ML19309H187
| ML19309H187 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/30/1980 |
| From: | Will Smith DAMES & MOORE |
| To: | |
| Shared Package | |
| ML19309H184 | List: |
| References | |
| 5182-068-09, 5182-68-9, NUDOCS 8005090314 | |
| Download: ML19309H187 (30) | |
Text
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l FINAL REPORT -f SIGNIFICANCE OF THE MONTICELLO RESERVOIR EARTHQUAKE OF AUGUST 27, 1978 TO THE VIRGIL C. SUMMER NUCLEAR STATION I FOR SOUTH CAROLINA ELECTRIC & GAS COMPANY I
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7j , g, ; __ 2 April 30, 1980 South Carolina Electric & Gas Company Post Office Box 764 Columbia, South Carolina 29218 Attention: Mr. Mark B. Whitaker ,
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, Gentlemen:
Re: Monticello Reservoir Earthquake of August 27, 1978 We are pleased to transmit herewith 30 copies of our report entitled
" Significance of the Monticello Reservoir Earthquake of August 27, 1978 to the Virgil C. Summer Nuclear Station for South Caro 1.ina Electric & Gas Com-pany".
This report provides analyses, discussions, and conclusions pertaining to the ground motion felt at the Virgil C. Summer Nuclear Station site due to the earthquake which occurred near the Monticello Resereoir dam on August 27, 1978. The report evaluates pertinent response spectra data for the August 27, 1978 event which were derived previously for a comparison to NRC Regulatory Guide 1.60 Operating Basis Earthquake (OBE) spectra. Withir this report, response spectra for the August 27, 1978 event are compared to the nuclear station OBE design spectra, and attenuation of the ground inotion due to four inherent physical phenomena is analyzed and the resultant prob-able ground motions at the nuclear station are presented.
The scope of the analyses performed, as presented in this report, was defined through discussions that included participation by Mr. Mark B.
Whitaker and Mr. Bob Whorton of South Carolina Electric & Gas Company, Dr.
Robert Pyke of Civil Systems, Inc., and Dr. Neville C. Donovan, Mr. James G. l McWhortar, and Mr. William G. Smith of Dames & Moore. l l
DAMES 3 tVIO O R C South Carolina Electric & Cas Company April 30, 1980 Page 2 Should any additional information be required, or should any questions arise pertaining to this report, please do not hesitate to contact us at your convenience.
Yours very truly, DAMES & MOORE fY' , .
William G. Smith Project Manager j WGS:tjr l
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Enclosures
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6 c TABLE OF CONTENTS
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i 1.0 GENERAL AND BACKGROUND...................................... I e
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2.0 INTRODUCTION
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- 3.0 ESTIMATES OF PROBABLE DIFFERENCE IN MOTION WHICH OCCURRED AT THE 5:M AND THE PLANT SITE.................................. 5
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3.1 At tenua tion By Geome tric Spreading. . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Attenuation By Material Damping............................. 6 3.3 Effects Of Alteration Of Motion Due To The Finite Size Of The Plant Foundation........................................ 8 3.4 Ef fect o f Dif ferent Site Conditions . . . . . . . . . . . . . . . . . . . . . . . . 9 4.0 DISCUSSION.................................................. 10
5.0 CONCLUSION
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LIST OF FIGURES L
I TITLE FIGURE NO.
