ML17276A636

Forwards Responses to Open Items Discussed at 811117-18 Geosciences Meeting.Remaining Reponses Will Be Transmitted Prior to 811231

ML17276A636
Person / Time
Site:	Columbia
Issue date:	12/22/1981
From:	Bouchey G WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	Schwencer A Office of Nuclear Reactor Regulation
References
GO2-81-541, NUDOCS 8201070059
Download: ML17276A636 (53)

Text

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REGULA JRY INFORMATION DISTRIBUTIO SYSTEM ('RIDS)

AGCE6SION NBR:8201070059 DOC.DATE: 81/12/22 NOTARIZED: NO DOCKET FACIL:50-397 hPPSS Nuclear ~Projeatg Uni,t 2~ Hashington IPublic Powe 05000397

'AUTH,NAME I AUTHOR AF F IL ATION BOUCHYgG ~ DE Yashington Public lpower Supply 'System

-REC IP ~ NAME REC IP IENT A F F IL'IATION SCH'FENCER P A ~ Licensing Branch '2

SUBJECT:

Forwards responses -to open i~tems discussed at 811117-18 Geosciences meeting. Remaining reponses will be transmitted pr i or to 811231 ~

DISTRIBUTION CODE: B001S )COPIES iRECEIYED:LTR

,TITLE: PSAR/FSAR AHDTS and Related Correspondence l ENCL. SIZE;,m~

NOTES:2 copies all matl:PY~ ~ 05000397 REC IP IENT COPIES RECIPIENT COPIES ID CODE/NAVE LTTR ENCL ID CODE/NAKE LTTR ENCL

'ACTION: A/D LICENSNG 1 -0 LIC BR ¹2 BC 1 0 LIC BR ¹2 LA 1 "0 AULUCKrR ~ 01 1 1 INTERNAL: ELD 1 0 IE 06 3 3 IE/DEP/EPDB 35 1 IE/DEP/EPLB 36 3 3 tlP A 1 '0 NRR/DE/CEB 11 1 1 NRR/DE/EQB 13 3 3 NRR/DE/GB 28 '2 2 NRR/DE/HGEB 30  ? 2 NRR/DE/NEB 18 1 1 NRR/DE/PITEB 17 1 1 NRR/DE/QAB 21 1 1 NRR/DE/SAB 24 1 NRR/DE/SEB 25 1 1 NRR/DHFS/HFEB40 1 1 NRR/DHFS/LQB 32 1 1 NRR/DHFS/OLB .34 1 1 NRR/DHF S/iP TR8? 0 1 1 NRR/DS I/AEB 26 1 1 NRR/DS I/ASB 27 1 1 NRR/DSI/CPB 10 1 1 NRR/DS I/CSB 09 1 1 NRR/DSI/ETSB 12 1 1 NRR/DSI/ICSB 16 1 1 NRR/DSI/PSB 19 1 1 NRR/DS I/RAB 22 1 1 23 1 1 NRR/DST/LGB 33 1 1 EG LE 04 1 EXTERNAL: ACRS 41 16 16 BNL(AMDTS ONLY) 1 FEMA REP DI V 39 1 1 LPDR 03 1 1 NRC PDR 0? 1 1 NSIC 05 1 1 NT I' 1 1 go TOTAL NUMBER OF COPIES REQUIRED: L>TTR Pf ENCL Pf

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Washington Public Power Supply System P.O. Box 968 3000 George Washington Way Richland, Washington 99352 (509) 372-5000

'ecember 22, 1981 G02 541 SS-1-02-CDT-81-111 Docket No. 50-397 RECEIVED Mr. A. Schwencer, Director Age Licensing Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555 CCRQf ~

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Subject:

NUCLEAR PROJECT NO. 2 GEOSCIENCES BRANCH OPEN ITEMS

Reference:

, Letter, A. Schwencer to R.L. Ferguson, "WNP-2 Request for Additional Information",

dated December 1, 1981 Enclosed are sixty (60) copies of the completed responses to the open items discussed at the Geosciences meeting on November 17-18, 1981.

The remaininq responses will be transmitted to the NRC prior to December 31, 1981.

Very truly .yours, G. D. Bouchey Deputy Director, Safety & Security CDT/jca Enclosures cc: R Auluck - NRC I Alterman - NRC J Kimball - NRC WS Chin - BPA R Feil - NRC Site 8>oiozoos9 "D~ aoacg9>>laag, osooo397 PDR

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4 WNP-2 A. 360. 01 5 Concerning the WaLlula Gap fauLt near Yellepit:

a ~ Provide an explanation of the differ" rice in ago ui the Kennewick fanglomer ate as reported in FSAR amendment 2.5.1.2.4.5 on p. 2.5-96 and in Appendix "2.5N.8.1.6.

18'ection bo Was the block of ash that was observed in the down dropped block at the fault in the Yel lepit,trench dated? If soi. what age has been determined.for it'? If nots are there samples of that ash presently available for dating?

Response

a. Based on the most recent calculations by Dr." T.L. Kui the more correct age of the Kennewick fanglomerate is "at least 20i000 years old." Early in 1981'oodward-Clyde Consultants Learned that the age of the Kennewick fanglomerate given in Woodward-Clyde ConsuLtants repor t "WPPSS 1872 Earthquake studies"r July,1978'as regarded by Dr. Kur who made the original age calcalationi as being incorrect.

On February 26'981 J.H. BLack spoke to Professor Ku about a possible discrepancy in the age of the caLiche that had been dated using the uranium-thorium method. Professor Ku reported that an error had been made in calcuLating the age of sample Br and that the sample should be regarded as at Least 21 + 4 x 103 years old as cited in the above report.

A copy of the telephone conversation record which documents this discussion with Dr. Ku is appended.

b. The only known occurrence of volcanic ash in the Yellepit trench was .reported by S.N. Farooqui in the WNP-1/4 PSAR Amendment 23'ctober 1977'p 2RH.4-2 to -4. Section 4.2.3.1 contains a description of the ash unit as follows:

"A Lens of white ashy about 15 feet long and 2 to 6 inches thickr occurs in the Loess just above the top of the gravel bed near Sta 0+12. Trace elements and petrographi c ana Lysi s of a sample (PA1-48) of this ash indicates a Mt. Nazama a f f ini ty (see Subappendi x 2RH-b) ."

