ML19347C048
| ML19347C048 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 10/08/1980 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8010160512 | |
| Download: ML19347C048 (43) | |
Text
{{#Wiki_filter:_ t '; south CAROUNA ELECTRIC a gas COMPANY res e.r :t ev 744 CCLuweiA. Souf
- CapetimA reais T c N,c, as.Ja October 8, 1980 c, %, y.,c. n. c.. a.,
a.. :.... o s Mr. Harold R. Der _ ton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Subject:
Virgil C. Summer Nuclear Station Docket No. 50/395 Seismology Questions
Dear t!r. Denton:
South Carolina Electric and Gas Company, acting for itself and as agent for South Carolina Public Service Authority, herewith fr. wards forty-five (45) copies of our completed response to NRC Question 361.17 relating to comparison of earthquake time histories spectra to the Summer Station design response spectra. Included also within this sub-mittal are revised pages to earlier responses to 361. Series questions previously transmitted to the Staf f by letter dated September 5,1980. This completes our response to all issues discussed at the July 30, 1980 meeting with NRC Staf f in Bethesda. Additional information re-lating to the Charleston earthquake studies will be provided in the near future as requested by the NRC Staff by telephone conference call on September 25, 1980. Very truly yours, T. C. Nichols, Jr. RBW:TCN:jw 1 cc: B. A. Bursey W. F. Kane V. C. Summer G. H. Fischer A. J. Murphy R. E. Jackson W. A. Williams, Jr. Dan Cash T. C. Nichols, Jr. l E. H. Crews, J r. J. L. Skolds H. T. Babb D. A. Nauman
- 0. S. Bradham O. W. Dixon, Jr.
J. B. Knotts, Jr. R. B. Clary NPCF/Whitaker File i 20101606l9-3
l 1 A. FEAK ACCELERATION ESTD%TES To estimate amolitudes of peak acceleration, the Brune (1970, 1971) model of seismic sources is used to determine the rcot-mean-square acceleration a and duration Td of direct shear waves at the site of rms interest, and a simple apolication of random vibration tneory is used to estirrate the peak acceleration a from a and T. This method has been shown to be p rms 3 appropriate by comparison to recorded ground motions in California (McGuire l and Hanks,1980; Hanks and ficGuire,1980) and is applied to the project site with certain modifications as discussed below. The model used here to estimate characteristics of motion begins with a description of the Fourier amplitude soectrum of displacement u, at source-to-site distance R, caused by shear waves in the far field. The initial description given here is for ground motion in all directions at a site located in a uniform, isotropic full space. A correction factor to account for free surface amolification, vectorial partitioning of energy into instrumental co.~acrants, and radiation pa ttern will be introduced below so that predictions can be compared with observations. The salient characteristics of the spectrum u are shown in Figure 361.17.4-la. The long period level % is given by (Haskell,1964): Mo % * ; g g33 R (1) 9 where M is seismic mcment, R9; is the radiation pattern of the shear excita-o tion, o is density, and 3 is shear wave velocity. In Figure 361.17.J-la, the corner frequency f is inversely procortional to source radius r and can be g astimated witn the relation (3 rune.1970): 2.343 (} Y.o"2r 361.17.4-2
High frecuency (f>>fo) spectral amplitudes fall off as f~, y = 2, and this is an important feature of the assumed model. Hanks (1979) has argued from an observational basis that the 'f =2 model is the one generally applicable to crustal earthcuakes. ( The Fourier amplitude spectrum of acceleration a can be obtained l l trom u by mul tiplying by (2:f),, leading to the typical spectrum shown in l l Figure 361.17.4-lb. Amplitudes for all frequencies are decreased by the l anelastic attenuation factor k = exp ( 7fR/03) (3) a l t where Q is the specific attenuation. Anelastic attenuation for typical values of Q and 3, and for distances of interest, is only important for j l l frequencies >>f o l The earthquake stress drop ic is related to M and r in the Brune g (1970,1971) model by: u O ic = (4) 16r3 Relations (1) Through (4), together witn Figure 361.17.4-1, constitute the model used to estimate shear wave Fourier amplitude spectra of accelera-1 tion. To estimate Fourier amolitudes of single components of ootion at the ground surface, we account for the free surface effect (a f.ctor of 2), i vectorial partitioning of energy into two components of equal amplitude 1/ s/li,and the root-mean-square (rms) of the double-coucle radiation pattern (0.6), or a combined correction factor of 0.85 The divi ion of energy into two equal components of motion is considered apcropriate for the low nagnitude, near-source ground motions of interest here, in spite of recent strong motion data obtained in California which show high-fregi ncy vertical motions to have 361.17.J-1
