Deep saprolitic soils have developed throughout the Piedmont and erosion has produced a smooth, rolling landscape.
A compressing stress field with the maximum principle stress oriented horizontally to the northwest can be inferred for the region during the orogenic period in the late Paleozoic.
From the Triassic to present an extensional (tensional) stress field with a minimum principle stress often in a northwest-southeast orientation is postulated by Hatcher 19 and this report (sections 7.2 and 7.3) .
3.2 Local Geology The Piedmont and Blue Ridge physiographic prcn/ince boundaries do not exactly coincide with the similiarly named Blue Ridge and Piedmont geologic provinces in the Lake Jocassee area.
Variations in erosional rates have resulted in the Blue Ridge Front diverging from the Chauga Belt. A summary of geologic rock units and structure for the geologic provinces follows.
Conn's 1973 and 1965 engineering geology reports provide more detail.7,8 Folding on a relatively large scale in the Blue Ridge, Low Rank Belt, and High Rank Belt of northwestern South Carolina is predominately isoclinal and isoclinal recumbent. These types of folds also predominate on a smaller scale in the Low Rank Belt and have open folds superimgosed upon them. The predominant trend of fold axes is N50 E with a cross trend of N200W. Most fold axes plunge northeastward at less than 200 and most axial planes dip southeastward.
the larger folds have similiar orientations It{sinferredthat Jointing, or fractures without displacement formed in brittle rocks, can be formed by many mechanisms. In the Jocassee area joints may be the result of cooling following regional matamorphism, folding and faulting, and isostatic uplift.
These joints may have formed during the early tectonic history 1697 17I mm_mmo ,m.o _.
Mr. L. C. Dail September 30, 1976 Page Eight of the region. However, many geologists believe joints to be younger features possibly related to Mesozoic and Cenozoic isostatic uplift of the region. Two major joint sets with N450E and N450W strikes and near vertical dips parallel and
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cross major late ductile and brittle folds. Early joints have been filled with pegmatite and quartz and later joints are not filled or filled with zeolites and/or prehnite-calcite.
Laumontite-calcite fracture filling has been dated at 86~+ 30 million years at the Catawba Nuclear Site.25 Joint orientations were strongly influenced by pre-existing structural features.19 Jocassee Dam lies within the Low Rank (Metamorphic) Belt as shown on Hatcher's geologic map of the Bad Creek and Lake Jocassee Area (Figure 3). The Chauga (low rank) Belt is located between the rocks of higher metamorphic rank of the Blue Ridge geologic province and the migmatized high rank Inner Piedmont Belt. Within the Chauga Belt, the Brevard and Poor Mountain series of phyllites, mylonites, carbonates, amphibolities, and quartzites are overlain by the Henderson Gneiss.
The Henderson Gneiss is commonly a coarse or very coarse-grained aucen gneiss with some layers of granite gneiss and quartzite.S Also, fine and medium-grained augen gneiss was found in the dam area.9 The Henderson Gneiss is in fault contact with other units in the Chauga Belt; thus, the true thickness has not been measured. The thickness is probably about 2.8 km based on seismic reflection data.5 The regional strike of the foliation in the Low Rank Belt is N500 to 650E and dip is at a low angle to the southeast in the Henderson - Poor Mountain zone and somewhat steeper in the Brevard Zone, according to Acker and Hatcher.6 They also believe that the Chauga Belt may be a synclinorium with folds oriented northeast-southwest and overturned to the northwest. Radiometric age dating by Odom and Fullagar10 yielded Rb-Sr whole rock and U-Pb zircon ages of about 535 million years for formation of the Henderson Gneiss. Other Rb-Sr whole rock dates for this gneiss in the Brevard Zone gave a date of 356 million years. This latter date probably reflects a time of shearing in this zone.
The Brevard Zone is on the northwestern side of the Chauga Belt. This complex zone is made up of recrystallized, sheared
' rocks; however, it is remarkably uniform as a narrow continuous belt from Alabama to Virginia. Many geologists have studied the origin of the Brevard Zone and have many hypotheses as to its formation. Some of the latest ideas are that it is a detachment zone reactivated by plate collision; an isoclinal 1697 172 mm--- mmo -
Mr. L. C. Dail September 30, 1976 Page Nine synform overturned to the northwest; a thrust fault; a paleo-subduction zone; a strike-slip fault.5 Estimates of thickness for the Brevard Zone range from about 0.5 kmll to about 0.9 km.5 In South Carolina the rocks of the Brevard Zone dip about 25 to 70 degrees southeastward with the average near 450.26 Figure 4 is a very generalized northwest-southeast geologic section through the Jocassee Lake area. This section primarily depicts the Brevard Zone based upon interpretations of seismic reflection studies near Rosman, North Carolina.5 Rosman is about 12 miles northeast of Lake Jocassee along the strike of the geologic structure. As shown on the cross section, the rocks of the Blue Ridge geologic province directly underlie those of the Brevard Zone.
The primary units of the Blue Ridge province in the Lake Jocassee area (see Figure 3) are the Toxaway Gneiss and the Tallulah Falls formation. The Tallulah Falls formation has been further subdivided in the Lake Jocassee area into a Lower Member, Pelitic Schist Member, and a Graywacke-Schist Member.
The Toxaway Gneiss is a felsic gneiss of granitic to quartz dioritic composition. It is medium to coarse-grained, well fol iate d , and very uniform in appearance. This unit contains s oI..e pegmatite, amphibolite, and biotite schist.
Uncomformably overlying the Toxaway Gneiss is the Tallulah Falls formation. The upper part of the formation has been cut off by the Brevard Zone; thus, the thickness of the unit is unknown. The remainder of the formation can be divided into the mapped units as listed above. The Lower Member is a meta-graywacke, amphibolite, muscovite and biotite schist with some granitic gneiss and pegmatite. This member is thought to have been deposited in topographic lows on the erosional surface (unconformity) of the Toxaway Gneiss. The Pelitic Schist Member is a muscovite-biotite-garnet-kyanite schist with some amphibolite, muscovite schist, metagraywacke, granite gneiss and pegmatite. The uppermost unit, the Graywacke-Schist Member, is a metagraywacke and muscovite schist with minor amphibolite, gronitic gneiss and pegmatite.
