INTERPRETATION OF VIBROSEIS REFLECTIONS Jeanne L. Brennan · INTERPRETATION OF VIBROSEIS...

INTERPRETATION OF VIBROSEIS REFLECTIONS

FROM WITHIN THE CATOCTIN FORMATION OF CENTRAL VIRGINIA

by

Jeanne L. Brennan

Thesis submitted to the Faculty of the

Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science

in

Geophysics

APPROVED:

John K. Costain, Chairman

G. A. Bollfnger 17 Eynn Glover, III

September 1985

Blacksburg, Virginia

INTERPRETATION OF VIBROSEIS REFLECTIONS

FROM WITHIN THE CATOCTIN FORMATION OF CENTRAL VIRGINIA

by

Jeanne L. Brennan

John K. Costain, Chairman

Geophysics

(ABSTRACT)

Large amplitude seismic reflections from within the

Catoctin Formation of central Virginia are interpreted to

originate from acoustically thin beds of interlayered

metabasal ts and metasediments. Large acoustic impedance

contrasts exist between epidotised layers ( epidosi tes and

volcanic breccia) and non-epidotised layers (greenstones and

phyllites) within the Catoctin Formation. Acoustic impedance

contrasts also exist between greenstones (metabasalts) and

phyllites (metasediments). Constructive interference of

small amplitude reflections from thin beds result in large

amplitude, reverberating reflections.

Thin bed reflections that approximate the first deriva-

tive of the source wavelet constructively interfere to give

even larger amplitude reflections than those originating by

conventional tuning. Computer modeling based on two geologic

sections of thin beds of epidosites interlayered with

greenstones and of greenstones interlayered with phyllites

and epidosi tes indicates that large amplitude reflections

result from constructive interference of thin bed re-

flections.

ACKNOWLEDGEMENTS

This research was supported by ARCO and CONOCO Fellowships

through the department of Geological Sciences, and by NRC

Contract #NRC-04-75-237 to L. Glover, III and J. K. Costain,

Principal Investigators.

I express great appreciation to my major advisor, Dr.

John Costain, for bringing geologists and geophysicists to-

gether to solve this interpretation problem. Dr. Lynn

Glover, III, provided extremely valuable comments concerning

presentation and analysis of the data and was instrumental

in relating geophysical and geological studies. Revisions

suggested by Dr. Gil Bollinger will hopefully make this paper

more meaningful to members of the science community in dis-

ciplines outside of reflection seismology and geology.

Graduate student organized and guided one of the

field trips that resulted in sample collection and provided

preliminary geologic sections used in the modeling. The ul-

trasonic velocity data would not have been obtained without

the patience and ingenuity of of the

Geophysical Instrumentation Laboratory. I am grateful to

for the petrographic modal analysis of the

Catoctin Formation which he did for us on a very rushed

schedule.

Acknowledgements iv

I express my deep love and appreciation to my brother

and sisters, and to my good friend , for their

support and encouragement during the last two years. I owe

everything to my parents, and , who have made many

sacrifices for me during my life but have never reminded me

of it. I dedicate this paper to my father, who has an en-

thusiasm for science from which I have always benefited.