amplitudes as large as horizontal motions at small source-to-site distances. Data from lower magnitude events (ML =4-5) do not show such characteristics: vertical motions generally show amplitudes which are one-half those of horizontal motions. The Fourier amplitude of single horizontal component acceleration at frequency f is given by: I i (f) = (0.85) R2 exp ( i fR/Q3 ) ( (5) 1 + (fo/f)j) O 4 Alternately, a(f) can be excressed in terms of source parameters is and r using equaticns (2) and (4): a (f) * (0.85) exP (-ifR/05) { l . ) (6) 1+( fo/f)2 The method used here to estimate peak acceleration a requires p calculation of the root-mean-square acceleration arms of shear waves. l Following Hanks (1979), and McGuire and Hanks (1930),we estimate arms using Parseval's theorem. The estimate is valid for a time window equal to the faulting duration Td beginning with tne direct shear arrival; in Hanks (1979) l is taken equal to f -I. In terms of spectral parameters as and r the a a resul' is 3/2 20r ' rms = (0.85)(27)2 a (7) a q u 106 2.34 wnere f ( (-2 f R) b u % *II-*XD (8) Q3 \\ ) Note, from ecuation (4), that r is proportional to M 1/3; thus the rms 3 acceleration is only very weakly deoendent on the earthquake size (arms is proportional to h l/6) but is directly proportional to stress drop. The o factor 2 accounts for limits on soectral amplitudes, and nence on arms' u resulting from tne maximum frequency f whicn can be recorded by the instrument u and maintained with accuracy by tne strong motion record filtering and proces-sing procedures. 35i.17.4 2 i
To estimate a from arms, a simale result is adopted from Vanmarcke and p Lai (1977), which assumes that ground acceleration time histories are stationary, random, and Gaussian in a time interval ~: 2 In (E) (9) = arms To is the where T is the " predominant ceriod of the eartncuake motion" and ap o peak acceleration which will be exceeded once, on the average, in time T. In and for T the reciprocal of f is used, that is, this study T is ecuated with Td o u the reciprocal of the highest frequency preserved in the processed strong motion recording. In contrast to ground motion studies made for longer source-to-site distances, the small distances examin'ed here imply that the highest frequencies in the (digitized version of the) strong motion record will be limited by instrument characteristics and processing procedures, rather than by anelastic attenuation or other physical phenomena. To calculate peak acceleration for a specified eartncuake magnitude, it is necessary to determine source parameters for the abcve model. (It is assumed here that magnitudes specified by ?!EC re local magnituces). Seismic moment can be determined using the relationship of Thatcher and Hanks (1973): log M = 1.5 t't + 16 (10, a where M is local magnitude. For static stress drop associated with L crustal earthquakes, the results of McGuire (1980) and Hanks and McGuire (1980), indicate that a value of 100 bars is appropriate to estimate a for the high frecuencies of interest. This has been shown to rms be the case for a large numcer of events in California, anc is adopted here c I for the R = 10 km event to be censidered in this study. Values for the otner earchcuakes are discussed belcw. With M and _; specified. the source a dimension r can be calculated from ecuation J. 361.17.4-5
E f For a: a value of 100 bars was assumed for earthquakes wnich occur at R = 10 km, since the source of these events could be as deep as 5 or 10 km, i.e. they cou'.d be similar to California shocks. For events at R = 3 and 1 km, which must necessarily occur at shallower depths than 5 km, it is reasonable to assume that the appropriate values of 10 are lower than 100 bars bacause lithostatic pressures at these shallower depths will be reduced. To determine an appropriate value of 1:, comparisons were made to the ML = 2.7 eartnquake which occurred in the vicinity of the site on August 27, 1978. A 2 of 121 cm/sec for a source-to-value of ?. = 25 bars gives estimates of ap site distance of 0.8 km. This comaares well with the digitized peak accelera-tions of 130 and 106 cm/sec2 (for the two horizontal components) and 40 cm/sec2 (for the vertical component). The specific parameters used for this calcula-tion are shown in Table 361.17.4-1. Note that, since the theory accounts for truncation in frequency content due to record digitization and processing, it is consistent only to compare theoretical estimates with peak accelerations obtai ned