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MNp-2 Subappendix 2RH-b presents geochemical and petrographic analyses of the volcanic ash:

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1. Report on Volcanic Ash Samplesi by N.H. Beeson.

Five samples of ashy including PA1-48'rom t h'ell..pi".

trench wer e an'alyzed.

Hydration rinds were absent from four of the samplesi but present in sample PA1-48'uggesting that thi s i s younger than the other four All the other four samples were taken from the Touchet beds. (Sample PA1-48 presumably is younger than the Touchet beds.)

2- Report of Petrographic Analyses of Ash Samplesr by R.O. Van Atta indicates that five samples from the study ar ea (Pasco Basin~ including Yelle pit trench) r plus one from Nt. Nazama were analyzed. All were similar in con-centr ations of Lanthanum and Saumarium (see Fig. 2RH-b-1) and were distinct from St. Helens'S" and St. Helens'J".

It was. concluded that all could be from a Nt. Nazama source.

(he ash over lies the Kennewick fanglomerate~ which is unfaulted.

The age of the Kennewick fanglomerate has been estimated (see response to part "a" of this question) to be at Least 20r000 years old- Van Atta (see above) concludes that the ash is probably younger than ashes taken from the Touchet beds dated at approximately 13>000 yea'rs P B. (Mullineaux and others~

1977). Beeson (above) concludes that the ash could be from a Nt. Mazama sources dated at approximately 7r000 years B-P (Davisr 1978).

In addition to the volcanic ash encountered at Station is a block of Light colored tuff Locatednear Station 2+70.

0+12'here The tuff occurs within the ba'sal par t of the fanglomerate and

'"over lies the,er oded surface of Umatil La basalt' Tertiary basalt. A similar tuff that crops out is an interbed within the basalt sequence is exposed in the north face of the trench near Station 3+20. Based on the Lithologic simiLarity between the tuff fragment in the fanglomerate and the tuff interbed and on their close proximityr the block found at Station 2+70 is concluded to have been derived from the interbed which is regarded by Farooquii 1977 (Fig. 2RH.4-8) r as belonging to the Selah Nember. The Selah interbed underlies the Pamona Formationi which is about 12 million years old.

These relationships are still exposed and were examined by the NRC staff during a site review on December'9i 1981. Based on this field reviews it was concluded that it is not necessary to sample and analyze the tuff exposed in the Yellepit trench.

I

~ 4 WNP '2 Peferences:

I Farooqui~ S.M.i 1977'eologic Studies of the Wallula Gap Fault as exposed in the trench: Subappendix ?RH to WNP-1/4 PSAR Amendment 23.

Davisi J.O.i 1978'uaternary tephronchronology of the Lake Lahontan arear Nevada- and California: Nevada Surveys Archeological Research Paper No. 7.

Mullineauxr, D.R.i Wilcoxi R.E.r Ebaughr W.F.r Fryxelli R.r and Rubbingr M r 1977r Age of the last major scabland flood of Eastern Washingtonr as inferred from associated ash beds of Mount St. Helens Set S: Geological Society of America Abstracts with Programsr p. 1105.

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WNP "2 A. 360.016 In a report prepared foi the U.S. Corps of Engi.".ors (S'.emmoii and O'NalLeyr 1979-1980):

a. Figures 20a and 20b are from Vansyc le Canyon: Have the youthful-appearing faceted spurs having Linear character been investigated for possible yound age andi thereforei capability? What is the explanation for this feature?

be Figures 21a and 21b taken South of Umapine: Has the pronounced escarpment on the Lower third of the hill in the center/upper right of 21a and in the center/right of 21b been investigated for possible recent movement? What is the explanation for this feature?

Response

The origin of the faceted spurs east of Wallula Gap was investigated as part of the trenching and mapping investigation of the Wallula Gap fault (Woodward-Clyde Consultantsi 1981) . A regional reconnaissance was made of the Lineaments and faceted spur s between Wallula Gap and Warm Springs Canyoni including the Vansyc le Canyon Lineament'nd three trenches were excavated across the Mallula fault southeast of Warm Springs Canyon (Figure 360.016-1). Based on these studiesi the faceted spurs are interpreted to be the resuLt of differentiaL erosion across geologic contacts (both depositionaL and fault contacts) between different basalt flow units- The scarps south of Umapine were not specifically investigated as part of this study.

Lineament no. 1 near Warm Springs Canyon (Figure 360.016-2) is defined by an alignment of north facing faceted spurs and a broad bench that Lies immediately north of the break in slope at the base of the spurs. Lineament no. 1 is coincident with the Wallula Gap fault. The bases of the higher and more-pronounced faceted spurs along 4.ineament no. 2 are approximately coincident with the contact between the upper and Lower units of the Frenchman Springs Nember.

The Frenchman Springs Lower uniti which occurs,to the north of L.ineament no. 2 consists of an interbedded sequence of two distinctly different textural basalt types. The first type consists of dark black basalt that has very fine microphenocrysts in an aphanitic ground mass. This basalt breaks into equant clasts less than 15 cm in diameter. The first basalt type is interbedded with a second type that has a fine-grained ground mass and no aphanitic ground mass. The second basaLt type commonly fractures into coarse joint blokcs that are typicalLy.

greater than 0.3 m, in diameter. Coarse (S0.6 m) columnar joints

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The upper unit of the Frenchman Springs Nemberr which occurs on the south side, of Lineament no. 2 and underlies the spursr consists of massive basalt flows that are petrographicaLLy simiLa r to the fine,", grained (non-aphanitic) rocks in the Lower unit.