Acknowledgements v

TABLE OF CONTENTS

INTRODUCTION AND PURPOSE OF STUDY

OVERVIEW OF GEOLOGIC FRAMEWORK

REFLECTIVITY OF CATOCTIN FORMATION

Modal Analyses

Velocity Determinations

Density Determinations

Reflection Coefficients

THIN BED THEORETICAL MODELS

Results

CONCLUSIONS

REFERENCES

APPENDIX A. CALIBRATION CURVES

APPENDIX B. REFLECTION COEFFICIENTS

VITA

Table of Contents

1

6

12

12

12

21

24

29

46

57

58

60

64

95

vi

LIST OF ILLUSTRATIONS

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

1. Central Virginia study area . . . 2. Stacked section of line NSF-2

3. Schematic geologic cross-section of Eastern Blue Ridge . . . . . . . . . . . . . . . .

4. Catoctin Formation section and core sample lo-cations. . . . . . . . . . . . . . . . .

5. Stratigraphic sections of Catoctin Formation

6. Modal analyses of 12 Catoctin Fm and 1 Chilhowee Fm sample . . . . . . . . . .

7. Velocity versus pressure of Catoctin greenstones . . . . . . . . . . . .

8. Velocity versus pressure of Catoctin epidosites . . . . . . . . . . . .

9. Velocity versus density of Catoctin greens tones . . . . . . . . . . . . . . .

10. Velocity versus density of Catoctin epidosites

11. Acoustic impedance versus pressure of Catoctin greens tones . . . . . . . . . . . . . . . .

12. Acoustic impedance versus pressure of Catoctin epidosites . . . . . . . . . . .

Figure 13. Synthetic 14-56 Hz Klauder wavelet

Figure 14. Resolution limit of 14-56 Hz wavelet

Figure 15. Tuning thickness

Figure 16. Tuning of reflections for two dipoles of same polarity . . . . . . .

Figure 17. Tuning of reflections from two dipoles of same polarity . . . . . . . . . . . . . .

Figure 18. Tuning of reflections from two dipoles of op-posite polarity . . . . . . . . . .

List of Illustrations

2

5

7

8

9

13

19

20

22

23

25

26

30

32

33

34

36

37

vii

Figure 19. Tuning of reflections from two dipoles of op-posite polarity . . . 38

Figure 20. Thin bed models 40

Figure 21. Multiple thin bed model 42

Figure 22. Simplified thin bed model . . . 43

Figure 23. Multiple thin bed model for i:::T/2 44

Figure 24. Catoctin thin bed model constructed from sec-tion A . . . . . . . . . . . . 48

Figure 25. Section A without beds <l ms and with beds replaced . . . . . . . . . . . 49

Figure 26. Section A - previous figure without layer JB4-4G . . . . . . . . . . . . . . 50

Figure 27. Section A - previous figure with layers re-peated and replaced . . . . . . . . . 51

Figure 28. Section A - previous figure with layers re-peated . . . . . . . 52

Figure 29. Catoctin thin bed model constructed from sec-tion B . . . 54

Figure 30. Section B - layers replaced and removed 55

Figure 31. Section B - two layers removed 56

Figure 32. Steel calibration curve for 200 atm 61

Figure 33. Steel calibration curve for 400 atm 62

Figure 34. Steel calibration curve for 600 atm . . . 63

List of Illustrations viii

LIST OF TABLES

Table 1. P-Velocities and Densities of Catoctin

Samples 15

Table 2. Anisotropy of Catoctin Formation 28

Table 3. Catoctin Reflection Coefficients(600atm) 65

List of Tables ix

INTRODUCTION AND PURPOSE OF STUDY

The Catoctin Formation of central Virginia is a rift

volcanic sequence of metabasalts interlayered with

metasediments. Seismic reflections from within syn- and

post-rift sediments are commonly observed along passive mar-

gins, including the Bay of Biscay and the U.S. Atlantic mar-

gin (Brun and Choukroune, 1983; Bally, 1981). In central

Virginia, it is primarily the reflectivity of metamorphosed

basalts that allow an interpretation of the subsurface thrust

geometry using reflection seismology.

The record of rifting in the southern Appalachians is

incomplete due to erosion, deformation, and metamorphism

(Wehr and Glover, 1985). An interpretation of the origin of

the reflections from the Catoctin Formation provides further

information about the tectonic architecture in central

Virginia. Such information may be used to constrain geologic

and tectonic models. An interpretation of the reflections

is possible in large part because of the acoustic impedance

contrast between thin layers of epidotised and non-epidotised

rift basal ts and sediments. On a broader scale, an inter-

pretation of the reflections may be used to help identify the

seismic signature of thin bed sequences from other geologic

settings as well as along passive continental margins.

Introduction and Purpose of Study 1

0 co C

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ure

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Vibroseis reflection data collected and processed by the

Regional Geophysics Laboratory (RGL) along the James River

in central Virginia (Figure 1) include segment NSF-2 of

seismic profile JRT-1 extending from Richmond to the crest

of the Blue Ridge. NSF-2, which has particularly good re-

flection quality and excellent signal to noise ratio, con-

tains large amplitude, east-dipping reflections (Figure 2)

with a reverberating nature. Reflections are defined as

reverberating when successive reflections blend together into

a steady oscillation (Sheriff, 1973). The reverberating re-

flections present on NSF-2 are interpreted to have developed

from within the Catoctin Formation.

