ML19256E332

Forwards Supplemental Testimony Re Methods Used to Measure Ground Motion

ML19256E332
Person / Time
Site:	Skagit
Issue date:	09/25/1979
From:	Kelleher J WOODWARD-CLYDE CONSULTANTS, INC.
To:	Rolonda Jackson Office of Nuclear Reactor Regulation
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NUDOCS 7911020110
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Text

.

Appendix E Dr. John Kelleher Report _

l'.25M.....:S""',.....

.. . m. _ ..

Woodward C[yde Co."eu!tants 20 4n z:co 2:2 tis c7si Te.er 133-54' .

25 September 1979 ,

Dr. Robert Jackson N; 1sar 7.ts.:1Etcry Oc=.issicr.

P-314 Washington, D.C. 20555

Dear Bob:

Enclosed is my supplemental testimony for the Skagit Environmental Hearings. In this testimony I afdressed the request of the Board for the methods used by the staff to estimate strong ground motion. In addition I presented srme site specific considerations for the Skagit facility.

I wish to state at this time that I have reread the Safety Evaluation Report (SER) including the most recent draft and that my own views are in agreement on all points of substance.

Sincerely,

, 6

' ljn " }' W John 7elleher JK:eks enclosure 1259 024

.sut:e; En;meem Ge:ic;'sts a :: En..ranmertal S::ent:sts C.:es in C:ter Prir.:i:at Cities 7911020 // O E-1

- Appendix E (Continued)

Woc,dward Clyde Consunants SJ7?* _.':r :T?.I. TESTIMONY OF JOFN FELLEiiER RELATING TO ESTIMATES OF STRON,G GROUND MOTION This supplemental testimony is to respond to the request of the Boced for additional information on methods of determining ground motion parameters. Initially the staff would nota that no teck.nique for ::timatin? strong ground motion is clearly superior to other methods under all conditions.

The choice of method is usually determined by the type of information available for the specific seismic hazard or by site specific considerations. However, to help the Board in its understanding of the dif f erent tech-niques to estimate ground motion, we provide some site q,eci-fic remarks on the Skagit site and some general remarks Sescribing the position of the staff on techniques of esti-mating ground motion.

1. Large earthquakes occurring within the near surface environment (H 1 15KM) are typically accompanied by surface r ipture or surf ace faulting. For the specific evaluation of the SKAGIT site for potential sources of strong motion an important consideration is the virtual absence of evi-dence inferring surface faulting. Indeed with the possible exception of a location on the Olympic Peninsula there is no evidence that surface rupture has ever accompanied a large shock during Quaternary time throughout the entire province in which the site is location.1 Thus while surface faulting cannot be categorically precluded the evidence indicates that it is minor or absent throughout most of the province and that there is no reason to anticipate major release of seismic energy in a near-surface environment.

1 The staff considers the Skagit site to be in the tectonic province formed by the overriding continental lithosphere and beunded on the north by an extension through Vanccuver Island of the zone of decoupling between the Explorer and Juan de Fuca plates, on the south by the zone of transition associated with the Mendocino triple junction, on the east by the volcanic chain and on the west by oceanic lithosphere of the Pacific plate. The bounds are not included in the prevince.

,9 , ,

n ea 1259 025 N. .

I

Appendix E (Cor.tinued)_

Woodwcrci Ciyde Consuhcnts

_ age r

By way of cantrast, rsjer earthquanes in central or so u the r n Calif ornia commonly are acccmpunied by surf ace f aulting; major energy relecse has typically occurred at depths of 10 km or less.

The significance of this tectonic feature is that earthquakes of given magnitudes which have caused the most sericas destruction have been extremely shallow earthquakes usually accompanied by surface faulting. For example the Tangshan, China earthc.uake of 1976 (M=7.6) and the Managua, Nicaragua earthquake of 1972 (M =6. 4 ) caused great devasta-tion. These earthquakes had major seism'ic energy release at extremely shallow depths as evidenced by the surf ace rupturing in the central part of the respective cities.