Figure 360.6-3 is a schematic cross section showing the relation" ship between the Lineaments (faceted spurs) and the bedrock geology. Lineament no. 2i'hich is geomorphicalLy similar to the Lineament along Vansycle Canyons is clearly not the result of recent tectonic displacement. In placesi the break in slope at the base of the faceted spurs Lies more than 400 m west of the Wallula Gap fault. The faceted spur s are the result of differentiaL erosion across the depositional contact between the upper and Lower units of the Frenchman Springs Nember. The subparaLleL alignment and relative position of lineament no. 2 to the Wallula Gap fauLt may be indirectly related to displacement on the fault. If soi the faceted spurs are erosional .fault-Line features and the distance between the fault trace and the base of the spurs attests to the Long time. that would have been required to backwaste the scarp. Trenches across the Wa llula Gap fault near Warm Springs showed t'hat there has been no displacement since deposition of the Late PLeistocene Touchet deposits (13i000 years BP). h'asTrenches across the Wallula Gap fault at Yellepit indicate there been no displacement during at Least the past 20r000 y ear s.

Detailed'geologic mapping of the Vansycle Canyon area shows that the lineament aLong Vansycle Canyon (Slemmons and O'Nalleyi 20b) may be either a fault scarp or a fault Line erosional 1980'igure scarp. The faceted rpurs between Vansycle Canyon and Wallula Gap are coincident with a breccia zone that defines the Wallula Gap fault. Both sets of faceted spurs are underlain by the Frenchman Springs Nember. ALthough the faceted spurs shown in the report by SLemmons and O'Nalley (1980) [i.e.r Figures 20ai 20br 21a and 21B) have not been trenchedr the detailed mapping and trenching near Warm Springs Canyon and the trench at Yellepit indicates that faceted spurs are not a ~riori evidence for recent tectonic displacement. They are most Likely the result of differential erosion across contacts (either depositional or fault contacts) between different flow units.

I WNP-2, Re ferences:

Slemmonsr D.B and O'Nal leyr 1980r Faul t and Ear t>,qi.awe I a"- rd Evat.uation of Five U.S. Corps of Engineer s Dams in South<<

eastern Washington: Report prepared for U.S. Corp" uf Engineer si Seattle districtr 60 pp.

Woodward-Clyde Consultantsr 1981r Wallula Fault Trenching and Napping: Draft r eport prepared for Washington Public Power Supply Systems Richlandi WA.

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0 WNP-2 Q. 360.018 Describe the uni queness of Toppeni sh ic idge that Lead you to conc t.ude that an earthquake (or earthquakes) Like that which produced the young scarps on Toppenish Ridge i- i il ik'Ly tc occur on other folds closer to the site

Response

1.0 ConcLusions of Toppenish Ridge Investigations The various investigationsr to datei concerning the origin of topographic scarps on Toppenish Ridge have had differing approaches and differing Levels of effort and detaiL. ALL of

.the studies have concentrated on reconnaissance level geomorphologic investigations and geol.ogic 'mapping and none have'tilized 'subsurface investigative techniques.

1.1 Background of Previous Studies The initial field work on the topographic scarps and geology of Toppenish Ridge was conducted in 1978 and 1979 by NeweLL Campbell and Robert Bentley and reported in Rigby and Othberg (1979) r Bentley and others (1980) r and Campbell and Bentley (1981) .

Campbell and BentLey (1981) report a zone of scarps 0.5 km to 2-2 km wide that extends 32 km along the north slope of the Status Peak anticline segment of Toppenish Ridge. The scarps occur in three sets: the crestali hinge and fan sets. The crestal and hinge sets cross topography suggesting steep dips whiLe the fan set is sinuous suggesting a gentle southerly dip. The scarps di splace sur faces that are underlain by Niocene through Holocene age'aterials.

Bentley and others (1980)r and CampbeLL and Bentley (1981) conclude that the topographic scarps present on Toppenish Ridge are likely to be tectonic features that'formed at the same time as tectonic folding and thrustingr and that they record some of the latest north-south compressionaL deformation in the region.

The scarps are probably related to uplift folding and thrusting of the Satus Peak antic line segment of Toppenish Ridge as it moved northward along northwest-striking fracture systems (Campbell and BentLeyi 1981). Campbell and Bentley (1981) further conclude that extension of the hinge area of the fold formed the hinge and crestal scarps while compression occurred at. the base of the slope forming the fan set or thrust-Line scarps. Although the scarps are probably tectonic in origin~

this has not been conclusively proven and alternative non-tectonic origin include gravitational ridge spr eadingi Landslidingi and ground-water withdrawal (Campbell and Bentleyr 1981) .

WNP-2 Based on a remote sensing analysis using sma L L scale aei"i at photographsi Glass (1979) conc luded that the most Likely candidates for active faults associat~~ with t~~ i'."";. i-'.h Ridge are the northwest-trending lineaments near the western portion of the ridge. He also concluded that the faults associated with the east-vest antic l ine are probar~; y nor. act if they are activer the northwest-trending Lineaments are also probably active. Based on the length and character ive,'oweverr of the zone of scarps observed during aerial reconnaissance~

GLass (1981) concluded that the scarps are probably tectonic in origin but that a non-tectonic origin cannot be ruled out.

In additions he stated that the scarps on Toppenish Ridge are the youngest of any he has observed on the Columbia PLateau.

Based on aerial reconnaissance and preliminary analysis of the observed geomorphic character of the scarpsr Kiel and Davis (1980) and Davis (1981) concluded that gravitationally induced slope failure is a viable alternative to a tectonic origin for the scarps on toppenish Ridge.

The resuLts and conclusions from previous studies of Toppenish Ridge generally suggest a tectonic origin for the scarps that occur along a 30 km segment of the ridge. In generalr the scarps are considered to be the result of primary movement of a thrust fault along the north base of Toppenish Ridge and secondary faulting within the upper slopes due to tectonic extension or gravitational adjustments within the overthrust block. In additioni the previous work has noted that the scarps appear to be confi'ned to the segment of Toppenish, Ridge that is separated from adjacent segments bye or reL'ated toe northwest-trending fractures and Lineaments (Bentley and othersr 1980; Campbell and Bentleyi 1981'lassy 1979) . ALthough the generaL conclusion is that the scarps may be tectonics there is still uncertainty in this conclusion~ voiced by the previous workersi such that a non-tectonic origin cannot be precluded.