Velocity analyses of the reflections indicate that these

reflections are primary reflections ( Coruh and others, in

review). The seismic signature of the reflections from

within the Catoctin Formation have been characterized as

parallel reflections from the tops and bottoms of thick beds

(Coruh and others, in review). The purpose of this study is

to determine the origin of these reflections from the

Catoctin formation in the crystalline Blue Ridge terrane of

central Virginia. The author hopes to show that large am-

plitude, reverberating reflections result from constructive

interference of reflections from a series of thin beds rather

than thick beds. This hypothesis is substantiated by

reflectivity data (velocity and density), stratigraphic


sections, and synthetic seismograms of the Catoctin Forma-

tion.


A c;;) c;;)

Figure 2.

·-o -0 w N I

c;;) g (J1 (Si Eil -i

D -i

Stacked section of line NSF-2: Reflections from the Catoctin Formation along the James River traverse in central Virginia.


OVERVIEW OF GEOLOGIC FRAMEWORK

The Catoctin Formation of central Virginia is composed

of metamorphosed basalts and sandstones that are believed to

represent part of the Eocambrian rift facies of the eastern

continental margin of North America (Wehr and Glover, 1985).

Rifting and crustal attenuation occurred predominantly during

the Precambrian, although there is some evidence of rifting

continuing into the Eocambrian. The axial zone of the Blue

Ridge anticlinorium in central Virginia is believed to be a

reactivated hinge zone separating attenuated crust to the

east from normal continental crust to the west (Wehr and

Glover, 1985).

On the west side of the Blue Ridge near line NSF-2 and

the study area, granuli te facies grani toid rocks of 1 Ga

Grenville basement are overlain nonconformably by a thin unit

of Eocambrian (?) Swift Run shallow-water elastics and non-

marine Catoctin volcanics metamorphosed to greenschist facies

(Figure 3). These formations were probably deposited

subaerially in rift basins which developed landward of the

hinge zone (Wehr and Glover, 1985). Nonconformably overlying

the Catoctin Formation in the adjacent Valley and Ridge are

shallow marine and alluvial elastics of the Cambrian

Chilhowee Group (Wehr and Glover, 1985). Preliminary

stratigraphic sections of the Catoctin Formation (Figure 5)

Overview of Geologic Framework 6

NW AXIS Of

BLUE RIDGE ANTICLINORIUM

ROCK FISH VALLEY

FAULT

SE

C/§f?C'.t;;~=~~~-;~~L~~-;:~~~!/{(\Utmnx\:Y! ~~ 1l 11 ;;;~-~~~:;;; '~;'~~~ l 1 :;:,:,:.:,:,:::::::::::<.Fm.::::./: Lynchburi;i ·Gp.

,,,,, .. ,, .. v L

.._.__,..___...____,_--'-'-~--=-"-~~~~-'-~

11 11 .., I 1 .. -

. (Wehr and Glover, 1985) Schematic restored cross sections across the Blue Ridge (not to scale) showing

relations among earty PaJeozoic-late Proterozoic units. Patterns as in Figure l: d2l"k stipple represents volcanic rocks; random dashes represent Crossnore plutons.

Figure 3. Schematic geologic cross-section of Eastern Blue Ridge: central Virginia Precambrian to Paleozoic sediments (Glover and Wehr, 1985).


8

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. ;;.,_::_:------: .. ~

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SCHISTOSE BASALT

EPIDOTISED SANDSTONE SCHISTOSE BASALT

PHYLLITE SCHISTOSE BASALT

PHYLtrTE SCHISTOSE BASALT


EPIDOTISED SCHISTOSE BASALT

SCHISTOSE BASALT

PHYLLITE EPIDOTISED SCHISTOSE BASALT


PHYLLITE

0

"' '::! ... 0 Q 0..