By contrast the largest earthquakes of the tectonic prov-inces of the northwest have consistently occurred at the base of the crust or below. Even for the largest earthquakes of the northwest no single observation of intensity has ever exceeded MM VIII. A key consideration, therefore, in the site specific evaluation of the proposed Skagit facil-i ty is the absence of any evidence suggesting the likelihood that large earthquakes would be accompanied by surface fault-ing and by inference by major seismic energy release in the near surface environment.

2. Some studies heve estimated relationships among earth-quake magnitude, distance and peak horizontal ground acceler-ation. Such studies include Schnabel and Seed (1973), Tri-funac and Brady (1976), and U.S. Geological Survey Circular 795. Other studies have provided correlations between. peak ground accelerations and seismic intensity. These include Trifunac and Brady (1975) and Murphy and O'Brien (1977).

1259 026 E-3

Apoandix E (Continued)

:'cd':::.-d C!"de C.'nsultants 7,g, 3 These latter sources are used if only intensity information is available, while the other studies are useful if esti-mates can be made of source parameters such as magnitude, .

f ocal depth and distance to generating structure.

If instrur. ental determinations of magnitude exist, then estimates of strong ground motion relationships should be useu such as Schnabel and Seed (1973), Trifunac and Brady (1976) or U.S. Geological Survey Circular 795. If no instru-mental determination of magnitude exists for earlier earth-quakes, then intensity estimates are the most direct kind of information. In such cases intensity-ground motion rela-tionships such as Trifunac and Brady (1975) or Murphy and O'Brien (1977) should be used.

No instrumental determination of magnitude is avail-able for the 1872 earthquake of the Pacific Northwest.

Only intensity estimates are available and these are gen-erally sparse. The staff concluded that the maximum inten-sity associated with the 1872 earthquake was intensity VIII MM. For reasons discussed below, the estimate of Trifunac and Brady (1975) of .25 g for intensity VIII MM would pro-vide a conservative reference for the specific purpose of bounding the ground motion associated with the 1872 earth-quake in accordance with Reg. Guide 1.60.

In the original Safety Evaluation Report (SER) the staff compared the 1872 earthquake to a series of attenua-tion curves for an earthquake of magnitude 7.5. This was done because at that time the series of attenuation curves (PSAR for WPPSS No. 3 Figure 2-5-57b) was the most complete set available. The set of curves was compiled for earth-1259 027 E-4

Aopendix E'(Continued)

Pace 4 's'h:s:.*v.*:..-C CV> da Conskr.nts quakes of magnitude 7.5. Thus eve.- though the m:7.-itude of 7.5 was larger than any estimated _ for the 1872 earthquake, the completeness of the set of curves justified some corFer-

~

ison. At no time, however, did the staff make a determi".-

ation that the 1872 earthquake was of magnitude 7.5 and this fact was so stated in the SER.

The study by Murphy and O'Brien (1977) probably pro-vides better estimates of actual peak ccceleration at var-ious intensities than does the study by Trifunac and Brady (1975). The reason is that Murphy and O'Brien (1977) had a larger data set and improved statistical techniques.

Nevertheless, the more conservative relationship of Trit'unac and Brady (1975 ) is considered more appropriate for setting reference accelerations because at iatensities V, VI and VII the Reg. Guide 1. 60 spectra de termined by the mean of the peaks (i.e., the method of Trifunac and Brady) falls be . ween the mean and 84 th percentile spectrum for the fre-quencies of interest (Agbabian Associates, 1977). For inten-sity VIII, Trifunac and Brady (1975) appears to be conser-vative for their cited data set, in that the mean of observed peak accelerations is .167 g whereas their relationship predicts .256 g.

3. For near field location of earthquakes (within about 10 km for M=6 and within about 20 km for M=7), there is no ganerally accepted method for estimating strong ground motion. Each such situation requires an extensive and speci-fic examination. For earthquake locations between approx-imately 20 or 30 km to 100 km there is reasonable agreement on estimates of strong ground motion among many recent studies including Schnabel and Seed (1973), Trifunac and Brady (1976) and the U. S. Geological survey Circular 795.