4.0 History of Instrumentation Microearthquake recording instrumentation was initially installed in the Jocassee area following the event of October 18, 1975. The first network was installed by University of South Carolina and the Georgia Institute of Technology. The majority of the recorders were removed within several days. Following the ML =3.2 event of November 25, 1975, the network was re-established and operated continually up to June 30, 1976.
uw enaineenino resrina company a 1697 173
Mr. L. C. Dail September 30, 1976 Page Ten The recording station locations were adjusted during the recording period to provide the best coverage of the changing seismic activity. The locations are shown on Figurcs 6 A-G.
, Three types of seismic recorders have been utilized in this study. The majority of the work used Sprengnether Instrument Co.
Model MEQ-800, smoked paper, drum recording systems. For this
. study, instrument gains were between 60 and 72 db, with a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> record length. One hertz, vertical geophones were utilized with these recorders.
Some early work utilized smoked paper drum recorders developed at the Georgia Institute of Technology. These instruments were limited by their short record lengt.h.
In specific instances and during the seismic velocity survey, portable magnetic tape recorders were utilized. These instruments were developed at the Georgia Institute of Technology.
Strong motion recorders were employed during the early portion of the recording program. These instruments utilized an acceleration sensitive trigger, set at .005 and .01g, and recorded on photographic film. Their locations were originally; Station 1, near the microwave tower on the right-hand abutment of the dam in the equipment shack for environmental instrumentation; Station 2, located in the powerhouse structure on the lower floor; Station 3, located on the left side of the emergency spillway structure; and Station 4, located across the reservoir adjacent to portable Station WWF. The strong motion recorders were installed and maintained by personnel of the University of South Carolina, under the direction of Professor Pradeep Talwani, also of the University of South Carolina. The only verified triggering of some of these instruments occurred during the activity of January 13, 1976.
Prior to the installation of the Jocassee net, the nearest seismic stations to the Jocassee area were those of the So :th Carolina seismic net. The closest is PRM, installed in July 1975 and located 104 km (65 miles) southeast of Jocassee. Due to the recording mode at PRM, this station is not normally utilized for magnitude determinations. The next closest recording station
' is JSC, installed in May 1974 and located 168 km (105 miles) ,
j southeast of Jocassee. Data from JSC is applicable to magnitude j determinations of Jocassee earthquakes.
1697 174 ,
Mr. L. C. Dail September 30, 1976 Page Eleven More distant recording stations are located at Oak Ridge Tennessee (ORT), Atlanta (ATL), and Carters Dam Reservoir, Georgia (CDG), and are shown on Figure 7.
To accurately locate a seismic event at least three separate stations must have recorded it. It is our estimate that the smallest Jocassee event that would be locatable utilizing recording stations other than the Jocassee network would have a local magnitude of about 2.5 to 3.0.
5.0 Data Reduction and Analysis 5.1 "a" Values and "b" Values The number of events per day with durations equal to or greater than .04" (about 0.5 seconds) is herein referred to as the "a" value. The local magnitude corresponding to the duration lower limit of .04" is approximately -2.
The "b" values refer to the b term in the relationship:
M=A + b Log (trace amplitude) where M = earthquake magnitude.12 Duration is used in this study as a proportional measure of event magnitude. In close-in studies such as Jocassee duration is preferred over amplitude because of the limited dynamic range of the amplitudes measured on microearthquake recorders. Earthquakes have been observed to be distributed according to the Gutenberg-Richter Relation (Log Nc = a - bM),
where "M" refers to any convenient magnitude scale is the magnitude and "Nc" is the number of events of magnitude "M" and greater. For application to the Jocassee study, "M" was replaced by Log (Duration X 100). The exact relationship between magnitude and duration is unknown for this arca, but could be determined later. This would involve a comparative study of durations of larger Jocassee events that were recorded by a standard station capable of accurate, magnitude determinations.
Our computed "b" value is meant to show relative changes in "b" with time, and not absolute values, and therefore such a study is unnecessary.
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Our "b" value was computed from a maximum likelihood estimate of "b" where:
b = .4343/ (1/a)E Log (D) -
Log (Do
- m. --- 1m.o _.m i697 173
'Mr. L. C. Dail September 30, 1976 Page Twelve where "Do" is the minimum duration for which complete data are available; Do = .04 inches (1 mm) for this study.13 The precision for such measurements (95% confidence levels) is given by + 1.96b/
(a, where "a" = number of events. Since December 28, 1975 a seven-day running average of "b" was computed, (b 7 ). This allows a significant number of events to be utilized in the "b" value calculations and allows examination of longer period trends in the "b" values. The "b 7 " value should not be compared directly to "b" values computed in other locations.
5.2 Hypocenter Computations Hypocenter locations for this project were computed by using an iterative weighted least squares hypocenter determination program developed at the Georgia Institute of Technology. The program utilizes a crustal velocity model determined from a velocity survey conducted in the site area.
The hypocenter program could not compute a focal depth for all events. Due to the nature of the calculations made by this or any hypocenter location program and the limitations on timing accuracy imposed by the microearthquake recorders, depth calculations for very shallow earthquakes often become mathematically indeterminate. For this reason the focal depths of some shallow earthquakes could not be computed. In addition, this or any such program has difficulty computing depths for shallow events that occur outside of the recording station net.
5.3 Magnitude Calculations We have calculated local earthquake magnitudes (Mn ) for the Jocassee earthquakes by utilizing a magnitude-duration relationship of the type discussed in section 5.1 of this report.
We have used a relationship derived at the Clark Hill Reservoir Area:14 ML = - 1.32 + 1.98 Log (duration)
This relationship was chosen because Clark Hill was the closest Piedmont area where such a relationship (magnitude vs duration) had been derived. Direct comparison with the regional local magnitude formula (MLSE)l3 is not possible in that MLSE relates magnitude to trace amplitude and not duration. Other magnitude scales such as mb and M are used for other applications but are not appropriately applied to our data.
i697 176 mm_m.mmm- @
Mr. L. C. Dail September 30, 1976 Page Thirteen 6.0 Discussion of Events Recorded 6.1 Number and Size of Events
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Over two thousand seismic events between local magnitude
-2 and 3.2 were recorded during the seven and a half month period the network was in operacion. Twenty of these events had local magnitudes greater than or equal to 1.5. Figure 8 shows the number of events per day ("a" value) and the twenty larger events.