"'

SCHISTOSE BASALT

AMYGDALOIDAL

METASANDSTONE 60

VOLCANIC BRECCIA . SCHISTOSE

~PHYLLITE

DSCHIST

SECTION A

-

/' //, /,// //Jfi/@,/

-

-

SCHISTOSE BASALT

AMYGOALOIDAL EPIDOTISED BASALT

SCHISTOSE BASALT

EPIDOTISED BASAL TS AND AMYGDALOIDAL

VOLCANIC BRECCIA

SCHISTOSE BASALT

EPIDOTISED BASALT AND VOLCANIC BRECCIA

PHYLLITE

SCHISTOSE BASALT

SECTION B

: 0 •• ' ••••••••• • : • ••• • • • •• 0 . . ...... ·.· .. . . . . . . . . . . • 0 • • •••• ' •••

•• • ••••••• 0 ••

. . . . ... '• '•'a 111 .' , 0 • ' 0 1' . · ... · ....... . ,o•''.o•o•'•o

• • • • 0. • • ••• . "... .

Figure 5. Stratigraphic Formation: (a) Section B.

sections Section A

of Catoctin on Figure 4; (b)


at two locations (Figure 4) include thin beds ( <30 meters

thick). Section B consists of thin beds of metamorphosed,

epidotised basal ts and sandstones interlayered with non-

epidotised, foliated metabasalts and

Figure 5, (R. Badger, pers. comm., 1985).

zones are flow breccias or highly altered

and quartz (R. Badger, pers. comm., 1985).

metasediments,

The epidotised

zones of epidote

Gathright (1976)

refers to these zones as epidote-amygdaloidal breccia.

Basalt flows and rift sediments are also commonly interlay-

ered within the Catoctin Formation ( R. Badger, pers. comm.,

1985) as in section A, Figure 5.

East of the Blue Ridge, Grenville age basement and Late

Precambrian intrusives are overlain nonconformably by east-

dipping Eocambrian shallow to deep marine elastic rocks of

the Lynchburg Group deposited in large rift basins (Wehr and

Glover, 1985) . Overlying the Lynchburg Formation are ap-

proximately 2 km of Catoctin greenschist-facies metamorphosed

basal ts interbedded with metasediments. This sequence is

believed to have been deposited in a submarine environment

because of the presence of interlayered turbidite sandstone

beds, pillows, and volcanic breccia (Wehr and Glover, 1985).

Coarse epidote amygdules are also present in outcrop (Wehr

and Glover, 1985). The Evington deep-water sequence, a pos-

sible equivalent of the Cambre-Ordovician Valley and Ridge

Chilhowee shelf sequence, stratigraphically overlies the


Catoctin on the east side of the Blue Ridge (Wehr and Glover,

1985) .

A geologic interpretation of seismic reflection profile

NSF-2 places the Catoctin Formation above the Lynchburg For-

mation and below the Evington Group (Coruh and others, in

review). This stratigraphy corresponds to the east side of

the Blue Ridge. The seismic reflections originating from

within the Catoctin Formation on NSF-2 are therefore origi-

nating from within a rift sequence believed to have been de-

posited in a submarine environment.

Stratigraphic sections, Figure 5, and sample collection

locations, Figure 4, are located on the west side of the Blue

Ridge. The Catoctin Formation outcrop on the east side of

the Blue Ridge is more heavily foliated than Catoctin Forma-

tion outcrop on the west side of the Blue Ridge, making it

more easily waethered than Catoctin outcrops on the west side

of the Blue Ridge. Rock samples were not collected at the

Catoctin Formation outcrop on the east side of the Blue Ridge

because of the poorer sample quality of the heavily foliated

section.


REFLECTIVITY OF CATOCTIN FORMATION

MODAL ANALYSES

Modal analyses of 12 samples of Catoctin Formation and

1 sample of the Chilhowee Formation were done by Russell Guy

on a 1000 point grid (Figure 6). Zircon was seen in each thin

section, although it did not appear in the count grid. Min-

ute traces of calcite and chlorite were seen in many samples,

al though in insufficient amounts to be counted. Only one

sample had more than 10% plagioclase (JB4-4D); several other

samples had minor amounts. The small grain size and lack of

twinning in the fine-grained samples made the distinction of

quartz from feldspar very difficult (Russell Guy, pers.

comm., 1985). For this reason, percentages of quartz and

feldspar were combined for sample descriptions.