rom the digitized, processed record. The assumption of 0.5 km depth for this event is conservative, and a shallower depth would i: ply a closer source-to-site distance and a smaller value of ac. From this comparison we conclude tnat a value of 1: of 25 bars is appropriate for very shallow'eartnquakes (depths < 1 km). Therefore, this value is used below for estimating ap for events with R = 1 km. For source-to-site distances of 3 km, a value of : of 50 bars is tncught to be appropriate. This event is not specifit: to occur directly under the site at a death of 3 km, but may occur away from the site at a depth between 0 and 3 km, and presumably at a depth closer to 3km. The values of 1: assumed here are based on only one earthquake and on substantial judgment. 361.17.4-7 7 l l l
f However, they do form a preliminary basis for estimating ground motions at the small source-to-site distances requested by NRC. Estimates of peak acceleration for the six combinations of magnitude ) and distance requested by NRC are shown in Table 361.17.4-2, along with the parameters used to obtain these estimates. For one case, where R = 5.8km for aM = 5.3 event, the significant distance of 5.8 km was arrived at using a L horizontal distance of 3.9 km and a hypocentral depth of 5.0 km. The 3.0 km i horizontal distance was chosen as representing the closest " cluster" of events f (Cluster IV, Figure 361.14-1) of the five reported " clusters" surrounding the site, corresponding to a " mixed", more fractured, rock type unit in comparison J l to the less fractured granodiotite bedrock at the plant site. The focal depth of 5.0 km was chosen based on required physical constraints such as: 1) stress l drop; 2) lithostatic pressures;and 3) recent near-field observations of peak accelerations which suggest that, because of a lack of attenuation of strong ground motion in the range of 0 to 5 km from the fault trace, the energy-causing strong ground motion effectively is generated at depths of 5 km rather than at the surface. For several cases (indicated by parentheses) the distances involved are less than several source diameters (R < 4r) so that the estimates are actually made for near-field conditions where the theo,y is not strictly I applicable. In these cases the estimates are conservative. 1 B. RESPONSE SPECTRA ESTIMATES Response spectra were estimated based on a procedure developed by Newmark and Hall (1969) and later modified by Mohraz (1976) and Johnson and Traubenik (1978) to incorporate site conditions, and magnitude and distance respectively. l 361.17.4-8 4 .---r-
A general description of the procedure used by Johnson and Traubenik (1978) to obtain ground motion ratios and amplification factors is as follows: 2 1. Ground motion ratios, v/a and ad/v, for various percentiles using a normal and a log-normal distribution were calculated. 2. The selected response spectra were normalized to obtain amplifi-cation factors. The procedure is to obtain, at each frequency point, the ratio of the spectral response to the maximum ground l motion (i.e. amplification factor) for acceleration, velocity, and displacement in the corresponding frequency ranges. Averaged 361.17.4-8a
I l l l l banded and contain less long period energy than the Mt = 4.7 to 4.9 average i l spectrum, as should be expected. i To make comparisons with design spectra, these earthquake response spectra were scaled by the peak acceleration values shcwn in Table 361.17.4-2. l These scaled spectra are shcwn in the next section, along with OBE and SSE l spectra. l C. COMPARIS0N WITH SSE AND OBE SPECTRA For comparison of response spectra estimated for the hypothetical events and response spectra corresponding to the Safe Shutdown Earthquake (SSE) and Operating Basis Earthquake (0BE), we show here only spectra corresponding to 5% damping. Comparisons for other damoings would be similar, and the conclusions drawn here would be the same. Figure 361.17.4-4a shows the 55 damped response spectrum for the ML = 4, R = 1 km event, obtained by scaling the 55 damped spectrum in Figure f 361.17.a-3 to a peak ground acceleration of 0.309 Also shown are the SS: and OBE spectra for horizontal motion and 5" damoing. Figure 361.17.4-ab shews a similar comparison for this event (Mt = 4.0, R = 1 km) for vertical mo tions. It should be emphasized that the spectrum for the hypcthetical event is conservative because the peak acceleration estimate is conservative, as discussed previously. Figures 361.17.4-5 througn 361.17.4-9 show similar comparisons for the other hypothetical earthquakes: ML = 4 and R = 3 km (Figure 361.17.a-5), M, =a and R = 10 km (Figure 361.17.4-6),Mt = 5.3 and R = 1 km (Figure 361.17.a-7),Mt = 5.3 and R = 3 km (Figure 361.17.a-8), and M = 5.3 and t i i 361.17.4-10