L Location Map..................................................... 1 F
L Logarithmic Decrement Values Observed in Different Types of Rock.......................................................... 2 I
Combined Attenuation of Geometric bpreading and Material Damp i ng E f f e c t s ( 180
- Com pone n t ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 p Combined Attenuation of Geometric Spreading and Material L Damping Effects (90* Component).................................. 4 y Combined Attenuation of Geometric Spreading and Mr.terial L Damping Effects (Vertical Component)............................. 5 Combined Attenuation of Geometric Spreading, Material Dam ing,
{ and Tau Filtering Effects (180* Component)....................... 6 Combined Attenuation of Geometric Spreading, Material Damping, and Tau Filtering Effects (90* Component)........................ 7 Combined Attenuation of Geometric Spreading, Material Damping, and Tau Filtering Effects (Vertical Component)................... 8
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L 1.0 GENERAL AND BACKGROUND
[ The Virgil C. Summer Nuclear Station, located near Parr, South L
Carolina, is part of an electrical generating complex which includes the hy-dro capacities of the Fairfield Pumped Storage Facility (including Monti-L cello Reservoir) and the Parr Reservoir / Dam. Following the filling of Mont-icello Reservoir during the winter of 1978, numerous low magnitude earth-quakes occurred which have generally been attributed to the filling and pre-sence of the filled reservoir. These events have been documented by the Ap-plicant's four-atation microearthquake network and USGS seismograph sta-
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tions. The data acquired and analyses performed have been submitted to the Nuclear Regulatory Commission (NRC) as quarterly reports since the filling
{ of the renervoir. The microearthquake monitoring system is described in Section 2.5.2.6 of the Final Safety Analysis Report (FSAR) for the Virgil C.
Summer Nuclear Station.
While some documentation exists addressing seismic effects due to re-servoir filling, it is a relatively new phenomenon and is not well under-stood. The occurrence of induced seismicity in other reservoirs in South Carolina and the eastern United States suggested that low magnitude earth-quakes could be expected, and the aforementioned monitoring system was h therefore installed prior to filling Monticello Reservoir. A few of the re-corded events were strong enough to trigger a USGS strong motion instrument
{ in the vicinity of Monticello Dam. The strongest of these, an event of mag-nitude 2.7 (local magnitude), occurred on August 27, 1978. Unfortunately, the installation of strong motion instrumentation within the Virgil C.
Sumeier Nuclear Station had not been completed when this event occurred. The nearest recording instrument, a USGS strong motion accelerograph (SMA), was remotely located northwest of the nuclear station at a distance of well over 3/4 mile. The SMA was not located at the plant site, and was situated on a h significant thickness of saprolitic soil. The nuclear plant has a bedrock foundation, but data recorded by the SMA is the only data available and has therefore been used as a basis for evaluating the motion felt at the nuclear
{ station site. These data show, af ter digitization, that the maximum ground
[ DAMES E MOOR 4C
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[ acceleration felt at the site of the SMA occurred as a 0.25g peak for the L
180* component. Lesser peak accelerations of 0.20g and 0.08g were recorded p for the 90' component and the vertical component respectively. A bracketed duration of about 0.06 seconds was indicated for ground motion greater than 0.lg for the 180' component (USGS, 1979).
Following a meeting between the Applicant and the NRC on June 22, 1979, which addressed the induced seismicity at Monticello Reservoir, the NRC in-formally requested that the Applicant utilize data acquired from the remote-ly located SMA to compute response spectra of the August 27, 1978 event, and compare the computed event spectra to the NRC OBE response spectra. This comparison was performed, as requested, recognizing that the computed event
{ spectra was relevant to a remotely located and soil-based instrument and, as such, did not constitute a pertinent basis for direct comparison. A report of the comparison and relevant data was submitted to the NRC on November 2,
{ 1979. Digitization of the original analog records of the event was perform-ed by the Seismic Engineering Branch of the USGS. The comparison indicated
[ that spectra of ground motion felt at the SMA site lies above the NRC OBE response spectra in the 25 hertz range. The NRC Regulatory Guide 1.60 spec-
[ tra were used for the comparison as requested, although the Virgil C. Summer Nuclear Station is designed to modified Newmark and Blume response spectra
{ which are similar but not identical to that suggested in Regulatory Guide 1.60. The spectral comparison included the opinion that ground motion felt by the nuclear station effectively did not exceed the plant design OBE due
{ to the short duration and high frequency of the event. Consideration of the inherent physical ef fects of the di tant plant location, geometrie attenua-tion, material damping, and alteration of motion due to the finite size of the plant were neither requested nor provided in the earlier spectral com-parison report.
During an orientation meeting on February 21, 1980 for Los Alamos Scientific Labore.?ory personnel which also included NRC staff members and the Applicant, it was requested that a realistic and conservative analysis
( of the probable ground motion at the nuclear station due to the August 27,
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DAMES B MOOETC
L 1978 event be performed. Pertinent analyses have been completed and are in-
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cluded in this report.