The "a" values for the time period of November 1975 through June 1976 (see Figure 8) show a pattern of increasing values from the beginning of the record (November 16, 1975) to a peak in mid-January, 1976. The peak activity day was January 13, 1976, with a total of 78 events recorded. From this peak, the activity level has shown a general decrease through the end of June, 1975, although the daily rates have been variable.
The largest event of the recording period occurred on November 25, 1975. This event has a MLSE=3.2 (determined at seismic station ATL). MLSE is compatible with Richter's magnitude. The next largest event was a ML =2.35 that occurred January 13, 1976.
6.2 Hypocenter Locations One hundred and seventy-six events were recorded with sufficient detail by the seismograph network to allow accurate location by the hypocenter program described in section 5.2.
The areas of concentrated activity are within 2 km of the boundary of the lake. During the recording period, the area of earthquake activity has increased in size. This spreading of events with time is more pronounced to the west, southwest and south of the lake (see Figures 10, a through d) . Little spreading has been noted to the east or north. The northern limit of earthquake epicenters coincides with the Brevard Zone outcrop band, which crosses the northern part of the lake and strikes northeast-southwest (see Figure 3) .
To examine the earthquake distribution, the computed earthquake hypocenters have been projected to a vertical plane striking northwest through the site (see Figure 4). Forty-seven of the 176 computed hypocenters had very shallow inderterminant depths as explained in section 5.2. They are not plotted in Figure 4 but can be assumed to have occurred between the ground surface and 1 km below msl. A projection of the Brevard Zone as it dips under the site area is also shown. The Brevard Zone 1697 177
Mr. L. C. Dail September 30, 1976 Page Fourteen depth was determined by seismic reflection work conducted approximately 19 kilometers (12 miles) northeast of the site 5, and may not necessarily be correct at the reservoir.
The events that have been recorded in the Jocassee area are shallow. The deepest event recorded was approximately 6 kilometers below mean sea-level, the shallowest events were computed to be above mean sea-level. Most events appear to occur between the ground surface and 3 kilometers below mean sea-level. About 75% of the earthquakes with computed hypo-centers are seen to occur above the projection of the Brevard Zone.
6.3 Lake Levels, "a" Values and "b" Values The influence of reservoir water levels on seismic activity has been previously studied at several sites.16 At the Jocassee reservoir, comparison of the larger events (MLhl.5) with reservoir level fluctuation does not indicate a direct relationship (see Figure 8) . There appears to be a weak correlation between reservoir water levels and total number of events ("a" values).
This relationship appears superimposed on the overall decrease in activity with time since January 13, 1976.
Seismologists generally believe that prior to an event, the number of events per day begins a general increase. Then immediately preceeding the event, an anomalous drop in the activity rate occurs. This pattern was evident precceding several of the largest events (Mn =1.5 to 3.2) during the recording period. However, in some instances, such as the events of February 6 and 11, there was no such pattern in the preceeding "a" values. Thus, "a" values have not proven to be a reliable indicator for larger earthquakes in the Jocassee area. One reason for this is that the seismically active area at Jocassee is acting as a series of discrete zones, each of which appears to be in a different stress condition. The resulting "a" and "b" valtes are a summation of the activity of these discrete areas wh.ch may be acting in or out of phase with each other.
Values for "b "7 are plotted from January 1976 through June 1976 on Figure 8. The trend of "b 7 " has been cyclic for this period. The values range from a low of approximately .65 to a high of almost 2.0.
The relationship between the "a" and "b 7 " values and earthquake activity has been variable through the entire period.
There appears to be both short period and long period trends in the s11ues. In some cases during this study, prior to the 1697 178
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Mr. L. C. Dail September 30, 1976 Page Fifteen larger events or series of events, there has been an increase of "b 7 " values lasting from 10 to 15 days. A decrease follows the increase and "b 7" thereafter becomes more stable at a lower value. A significant event often occurs 3 to 4 days after the beginning of this stable period. As with the "a" values, the "b7 " pattern has not been consistent throughout the recording period. There are instances where "b 7" followed the described pattern, but was not followed by a significant event.
7.0 Fault Plane Solutions 1.1 Techniques Used For Fault Plane Solutions and Stress Field Computations Large earthquakes are thought to represent movement along a single coherent fault. If it is assumed also that minor earthquakes represent movement on small faults at Jocassee, it is possible to hypothesize the nature of the faulting with fault plane solutions. Fault plane solutions have been used extensively in seismic literature to study the mechanisms of faulting associated with earthquakes. The term " fault plane solution" refers to any method of descriptive geometry which uses the first motions of seismographs to determine the orientation and relative motion of hypothetical faulting occurring at an earthquake hypocenter. The traditional procedure is to plot the first motions recorded by several seismic stations on a sterographic projection of an upper or lower hemisphere on a projection plane, with the earthquake focus at the center of the projection plane. The resulting pattern of first motions is then analyzed to determine the orientation of the
" fault plane" and the relative motion of the fault. The solution yields two possible fault plane orientations, and other means need to be used to determine which of the two best represent the movement at the earthquake hypocenter.
In this study, we have utilized composite fault plane solutions in which we plotted the first motions from groups of earthquakes on one sterographic projection. This was necessary becausa, with only five stations, no one earthquake alone would generate sufficient data to allow a solution. The grouping of earthquakes was based on geographic and first motion similarities between events. The first motions were plotted on the upper hemisphere of a Wulff sterographic net, and the solution made using standard interpretation techniques.17 Once a fault plane solution is available, the stress field inferred by the solution can be calculated. We have used a technique suggested by Sbar and Sykes which has been shown to be in agreement with laboratory experiments for fracture of rock.18 uw enaisetniwa restino coupswv i697 179
Mr. L. C. Dail September 30, 1976 Page Sixteen 7.2 Fault Plane Solutions and Stress Field Results Data to perform plane solutions have been available for about four months (March through June 1976). During this time period, 63 earthquakes were utilized, these having good hypocenter and first motion data. Dr. Pradeep Talwani of the University of South Carolina has also made fault planc solutions at Lake Jocassee using carthquakes prior to our data period.