1.2 Results of Investigations by Applicant The purpose of the applicant's studies (Woodward-Clyde Consultants'981) was to assess whether the scarps are non-tectonic or tectonic in origin and to assess the capability of scarps that were identified as being tectonic. The scope of work included a review of available data and Literaturei photogeologic interpretation of available aeriaL photographsr and aerial reconnaissance. Ground access to the Yakima Indian Reservation was restricted. Because of the Lack of ground ect measurement of scarp heightsr geometry'nd slope morphology access'ir was not possible. Likewisei direct information related to bedrock structure and its relationship to the scarps is based on previous work by others.

WNP-2 The results of the applicant's investigations (Woodward-Clyde l onsultantsr 1981'oncurred in "eneral w i th r e u. '..-;

investigations (Rigby and Othbergr 1979; Bentley and othersi Woodward-Clyde Consultants (1981) reports that the zonn '980).

of scarps on the north slope of Toppenish Ridge ranges from 7 co 2 km wide and extends a Length of 24 km along the Satus Peak segment of the ridge. Three sets of scarps are identified: the crestali midsloper and basal set. The basal set is the Longest (24 km) and most continuous and is sinousi following topography which suggests a gentle southerly dip. The crestal and midslope sets are Less continuous and cut across topography suggesting steep dips. Two possible mechanisms for the primary origin of the scarps were identified (Woodward-Clyde Consultants'981):

o gravitationaL failure (non-tectonic) o thrust faulting (tectonic)

Tt was concluded that the scarps observed on Toppeni sh Ridge are most likely tectonic in origin and because of the Holocene age of th'e scarpsr they are considered capable. They wer e formed'ue to displacement on a Low anglei south-dipping thrust fauLt. The thrust displacement occurred along the base of the north slope of Toppenish Ridge for a distance of 24 km. The midslope and crestal set scarps are secondary features formed either by gravitationaL adjustments in the over thrust block or by tectonic extension in the upper block (Woodward-Clyde Consultantsr 1981) The 24 km-long zone of scarps occurs along the 30 km-long segment of Toppenish Ridge that coincides with the Satus Peak anticlinei which was first described by Bentley an'd others (1980) . Segments of Toppenish Ridger which has a total Length of 95 km'an be defined on the basis of stratigraphyr structure and geomorphology (refer to Question 360.019). Although the tectonic origin seems most likely based on the available data' non-tectonic origin cannot be precluded because of= the Lack of'etailed geologic and geometric data for the scarps.

2.0 Uniqueness of Toppenish Ridge In a general sensei the folds of the Yakima foLd belt have many stratigraphic and structural similarities and it is these similarities that have previously allowed the definition of, the fold belt- Howevers each fold has unique geologicr structural and geomorphic characteristics that distinguish it fr om other folds. These variations in structural styles and fold develop-ment between the different folds reflect a spectrum of fault/fold re lat ion shi ps.

WNP<<2 Xn generals Toppenish Ridge is different from the other east'west Folds of the Yakima fold belt in the following ways.

o The young topographic scarps observed on Toppenish Ridge have not been observed on other folds of the Yakima foLd belt (Woodward-Clyde Consultantsr 1981; CampbelL and Bent leyr 1981) ~

o Association of the folds to regional northwest"trending strike slip faults (Bentley and othersi 1980; Bentley and Anderson'9?9) has only been documented for the south-western Yakima fold belt in the area of Toppenish Ridge ~

o Thrust faults having opposing dips have been mapped along both flanks of much of Toppenish Ridge and this is not common in the rest of the fold belt.

o The Location of Toppenish Ridgei west of Longitude 120 (in the western and southwestern portion of the Yakima fold Belt) has undergone more north-south crustal shortening than to the east (Bentleyr 1981) .

Because of the variations in the styLe of deformation associated with di f ferent plateau fo'Ldsr the seismic potential of each fold should be evaluated on the basis of its own structure and deformation. The characteristics of the structures closest to the siter the Rattlesnakes, Wallula aLignment and Umtanum;Ridges GabLe Nountain structural. trends are summarized in response to Question 360.14 and 360.20 and deterministic assessments of the potential ground motions from these structures are made. The characteristics and seismic potential of these and all other plateau structures that extend to within a 50 km radius of the site are summarized in Amendment 18'ppendix 2.5K. The results of these anaLyses indicate that an event similar to the one that is assumed to have produced .the scarps .aLong Toppenish Ridge is unlikely on the other folds c l'oser to the site.

References:

Bentleyr R.D.r and Anderson'.L. 1979i Right-lateraL strike-slip faults in the western 4'6i Columbia Plateaus Washington:

Abstractsi EOSr v. 60'. p. 961.

Bentleyr R D.r Anderson'J.L.i Campbelli N.P.i and Swansonr D.A.r

,1980'trat'igraphy and structure of the Yakima Indian Reservation with emphasis on the Columbia River Basalt Group'. U.S. Geological Survey Open-File Report 80-200'9p.

D MNP-2 Bentleyi R.D.i 1981i Nagnitude of Neogene Horizontal shortening in the western Columbia PLateau Mashington " Oregon:

Abstractsi EOSi v. 62i n. 6i p. 60.

Campbelli N P. and Bentleyi R.D.r 1981i l ate Quatel >>ary

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de for mat ion 'o f the Toppeni sh Ridge upli f t in south-cent ra l

'Washington:,Geo Logyi v. 9r p. 519-524.

Davisi G.A.i 1981r Late Cenozoic tectonics of the Pacific Northwest with speciaL reference to the Columbia PLateau:

Appendix. 2.5N to Final Safety Analysi s Report MNP-2 and 1/4.

GLassi C.E.i 1979i Interpretation of U-2 and Forest Service photographyi Letter to David .Tillsoni Principal Geologistr Washington Public Power Supply System regarding air photo inter pretation of Toppenish Ridge Glassr C E 1981i.WPPSS Hanford Projects Remote Sensing Task C-9r Tr i p Report 2"21-81: Letter to John Dohertyr Project Nanageri Weston Geophysical Corporation regarding aerial reconnai ssance of Toppenish Ridge.

Kieli W. and Davisi G.A.r 1980i UnpubLished field trip notes of aer ial r econnaissance of Toppenish Ridge conducted 7/2 7/3/80.