[ Prior to implementation of the analyses, the scope of work that was de-rived to evaluate the motion felt at the nuclear station site relative to the design OBE was reviewed and approved by an independent consultant, Dr.
Robert Pyke of Civil Systems, Inc. Upon completion of the analyses and formulation of this report, Dr. Pyke thoroughly reviewed the analytical pro-cedures utilized, results obtained, and conclusions. Dr. Pyke concurs with the findings of this report and the supporting information presented as stipulated in his letter of April 16, 1980. This letter is included with this report as an attachment.
2.0 INTRODUCT.ON This report presents a thorough discussion of a prograu of studies de-veloped to demonstrate the probable level of motion felt at the nucle r plant site during the August 27, 1978 event.
The locations of the epicenter of the event, the SMA, the plant, and other facilities are shown on the Location Map, Figure 1. The location Map shows that the surface distance from the nuclear station to the computed lo-cation of the epicenter for the August 27, 1978 event is approximately 6465
[ feet. The distance from the nuclear station to the SMA is approximately 4400 feet, and the distance from the SMA to the epicenter is about 2120 feet. As shown on the Location Map, the locations of the plant, SMA, and
{ epicenter almost fall on a line defined by the ground surface and a vertical plane, except that the SMA lies very slightly southwest of the line passing through the epicenter and the plant.
Analysis of the data acquired by the SMA indicated that the maximum peak acceleration occurritd for the 180' component. Response spectra for the event have been computed using the records as digitized at a time-step of 0.01 seconds anu corrected by the Seismic Engineering Branch of the USGS.
Frequencies up to 50 hertz are included in the digitized records. Use of an h even shorter time-step would, of course, lif t the zero period accelerations of the computed spectra so that they would more closely approximate the peak
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l l accelerations of the analog records; however, the peak acceleration is con-sidered to be of little or no practical significance because the frequencies of interest are included in the digitized records, and it is generally ac-cepted that the motion characteristics that are of importance to engineered structures and equipment are adequately represented.
Subsequent to the provision of the aforementioned spectral comparison, there have been two significant developments:
(1) The focal depth as reported by Talwani (personal communication, 1980) is now computed to be between 100 and 500 meters. Original-ly, the focal depth was determined to be about 1.5 kilometers, but I later additional instrumental records permitted a more precise -
evaluation. The most conservative value, that of 500 meters which leads to the least attenuation of motion from the SMA recording site to the plant site, has been used in the calculations provided in this report unless otherwise noted. As the August 27 event was small (Mt - 2.7), for analytical purposes it may be considered as a point source. The hypocentral distances of concern are therefore 2680 feet and 6670 feet to the SMA and plant site, re-spectively.
(2) At the time that the original spectral comparison was performed, precise information pertaining to the thickness of soil underlying I the SMA was not available. Bedrock was thought to occur at a depth of approximately 10 feet. Recently, a boring has been com-I pleted adjacent to the SMA which shows that the instrument actual-ly rests on 56 feet of soil.
The various analyses which have been performed and which are described in this report show that significant attenuation of the recorded motions oc-curs when considering the distant location and bedrock foundation cd the nu-clear station. Four pertinent and separate phenomena have been addressed.
Initially, the attenuation due to each phenomenon is discussed separately.
In the final section of the report (5.0 Conclusions) the cumulative effects of the various types of attenuation are discussed, and figures are presented I on=csamoonc
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L which show the resulting attenuated response spectra for each component of motion compared to the plant design OBE response spectrum.
3.0 ESTIMATES OF THE PROBABLE DIFFERENCES IN MOTION WHICH OCCURRED AT THE SMA AND THE PIANT SITE There are four separate effects which could result in differences of j motion at the two sites. These are:
(1) attenuation by geometric spreading (2) attenuation by material damping (3) alteration of motion due to the finite size of the plant founda-tion (4) different site conditions The following paragraphs describe the methodology used and the results ob-tained in addressing the four possible ef fects. During the study, two val-ues were used for the key parameters included in the analysis; a probable or best estimate which reflects overall experience and engineering judgment,
[ and a very conservative estimate that has been provided for comparative pur-poses although reflecting an unlikely or improbable value.