He presented these in slide form on April 15, 1976 at the American Geophysical Union (AGU) meeting in Washington, D.C.
The following Fault Plane Solution Summary lists and describes the six separate fault plane solutions derived, and following it the Stress Field Summary Lista the stress fields computed from the fault plane solutions. Figures 11 through 14 show the locations of the groups of earthquakes which yielded the six composite fault plane solutions.
This fault plane study has shown that all types of focal mechanisms (normal, reverse, and strike-slip faulting) are or have been active at the site. However, normal and strike-slip faulting with a normal component predominate. The solutions themselves change in time as well as space. Figures 11 and 12
, depict the fault plane solutions and resulting stress field orientations at shallow and intermediate depths during the time period February 25, 1976 to April 3, 1976. Figures 13 and 14 depict the stress conditions for the period April 4, 1976 to June 16, 1976.
Figure 11 shows reverse faulting, resulting frcm a com-pressional stress field, occurring shallow near the dam and the deepest part of the reservoir (Area 3) . The arrows represent the horizontal projection of the greatest principle stress (al) and the fault symbols represent the two possible faulting orientations resulting from the fault plane solution. Two separate stress field orientations corresponding to the two ault plane orientations are computed, but as t'tey trend to be very similar to each other two sets of arrow s are now shown.
Normal faulting is indicated for shallow events in Area 1, northwest of the center of the lake. As normal faulting is extensional, the horizontal projection of the least principle stress (c3) is shown rather than the greatest principle stress as in the case of compressionil faulting.
Figure 12 depicts the stress conditions deeper than one km below msl during the same time period. The earthquakes used in the composite fault plane solutions for Area 2 show strike-slip faulting with a normal component. One of the two uw ruainernino restino company n 1697 180
Mr. L. C ,. Dail *
- September 30, 1976 Page Seventeen FAULT PLANE SOLUTION
SUMMARY
Area, depth range, Events Data time-period Used Points Solution I Solution II
- 1) NW of lake 3 9 Normal Faulting Normal Faulting
( .2 to .8 km) N42 E, 50 SE N560, 42 NW 2/29 to 3/17 1976
- 2) NE and SW of 22 63 Strike Slip with a Strike Slip with a lake normal component, normal component, (1.1 to 3.1 km) left lateral right lateral 2/29 to 6/17 1976 N37 W, 470NE N69 E, 740SE
- 3) Near dam 7 15 Reverse Faulting Reverse Faulting
( .1 to 1.2 km) N51 W, 52 0SW N670W, 4 00NE 2/28 to 6/16 1976
- 4) Center of lake 17 60 Normal Faulting Normal Faulting and south of dam N2 0E, 380SE N14 W, 52 SW (1.4 to 4.6 km) 2/28 to 6/12 1976
- 5) Shallow ex- 6 19 Strike slip with a Strike slip with a cluding Area 4 normal component, normal component, (O. to .9 km) left lateral right lateral 4/10 to 6/16 1976 N7 0 W, 63 NE N76 N, 55 SW
- 6) NW of dam 8 21 Normal faulting Normal faulting (1.3 to 2.4 km) N740 E, 45 NW N84 E, 45 SE 4/20 to 6/19 1976 TOTAL 63 177 ON wO N
00
Mr. L. C.* Dail , ,
September 30, 1976-Page Eighteen i STRESS FIELD
SUMMARY
STRESS CONDITIONS COMPUTED FROM FAULT PLANE SOLUTIONS Area, depth range,
- Pressure Axis Tension Axis Solution I Solution II time period Mechanism trend, plunge trend, plunge trend, plunge trend, plunge
o y =N58 W 69 NW
(.2 to .8 km) 02=N480 E 70 NE 0
02=N48 E 7 NE 0
2/29 to 3/17 1976 0 3=N43 W 10 NW =N400W 190SE 3
- 2) NE and SW of Strike- N63 W, 420NW N20 0 E, 16 0SW 0 c1=N46 W 36oNW 0
c1=N830W 46 0NW 0
lake slip with 0 c2=N850E 0 4 2 NE 02=N85 E 4 20NE (1.1 to 3.1 km) normal 03=N23 E 27 SW 0 3=N10E 6 SW 2/29 to 6/17 1976 component
c1=N33 E 90NE 0
( .1 to 1.2 km) 0 2=N580W 80NW 02=N58 W 8 NW 2/28 to 6/16 1976 0 3=N530E 670NE 0 0 3=N8 W 78cSE
- 4) Center of lake Normal N37 0E, 80 NE N84 0E, 70SW c y=N660E 670NE 0 1=N52 W 790NW and south of 0 80SE 0 80 SE c2=N6 W 0 02=N6 W dam 0 0 0
3=N860E 22 SW 0 3=N81 E 8 NE (1.4 to 4.6 km) 2/28 to 6/12 1976
- 5) Shallow ex- Strike- N46 0W, 47 0NW N50 E, 60 NE o =N240 W 48 0 NW c1=N670W 43 NW ciuding Area 4 slip with ch=N36W43SE 0 0 2=N36 W 43 SE (O. to .9 km) normal 5 SW 0 3=N390E 170NE 3=N600E 4/10 to 6/16 1976 component
- 6) NW of dam Normal N79 0E, 850SE N11 W, 0 c y =N70 E 75 NE o =N280 W 75 SE (1.3 to 2.4 km) 0 2=N790E 50SW _of=N790 E 50SW 0 =N100W 150NW 4/20 to 6/19 1976 0 3=N120W 15 SE 3 CyUydrofracture Horizontal 0 0 '
c1=N600 E 0 0 scResults from compression c2=N30 W 0
Ead Creek (reverse) 0 3= Vertical (300-900')
00 PY - indicates above mean sea-level
+ indicates below mean sea-level -
Mr. L. C. Dail September 30, 1976 Page Ninteen solutions was left lateral and the other right lateral. The horizontal projection of the least principle stress is shown to strike slightly cast of north. Normal faulting with the least
, principle stress (o3) striking about east-west is indicated for Area 4, nearly below Area 3 in the center of the lake and to the south and southwest of the dam.