i R = 10 km (Figure 361.17.4-9). Similar comments regarding conservatism apply to Figures 361.17.4-7 and 361.17.4-8, because a for these events are conser-p vatively estimated as noted in Table 361.17.4-2. Figure 361.17.4-10 is presented to show the comparison of a Magnitude 4.0 earthquake at R =3 km, and a Magnitude 5.3 earthquake at R =5.8km to the design OBE and SSE Spectra (where R is the significant distance from the focus of energy release to the plant site). The former event, a M =4.0 earthquake, represents the maximum L induced earthquake by Monticello Reservoir and has been discussed in detail in response to Questica 361.18. The latter event, a M =5.3 earthquake, has L been suggested by the NRC to be representative of the magnitude associated with an Modified Mercalli Intensity VII event (the SSE for the V. C. Summer i Plant). Even though the spectrum due to the M =4.0 and R=3.0 km event L exceeds the original OBE spectrum in certain frequency regions as snown in Figure 361.17.4-10, there is no adverse effect on the structure and equipment. This is due to the fact that a 2% structural damping value was used in the i original design and Regulatory Guide 1.61 allows 25 damping for prestressed concrete structures and 4?> damping for reinforced concrete structures. In the evaluation of the effect dt.e to the M =4.0 spectrum, 25 and 43 L composite damping values were used. The time history method was used to generate the structural responses and floor response spectra. Four norizontal components of two M = 4 aftershocks of the 1975 Oroville, California L 1 361.17.4-11 l 1
earthquake, recorded at rock sites, were modified to match the target spectrum of Fig. 361.17.4-10 in the mean. These four components were extended into 36 components by adjusting the time increment, which achieves the effect of shifting the frequency content of the accelerograms (Tsai,1969). The 36 components of time histories were used as input to generate statistically the floor response spectra. Comparisons of the original floor response spactra versus the newly generated mean value floor response spectra are shown in Figures 361.17.4-11 to 361.17.4-19. The original spectra essentially envelop the mean snectrum due to the M =4.0 event at all frequencies. t As seen on Figure 361.17.4-10, the spectrum for the M =5.3 earth-t quake at R=5.8km exceeds the SSE design spectrum. This exceedance is not surprising, considering the wide disparity between the method used to derive , the SSE design spectrum for an Intensity VII event, and the method used to ! estimate the response spectrum for the near-field, M =5.3 earthquake. Com-L parison of the two spectra is inconsistent with established practice in ' conformance with Regulatory Guide 1.60. Moreover, recent studies supported by the NRC suggest that the SSE for existing facilities is roughly equivalent to ground motion having a return period of 1000 years, and analyses conducted for the V. C. Summer plant show that the factor of safety is i three-to-ten times greater at the subject facility. The reason for the difference between the two spectra lies in the manner in which these spectra were derived. The SSE represents a Modified Mercalli intensity VII event (the 1913 Union County earthquake) occurring near the site. Following standard procedures, the acceleration for this event was estimated using data compiled by Trifunac and Brady. For intensity VII, these data represent, on average, the ground motion to be expected at 361.17.4-12
a distance of 40 to 50 km from a moderate earthquake (M = 6 to 6.5). The M =5.3, R=5.8km event, while also representing intensity VII ground motion, L contains substantially more high frequency content due to the close distance, and the spectra estimated here logically reflect this frequency content. At the other extreme, one could envision ground motion of intensity VII caused by a reoccurrence of the Charleston earthquake, some 220 km distant. This ground motion would contain significantly less high frequency energy, and more long period energy, than either of the motions considered here. Although hypothetical ground motions indicate larger peak accel-erations than that used for the SSE, the ultimate adequacy of the seismic design can be judghd by the probability c.' exceedance of the SSE. Studies undertaken here show that the SSE has a return period of between 3000 and 10,000 years, deperding on the assumptions used in the analysis (See Section 361.19). In comparison to other studies and facilities, this indicates an adequai:e seismic design for the Virgil C. Summer plart.