Rigbyi J.G.i,and Othbergr K.i 1979iReconnaissance surficiaL geologic mapping of the Late Cenozoic sediments of the Columbia Basinr Washington: State of Mashingtoni Division of Geology and Earth Resourcesi Open-File Report 79-3.

Moodward-Clyde Consultantsi 1981i Task D5 Toppenish Ridge Study: report prepared for Washington Public Power Supply Systemi 33 p.

WNP-2 Q. 360.020 Provide a sumnary of aLL prominent s"ructures (other than those incorporated into Question 360.014 as part of the (CLEW) in the site regions discussing in detail their character and capability with supporting evidence for your judgement. If you determiJie any to be segmentedi provide a map on topographic base deline-ating the segments and discuss in detail the character and capa-bility of the individual segments with supporting basis.

Response

The faults that may be potentiaL seismic sources of signifi-cance to the site are those associated with the Pattlesnake'-

Wallula alignment (discussed in Question 360.014) and with the Umtanum Ridge-Gable Nountain structuraL trend. These struc-tures are the closest to the site andr thereforei are the most significant to a deter ministic assessment of ground motions at the site. In response to this questionr the data regarding the tectonic models and segmentation of the Umtanum Ridge-Gable Nountain structura l trend wiLL be summarizedr followed by a discussion of the capabilityr fault parametersi maximum magni-tudesi and site ground motions for the potential seismic sources associated with the structural trend.

Tectonic Models and Se mentation The data and intrepretations regarding the Umtanum Ridge-Gable Mountain structural trend are summarized in 2.5.1.2.4.2 and 2.5.1.2.4.3 and are presented in detaiL in Golder Associates (1981a and 1981b) . The principle conclusions of these studies regarding tectonic models and segmentation are summarized below:

o The Umtanum Ridge"Gable Nountain structural trend is a segmented anticlinal high.

o The structural trend is comprised of five segments (Figure 360.020-1) that are separated from each other on the basis of changes in the style .of deformation and fold orientation. Individual segments show marked differences in fold vergencei fold amplitudes and widthsr

~

and development of firstr second< and third-order folds."

o The Umtanum fault and other east-west trending reverse faults ar'e inferred to be products of fold deformation in a north-south compressional stress regime. Geologic

WNP-2 data support the hypothesis that the Umta'num fault was generated from the core of a concentric fold and that fauLting is a direct resul ~ o f folding on t,'-,s .:t" i<<."u "e.

On this basisr the faults associated with Umtanum Ridge are discontinuous and confined to the Length and width of individual fold segments.

o Three prominent second-order folds are superimposed on the fir st-order fold that forms'he Gable Butte-Gable Mountain segment of the Umtanum Ridge-Gable Nountain structural trend (Figure 360.020-2).

o Faults associated with the Gable Butte-Gable Mountain segment are inferred to be the product of folding of the secondorder folds. For this reasons fault Lengths and widths are constrained by the dimensions of individual folds.

o The southeast anticline segment of the Umtanum Ridge-Gable Mountain structural trend is interpreted to be a first-order fold of Low amplitude that is separate from the Gable Butte-Gable Mountain segment.

The mapped faults along the Umtanum Ridge-Gable Nountain structuraL trend that will be c'onsidered in the assessment of capability are the Umtanum faulted the central fault on Gable Mountaini the north-dipping reverse fault on the west Gable Nountain anticlinei and the southeast anticline fault.

The Umtanum fault has been investigated by Golder Associates (1981a) and no evidence of Quaternary faulting was observed-A fanglomerate that is inferred to be at Least 200i000 years old is not displaced where it was found to overlie bedrock faults (Golder Associatesr 1981a). In additioni the absence of any marked geomorphic expression along most of the mapped Length of the Umtanum fault in the study area suggest an absence of dis-placement during the Late Quaternary on this structure (Golder Associatesr 1981a). Based on these evaluationsi the Umtanum fault is interpreted to be not capable.

The central fault on Gable Mountain displaces glaciofluvial deposits correlative with Late-pleistocene Nissoula fLood deposits that are between 13i000 and 19~000 years oLd. The evidence indicates that the faulting may be coincident with the late PLeistocene floodsr which suggests that the faulting may have been flood induced. ALthough some evidence supports

l IP

nontectonic hypotheses for the origin of the displacements in the glaciofluviaL depositsr data gathered to date are insu/ficieni:

to demonstrate a nontectonic mechanism for the origin of t>::,

observed displacement (Golder Associatesr 1981b) ~ Based on tn se data'he central fault is interpreted to be capable'ithin the criteria of 10CFR100.

The existence of the north-dipping reverse fault on the west Gable Nountain anticline is inferred from borehole data and no information is available'or directly assessing its capab~lity-The south fault is interpreted to be antithetic to the no~ th-dipping reverse fault (Golder Associatesi 1981b)r although the insufficient this association, data are to confirm Assuming an antithetic relationshipr data on capability of the south fault may aLLow inferences regarding the capability of the north" dipping reverse fault. The south fault does not displace overlying glaciofluvial deposits; howeverr slickensides in clastic dikes that are apparently derived from these deposits suggest minor dip-slip displacement has occurred on the south fault since dike emplacement (Golder Associatesi 1981b). This displacement may have been flood induced but tectonic movement cannot be disproved. Because the south fault is inferred to be a minorr antithetic fault in the hanging waLL of the north-dipping reverse fault (Golder Associatesi 1981b)i it is not considered for magnitude assessment.

Because of the undertainties in the capability of the south fault and its relation to the north-dipping reverse faulted the capability of the north-dipping reverse fault is uncertain. Howevers because of the possible structural relationship between 'the north-dipping reverse fault and a presumed capable fault (the south fault) r the north"dipping reverse fault may be interpreted to be the criteria of 10CFR100i and resultant magnitudes and capable'ithin grand motions are therefore discussed below.