Figures 13 and 14 show that for the next time period (April 4, 1976 through June 16, 1976) the mechanisms of Areas 2,3 and 4, remain the same while that of Area 1 does not. Other new mechanisms in Area 5 and 6 are indicated. In the vicinity of the dam and the deepest portion of the reservoir, the situation remains constant with re. verse faulting occurring above 1 km below msl and normal faulting deeper than l'km'below msl. Several scattered shallow events (Area 5) yielded a strike-slip with normal component faulting mechanism. Deeper than 1 km below msl, Area 2 has enlarged to the southeast and events have occurred further to the northwest than during the previous time period.
These events (Area 6) fit a pattern of normal faulting with the horizontal projection of the least principle stress striking about N10 0W.
7.3 Comparison of Results With Other Local and Regional Stress Field Measurements. .
In a report prepared for Law Engineering as part of the Jocassee project, Professor Robert D. Hatcher described the Southern Appalachians tectonic history from the point of view of the stress fields in effect from the Triassic Epoch to present. Professor Hatcher's conclusion is that the area has been in an extensional stress condition from Triassic to present. Primary geologic evidence include Triassic normal faulting, Jurassic diabase intrustions, siliceous ultramylonite dikes, joint patterns, coastal plain depositional history and local topography.19 The results of Dr. Hatcher's investigation allow the conclusion that the extensional field derived from fault plane solutions is typical for the Southern Appalachlans.
In apparent contradiction to our findings, several shallow insitu stress measurements have been carried out in the Southern Appalachians with compressional results.18 The nearest such test location is at the Bad Creek Pumped Storage Project (6 miles northwest). The results of this test are included on the Stress
. Field Summary (page 17) for comparison with the stress field orientations computed at Jocassee. The Bad Creek hydrofracture results show the maximum principle stress (al) horizontal, striking N600E with the minimum principle stress (03) vertical.
uw ruaintenino resriua COMPANY I 1697 183
Mr. L. C. Dail September 30, 1976 Page Twenty This corresponds well to the inferred stress direction of the very shallow group of earthquakes near the dam (Area 3 in our Fault Plane and Stress Field Solution Summaries). The composite
. fault plane solution yields a compressional stress field (reverse faulting) with a maximum principle stress b 1) nearly horizontal and striking N300-330E, and the minimum principle stress (o 3)
. nearly vertical.
The calculated stress field at Jocassee is considered to be in good agreement with geologic and insitu testing approaches to stress field determination. The stress field is seen to be extensional below 1 km below ms1 with both extensional and compressional zones shallower tha 1 km. The observed stress field pattern suggests a broad flexure in the underlying formations centered in the vicinity of and just northwest of the dam, below the deepest part of the reservoir.
The filling of a reservoir increases pore pressure and thus reduces the effective stress in the joints and fissures in the underlying rocks. In the case of normal or strike slip faulting environments such as Lake Jocassee, the reduction in effective stress drives the Mohrs' circle toward failure. It is required for failure, of course, that prior to the filling of the reservoir the stress conditions be near failure, and this was apparently the case in the Lake Jocassee area.
8.0 Site Geologic Reconnaissance During the week of August 2, 1976 a geologic reconnaissance of the Jocassee Reservoir was made for the purpose of determining if any surface rupture or other manifestations of the recent seismic activity existed. The field work concentrated on areas where numerous shallow earthquakes have occurred during the past nine months. The field geologist traveled by motor vehicle, small boat and on-foot and recorded his findings in field notebooks, on topographic maps and with the aid of photographs.
In particular the geologist was looking for evidence of cracking, fissuring or other disruptions of the surficial materials which could be of recent seismic origin.
. Three faults were found along the lakeshore within the outcrop area of the Henderson Gneiss. Two had fault planes striking east of north and one west of north. All were in
. partially weathered rock or saprolite. More detailed information on each fault follows.
i697 184
- m. ._ _ m- _m g
Mr. L. C. Dail September 30, 1976 Page Twenty-One
- 1. The first fault had a fault plane striking N250 E and dipping 40 0NW. This was a reverse fault with about one foot of displacement. Some very small drag folds are
~
present that also show a similiar sense of movement.
The faulted material is partially weathered Henderson Gneiss. The fracture contains what appears to be black manganese oxide. The fracture splits into two fractures separated by a block of Henderson Gneiss about 8 inches thick. The foliation of the gneiss is oriented about N370E and dips 570E. Very near the first fault is a second fracture oriented N340W, 51 SW on the north'ern side of the point and N23 W, 55 SW on the southern side.
Amount of offset could not be determined as no markers were present; however, small drag folds show the same movement as for the above described fracture. A slickenside in the plane of the fault plunges 390NW.
Each of these fractures is truncated by the B soil horizon and no evidence for recent movements was noted.
- 2. The third fault consists of a zone of limonite-filled fractures that strike about N70E and dip 22 SE. This sheared zone is about 1 foot thick and contains slicken-sided surfaces that strike about N68 0 E and plunge 190NE. Unfilled joints do not appear to cross the zone and earlier quartz veins die within it. Closely spaced, steeply dipping (N28 E, 880 SE) limonite-filled veins occur within the zone and may be traced for short distances outside it. This zone could not be traced beyond this one exposure. The development of the zone appears to have been later than the youngest joints, but prior to development of saprolite and area topography.
We believe that these faults are very old with a minimum age of 0.5 to 1 million years based on rates of saprolite formation.
Therefore these features are not related to the present seismic activity.
While conducting the reconnaissance, numerous small shore-line slumps and rockfalls were noted. These features were probably caused by erosion and undercutting of banks by wave action, and by rainfall saturating the bank materials and re-ducing their stability.
1697 185
Mr. L. C. Dail September 30, 1976 Page Twenty-Two These observations reflect Professor Robert D. Hatcher's comments. Professor Hatcher is very familiar with the structural geology of this area. He concurs with us that neither the faults nor the slumps were produced by present seismic activity.