1259 028 E-5

• Accendix F Dr. Robert E. Recan Reports .

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1. 703 790 1450 e TWx 710-633 C323 ,

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i i..

A Critical Evaluation of the l Interpretation Report of  ;

Aeromagnetic Coverage of the '

Skagit Nuclear Power Project  :

i Prepared for i

Nuclear Regulatory Commission .

Under I

Contract No. NRC-03-79-156 I l

l l

Phoenix Corporation ,

1600 Anderson Road McLean, Virginia 22102 September 1,1979 B r' "- -

I p,]

1259 029 9 T11)l?$Bof - _ _ _ _

Appendix'F (Continued) .t a

(

'c CO:CE CS g en Pace l l 1 '

Introduction . . . . . . . . . . . . ..

2 Survey Objectives . . . . . . . . . .. ...............  ;

............... 3 l[

Geologic Setting . . . . . . . . . . .. IE 4

Magnette Survey Data . . . . . . . . . . ............... Q -

4 l Primary Data . . . . . . . . . .. ...............  ! !

6 Supportive Data . . . . . . . . . . ............... i l 7  ;[

Laboratory Heasurements of Magnetic Properties ............

8 Interpretation . . . . . . . . . . . . . ...............

9 i, Regional Coverage . . . . .. ...............

9 l Detailed Interpretation . . . ............... l i :

10 Inf erred Church Mt/Decatur-Shuksan Plate Contact ...... 10  !  :

Results of Main Objectives .. . ...............

15 General Interpretation . . .. ................

17 '

Conclusions . . . . . . . . . . . . . . .........

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1259 030 i e

F-2 .

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___ - n_

Apoendix F (Continued _) .

.E i..,E.

.e FIGURES iG

!b

- Page ,g Ficure No. I E

... 12 j b 1 Little Haystack Mountain Model With NE Dip . . .

• l.

13 f $

2 Little Haystack Mountain Model With Vertical Dip . . . r

.... 14 ,

3 Little Haystack Mountain Model With SW Dip . . _L i

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1259 031  !

o F-3  !*

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'r

Appendix F (Continued)

. IKTRODUCTION Phoenix Corporation was contracted by the' Nuclear Regulatory Com=ission (NRC) to provide an objective and critical evaluation of a report int erpret in g ,

aero=agnetic survey data of the Skagit Nuclear Power Project by Exploration Data Consultants, Inc. (EDCON). The purpose of such a review is to afford

~

the NP.C :n eb.4eeti'?e snelysis of these data by a disinterested yet qualified third party. The report was to be analyzed with the objectives of the NRC

nterest in such a project borne constantly on mind.

In reviewing such a proj ect two approaches can be taken. One is that the material be viewed independently of the aims and objectives of the survey b

whereas the alternative is that the rationale of the survey becomes of para-

' mount import ance. For the purpose of the NRC project the latter approach was selected although some suggestions and comments on the data reduction are

- also offered.

3 J

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1 1

1

~'-

. 1259 032 F-4

~. ,

Appendix F (Continued)

. SURVEY ^BJECTIVES

~

J

- The objectives of the aeromagnetic survey project are well stated in d the EDCON Report.

5 A. To determine whether or not there is a fault paralleling the

,e

[ trend to Gilligan Creek which may have displaced the Shuksan thrust fault. A normal fault with a displacement of at least h

J 1500 feet had been hypothesized along the creek. Alt e rnat ively ,

a tear or strike slip fault with a displacement of about 4 miles

( This proposed fault would be approximately j had been hypothesized.

coincident with a change in the trend of the contours on the U.S.C.S. aeromagnetic maps.

B. To determine whether or not there is a fault associated with 7

j Day Creek.