3.1 Attenuation By Effects Of Geometric Spreading As wave motion propagates outwards from a source the surface area that the motion is passing through at any one instant of time is continually in-creasing. As the energy of the motion cannot increase the energy transmit-ted per unit of surface area must continually decrease. The result of this attenuation by geometric spreading in a perfectly elastic medium would be a
{ uniform reduction of the motion at all frequencies. The extent of the re-duction depends upon the assumptions made for the surface over which the mo-tion is spreading. In a purely elastic medium the spreading would te over a hemispherical surface and the reduction in amplitude would be in proportion to the square of the hypocentral distance.
E Because there is a non-uniform soil and rock profile in the vicinity of the plant site it is possible that much of the energy may be transmitted within the shallower soils and bedrock layers. If all the energy were DELMES U MOO 5tE
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[ transferred in this way in an elastic medium the reduction in amplitude would be in proportion to the epicentral distance.
Although the true form of geometric spreading is not known, the two as-sumptions discussed in the previous two paragraphs represent the physical l
{ bounds within which geometrical spreading is expected to reduce the ground motion amplitude. Focusing of energy by constructive refraction and re-flection is considered to be unlikely in this case because of the limited size of the source and the relatively gentle topography. The amplitude ra-tio, considering geometric spreading, for the motions at the SMA and plant sites should therefore be between the values of 0.16 and 0.33 for spherical and surface spreading respectively. Observational data from strong motion data (Donovan,1973) suggest a rate between these two limits, or an exponen-tial factor of 1.4 as a reasonable choice. If this value is used the ampli-
[ tude ratio would be 0.28, which reduces the motion occurring at the plant site to a level below tha design OBE spectrum at all frequencies of signifi-cance.
3.2 Attenuation By Material Damping Material damping in soils and rock is well recognized as being hyster-etic, i.e. independent of frequency. Thus the damping of different frequen-
{ cies becomes highly dependent on distance. This situation occurs because a uniform amount of damping occurs for each wavelength of the motion, and a high frequency wave travelling a set distance m at traverse more wavelengths than a low frequency wave.
{ The term by which damping is most easily expressed so that the reduc-tion in succeeding amplitudes of waves can be related to material properties is the logarithmic decrement. The logacithmic decrement A is defined ao:
X a = In (1) p o L where xo and xi are the amplitudes of successive waves. The logarithmic decrement can be related to the critical damping ratio (C) by the simple re-
{ 1ationship a = 2n( (2)
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l To consider the possible damping of individual frequencies between the SMA and the plant site, the logarithm of the ratios of the amplitudes at the l two locations is a function of the distance such that A" = 2nE f (3) where D is the distance of 4400 feet between the two stations, V is the es-timated mean shear wave velocity for the upper 500 meters of rock and the soil cover, and f is the wave frequency in hertz.
The value of the critical damping ratio considered for this demonstra-tion of the possible effect of material damping was 0.25 percent or a loga-rithmic decrement of 0.02. Data showing the logarithmic decrement in a wide range of rock types presented by White and reproduced here as Figure 2, show values ranging between 0.004 and 0.15.
It is believed that a value of 0.02 is an appropriate value of the log-arithmic decrement for this site. In addition, results for a conservative value of 0.01 have been computed to illustrate the sensitivity of the choice of this parameter. The average shear wave velocity of the upper 500 meters I of rock and soil was assumed to be 10,500 feet /sec. While there is evidence from geophysical data that this value is on the high side, its use has been retained as it can be seen from equation (3) that the higher velocity as-sumption results in a lower (more conservative) rate of attenuation with distance. Using these values in equation (3) gives values for A" of 0.0066f and 0.0033f, respectively. The amplitude for each frequency at the plant site can then be approximated by the relationship Ap = (1-A") ASMA (4)
Using fast-Fourier transform techniques it is possible to convolute the relationship in equation (4) with the Fourier transform of the SMA strong motion records and obtain a computed damped acceleration record at the plant site. These computations show that the ground motions which occurred at the plant site were significantly attenuated relative to the SMA record. As noted previously, there is some uncertainty in the focal depth of the I
August 27, 1978 event and this leads to a possible variation in the ray length between the focus and the recording and plant sites. However, onmouomoonn
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computation of the effects of material damping assuming focal depths of 100 meters and 500 meters shows that the use of the 500 meter focal depth, as
[ used in other calculations throughout this report, is the more conservative value and that the difference is in any case small.