9.0 Maximum Earthquake Calculation In this study we have approached the question of the maximum possible earthquake for the Jocassee Reservoir area by estimating the largest practical fault plane and the typical stress drop for the hypothetical maximum earthquake on that fault plane. Figure 15 illustrates our maximum fault plane. The orientation of the plane was taken from Solution II of the comoosite fault plane solution for Area 6 (see Fault Plane Solution Summary) . The depth of the fault plane (ground surface to 2.7 km below sea-level) includes 95% of the computed earthquake depths (see Figure 4) and the length from the envelope of epicenters which includes 95% of the computed epicenters (see Figure 9). The area of the 2
hypothetical fault plane was then calculated to be 39.5 km ,
The stress drop was assumed to be 7 bars. This is the stress drop calculation for the August 2, 1974 Clark Hill Reservoir earthquake.20 The 7 bars is also compatible with estimates of stress drop for Eastern United States earthouakes of magnitudes
=4 computed by Street, Herrmann and Nuttli (1976).21 In order to compute an equivalent magnitude for a stress drop of 7 bars over a 39.5 km2 fault plane the area was converted to an equivalent radius of 3.54 km and the theoretical relation of Randall (1973)22 was used. Randall's theoretically derived relation relates Richter's local magnitude, ML, to fault radius and stress drop and is consistent with observed data over a wide range of magnitudes. Randall's relations give M n=5.6 for the maximum possible earthquake at the Jocassee Reservoir area.
In that our maximum fault plane area is very conservative and our stress drop estimate quite reasonable, we feel out computed hypothetical maximum earthquake is conservatively large.
10.0 Continuing Monitoring Program The purpose of the seismic data gathering program at Jocassee Reservoir between November 1975 and June 1976 has been to gather sufficient data to achieve the following:
- a. To monitor activity, including number of earthquakes per day and their magnitudes.
1697 186
- m. --mmo m1-o -m gi
Mr. L. C. Dail September 30, 1976 Page Twenty-Three
- b. To determine the maximum possible carthquake for the site.
In order to achieve this a ietwork of portable microcarthquake
- recorders was installed to accurately locate earthquakes and to perform mechanism studies, as well as monitor the number and size of the continuing earthquake activity. This has been accomplished.
- Earthquake mechanisms have been described and a maximum carthquake determined for the site.
The purpose of continuing data collection beyond June 30, 1976 is to monitor the number and size of earthquakes occurring at Jocassee Reservoir. To meet this objective two portable micro-earthquake recorders have been maintcined in the site area, one recorder is located at station SMT (the proposed future location of the semi-permanent seismic station) , and another recorder is located at station LAW which is in the vicinity of the proposed Bad Creek Pumped Storage Reservoir, about 6 miles northwest (see Figure 16) .
Duke Power plans to include the semi-permanent seismographic station in the South Carolina seismograph network We feel that this is a sufficient response to the continuing seismic activity at Lake Jocassee assuming that the activity continues to decrease, or remain at its present level; events larger than those presently recorded do not occur and that the general location of the events remains constant.
If the activity level or event magnitudes, increase significantly or if the events obviously change location, a microearthquake recording network of about 5 stations should be reinstalled and maintained for a period sufficient to allow reevaluation of the maximum carthquake for the reservoir area.
An event of local magnitude greater or equal to 3 or more than 100 events in a week would constitute a significant increase.
1697 187
- m. .. m _ _ _, g
REFERENCES 1 United States Earthquakes, 1971: National Oceanic and Atmospheric Ad.ninistration, Boulder, Colo. 1973.
2 Sowers, George F., Fogle, Gerald H., Seneca, South Carolina Earthquake, July 13, 1971: Law Engineering Testing Company, Marietta, Georgia, 1975.
3 Hatcher, Robert D., Jr., Developmental Model for the Southern Appalachians: Geological Society of America Bulletin, Vol. 83, pp. 2735-2760, September, 1972.
4 Butler, J. R., Age of Paleozonic Regional Metamorphism in the Carolinas, Georgia, and Tennessee Southern Appalachians:
Amer. Jour. Sci., Vol. 27, pp. 319-333, 1972.
5 Clark, H. B., Costain, J. K. and Glover, L. III, Preliminary Seismic Reflection Studies of the Brevard Fault Zone Near Rosman, North Carolina: Virginia Polytechnic Institute; (unpublished manuscript) March 1976.
6 Acker, Louis L. and Hatcher, Robert D., Jr., Relationships Between Structure and Topography in Northwest South Carolina:
Geologic Notes, S.C. Div. of Geology, Vol. 14, No. 2, pp. 35-48.
April, 1970.
Conn, William V., Engineering Geology of the Keowee-Toxaway Project: report to Duke Power Co., 75 p.,
December 16, 1965.
8 Conn, William V., Engineering Geology of Bad Creek Pumped Storage Project, Oconee County, South Carolina: report to Duke Power Co., 47 p., August 1, 1973.
9 Law Engineering Testing Co., Keowee-Toxaway Project, Jocassee Development Foundation Report report to Duke Power Co., LETCo Job No. CH-1065A, 1965.
O Odom, A. L., and Fullagar, P. D., Geochronologic and Tectonic Relationships Between the Inner Piedmont, Brevard Zone, and Blue Ridge Belts, North Carolina: Amer. Jour. Sci., Cooper Vol. 273-A, pp. 133-149, 1973.
1697 188 m.__1mmm_m@
REFERENCES CONT'D 11 Hatcher, Robert D., Jr., Stratigraphy, Petrology, and Structure of the Low Rank Belt and Part of the Blue Ridge of Northwesternmost South Carolina: Geologic Notes, S.C. Div.
of Geol., Vol. 13, No. 4, pp. 105-141, October, 1969.
12 Richter, Charles F., Elementary Seismology: W. H. Freeman and Company, page 340, 1958.
13 Page, Robert, Aftershocks and Microaftershocks of the Great Alaska Earthquake of 1964: Bull. Seis. Soc. Amer.,
Vol. 58, pp. 1141-1142, June 1968.