A fault has been inferred along the southwestern flank of the southeast anticline from borehole and geophysics data (Figure 360.020-2). Several aspects of the relationship between the Gable Butte-Gable Mountain segment 'and the southeast anticline indicate that the southeast anticline is a separate first-order Golder Associates (1981b) and are summarized here:

defined from gravity data in the buried basalt fold segment. The bases for this conclusion are presented in surface a saddle at the east end of Gable Nountain separate the segments') the southeast antic line extends about 1.6 km to the northwest beyond the eastern end of the Gable Butte-Gable Mountain segments 3) the Gable Butte-Gable Mountain segment is bounded on the east by the Nay Junction monocliner and 4) there is a marked change in trend of'he first-order fold segments from nearly east-west (Gable Butte-Gable Mountain segment) to approximately N45oM (southeast anticline segment).

I WNP=2 As presented in the FSAR Amendment 18 (Section 2.5.2.4.2.2) i Lhe preferred estimate of the maximum earthquake magnitude for the central fault on Gable Nountain is N 5. Based cn ti::;

parameters presented above for the north-di pping reverse faulti the area-magnitude relationship (presented in response to Q. 360.014) yields magnitudes of 3.9 to 5.1 (+ 0.3) - fhe Length " magnitude r elationship is not considered applicable for rupture lengths as short as 3 km andi thereforei is not used in estimating maximum magnitude. The preferred estimate of maximum magnitude for the north-dipping reverse fault is N 5. As presented in the FSAR Amendment 18 (Section 2.5.2.4.2.2) i the maximum magnitude for the central fault is N 5.

Two important points should be considered in evaluating these maximum magnitude estimates: 1) the seismogenic character of these faults andi 2) the applicability of the fault parameter magnitude relationships. ALthough the central fault is con-sidered to be capable and "the north-dipping reverse fault is treated here as being capable according to 10CFR100 criteriai their tectonic role as secondary faults related to r elatively minor second"order foldsi their Limited physicaL dimensionsi their Lack of correlation with historical seismicityi and possible non-tectonic origins for the displacement in the flood deposits raise questions regarding'heir potentiaL to generat'e earthquakes-The estimated maximum dimensions of these faults is weLL below the empirical. data base typically used for making magnitude estimates (see resporise to Q. 360.014) . For examplei the smallest magnitude and associated rupture Length in the reverse fault data set of Slemmons (1977) is NL 7.1 associated with a 20 km rupture Length. 'Extrapolation of this relationship back to rupture Lengths as short as '1/2 km to 3 km is inappropriatei and Slemmons (1977) attempts to di scour age such extrapolations by'efining a "boundary of applicabiLity" to his relationships.

The fault area - magnitude relationship is considered valid for N ~ 5.7 (Wyssi 1979)i but the fault dimensions associated with N 5.7 are still greater than those proposed for the centraL fault and north-dipping reverse fault.

Ground Notions The ground motions resulting from a N5 earthquake on the centraL fault at a distance of 18 km is discussed in FSAR Amendment 18 (Sect ion 2.5.2.6.1) . The estimated peak acceleration at the plant site for this earthquake is Less tha 0.1 g. The north' dipping reverse fault's also at a distance of 10 km from the site and is also assessed a maximum magnitude of 5; ther eforei the site ground motions are the same.

WNP -2 Because of their close proximity to the WNP 2 and WNP 1/4 site relative to other plateau, structuresr the most Likely source for an SSE is either +he Rattlesnake-Wallula alignment discussed in r esponse to Question 360.014 or the Umtanum Ridge-Cable Nountain structuraL trend discussed above. This is confirmed by the Seismic Exposure analysis which includes an analysis of all plateau structures within a 50 km radius of the site (see Amendment 18m Appendix 2.5 Kr WNP-2 FSAR).'here i s uncertainty, regarding the nature of plateau deformation and the seismic potentiaL of the structures in the site region.

Because of these uncertai'nties conservative assumptions have been made in the deterministic assessments of the capability of the potential sources of the SSE. Although tectonic modeLs can be postulated that might suggest these faults have greater seismic potentiali these models are only permissive and not supported by the weight of available geologic and .seismic evidence in the Columbia Plateau. Alternative tectonic models and their significance to the SSE are evaluated in the WNP-2 FSARi Amendment 18'ppendi x 2.5K.

References:

Fultonr RE Ger and Smiths G W r 1978'ate Pleistocene stratigraphy of south central British Columbia: Canadian Journal of Earth Sciences v. 15'. 971-980.

Golder Associatesr 1981ar Geologic structure of Umtanum Ridge:

Priest Rapids Dam to Sourdough Canyon: Appendix 2Nr Skagit/Hanford Nuclear Project Preliminary Safety Analysis Reportr for Northwest Energy Services Companyr 44 p-Golder Associatesi 1981br Gable Mountain: Structural Investi-gations and Analyses: Appendix 20: Skagit/Hanford Nuclear Project Preliminary Safety Analysis Reports for Northwest Energy'ervices Companyr 58 p-Waitti R.B.i Jr.r 1980'bout forty Last-glaciaL l.ake Nissoula jokulhaups through Southern Washington: Journal of Geologyi v 88r p ~ 653-679 Websterr G ~ Der and Crosbyw J ~ W p I'IIr 1'R81p Stpatlgl'aphic investigation of the Skagit/Hanford Nuclear. Project:

Preliminary Safety Analysis Reports Appendix 2Ri Not thwest Energy Ser vices Companyi Kirklandi WA.

WNP-2 The results o'f investigations by Webster and Crosby (1981) that r Late to the assessment of the capability of the southeast anticline fault are summarized below- The fault is inferred from the borehole data by a thickening of the Elephant Mountain basalt (10.5 m.y. old) and by several thin (maximum thickness appr oximately 1 m) shear zones within this ananomalously thick section. Cumulative vertical displacement of this unit is no more than about 30 m- The overlying Ringold section is anomalously thin along the inferred trend of the fault but it is not clear whether Ringold sediments are, deformed by the fault-The Ringold section in the so'utheast anticline area is interpreted to be between 3.3 and 10 million years old. No deformat'ion is recognized in the p're-Ni ssoula f lood gravel s nor the Ni ssoul a flood graveLs across either the southeast anticline or the southeast anticline fault. The Missoula flood deposits are estimated to be 13r000 to 19r000 years old (Fulton and Smiths 1978; Waittr 1980) . 'The age of the pre"Ni ssoula deposits is not known'ut they may be as old as the youngest underlying Ringold formation (approximately 3 million years old) . Possibly correlative fLood deposits have yielded dates on=the order of several hundred thousand years (Webster and Crosbyr 1981).