SUMMARY
The applicant has estimated peak accelerations and response spectra for two events of M =4.0 and 5.3. The first event represents the L largest earthquake which is capable of being induced by the reservoir. While this motion is rich in high frequency energy, there is no adverse effect on structures or equipment in the facility, based on comparison of floor response The larger event, (M =5.3) represents an earthquake which must spectra. L occur very close to the facility to cause ground motion exceeding the SSE level. Such ground motion will be rich in high frequencies; however, the probability of 361.17.4-12a i
} occurrence of such an event is very low, based on the results of probability j studies presented in Section 316.19, and in comparison to similar studies at ) other sites. Moreover, there is no evidence to suggest that the original design l basis for the subject facility should be changed. Therefore, the applicant concludes that the seismic design for the V. C. Sumer plant is adequate. i i i 5 i i 1, i i i I 1 4 1 J i 361.17.4-12b
l l l REFERENCES Brune, J.fl. (1970), " Tectonic stress and the spectra of seismic shear waves l from earthquakes", J_. Geophys. Res. 75, 1997-5009. Brune, J.fl. (1971). Correction, J. Geophys. Res. 76, 5002. l Hanks, T.C. (1979), "b-Values and f" Source Models: Implications for Tectonic Stress Variations along Crustal Fault Zones and the Estimation of High Fre-quency Strong Ground Motion", J_. Geophys. Res. l Hanks, T.C. and McGuire, R.K. (1980), "The Character of High Frequency Strong l Ground Motion," (in preparation). l Johnson, J. A. and Traubenik, fi.L. (1978),1 Magnitude-Dependent flear-Source l Ground Motion spectra", Proc. A.S.C.E. Conf., Earthquake Engineering and Soil Dynamics, Pasadena, June, p. 530-539. McGuire, R.K., and Hanks, T.C. (1980) "RMS-Accelerations and Spectral Amplitudes of Strong Ground Motion During the San Fernando, California Earthquake," l Bull. Seis. Soc. Am., 70, 5, Oct. l l Mohraz, B. (1976), "AStudy of Earthquake Response Spectra For Different Geological Conditions, " Bull. Seis. Soc. Am., v.66, flo. 3, June. Newmark, fi.M., and Hall, W.J., " Seismic Design Criteria for fluclear Reactor Facilities," Proc., 4th World Conf. on Earthquake Eng., Santiago, vol. 2
- p. 85-1-B5-12.
- Thatcher, Wayne, and Hanks, T.C. (1973), " Source Parameters of Southern California Earthquakes", Journal of Geophysical Research 78, 8547-8576.
Vanmarche, E.L., and Lai, S.P., " Strong Motion Duration of Earthquakes", M.I.T. Dept. of Civil Eng., Report R77-16, 32p. l McGuire, R.K. (1980), " Geophysical Estimates at Seismic Shear Wave Motion, j Prnc, 7th World Cont. on Earthquake Engineering, Istanbul, September Tsai, N. C.," Transformation of Time Areas of Accelerograms", Proceedings of ASCE, Engineering Mechanics Division, Vol. 95, fio. EM3, June 1969. i I l 361.17.4-13
TABLE 361.17.4-1 PARAMETERS USED FOR COMPARIS0tl TO AUGUST 27, 1973 EARTHQUAKE 2.7 Mt it 1.12X1020 dyne-cm o depth 0.5 km R 0.8 km 2 25 bars r 0.125 km f 9.5 hz c 0.105 sec Td Q 1000 1.69 ap/a rms as 72cm/sec2 r 2 a 121 cm/sec p Observed" ap (180 ccmp.) l 13'O cm/sec2 I l 0 Observed
- a7 ( 900 camp.)
106 cm/sec2 Observed
- ap (vert. ccm.)
40 cm/sec2 Os ?
