ML20004D650

Draft Rept, Recurrence Frequency of Obe

ML20004D650
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Site:	Fermi
Issue date:	06/05/1981
From:	WESTON GEOPHYSICAL CORP.
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{{#Wiki_filter:- O RECURRENCE FREQUENCY OF THE OPERATING BASIS EARTHQUAKE l AT THE ENRICO FERMI-2 NUCLEAR PLANT SITE I DRAFT REPORT Prepare.1 for DETROIT EDISON I by WESTON GEOPHYSICAL CORPORATION June 1981 -P.if Weston GeophyCORPORATION sical THIS DOCUMENT CONTAINS POOR QUAllTY PAGES 6106 0 9 0 Gib i

1 TABLE OF CONTENTS Page LIST OF FIGURES i

1.0 INTRODUCTION

1 2.0 ATTENTUATION MODELS 1 3.0 GROUND MOTION RESULTS 3 I

4.0 CONCLUSION

4 TABLE' FIGURES / e G 9 i I J I M d 4 e, --.n,- ,,--_----_,.,..-w...,,,,..,,

1 LIST OF FIGURES i 1 Figure 1 Modified Mercalli Intensity Figure 2 Sustained Acceleration (g) Figure 3 Sustained Velocity (cm/sec) Figure 4 Peak Acceleration (g) Figure 5 Peak Velocity (cm/sec) 3 d e 5 i Weston Geophysical -ev y 4 r--,yer ,yy_tr-t=-M-* w r-*--w-m+- - - O e-V-e --e--&-r-,mw*,3-*- e.-wy w-w ,wp-m.,-m,,yy., - ,,,vg,, v1my,-,wwy ,wy,, ,y. w-, ,,gy,

RECURRENCE FREQUENCY OF THE OPERATING BASIS EARTHOUI E AT THE ENRICO FERM't-2 NUCLEAR PLANT SITE

1.0 INTRODUCTION

The Operating Basis Earthquake (OBE) for the Enrico Fermi Power Plant, Unit 2, is characterized as a horizontal ground surface (rock foundation) acceleration of 0.08g (EF-2 FSAR, Amendment 3, June,197 6). The frequency of occurrence of the OBE was estimated by interpreting the historical levels of seismic loading at the site resulting from earthquake activity known for the Central U.S. region. This procedure is not considered to be a formal probabilistic seismic hazard assessment, since hypothetical activity is not considered. However, this historical analysis does yield useful results for the reccurrence frequency of low amplitude ground motion. 2.0 ATTENUATION MODELS The foundation material at the EF-2 site is rock (Paleozoic dolomit e). The observation at near epicentral distances is that seismic in' tensities are lower by one or more intensity units (MM scale) at localities situated on rock or sound foundation materials than at adjacent localities underlain by alluvial materials. On th e othe r hand, it is also observed that peak nround motion parameters can be larger on firm foundation materials than on sof ter materials for the same seismic intensity. To account for these observations, attenuation models are developed using the following assumptions; first, seismic intensity attenuation on rock is ( weston Geophysical

characterized by a median valuer second, the ground motion for that intensity is characterized as the median to median +1 standard deviation values. Equation 1 is the form of the intensity attenuation model that predicts the median intensity at a distance (R in km) from l an earthquake with size defined by m -magnitude. b I (R) = 2.53 + 1.20 m - 0.0027R - 1.94 Log R (1) b Ground motion parameters are determined from che site intensity by using the correlations of Nuttli (1979) and McGuire (1977). Equations (2) and (3) are relations of sustained (3 cycle) acceleration and velocity determined from the data presented by Nuttli (1979). Log As = 0. 3 2 6 +. 214 IMM (2) o Log As = 0.3 2 I l Log Vs = -1.210 +.289 IMM (3) U = 0.36 Log vs Equations (4) and (5) are correlations of peak acceleration and velocity to intensity observed on firm foundation materials (McGuire,1977). Log Ap = .3 61 +.3 70 Igg (4)

.33 Log Ap Log Vp

-1. 7 5 +. 413 Igg (5) a =.3 3 Log yp Substitution of Equation (1) into Equations 2 through 5 results in the set of attenuation models used to calculate the i Weston Geophyscal

. historical seismic loading of the rock foundation at the EF-2 site. 3.0 GROUND MOTION RESULTS The ground motions at the EF-2 site were computed using earthquake activity located in the region bounded by 36 to 0 0 47 N latitude and 770 to 90 W longitude. This broad region was used so tha t all of the major activity in the central region would be included. Events documented with only l epicentral intensities (Io) were converted to mb magnitudes using Equation (6). i mb = 0.5 Io + 1.75 (6) Table 1 lists earthquakes which resulted in estimated intensities of II or greater at the site, and also the corresponding median plus standard deviation sustained acceleration and velocity determined using Equations (1), (2), and (3). The data in Table 1 were sorted to determine the number of exceedances of various intensity levels during the Period 1776-1976; these results are plotted in Figure 1. Similarly, the number of exceedances of sustained acceleration l l and sustcined velocity, using the median plus standard deviation and the median correlations of Nuttli (1979), are shown in Figures 2 and 3. Finally, in a parallel manner, results using the McGuire (1977) conversions for peak motions on firm site conditions are shown in Figures 4 and 5. Also plotted in Figures 2 through 5 are the maximum l historical, horizontal ground motions in comparison to the OBE Weston Geophysical l t e 9 v -.-+, -g m p-

e - ground motion levels. The OBE acceleration is 0.089, while the velocity is taken to be in the range of 5 to 7 cm/sec at frequencies in the vicinity of 1 Hz. This ground velocity range is determined from the 11.5 cm/sec level of the OBE response spectrum at 5% of critical damping at the frequency of 1 Hz., by dividing by the median and 84th percentile response spectrum amplification factors of 1.65 and 2.3, respectively (Newmark and Hall, 1978).

4.0 CONCLUSION

On the basis of the results of this historical analysis, it is concluded that the return frequency of the OBE at the EF-2 site is, as a minimum, on the order of 100 to 300 years. e

t 5-REFERENCES McGuire, R. K., 1977, The Use of Intensity Data in Seismic-Hazard Analysis, Proceed.ings of the 6th World Conference on Earthquake Engineering, New Delhi, Vol. 2,

p. 353-358.

Newmark, N. M. and Hall, W. J., 1978, Development of Criteria for Seismic Review of Selected Nuclear Power Plants, NUREG/CR-0098, prepared for U.S. Nuclear Regulatory Commission. Nuttli, O. W.,1979, State-of-the-Art for Assessing Earthquake Hazards in the United States, Report 16 - The Relation of Sustained Maximum Ground Acceleration and Velocity to Earthquake Intensity and Magnitude, U.S. Army Engineer Waterways Experiment Station Miscellaneous Paper S-73-1, Report 16. s 9 e a 9 7 l l Weston Geophysed ,---p---- w w, m m-w, -e, w~-- -w q w-- -,mw e-,---- -ewro, 3 w: 4 w

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