Neither the southeast anticline nor the fault aLong its flank have any geomorphic expression. Although the data regarding capability are somewhat Limitedi the available hvidence supports the interpretation that the southeast anticline fault is not capabLe.

Fault Parameters and Maximum Na nitudes The magnitude-related fault'arameters for the central fauLt on Gable Mountain are presented in the FSAR Amendment 18 (Section 2.5.2.4.2.2). Fault parameters for the north-dipping reverse fault on the west Gable Mountain anticline are'..presented in this section. The north-.dipping reverse fault is known from borehole data over a Length of about 1 km. The fault is interpreted to be the product of folding of the west Gable Mountain anticline (Golder Associytesi 1981b); thereforei its maximum inferred- Length is the total Length of the anitcliner.

6 km. Assuming a rupture length of one-half the total Lengthi the rupture Length may be 1/2 km 'to 3 km. Downdip fault width may be estimated from known fold geometry. The maximum fold amplitude of the Gable Mountain anticline is about 300 m.

The width Cwavelength) of. the west Gable Mountain antic line is Less than 1 km. A shallow-dipping fault associated with this fold would probably have a width of Less than 1 kmr and certainly Less than 3 km. In summaryi the magnitude-.related fault parameters for the north-dipping reverse fault are:

Total Length 1 -6 km Rupture Length 1/2 3 km Faul t Width 1 -3 km

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WNP-2, Q. 360. 021 Provide the Letter report and Lineanent maps from C. Glass to WPPSS of Lines of aerial reconnaissance of Toppenish Ridoe.

(Contact Ina Altermanr GSBr 301-492-785v)

Response

The Letter report from Dr. Charles E. Glass to Nr. D. D. Tillson (Washington Public Power Supply System) dated October 3i 1979 was mailed to Dr. Ina Alterman November 24'981. Upon receipt of that materials the air photos used in the original analysi.

plus the transparent overlay prepared by Dr. Glass were also requested. This material was transmitted to Dr. ALterman on December 22r 1981.

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WNP-2 361.018 Provide a discussion on how, and at what stage, uncertainty was accounted for in the seismic exposure anaLysis (includirg graphi ca L examples) .

Aesponse:

Two kinds of uncertainty are considered in the evaluation of seismic exposure at the Hanford site, inherent uncertainty'and statisticaL uncertainty. Inherent uncertainty refers to the situation where a future outcome of a process cannot be predicted with certainty even if a Large amount of historical data is available. For the present study, the uncertainty in predicting the actua l time and Location of future earthquakes and the result-ing Level of ground motion constitutes inherent uncertainty.

Statistical uncertainty consists of uncertainty in the process parameters which may be resolved or reduced with, additionaL data.

In the ana lysis described in Appendix 2.5K, the parameters which define the potential earthquake sources are treated as statistically uncertain. These parameters are source segmentation, capability, tectonic modeL geometry, maximum magnitude, and recurrence rate.

The basic exposure calculation includes the inherent uncertainty in the =ti me and place of earthquake occurrence and the generation of stong ground motion to estimate the probability of exceeding a specifi ed Level of ground motion at. the site. The occurrence of earthquak es,on a source is assumed to be a Poisson process. The probabili ty of the occurrence of at least once event in a specified time peri od, t, is given by the equation zero events) = 1' e where A is the mean rate of occurrence of earthquake on the source.

Assuming that t he probabiLity. of any one event resuLting in ground motions at the site in excess of a specified Level is independent of the occurrence. of other events, the occurrence of ground motions at the site is also a Poisson process. The li probabi ty of ground motion parameter Z exceeding a specified Level of z is g iven by p(Z> z) =.1 - e (2)

p in which v(z) is th~ mean rate of occurrence ot events in time t in which ground moti'on Level z is exceeded. For simplicity, v(z) termed the mean rate of exceedence. In the exposure is given by the expression v(z) = S t.R(m.) -8 p(R = r. (m.) p(ZPz[m.,r.) (5) 1 1 j 1 1 j The mean rate of occurence~ g (m.),, of magnitude m. earthquakes, is given by the expression 0

-b 1.n10 (m.-6m-m ) -e -b 1n10 (m.+4m-m 0 )

e 1 X(m.)1

= A n

1 (4) 1 = e b 1n10 (m -m )

Mhere m is the maximum magnitude possible on the source, m is the minimum magnitude considered in the analysis, 3m is a suitable discretization step, b is the slope of the magnitude frequency reLationship and A is the mean rate of occurrence of earthquakes of magnitude greater than m on the source.

The uncertainty in the Location of the earthquake on the source is characterized by assuming a uniform distribution for the Location of the rupture surface. This is shown schematically in Figure 361.18-1a.

The probability of exceedence given a particuLar magnitude and distance is calculated from the distribution about the median estimate of attenuation of ground motion, as shown in Figure 361.18-1b. By summing over all possible magnitudes and distances, a mean rate of exceedence is calculated which expresses the inherent uncertainties in a Poisson process.

The exposure model used in the analysis for the Hanford site was expanded to incLude statistical uncertainties in the input parameters to equations (3) and (4). This was accomplished by treating the rate of exceedence', v(z) as a random variable and considering the uncertainty in.v(z) as resulting from uncertainty in, the source definition parameters A , m , and source geometry.

is source geometry and maximum magnitude n'ncertainty was characterized by constructing 'a Logic tree representing the possible states of the various input parameters. The Logic tree constructed for Saddle Nountains is shown in Figure 361.18-2.

The end branches of the Logic tree define a discrete joint distribution for fault geometry and maximum magnitude.

The procedure used to calculate the distribution for the exceedence rate v(z) is iLLustrated schematically in Figure 3.

For each state of maximum magnitude and fault geometry defined by an end branch of the Logic tree in Figure 361.18-2 an exceedence rate was'alculated using equations (3) and (4) and the expected value of A for the source. The result is a discrete distribu" tion for viz) conditional on the expected value of An. This distribution is shown in Figure 361.18-2a.