- fron digitized, processed r; w>,
exclained in text. 361.17.'-10
TABLE 361.17.4-2 PEAK ACCELERATIO!i FOR SPECIFIED EVEtiTS, FOR HORIZ0tiTAL MOTI0liS* M 4.0 5.3 L i R, km 1 3 10 l1 3 5.8 10 depth, km 1 ~3 ~5 1 ~3 5 -5 ao, bars 25 50 103 25 50 100 100 23l 22 22 23 23 23 M, dyne-cm 10 10 1022 9x10 9x10 9x10 9x10 j g r, km 0.56 0.44 0.35 2.5 2.0 1.6 1.6 f, hz 2.1 2.7 3.4 0.47 0.60 0.75 0.75 { g T, sec O.47 0.37 0.29 2.1 1.7 1.3 1.3 d j Q 1000 1000 1000 1000 1000 1000 1000 i i a /a 2.4 2.3 2.2 3.0 2.9 2.8 2.8 p rms l (121) 2 70 35 (256) (150) (135) 75 ras,cm/sec 2 l_ p,cm/sec (293) 161 78 (763) (435) (378) 212 a Values in parentheses are calculated for distan<-a in near field (i.e., R < ;r) for which the theory is not strictly applicable; these values are therefore conservative. Peak acceleration for vertical motions ray be estimated a3 one-half the alues of the horizontal motions. 361.17.4-15
1000 + 1 ~ AESilM ATE FCA A:6.4km 500 \\ ESTIMATE FCR 9:3. ! km A + e a g p U 8* e w A ^}
- 8 T
A 8 o o + = o o ? + o x 100 w a w a 8 50
- e e
w 2- ~ e I I I I I I 10 3 4 5 6 7 8 M AGNITUDE(My oS ANT A B ARB AR A (! 978) .OTHER C ALIFORNI A EARTHQUAKES o COYOTE L AKE (197 9) AJAPAN + 1MPERI AL V ALLE Y (1979) EOTHERS FI GURE 361.17.k-2 PEAK HORIZONTAL ACCELERATIONS RECORDED AT SURFACE DISTANCES < 1 O KM, AND THEORETIC AL ESTIMATES 261.17.l-19
! 0. 0 0 [ t.5. 4 - 5. 6 M (5%) m O ( Nn Mt = 5.3 - p g ~ N H ~ d1.00 ~ Mt = 4. 7 - 4. 9 h (5%) s //8 \\ [ Mt =4. 0 5 O J W> W 2 H j0.10-W c: f I 7 O a h NOTE: SPECTR A SHOWN FOR I / ?.. M 5.AND 10 PERCENT CRITIC AL c. DAMPING 0.0I t'I O.01 0.10 I.00 10.C O UNDAMPED NATURAL PERIOD (SECONDS) 1 FicuPE 361.17.4-3 MEAN ROCK NEAR-SOURCE HORIZONTAL ELASTIC RESPONSE SPECTRA FOR A M AGNITUDE (M ) OF 5.3 AND 4.0 t ) 211.i7.l-20 1
i 10.0 _ 1 t L n 0 l W ca N H SSE D 1.0 >s CBE 5 O
- u w
2+ _aw Z o.ib a o w [ M =4.0 u CO I_ R=lkm c. I o.o i t O.O l 0.1 1.0 10.0' UNDAMPED NATURAL PERICD (SEC) FIGURE 361.17.k-ka HORIZCNTAL SPECTRUM FOR Mr =4.0, R = I km 1 i l 351.I7.;-21
't i i i J l O.0 i 4 ~ 1 4 O -ow m N H Ltv 1.0 4 H SSE 5 ~ O -I OBE w> W 2 J wc: Io 0.1
- a o
i w mc. Mu=4.0 R=1km i iriill f i i f f iri i n il i i i 0.01 i if O.01 0.1 I.O i U.0 UNDAMPED NATURAL PERIOD (SEC) FI GURE 361.17.4-4b VERTICAL SPECTRUM FOR M = 4.0, R = 1 km t 361.17.4-22
I o.c, L L L nOw en N '[ SSE
- 1. 0,-
w D CBE 5 o W w 2 _2w= O.1 o L w i OO l r M,=4,0 R=3km s 0.0 l o.' 1 O.O I 1.0 i CT.0 UNDAMPED NATURAL PERIOD (SEC) FIGURE 361.17.4-Sa HCRIZCNTAL SPECTRUM FOR M = 4.0, R = 3 km t 9 361.17.4-23
4 i e i i i 10 0 4 = + 1 f t m n O i w D a N Hb 1.0 4 H SSE 5 4 ~ i O J OBE i W l i W i N H 4 J W I (r. I 0.1 o a O ~ w CO C. l Mu=4.0 R=3km il 1 i i i iei e i il i e i ii 0.01 i i i O.0 I o.1 i.o i o,o UNDAMPED NATURAL PERIOD (SEC) FI GURE 361.17.4-56 VERTIC AL SPECTRUM FOR M = 4.0, R = 3 km t 361.17.a-24 =-
i o.0 4 g L i na w en N [ ssE 1.0 w [ C8E 5o Jw y 2+ a w c:: o 0I. n5 C w L cc I [ M =4,0 t g=1gkm 4 0.01 O.o I o.I i.0 t o.0 UNDAMPED NATURAL PERICD (SEC) FI GURE 361.17.4-6a HCRIZONTAL SPECTRUM FOR M =4.0, R = I O km t 361.17.2-25