[ 3.3 Effects Of Alteration Of Motion Due To The Finite Size Of The Plant Foundation (Tau Effect)
Newmark, et al., (1977) and Hall, et al., (1978) have shown by means of simple plane wave theory and by examination of the strong motion records re-corded at the Hollywood Storage Building that the finite size of a building foundation can reduce the translational response of the structure, particu- l larly in the region of high frequencies. Although, by use of the same argu-ments some torsional response may be introduced into the structure, conven-tional design practices are normally sufficient to account for this (Whit- l
[ ley, et al., 1977). Newmark, et al. , demonstrated a numerical procedure that gave good correlation between the computed and observed building re-
{ sponse. This procedure used a time-average acceleration over an assumed transit time, and has commonly been referred to as the tau iffect. The method takes a transit time T, chosen for convenience as one or more digi-tized time steps of the record, and moves the interval along the accelera-tion time history in the time domain. For any positioning of the interval T the average interval acceleration is obtained by dividing the difference in velocities at the start and end of the interval by the interval duration.
[ Therefore, E = f [5 (t + T) - p (t)] (5)
[ where S is the averaged acceleration and p is the computed velocity obtained from the measured acceleration record.
To correctly estimate the effect of the plant foundation size on the motion requires evaluation of the likely transit time for the ground motion.
The computations for this evaluation utilize the dimensions for the contain-ment structure. The structural concrete mat containment foundation has a
[ diameter of 154 feet and is located at elevation +396 feet. The foundation mat bears on a lean concrete fill which in turn bears on competent rock.
DAM E*L 8 MOO 51E
The rock surface is at an average elevation of +359 feet and the present ground surface elevation is +435 feet. The transit time is a function of both the foundation size and the average shear wave velocity. Shear wave data for the local materials were presented in Table 2.5-26 of the FSAR.
These data are summarized in Table 1.
TABLE 1 MATERIAL TYPE SHEAR WAVE VELOCITY (ft/sec) intact rock 7650-8000 decomposed rock 1550-2300 saprolite 860-1100 The depth of influence for shear waves affecting the reactor will be primarily influenced by the shallow soils to a depth approximately equal to l the foundation diameter.
If the higher values listed in Table 1 are averaged arithmetically to a l depth equal to one foundation diameter below the present ground surface, an average velocity of 5888 feet /sec is obtained. It is recognized that the effective shear velocity is only roughly approximated by the arithmetic average and may be more heavily influenced by the surficial materials. As such, the arithmetic average is a conservative estimate. The transit time for the motion across the containment structure foundation using the average iI velocity would be 154/5888 or 0.03 seconds. The average velocity based on both the maximum and minimum measured values suggests transit times of C.03 seconds so this value was used for both the assumptions of a most probable l value and for a conservative value. Comparing the response spectra of the transit averaged acceleration record and the directly processed acceleration I
record shows that the general spectral shape is similar, but high frequency perturbations are not transmitted. Therefore, the ground motions transmit-l ted to the plant are atte. 2ated.
3.4 Effect Of Different Site Conditions The effect of the different site conditions at the recording (SMA) and plant sites is not as amenable to quantitative analysis as the three effects I
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l discussed previously. The site conditions do differ considerably since the
- ski is located on the shared abutment of Dams B and C, which is underlain by 56 feet of soil over rock, and the embedded foundation of the containment structure bears on a lean concrete fill and then competent intact rock. De-convolution procedures which are sometimes used to infer motions at depth from surface motions are not applicable in this case, as they produce arti-ficial motions at depth which are only valid when used in an overall analy-sis procedure in which the control motion is subsequently recovered at the surface. Therefore, one must rely on inferences from more general analyti-cal studies of the variation of motions with depth and soil conditions and on empirical observations. These studies and observations have sometimes appeared to be contradictory. Many geophysicists believe that the ef fect of a soil deposit is always to amplify surface motions relative to those at depth or those on rock sites. Geotechnical engineers tend to emphasize the attenuation of peak accelerations and high frequency motions in general that can occur on soil sites due to the nonlinear behavior of soils. In this case, however, it is probable that the soil at the recording site responded linearly to the earthquake motions because of the high frequency content of the record. In such a case amplification of the motion probably occurred.