C. To evaluate whether or not there is faulting in the Skagit River y valley, south of the Butler Hill area, where there is a change

' in trend of the contour ?.ines on the U.S.G.S. aeromagnetic maps, i

- D. To avaluate t1 structural relationship between the rocks in the Cultus Mountain-Haystack Mountain a ea, and the rocks in a

the Snuksan Thrust Plate. Resolution between two models was requested, i.e., whether the rocks in the " horseshoe" area 1 (between Day ano cilligan Creeks, south of the Skagit niver) d overlie the Shuksan Plate, r1 inter, n ted by Dr. John tihetten;

] or underlie the Shuksan Plate, as interpreted in the PSAR.

E. To complete a general interpretation of the acromagnatic l coverage of the area, defining observable magnetic t'aits and r-their structural relationship. Epecial attention was to be

] paid to any f eatures that could help resolve any of the objec-

1. tives as outlined above.

] F. To examine the aeromagnetic data for evidence bearing on the existence of the hypothetical "B and P" fault, as discussed 1 in ASLB hearings, March,1978.

~

1259 033

"] F-5 f*

' Appendix F (Continued)

~

GEOLOGIC SETTING The pertinent geology of the site is succintly suc=arized in the EDCC :

report and need not be repeated here. The geology appears well mapped and .

- the sa ples identified agree with the mapping of the Shuksan and Church

' Mountain thrust plates. It should be noted that the samples identified in

. the magnetic properties study also agree with mapped geology.

M 2

r.s 1259 034

}

Appendix F (Continued)

-  :'a0:::::: SrTJirr r!.7/

Primary Dat data from two completely -

It is indeed fortunate for such a study that independent aerceagnetic surveys of the same area by two reputable geophysical contractors are available. Although appearing to be somewhat different at a consts cnt 'a h = :.

first overall inspection the data are essentially intera...;.

one considers the specifications of the individual surveys and the data

,, We think that it is reduction procedures selected by the two contractors.

safe to say that both data sets are valid even though their representations differ somewhat. Ne agree totally with EDCON's evaluation (p.10) cl.P.

"Any contour map must be considered to be only a representation of he observed magnetic field and the accuracy of the representation dep;nds on L- cl.e survey parameters as well as the operations perfor=ed on the data

.- set af ter acquisition."

s Defore discussing some of the differences between the data sets and

]'

commenting on EDCON's evaluation of the dif ferences,it is instructive to first present some background material on aeromagnetic surveys in general.

a

, - First of all the earth's magnetic field can be / vided 2 into three component i

L? fields; the internal or primary field arising f rom sort of dynamo action in i the core of tFa earth; the . nomalous or secondary field induced into crustal g,

I rocks by the primary field; and the external field due to ionospheric and magnetospheric current systems.

The total geomagnetic field is a dynamic

}_

field varying in both space and time. *he object ive of an aeromagnetic F.owever, survey is to map the spatial variations of the anomalous field.

"' any measure-ent of the magnetic field contains contributions f rom all

• ' three components of the geomagnetic field and the particular field of This can int e r est , in this case the anomalous field, must he extracted.

r~

~ be readily done at a stat ionary point by monitoring the field and remcving J-i any t emporal variations (thus removing the external field) and by subtracting from the measurement a mathematical representation of the internal field International Geomagnetic Ref erence Tield). 1:owever in

,I_ , in

( most cases the tne case of airborne reasurements the problem is note complicated in that the measurenent is being made from a moving plat form. Thus there are

.- .c.

1259 035 I

F-7

Appendix F (Continued)

~

pr:hicas f p::itica:1 10:::1:n :: well :: th: f :: that tc p:: 1 ign:1:

.~~

under this" condition can be tapped as apparent s ps- ia'. changes in th= ..

, =sgnetic field. The proble: is further cc= plicated by the turbulence

effects on the moving platform and the fact that relative rather than abso-

~

'- lute magnetometers are often employed. Another practical prob'em is that

~* only discrete sa=ples of a continuous field are being obtained over a

. broad area. All of these factors underscore the need for the cost detailed

,$ attention to the reduction of the cagnetic measurements. For, any measure-ment of the magnetic field from an airplane is an accurate measurement of

,; the cagnetic field but for this project what is needed is an accurate representation of the anomalous magnetic field.