VELOCITY DETERMINATIONS

Compressional wave velocities parallel and perpendic-

ular to the dominant foliation (when present) in 12 Catoctin

Formation samples and one Chilhowee Formation sample were

determined in a pressure cell in the Regional Geophysics

Laboratory at Virginia Tech using the method described by

Kolich ( 1974). Samples were collected at central Virginia

Reflectivity of Catoctin Formation 12

Percentage Minerals Sample Q Feld Ep Op Cc Chl Act Sph Bio z Total% ------------------------------------------------------------------------JB4·1 36.8 o. 7 8.6 15. 3 37. 6 0.6 0.4 100 (Chilhowee phyllite)

JB4·3B 21. 7 9. 1 37.9 1. 8 25.6 3.9 100 (Phyllite)

JB4·3C 42.9 1. 8 45. 2 10. 1 100 (Epidosite)

JB4·3D 13.5 46. 8 5. 7 6. 1 27.9 100 (Greenstone)

JB4·4A 17. 1 0.2 49.8 7.5 8.0 17.4 100 (Epidosite)

JB4·4D 1. 5 12. 6 18. 1 18. 9 5. 1 38.0 5.8 100 (Greenstone)

JB4·4G 2. 7 1. 2 21. 3 45.4 3. 9 25.5 100 (Greenstone)

JBS·SD 28.8 0.4 (Volcanic breccia)

37.8 22.6 10.4 100

JBS·SF 15. 6 1. 6 6.2 13. 6 5.2 42. 7 lS. 1 100 (Greenstone)

JBS·lOC 21. 3 12.6 21. 9 4.4 39.8 100 (Greens tone)

JBS·lOD 14. 1 1. 5 44. 7 33.6 6. 1 100 (Volcanic breccia)

JBS·llA 2S.4 0. 6 42.0 31. 7 0. 3 100 (Epidosite)

JBS·12A 3S.O 19. 7 4S.3 100 (Epidosite)

Figure 6. Modal analyses of 12 Catoctin Fm and 1 Chilhowee Fm sample: Q=quartz; Feld=albite; Ep=epidote; Op=opaques; Cc=carbonates; Chl=chlorite; Act=actinolite; Sph=sphene; Bio=biotite; Z=zircon; (Russell Guy, pers. comm., 1985). Lithologic names in parentheses are from R. Badger (pers. comm., 1985).


locations shown in Figure 4 and at Luck Stone Quarry in cen-

tral Virginia. Compressional velocities were determined at

pressures of 200, 400, and 600 atm, corresponding to depths

of approximately 0.75, 1.5, and 2.25 km respectively, assum-

ing a geopressure gradient of 266 atm/km (Dobrin, 1976).

Velocities determined at 600 atm range from 5. 13 km/sec to

6.47 km/sec for samples of the Catoctin epidosites,

greenstones, phyllites, and volcanic breccia (Table 1).


Table 1 (Part 1 of 4) · P-Veloci ties and Densities of Catoctin Samples

CORE P-VELOCITY DATA (KM/SEC)

SAMPLE PROP DESCRIPTION PRESSURE(ATM DIR Zoo L!oo (,00

JB4-l ..Ls1 Chilhowee 5.29 5.29 5.29 phylli te km/s km/s km/s 38%Chl,38%Q+F, 15%0p,9%Ep ( Phylli te)

JB4-3B __l_ s 1 Phyllite 38%0p, 5.13 5.14 5.13 26%Chl,22%Q,9%Ep 4%Sph,2%Cc (Phyllite)

JB4-3C no Meta sandstone 5. 72 5.73 5. 71 S1 45%Ep,45%Q+F,

10%0p (Epidosite)

JB4-3D II s1 Schist 6.26 6.25 6.28 4 7%Ep, 28%Chl I

14%Q,6%Cc,5%0p (Greenstone)

JB4-3D __L S1 Schist 5.95 5.98 5.97 47%Ep, 28%Chl, 14%Q,6%Cc,5%0p (Greenstone)