14 Talwani, Pradeep, Crustal Structure of South Carolina:
sponsored by the U. S. Geologic Survey, Contact No. 14-08-0001-14553, December 1975.
15 Long, L. T., A Local Magnitude Scale for the Sputheastern United States: Geological Society of America, Abstracts with Programs, Vol. 5 No. 5 p. 414, 1973.
16 Judd, W. R., Seismic Effects of Reservoir Impounding:
Engineering Geology, Volume 8 No. 1/2, August 1974.
I Herrmann, Robert B., A Student's Guide to the Use of P and S Nave Data for Focal Mechanism Determination: Vol. 46, No. 4, Earthquake Notes October - December 1975.
18 Sbar, Marc, L. and Sykes, Lynn R., Contemporary Compressive Stress and Seismicity in Eastern North Ameriaa: An Example of Intra-Plane Tectonics: Geological Society of America Bulletin V. 48 p. 1861-1882, June 1973.
19 Hatcher, Robert D., Jr., Post-Orgenic History of the Southern Appalachians: Its Relationships to Stress Fields Throuch Time in the Jocassee Reservoir Area: prepared for Law Engineering Testing Co., May 21, 1976.
20 Bridges, Samuel R., Elevation of Stress Drop of the August 2, 1974 Georaia - South Carolina Earthquake and Aftershock Sequence:
Master's Thesis, Georgia Institute of Technology, August 1975.
1697 189 m...,......m1,.o...,@
REFERENCES COMT'D 21 Street, R. L., Herrmann, R. B., and Muttli, O., Spectral Characteristics of Love Waves Generated by Central United States Earthquakes: Geophysical Journal of the Royal Astronomical Society Volume 41 p. 41-63, 1975.
22 Randall, M. J., The Spectral Theory of Seismic Sources:
Bull. Seis. Soc. Amer., Vol. 63 No. 3 pp 1133-1144, June, 1973.
23 Gutenberg, B., and Richter, C. F., Earthquake Magnitude, Intensity, Energy and Acceleration (second paper) : Bull. Seis.
Soc. Amer., Vol. 46, p. 105-145, 1956.
24 White, W. A., Blue Ridge Front - A Fault Scarp:
Geol. Soc. Amer. Bull., V. 61, P . 1309-1346, 1950.
25 Duke Power Company, Final Geologic Report on Brecciated Zones for Units 1 and 2 Catawba Nuclear Station, Page 6-1.,
March 1, 1976.
26 Hatcher, Robert D., Jr., Stratigraphic, Petrologic, and Structural Evidence Favoring a Thrust Solution to the Brevard Problem, American Journal of Science Volume 270,
- p. 177-202, March 1971.
O i697 190
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1697 195 MODIFIE D FHOM M ATCHE R.19 72(RE F.3)
FIGURE 5 REGION AL GEOLOGIC SECTION THROUGH JOCASSEE RESERVOIR AREA LAW ENGINEERING TESTING COMPANY S EPT E M B E R,1976 M ARIETTA, G A. [
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TABLE 1 Historic Earthquakes that occurred within a 60 mile radius of Jocassee Reservoir Listed by Decreasing Intensity COORDINATES DATE (UT) TIME (UT) LAT LONG INTENSITY (MM) LOCALITY REF 1916, Feb. 21 1739 35.5 82.5 6 N.C. 1 1957, July 2 0433 35.5 82.5 6 N.C. 3 1957, Nov. 24 1506 35.0 83.5 6 N.C. - Tenn. Border 3 1911, Apr. 20 -
35.2 82.7 5 N.C. - S.C. Border 1 1915, Oct. 29 0100 35.8 82.7 5 N.C. 1 1924, Oct. 20 0330 35.0 82.6 5 Pickens County, S.C. 1 1935, Jan. 1 0315 35.1 83.6 5 N.C. - Ga. Border 3 1940, Dec. 25 0150 36.0 82.8 5 Eastern Tenn. & Western N.C. 2 1958, Oct. 20 0116 34.5 82.8 5 Anderson. S.C. 3 1969, Dec. 13 0520 35.1 83.0 5 Western N.C. 3 1776, Nov. 6 -
35.5 83.2 4-5 Western N.C. 2 1916, Mar. 2 0502 34.5 82.7 4-5 Anderson, S.C. -
1924, Jan. 1 0106 34.8 82.5 4 Greenville, S.C. 7 1928, Nov. 19 2245 - -
4 West Ashville, N.C. 2 1929, Oct. 27 2115 34.3 82.4
- =4 Due West S.C. 3 cts 1930, Dec. 9 1902 34.2 '