In this project both con:ractors reduced the data in a reasonable canner although the AercService akscription of their data reduction sche =e is to be applauded as it shows a =ature and reascnable approach to the

~

[ problems associated with the reduction of aero=agnetic data. The LES

~

reduction is also valid and undoubtedly reflects a company philosophy

,' that the less you do with the data the better it is. However, in the case of providing a contour map representation of the results of a draped aero-magnetic survey, the AeroService technique appears the more reasonable.

The reduc'cion of the data, however, is not the only f actor affecting a

~

the presentation of the data, there are several others.

. The LKB survey was flown at 600 feet above terrain in a predominantly North-South direction with a proton magnetometer. The AeroService survey was flown at 1500 feet (for the most part) above terrain in botn North-South

~

and East est directions with a mo.re sensitive cessium vapor magnetometer.

The differences in the appearance of the maps are due to:

a) Contour Interval - The AeroService data because of the highet sensitivity instrument is contoured at 2 gammas whereas the LK3 data were contoared at 10 gammas. The textural appearance resulting from tnis contour 7 difference greatly af fects the human eye's perception of the map.

~

F-8 1250 036

Appendix F (Continued)

Flf-he if ne Direction - One need only connare ricures 2 c=d 5

] -

b) of thc C005N Rcpcrt tc cce the influence of fifbt t line direction. One only ..

['

• • has to examine the shape of the anomaly centered at approxi=ately 122 11' W

~

and 48 24'4' N to see the influence of flight direction.

~

c) Altitude - As the LKB survey was several hundred feet closer to 1

• 3 the magnetic sources the grodients would be somewhat sharper.

I t

Il The,a f actors a= well as the smoothine apolied by AeroService as i3 =entioned in the EDCON report contribute to the apparent differences j

between the surveys.

f}

l In summary it can be stated that both data sets are undoubtedly valid,

.] especially if the profiles are used and that they constitute a valuable data

?" set in that the magnetic field is measured at several elevations, t

M j

'l Supportive Data f1

• t il In additinn to the primary aeromagnetic data, regional aeromagnetic data (2 mile 11.nes at 3000' barometric, East-West in one sheet and North-h

[; South in the other) from the USGS as well as isolated ground data from Bechtel Inc. are also available. The USGS data adds a much needed regional picture showing how the detailed aeromagnetic surveys fit and the ground data provide much needed " ground truth." Unfortunat- y no information is l

[' provided on the quality of this data although f rom past experience we can k" expect the USGS data to be of substantial quality.

15 .

• I s'

??

e-e-o 1259 037 F-9

--o-

- Aopendix F (Continued)

• 1ALG7aTCTJ !CO'T."':T; OT l'*.0 :'~~;; 7T.0?ET.!:EF

.a .

Magnetic property measure = cats of representative rock t; pes in the j

area of a st rvey are inval *kle in the quantitative analysis of aeronagnetf c data. Howevsr, as a an i u a!. ed it is nuite difficult to obtain "represen-

' tative" samples s an crea uZ such complex -rology. Such saeples are

h ofr en obtained Is am ,rface or near-surface locations where weathering may 3 preJer a te and s ich could be u.relaten to more deep seated causative bodies.

[,  !!evertheless, Dr. Beck is a recognized authority in this area and has carried

,j out a reasonable and valuable piece of work in providing magnetic property ceasure:ents. His work serves to provide at least order of eagnitude values

' of susceptibility and indicares that the remanent nagnetization in these rocks i is nor=al. Both of these facts are of great significant in o:puter modeling of magnetic anomalies.