Therefore it is likely that, in addition to the attenuation of motions from the recording site to the plant site due to the three effects discussed pre-viously, the motion at the foundation level of the plant would have also been relatively lower because of the amplification at the recording site.
4.0 DISCUSSION In previous sections of this report each of the four phenomena which I have been studied were presented with minimum comment pertaining to the re-sulting effects. The four phenomena are entirely independent, and do not relate to or interface with one another in any way. Each of the results ob-tained has been derived using a range of values representing what is be-l lieved to be the most appropriate or probable value and a conservative I
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I estimate of the same parameter. In this way the effect of each phenomenon was examined separately to assure that none was unreasonably exaggerated.
The most straightforward form of attenuation is due to geometric damp-ing. Only if nearly all the seismic energy were radiating in near surface materials (a highly improbable event, but assumed for the conservative val-ue) would the geometric spreading between the SMA site and the plant site alone be insufficient to reduce the ground motion and the response spectrum to less than the design OBE at a frequency ranges. For example, for the 180* component the conservative computation provides an approximate 1.04 inch /sec reduction of the 20 hertz response spectrum value to 0.51 inches /
sec. Utilizing more probable values results in an approximate 1.30 inch /sec reduction of the 20 hertz spectrum to 0.25 inches /sec.
In earlier sections of this report it has been described how both mate-rial damping and the tau ef fect, resulting from the finite size of the plant foundation, are most effective in damping the high frequency motions. Indi-I vidually each of these effects produces substantial reduction of the esti-mated response at the ' reactor foundation, but will not alone reduce the re-sponse spectrum to less than the OBE value in the 20 hertz range. The esti-mated effect of material damping using a logarithmic decrement of 0.02 (for the 180' component) is an approximate 1.11 inch /sec reduction of the 20 hertz response spectrum value to 0.44 inches /sec. The tau effect will re-duce the motion below the OBE if the transit time is almost 0.05 seconde.
For example, for the 180' component a transit time of 0.05 seconds results in an approximate 1.37 inch /sec reduction of the 20 hertz response spectrum I
value to 0.18 inches /sec. A transit time of 0.03 seconds provides an ap-proximate 0.86 inch /sec reduction of the 20 hertz spectrum to 0.69 inches /
A realistic estimate of the motion that occurred at the plant site must consider the combined effects of each attenuation phenomenon. The analyses performed have included the combining of the attenuation effects, and the results are presented in the following Conclusions section of this report.
The numerical procedure for combining the effects involved first modifying l the SMA recorded motion for material damping, then reducing the resulting l
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I motion to account for the tau effect, and finally scaling all frequencies by l
the appropriate geometric spreading reduction factor. The results of the combined attenuation phenomena are presented on figures which show attenu-ated responae spectra for motion occurring at the plant site compared to the I OBE response spectrum. All spectra are presented at 2% damping since this level minimizes oscillations while preserving the general spectral shape.
5.0 CONCLUSION
S It has been shown in this report that attenuation of the earthquake re-I duced the level of ground motion experienced at the plant site below the value recorded by the SMA. Combining the various attenuation phenomena ex-I amined provides a realistic indication of the level of ground motion most likely experienced at the plant site.
The reduction in motion caused by the first two phenomena examined, i.e. , geometric spreading and material damping, is a function of the seismic wave transmission characteristics of the subsurface materials through which the seismic energy passes. Consequently, the combined effects of both phe-nomena provide a highly probable estimate of the minimum range of attenuated ground motion that occurred at the plant site. Figures 3, 4, and 5 demon-strate the combined effects of geometric spreading and material damping for the three components of motion, and show the level of motion at the plant site to be well within the limits of the OBE spectr %. Uncertainty in the I analysis is accommodated by assigning both " conservative" and "most likely or probable" values for parameters affecting computation of the attenuated spectra.