l I 1 l O.0 \\ 1 i eow 1 m H I b 1.0 t-SSE o O -I OBE w w 2 E Jw (T. I 0.1 o
- o 3
w m a, Mu=4.0 R=10kn e i i t il i i i it iri i i e i il i i i 0.01 i O.01 0.1 I.0 i O.0 UNDAMPED NATURAL PERIOD (SEC) FI GURE 361.17.4-6b VERTICAL SPECTRUM FOR M =4.0, R = I O km t l 361.17.4-26 l
4 e i O.0, L LL m O W cn N* SSE u. 1.0 v i [ CSE o l M =5.3 s R =1 k:a W W 2 ~ W T. Io 0-l ~ 1 o L D L W L - l co i 4 I j g 0.0 i 0.01 0.] I.O I O~.0 : i UNDAMPED NATURAL PERIOD (SEC) I i 1 FIGURE 361.17.4-7a HORIZONTAL SPECTRUM FOR M = 5.3, R = 1 km t 1 261.17.J-27
N 1 i i i o.0 mOw m i N> 1 LL. I.0 w 4 s x g o .J l w w 2 M,=5.3 4 g j R=1km g w CC l 0l .o o 3 w m o, C,Q l t 1 f I If I t f f I ffI I I I l f fff f 0.01 0.1 1.0 10.0 UNDAMPED NATURAL PERIOD (SEC) I i FIGURE 361.17.4-7b i VERTIC AL SPECTRUM FOR M, =5. 3, R = l km i 361.17.4-28
10 0 g b L L L b uw N &b I.0 f C N 5 O h ~ h w 2 w ~ M =5.3, I d R 3km c: 0.1 a '(. o W / mc. I 0.01 O.01 0.1 1.0 10.01 UNDAMPED NATURAL PERICO (SEC) FI GU RE 361.17.4-aa HCRIZCNTAL SPECTRUM ICR M = 5.3, R = 3 km t i I 351.17. -29
10 0 8w m N >-D l.0 -5 S / y w Q f ~, aw W I e r n,.s.3 3 R=3km w ma. 'il ' I ri'f i ' ' i ll i 0.01 i 0.01 0.I 1.0 10 0 UNDAMPED NATURAL PERIOD (SEC) FIGURE 361.17.4-8b VERTICAL SPECTRUM FOR M = 5. 3, R = 3 km t 1 i l r 361.17.4-30
l00-. F C L L m C w cn N [ SSE 1.0 w f. CBE 5 o J W 2+ a W \\' y '4, = 5. 3, C O.I R =10km o C 3 W t. c7 i c. L o.0 i a O.O I O.1 (.0 l O'.O UNDAMPED NATURAL PERIOD (SEC) FIGURE 361.17.4-9a HORIZONTAL SPECTRUM FOR M =5.3, R = I O km t i 261.17.a-31 i i t
i a 4 E 10 0 ~ r 4 i e 'O W 4 cc i N H I b l.0 b SSE 4 o O l J 08E i W W / >P - / Jw cc t 'i, = 5. 3, 0.1 o ic Z R=lGkm 3 w con. O.01 t/ i e i i rl i i e ieiril e i e i ei1 i 0.0 I o.I o i g,o 1 U".0AMPED NATURAL PERIOD (SEC) FIGURE 361.17.4-9b VERTICAL SPECTRUM FOR M =5.3, R = I O km t. 361.17.4-32
t j i0.0 _ L L i 1 l_ b l C W co N u. i. e.- / x t _/ 0 C, b 4 ~W> M = 5.3 5g t W R= 5.8km ~ i Iw= I 017 Cc = L W f? I I % =1.0 l R=3km 0.C l O.o l o.1 1.0 I c.C UNDAMPED NATURAL PERICO (SEC) Figure 361.17.4-10 ? C0f1 PARIS 0N OF TARGET AND DESIGN SPECTRA FOR HORIZONTAL MOTION (55 DAMPING) 361.17.4-33
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AN EMPIRICAL APPROACH Severy et al (1975) examined the seismicity at 59 reserviors which were constructed in the Piedmont Province between 1891 and 1974. Of these,12 were noted to be associated with seismic activity. This list has been updated to include Lake Jocassee and Monticello Reservoir (Table 361.18-3 and Pigure 361.18-3). Although the depths of the reservoirs and their capa-city varied by as much as a factor of 10, no_ reservoir in the Piedmont was associated with an earthquake of MM intensity greater than VI. This record is complete and, although the years elapsed between the impoundment and the observation of seismicity vary widely, the