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i-1259 038 F-10 t*

'

• Appendir F (Continued)

~

I:'! F.?P.IT!.TInP si -

~

In general the interpretation techniques e= ployed by ED00N in this report are adequate for the purposes of the study but do not use the full

' 1

'g potential of the data. While there are many valid approaches to the inter-8 pretation of aeromagnetic maps, the trend in this report has been towards the more si=plified ones. Indeed the codeling could have been much more involved,

,3 resulting ba more geologically plausibis Leclas and if s :c filtering had

• been e= ployed. core htformation could have been obtained on the stated diff er-

• • ence in trends between the magnetic provinces and on the " hypothetical E and

.J B .2 ult."

n. it is best to go

,J For purposes of discussing this phase of the report through the EDCCN report section by section.

I Profile Analysis - Unfortunately not many profiles were presented with the report. The Werner deconvolution approach of Aero Service

'l is adequate and the slope method used by EDCON is valid. Their s

i approach to susceptibility determination is valid and their deter-

} mination of dip and attitude is discussed in the section on modeling.

Reduction to the Pole - While a valid technique it is not critical i at this inclination (71 ) and despite their discussion no results are presented.

• 1 Macnetic Modeling - The modeling program described in the appendix appear adequate altho. ugh only the si=pler regular bodies appear to have been used in this report.

Macnetic Lineaments - It 'is unfortunate that at this stage some directional filtering was not employed to study the possibility of magnetic lineaments. Although agreeing with EDCON that no other lineaments similar to the Devils' Mt Fault zone are present in the data, there are hints of others in both the USGS and

~

contractor data, that should be more fully investigated.

e G

~

1259 039 F-11

"= esmee -,

Appendix F (Centinued)

". - Ee;ional Coverage

*GC USGS Aero=as;netic C.overcce - It should be ncted th: Fi;ure 11 u-Report 77-24) was co= piled fro: a servey flown in a North-South

,j direction while the data in Figure 12 (USGS Report 7S-354) were obtained -

se j

in an East-West direction. The fact that the surveys are different and that they were flown in different directions only serve to highlight l';' any differences between the data. The flight line orientation, separa-

'2 tions, and the fact that the change in contours south of the Mtler hill area occur at the edge of the data all contribute to the question of the at reality of such an effect.

jJ is While EDCON adequately describes the regional nature of the data it h

unfortunate that they did not utilize this regional data more in their d

int erpre tat ion. Of paramount interest is the " triangular-shaped" area g

[j outlined in Figures 11 nad 12 in their report. What is it? What is its 1

relationship +.o the Church Mountain Thrust plate end the contact mapped

.? ,

in Figure 16? What can this regional picture reveal about the high

] What can l

cagnetic anoirsly in the southwestern part of the study area?

it reveal about the hypothetical B and B fault? What would depth analyses of these data reveal? These questions should have been addressed.

Twin Sisters Dunite - This is of interest in that it is also over the l

same geologic units as the Goat Mountain anomaly interpc hted by EDCON

{ to be associated with part of the Church Mountain Thrust Plate.

I'

• Detailed Interpretation

• Macnetic Trend Map - Without information on the method utilized to

• - compute the trend map, it is difficult to analyze any discussion or e* interpretation of such a map are at best highly qualitative and as such the discussion in the text is not inconsistent with the cap.

r* Maenetic Intensity Map - The colored magnetic intensity map is invalu-able in studying these data. The centour calor interval o~ 200 ga==as

}-

- is reasonable as is the color selection. It should be noted that the i- cap could be colored in many wt.ys, but the EDCON renditien is reascnable.

It is unfortunate that the AeroService data were not also colored, r'

i

!- _g_

F 1259 040 h- F-12

N Appendix F (Continued) 5:4 b ,

Indeed the ELCON .:eport in their discussion of the data seems to f avor

+w w

2sM the AeroService data. In order that the data may be intercompared,

~;

({

' Phoenix Corporation has colored the AercService data on a fairly crude w Basically the map shows the same general fashion using colored pencils.

3.m_1 .l r features as the ELCON map and further demonstrates the similarity

M , between the data sets.

?.

t,.- .

Inferred Church 1.c/Decatur-Shuksan Plate Centact ef , Although und.aubtedly quite subjective, the mapped contact is consistent

('H r

with the magnetic and geological data. For the purposes of this study the ei j- ,

drawn contact is adequate.