V The parameter A is considered to be Lognc.'mo'. L; distributed.

Values of A di 7f erent from i ts mean vaLue wouLd result in

~

lifferent vaLues of v(z). Thus, as shown in Figur e .61. l8-"l..

i.ach mass point in Figure 361.18-3a can be expanded into a distribution. As the distribution due to A is assumed to br",

independent of the joint distribution on mu and fauL t g:omeiry, the individual distributions shown in Figure 361.18-3b can be summed to produce the finaL unconditionaL distrik'~'.n Figure 361.18-3c.

Shown in Figure 361.18-3 is the mean or expected value of v(z) both for the conditionaL distribution in (Figure 361.'l8-3a) and the unconditionaL distribution in (Figure 361.18-3c). Because of the Linearity of equations (3) and (4) in A , the means of the two distributions are identicaL. The effect of incLuding uncertainty in the recurrence rate A n is to widen dispersion about the mean as shown by the mean plus one standard deviation values in Figure 361.18-3.

The finaL step in the analysis is the calcuLation of the probability of exceedence. In the case of Low probability Levels

(<.01) the probability of exceedence is essentially equal to the rate of exceedence.

p(Z>z) = 1 - e -v(z) ~ v(z) (5)

This resuLt holds for any probability distribution. Thus for smaLL values of v(z); the assumption of a Poisson distribution is not criticaL. The distribution derived in Figure 361.18-3 for the exceedence rate applies also to the probability of exceedence.

The methology used in Appendix 2.5K is very similar to that proposed in NUREG/CR-1582, voL 2. As described in Appendix A of NUREG/CR-1582~ vol. 2i stat istical uncertainty in the input parameters is treated by defin ing a state vector of the possible states of the input parameters In the analysis conducted for the Hanford site the possible states of the input parameters are def ined by the end branches of 'the Logic tree.

Thus'oth methodologies def'ine a distribution for the rate of exceedence similar in form to .those shown in Figure 361.18"3; relying on subjective probability to calculate the probabilities assigned to individuaL states. The best estimate of the rate of exceedence is calcuLated in the same way for both methodologies, by summinq over alL possible states the exceedence rate calcu-Lated for e ach states multiplied by the probability of that state.

ln addition to the best estimate or expected value of the rate of exceedence other probabiLity Levels can be examined within the distribution. The 90% confidence Level reported .in Appendix ?,'i<"

represents the Level of exceedence rate below which 90% of the calculated probabilities of exceedence hi e. This le;o L '=. show>

in Figure 361.18-3 for the unconditionaL distribution. Similar probabi Lity Levels could also be reported for the distrih<<tions on exceedence rate developed in NUREG/CR-1582, voL. 2.

Xn summary the distributions on exceedence rate derived in Appendix 2.5K represent statistical uncertainty in the input parameters for source definition. The inherent uncertainty in time and Location of future earthquakes and attenuation of ground motions is used to calculate point estimates of exceedence rat'e for individual states of the input parameters.

REFERENCES:

TERA Corporation, 1.980, Seismic Hazard Analysis; A Nethodology for the Eastern United States: U.S. Nuclear Regulatory Commission NUREG/CR-1582, v. 2, July 1980.

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SITE P(R<r) ~0 for r<r>

Ground surface

'2 for r> <r<r>

for r<r2 a) Cumulative Probability Distribution for Closest Distance to Fault Rupture for Case of Fault Lying Completely on One Side of Site Probability of exceedance Median attenuation for rnagnitud e m; b) Conditional Probability of Exceedance WASHINGTON PUBLIC Figure POWER SUPPLY SYSTEM SCHEMATIC OF TREATMENT OF INHERENT UNCERTAINTY IN EXPOSURE MODEL 361.1&-1 Nuclear Project No. 2

~ 4 P ~ .o

r C ~ ~

Annua{ Mean Tectonic Fault Maximum No. Even".. Event Source Capability Exceeding Model Width/Dip Magnitude Probability 0.25g(10 G)

P OQ 6.0 (0.30) 0.02 0.043 ch m cn 6.25 (030) 0.08 0.043 O +X 5/60'0.4) cn ~ 7.25 (0.20) 0.029 ca 7.5 (0.20) 3.1 4.3 0.029 0

0 r p CO Ol ~

Z ~C= 6.25 (0.12) 0.4 0.017 0 gg M m 6.5 (0.18) 0.71 0.026

~O 11/45 (0.4) 6.75 (0.30) 1.2 0.043 7.25 (0.20) 4.1 0.029 Reverse 7.5 (0.20) 5.9 0.029 Primary (0,6) 6.5 (0.12) 60 ' 0004 6.75 (0.18) 7.3 0.006 fn 20/30 {0.1) 7.0 (038) 8.8 0.014

~ X 7.25 (0 12) 11 0.004 Ch

> O cn 7.5 (0.20) 14 0.007 O C- .

ON rm fll ~ Capable (0.6) 6.5 (0.12) 0.32 0.004.

KQ OQ 6.75 {0.18) 0.58 0.006

~n 23/60 {0.1) 7.0 (0.38) 0.95 0.014 7.25 (0.12) 1.6 0904

~m Z nl Saddle 7.5 {0.20) 2.8 0.007 CO

~ Mountain 0

Reverse 2/45 (0.6) 5.5 {1.0) 0.114 Secondary (0.4) 6/45 (0.4) 6.0 (1.0) 0.07 0.096 lb'on~apable Crl'l tl (0.4) 0 OA oa

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Distribution 02

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.o 0.1 0

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o lo-9 10 10 10 10 10 10 Annual Mean Number of Events Exceeding 025g 0.400 b) Expanded Condition Distribution 0.010 0.005 0

0 '10-9 ion 10-7 lo~ 10-5 10 Annual Mean Number of Events Exceeding 025g 0.400 c) Unconditional Distribution OA)50 "~ ~

OZ)25 0

0 10 10 10 10 10 10 10 Annual Mean Number of Events Exceeding 025g WASHINGTON PUBLIC Figure POWER SUPPLY SYSTEM EXCEEDANCE RATE DISTRIBUTION FOR SADDLE MOUNTAINS 36$ .18-3 Nuclear Project No.2