largest reported intensity is Modified Mercalli VI. This observation sugaests that MM VI is the largest i l estimate of an induced earthquake in the Piedmont region. In the eastern U.S., which is characterized by low attenuation, an MM Intensity VI would t I be equivalent to a ML 4.0 earthquake. Thus, the largest induced earthquake based on empirical data covering about 90 years is ML ~4.0. All the observed induced seismicity at Monticello Reservoir in the first 2 years has been < 2 km deep and none of the events has exceeded a local magnit,ude of 3.0. Thus, it appears likely that an induced earthquake with M(4.0 would occur deeper, considering the attendant increase in required lithostatic pressures for stress drops appropriate for such an earthquake. It is our opinion that a focal depth greater than 3km is appropriate for aMt = 4.0 earthquake. A TECTONIC EARTHQUA.- The largest tectonic earthquane in the Piedmont is the RF* Intensity VIII event ( MM Intensity VII) that occurred on January 1, 1913, at Union County. The exact cause of its occurrence is not known, although it has
- Rossi-Forel Scale 361.18-5
been suggested (Talwani, 1980, Personal Comm.) that it may be associated with the King's Mountain belt - Charlotte belt contact. If it is assumed, however, that the Union County event was a random event, and could occur anywhere in the Piedmont (as has been done in Section 2.5.2.9 of the FSAR), then the largest event that could occur near the Monticello Reservoir is MM Intensity VII. From the nature and extent of the isoseismals of the Union County event, its depth has to be at least ~5 km.
SUMMARY
From the empirical analysis which is based on all existing data, the largest induced earthquake is estimated to be 'ML 4.0 with a depth of at least 3 km. The largest tectonic earthquake is estimated at MM Intensity VII (or ~ML 5.3 for eastern U.S.) with a depth of at least 5 km. The return period for such an event is 4500 years, in keeping with expected annual probabilities of i { exceedance for an event such as the SSE (Discussed in detail in response i i to Question 361.19). REFERENCE
- Aki, K., (1965) Maximum likelihood estimate of b in the formula log N =
a + bm and its confidence limits. Bull. Earthq. Res. Inst. Vol. 43_,
- p. 237-239.
Gupta, H. K., and B. K. Rastogi, (1976), Dams and Earthquakes, Elsevier, Amsterdam, 229 pp. Gutenberg, B. and C. F. Richter (1944), Frequency of Earthquakes in California, Bull. Seis. Soc. Am., 34, 185-188. Severy, N. I., G. A. Bollinger, and H. W. Bohannon, Jr., (1975), A Seismic Comparison of Lake Anna and other Piedmont Reservoirs in the Eastern U.S.A., 1st Internat. Symposium on Induced Seismicity, Banff, Alberta, Canada, Sept. 15-19, 1975.
- Utsu, T., (1965), A method for determining the value of b in a formula log N = a - b M showing the magnitude-frequency relation for with English Summary).
-13, 99-103 (In Japanese earthquakes. Geophys. Bull'. Hokkaido Univ. 361.18-6 .}}