The tau effect, caused by the finite size of the plant foundations on the impinging vibratory ground motion, produced additional attenuation of the ground motion. The result of the tau filtering of the high frequency motion is further reduction of the overall level of motion experienced by the plant site structures. Figures 6, 7, and 8 demonstrate this further re-duction of motion by showing the combined effects of geometric spreading, material damping, and tau filtering for the three components.
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{ Additionally, amplification of the motion recorded by the SMA during the August 27, 1978 event due to the overburden soila effectively decreases further the motions shown on Figures 3 through 8 for the bedrock situated foundations at the plant site. It is our opinion that the ranges of motions presented on Figures 6, 7, and 8 are conservutive, and the motion that actu-ally occurred at the plant site would most probably fall within or below the ranges shown.
It can be readily seen on Figures 3 through 8 that each of the attenu-ated response spectra falls significantly below the planc design OBb spec-tra. All analyses and discussions presented herein support entirely a con-clusion that the ground motion produced at the Virgil C. Summer Nuclear Sta-
[ tion as a result of the August 27, 1978 earthquake was considerably less than the stipulated OBE response spectra at all frequencies 01 significance to the design of the structures and appurtenant equipment.
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I BIBLIOGRAPHY Donovan, N.C., 1973. A Statistical Evaluation of Strong Motion Data, l Including the Feb. 9,1971 San Fernando Earthquake. Proceedings of the I Fif th World Conference on Earthquake Engineering, Rome, Italy, June, pp. 1252-1261.
Hall, W.J. , Morgan, J.R. , and Newmark, N.M. , 1978. Travelling Seismic Waves I and Structural Response. Proceedings of the Second International Conference on Microzonation, Vol. 3, San Francisco, November, pp.
1235-1246.
Newmark, N.M., Hall, W.J., Morgan, J.R., 1977. Comparison of Building Response and Free Field Motion in Earthquakes. Proceedings of the Sixth World Conference on Earthquake Engineering, Vol. 2, New Delhi, I India, pp. 972-977.
White, J.E., 1965. Seismic Waves. McGraw-Hill.
Whitley, J.R., Morgan, J.R., Hall, W.J., and Newmark, N.M., 1977. Base Response Arising From Free-Field Motions. Trans. Fourth International I Conference on Structural Mechanics in Reactor Technology, Vol. K(a),
San Francisco, August.
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4 COMPUTED LOCATION OF EPICENTER OF O.25 g South Carolino Electric & Gas Co.
Virgil C. Summer Nuclear Station EVENT OF AUGUST 27, 1978 I O LOCATION OF STRONG MOTION ACCELEROGRAPH Figure 1
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Reference:
Seismic Waves by J.E. White.
McGraw-Hill,1965. Logarithmic Decrement Values I Observed in Different Types of Rock Figure 2 l
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E 5
I ROfl[Ri PYKL Geotec hnical Consultant d
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Cisil Systems Inc.
2450 Washington Avenue San Leandro California 94377 413/8 % % 10 April 16, 1980 Mr. William G. Smith Dames & Moore 455 East Paces Ferry Road, Suite 200 Atlanta, GA 30305 RE: Review of Attenuation Analyses i and Response Spectral Comparisons Regarding the Significance of the Monticello Reservoir Earthquake of i August 27, 1978, to the V. C. Summer Nuclear Station
Dear Mr. Smith:
I have reviewed the draft report dated April, 1980 that has been prepared by Dames & Moore on the above subject and 1 concur with its scope and conclusions. In addition to the fact that the high frequency and short duration of the motions generated by this earthquake would in any case be unlikely to cause damage to the nuclear station, it is beyond reasonable doubt that the motion felt at the site of the nuclear station could not have exceeded the OBE spectrum at any point.
Sincerely, 1 , ,
OW N (b
%l LL ROBERT PYKE j RP/bsb I
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