9, "

i.h Results of Main Objectives b-

y. .

Faulcing Along Gilliaan and Day Creeks - The data are consistent with

[ the interpretation aat there is no magnetic cvidence for faulting along

[f Gilligan or Day Creek. It is unfortunate though that the ground magnetic c.

{ data were not presented in this study.

F_aulting South of Butler Hill - The data definitely confirm the lack of any evidence f or a fault in the area and Icnd credence to the supposition i f, that the cha.nge in contours on the USGS maps is merely an artifact.

Structural Relationship of the Thrust Plates

, 1) I.ittle Haystack Mountain Area - It is difficult to look at the

1. contact of the platet by analyzing an individual anomaly located within one of the plates. Nevertheless the modeling could prove

( valuable.

l The two-dimensional assumption is not strictly justified in this modeling es the anomaly is quite limite d in extent ne il to the profile. However it is adequate for a first approximanen.

The anomalics throughout the entire study area all have a weli

{ "

developed low to the Northeast of the main positive. This is especially apparent in the, isolated cases such as I.yman Hill.

N Sech a structure is generally indicative of a Southwasterly i .

1259 041 F-13 p.

i; --

~

• Accendix F (Continued)

}

cipping body and indeed Lyman Hill and other such anomalies have been interpreted as the expression of bodies dipping to the South-west. In the case cf the anomaly chosen for study in Little Haystack Mountain area there is some question in our mind about anomaly separation. Basically this can be stated as "is the anomaly selected to be modeled in Figure 20 due to one bo.:y is it influenced by another_ body?" If the low part of the anomaly

• in the Southwest is indeed connected to a positive anomaly further to the Southwest then a different interpretatic ? could result.

However, Blakeley (pers comm) has effectively modeled this anomaly with a less extensive serpentine body dipping to the Northeast,.

J correctly matching the low to the Northeast which is so important.

Although his data were not available to us, we, in general, dupli-cated his results in Figure 1. This was done for two reasons.

First to study the influence of different orientations of the body and secondly to exanine the act.enuation of the signal with altitude.

Figure 1 shows, in general, a body similar to that described by Blakeley. It does not have as good a fit between measured and 1

' computed values as we were trying only to demonstrate a concept.

The fit Figure 2 and 3 show a similar body with different dips.

] between measured and computed values are about the same as in Figure 1 and could undoubtedly be improved with some remodeling.

H_owever the concept de ionstrated here is that a Southwesterly dip for these_serpen_ine t bodies.is possible. It would be , instructive is to have Blakeley and Whetten investigate this further if it deemed geological significant.

2) Modeled Dip of Thrust Plane - It is equally probable that the thrust plane could be dipping to the Southwest. The profiles selected by EDCON appear highly contaminated by other anomalies and the sharp discontinuities in the model for a Southsesterly dipping thrust plane could provide unreasonably sharp magnetic anomalies. Some more sophisticated modeling could aleviate this.

_J .

~1 - -

1259 042 F-14

Aopendix F (Continued) co-nute6 values 9 L 5 0$ ?.T.

g 5500 A5L

, 300 -

7 6500' ASL 1 0 750e' Ast 200 0 1 'h ogstyynn (4500' ASL) 3 O 3 5 A o 6 6 5

s 10 0

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.2 < g tOaO O O g a OO 6

0

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o a 3

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]'

4000'ASL

, SW

-2000' Agt K-8265

-6

.., x 10 NE J

.e

- O,

~

_ 2000' I

, Figure 1. Little llaystack Mountain Model With NE Dip.

F-15 S

1259 043

Appendix F (Continued) 5 300 r- cc-nut ed

• alues I.. e o /. 5 M ASL f' S' l <

s-

• 200 -

=

E. ' n .. .

=

3 E

• 2 <

10 0 -

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/ O

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1

-4000' ASL L_.

t 5-SW N~

I -2000 ASL K-7500

.: . x 10

-6 NE i

F*

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~=

4 *

-- 2006 Figure 2. Little F.aystack !!auntain Medel With

-f*

Vertical Dip.

s.