82.4 u4 Due West S.C. 3
'-J 1956, Jan. 5 0300 - -
4 Due Ucst S.C. 3 rs) 1956, May 19 1400 - -
4 Due West S.C.
- 3 Cys 1956, May 27 1825 -
.- 4 Due West S.C. 3
TABLE 1 Historic Earthquakes that occurred within a 60 mile radius of Jocassee Reservoir Listed by Decreasine Intensity COORDINATES DATE (UT) TIME (UT) L.\T LONG INTENSITY (HM) LOCALITY REF 1916, Feb. 21 1739 35.5 82.5 6 N.C. 1 1957, July 2 0433 35.5 82.5 6 N.C. 3 1957, Nov. 24 1506 35.0 83.5 6 N.C. - Tenn. Border 3 1911, Apr. 20 -
35.2 82.7 5 N.C. - S.C. Border 1 1915, Oct. 29 0100 35.8 82.7 5 N.C. 1 1924, Oct. 20 0330 35.0 82.6 5 Pickens County, S.C. 1 1935, Jan. 1 0315 35.1 83.6 5 N.C. - Ga. Border 3 1940, Dec. 25 0150 36.0 82.8 5 Eastert Tenn. & Western N.C. 2 1958, Oct. 20 0116 34.5 82.8 5 Anderson. S.C. 3 1969, Dec. 13 0520 35.1 83.0 5 Western N.C. 3 1776, Nov. 6 -
35.5 83.2 4-5 Western N.C. 2 1916, Mar. 2 0502 34.5 82.7 4-5 Anderson, S.C. -
1924, Jan. 1 0106 34.8 82.5 4 Greenville, S.C. 7 1928, Nov. 19 2245 - -
4 West Ashville, N.C. 2 1929, Oct. 27 2115 34.3 82.4 a4 Due West S.C. 3 1930, Dec. 9 1902 34.2 82.4 u4 Due West S.C. 3 1956, Jan. 5 0300 - -
4 Due nest S.C. 3 C7' 1956, May 19 1400 - -
@ 4 Due West S.C. 3
'd 1956, May 27 1825 -
.- 4 Duo West S.C. 3 N
= i COORDINATES DATE (UT) TIME (UT) LAT LONG INTENSITY (MM) LOCALITY REP 1958, May 16 1730 - -
4 Ashville, N.C. 2 1960, Feb. 7 2220 - -
4 Henderson County, N.C. 3 1960, Feb. 9 0900 - -
4 Henderson County, N.C. 3 1963, April 11 1245 - -
4 Greenville, S.C. 3 197'1, July 13 1145 35 . 83.0 4 Seneca, S.C. 6 1873, Apr. 26 1700 - -
3-4 Franklin N.C. 2 1877, Apr. 26 2200 23.2 83.4 3-4 Franklin N.C. 7 1931, May 6 0718 34.2 82.4 =3-4 Due West, S.C. 3 1884, Apr. 30 0646 - -
=3 Ogrecta, Cherokee Cty. N.C. 2
.1940, Dec. 24 2030 - -
3 Ashville, N.C. 2 1941, May 10 0612 - -
3 Ashville, N.C. 2 1923, Oct. 18 1930 35.3 82.5 -
=3 Hendersonville, N.C. 7 1940, Dec. 26 0500 35.7 82.7 3 Ashville, N.C. 7 1973, Aug. 12 1210 34.8 83 1-3 Northwestern N.C. 6
__ Listed Chronolocically 1776, Nov. 6 -
35.5 83.2 4-5 '
Western N.C. 2' 1873, Apr. 26 1700 - -
3-4 Franklin, N.C. 2 lb77, Apr. 26 2200 35.2 83.4 3-4 Franklin, N.C. 7 1884, Apr. 30 0646 - -
a3 Ogrecto, Cherokee Cty, N.C. 2 .
__, 1911, Apr. 20 -
35.2 82.7 5 N.C. - S.C. Dorder 1 f 1915, Oct. 29 0100 35.8 82.7 5 N.C . . 1 1916, Feb. 21 1739 35.5 82.5 6 N.C. 1
{]{ 1916, Mar. 2 0502 34.5 82.7 4-5 Anderson, S.C.
cc
COORDINATT.S DATZ (UT) TIME (UT) LAT LONG INTENSITY (P2) LOCALITY REF.
' 1923, Oct. 18 1930 35.3 82.5 .3 !!cndersonville, N.C. 7 1524, Jan. 1 0106 34.8 82.5 4 Greenville, S.C. 7 1924, Oct. 20 0330 35.0 82.6 5 Picken County, S.C. 1 1921, Nov. 19 2245 - -
4 West Ashville, N.C. 2 1929, Oct. 27 2115 34.3 82.4 =4 Due West, S.C. 3 1930, Dec. 9 1902 34.2 82.4 =4 Due West, S.C. 3 1931, May 6 0718 34.2 82.4 =3-4 Due West, S.C. 3 1935, Jan. 1 0315 35.1 83.6 5 N.C. - Ga. Border 3 1940, Dec. 24 2030 - - 3 Ashville, N.C. 2 1930, Dec. 25 0150 36.0 82.8 5 Eastern Tenn. & Western N.C. 2 1940, Dec. 26 0500 35.7 82.7 3 Ashville, N.C. 7 1941, May 10 05;2, - - 3 Ashville, N.C. 2 1956, Jan. 5 0300 - - 4 Due West, S.C. 3 1956, May 19 1400 - - 4 Due West, S.C. 3 1956, May 27 1825 - - 4 Due West, S.C. 3 1957, July 2 0433 35.5 82.5 6 U.C. 3
~
1957, Nov. 24 1506 35.0 83.5 6 N.C. - Tenn. Border - 3 1958, May 16 1730 - - 4 Ashville, N.C. 2 1958, Oct. 20 0116 34.5 82.8 5 Anderson, S.C. 3 fh
' IIenderson County, N.C. 3 1960, reb. 7 2220 - - 4 0900 - 4 Henderson County, N.C. 3
{}d 1960, Fab. 9 -
'f) 1245 - 4 Greenville, S.C. 3 1963, Apr. 11 -
1969, Dec. 13 0520 35.1 83.0 5 Western H.C. 3
g 7 g .7 COORDINATES DATE (UT) TIME (UT) LAT LONG INTENSITY (MM) LOCALITY REF 1971. July 13 1145 35.8 83.0 4 Seneca. S.C. 6 1973, Aug. 12 1210 34.8 83 1-3 Northwestern N.C. 6
.. REFERENCES UTILIZED IN COMPILING TABLE 1 1 United States Earthquake History: Part 1 & 2 U. S. Coast Geodetic Survey, Washington D.C.
2 Berlin C. Moneymaker: Earthquakes in Ter.nessee and Nearby Sections of Ucighboring States, 1851-1970; Tennassee Valley Authority, Knoxville, Tenn.
3 United States Earthquakes, 1928-1972, National Oceanic and Atmospheric Administration, Boulder, Colo.
4 Earthquake Hypocenter Data File; prepared by National Geophysical and Solar-Terrestrial Data Center; National Oceanic and Atmospheric Administration; Boulder, Colo.
5 Preliminary Determination of Epicenters; National Earthquake Information Service, U. S. Geological Survey: Doulder, Colo.
6 Law Engineering Testing Company, Internal Earthquake Reference Files, Marietta, Georgia.
7 McLain, W. C., Myers, O. H., Seism.ic History and Scinnicity of the
-- Southeastern Region of the United States; Oak Ridge National Laboratory, Cys Cak Ridge, Tcnn., 1970. ,
W N1 N
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