'_. 1259 044 F-16

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Apoendix F (Continued) t i 3 0 0 ,-

- 1 I~~ Computed '.'alue s g o o 4500 ASL -

E

. 2 U

200 -

.a l5 -

o e J

'l 5

.] E 100 -

o

.J o o

0 -

oo o 1

O 6O

_, n ooo

- 4000' ASL 7

.] _

SW

-2000 ASL g.7oco

-6 x 10

]

O' I

a < #

. 2000

- Figure 3. Little Haystack 'tountain Model Uith S!? Dip.

. g_3 7 1M 9 045

.~._

'

• ADpendix'F (Continued) r.

3) Lyran Hill - It is not surprising that a body cculd be cf con-One only has L.i siderably larger extent than the surface outcrop.

to consider the practical example of seeing an apparently s=all rock sticking out of the dirt and setting about to remove it.

r L!

More often than not the observed rock is just the tip of an ice-t 4 berg and the rock is indeed a fair-sized boulder. Agafn more J

complex modeling could have bean used.

f* "utler Mill a.rea - T'..e-di-er.sf ocal nodeline is not justified in this y  !. '

case although the general results obtained are valid for the purposes t' of this study.

{

5) Goat Mountain Area - No detailed data are presented to judge the l, interpretation, u

6) Chuckanut Mountain - Although refine =er.ts could be made on the codel I*

it does appear' adequate.

In general these individual areas studied in detail wara not cde:;uctc13-related to the thrust sheet question.

= 7) Hyocchetical "B and B" Fault - There is definitely a trend in

-- the region of the "B and B" which follows the =apped contact of the thrust plates on Figure 16 with the exception of the

>' Butler Hill and Chuckanut Mountain extensions. The trend is i not as apparent on the USGS regional map. It would have been p instructive to have filtered the data to enhance this feature.

L'.

Howevt r, "B and B" fault does appear to be the signature of the thrust plate contact and the EDCON interpretation appears i.

reasonable.

?

General Interpretation l

The Magnetic Interpretation Results Map (Figure 24) is indeed difficult to analy e. Nonetheless, the textual description appears valid and helps in f digesting the map data. The most interesting aspect of this map is the t

continued : ortheasterly trends of causative bodies and major negative anoma-

~ lies of the Shuksan Plate Area. In Figure 16 attention was called to core L northerly trends in this area. These are not observed in Figure 24.

s' l F-18 l

_ ~*Wo

Appendix F (Continued)

It is unfortunate that tne USGS regional data were not interpreted tr.

more detail. We think that they definitely show that the caterial with one ,

more intense magnetic signature shown in the colored map is a coherent unit extending to the Decator Terrane as mapped by Whetten. This magnetic material is apparently missing in the region of the map associated with the Shuksan Plate. Indeed if it is not missing it cust be quite deep.

An indication of this is afforded by the curves shown in Figure 1. These .

show, for exa=ple, that if the serpentinized bodies were 3000 feet lower they would still have a positive anomaly of approxi=ately 60 gat =as asso-ciated with them.

I L

i P

L e

F r

r-

?

s C

l t

e

<b t

=

C E

1 t.

ie F-19 1259 047 f:

f-f-

--- L.

Aapendix'F (Continued)

C0"CLi'!IO.. S The data used in this report were both plentiful and valid. The interpretive techniques e= ployed, while not i=aginative, were adequate for the objectives of the study, k'e agree with the conclusions _nf_Ihe {

EDCON re2 ort and would further state that fro = the =agnetic data the plant site appears to be ideal.

It is unfortunate that having two co=plete surveys at different elevations that they were not better used to interpret the results.

Also the USGS regional data and the detailed surveys over areas 2A and 5 could have been better employed. More ambitious interpretation tech-niques could have been utilized. Such techniques would include filtering and = ore ce= plex =odeling.

6 O

w e

6 m

g g OAB F-20 mee