S1 REFERS TO PRIMARY FOLIATION

~S 1 =VELOCITY MEASURED 11s1

-L S 1=VELOCITY MEASURED _LS 1

PROP DIR=PROPAGATION DIRECTION

Reflectivity of Catoctin Formation

DENSITY

GM/CM 1

2.79

J. l~ 5

2.80

2.99

2.95

15

Table 1 (Part 2 of 4). P-Velocities and Densities of Catoctin Samples


SAMPLE PROP DESCRIPTION PP1"<:;SUREIATM DIR 1..00 'iOO (:,(0

JB4-4A no Metabasalt 6.22 6.23 6.24 S1 50%Ep, 1 7%Chl,

17%Q+F,8%Cc,8%0p (Epidosite)

JB4-4D is 1 Schist 38%Chl, 6.30 6.38 6.39 19%0p,18%Ep,5%Cc 14%Q+F,6%Sph (Greenstone)

JB4-4D _l_s1 Schist 38%Chl, 5.81 5.80 5.80 19%0p,18%0p,5%Cc 14%Q+F,6%Sph (Greenstone)

JB4-4G __Ls1 Schist 45%Chl, 5.84 5.90 5.92 26%Sph,21%Ep, 4%Q+ F, 4/'oAct (Greens tone)

JB4-4G i S1 Schist 45%Chl, 6.42 6.48 6.47 26%Sph,21%Ep, 4%Q+F,4%Act (Greenstone)


II S1 =VELOCITY MEASURED II s I _l_ S 1 =VELOCITY MEASURED _J_ S 1



DENSITY

GM/CM>

3.19

3.02

2.97

3.01

3.01

16

Table 1 (Part 3 of 4). P-Velocities and Densities of Catoctin Samples

CORE P-VELOCITY DATA (KM/SEC}

SAMPLE PROP DESCRIPTION PRESSURE(ATM DIR 200 400 (,,CO

JBS-SD no Metabasalt S.87 S.97 S.98 S1 38%Ep,29%Q+F,

23%0p,10%Cc (Vole Breccia}

JBS-SF _l__s1 Schist 43%Chl, S.24 S.S2 S.68 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone}

JBS-lOC !S1 Schist 40%Chl, 6.37 6.41 6.4S 22%0p,21%Q, 13%Ep,4%Cc (Greens tone)

JBS-lOC J_ S1 Schist 40%Chl, S.90 S.99 6.01 22%0p,21%Q, 13%Ep,4%Cc (Greenstone)

JBS-lOD ..l_ S1 Phylli te S.S4 S.6S S.68 4S%Ep,34%0p, 1S%Q+F,6%Cc (Vole Breccia)


~S 1 =VELOCITY MEASURED II s I _L_ S1 =VELOCITY MEASURED _Ls 1



DENSITY

GM/CM'

3.03

2.89

2.93

2.91

3 .11

17

Table 1 (Part 4 of 4). P-Veloci ties and Densities of Catoctin Samples


SAMPLE PROP DESCRIPTION PRESSURE(ATM DIR Zoo 'ioo ~oo

JBS-lOD I s1 Phyllite 6.22 6.26 6.21 45%Ep,34%0p, 15%Q+F,6%Cc (Vole Breccia)

JB5-llA no Amygdaloidal 6.11 6.14 6.16 S1 metabasalt

42%Ep, 32%0p,26%Q+F (Epidosite)

JB5-12A no Amygdaloidal 5.97 6.16 6.15 S1 metabasalt

45%0p,35%Q,20%Ep (Epidosite)


~ S1 =VELOCITY MEASURED II S1

_l_ S1 =VELOCITY MEASURED J....s 1

PROP DIR=P.ROPAGATION DIRECTION

DENSITY

GM/CM 2

3.07

3.30

3.15

Velocities parallel to foliation are higher than veloc-

i ty perpendicular to foliation for all of the samples for

which velocities in both directions were available

(greenstones) (Figure 7). Velocities of the epidosites gen-

erally lie between a velocity parallel to foliation and a

velocity perpendicular to foliation of the greenstones (Fig-


5.2

5.0 200 300 400 500 600

PRESSURE {atm)

Figure 7. Velocity versus pressure of Catoctin greenstones: Sample JBS-lOD is an epidotized, foliated volcanic breccia.


6.4 JB4-4A

6.2

- 6.0 a>

........ E 5.8 ~ JB4-3C - • • • >Q. 5. 6

5.4

5.2

5.0 200 300 400 500 600

PRESSURE (atm)

Figure 8. Velocity versus epidosites

pressure


of Catoctin

20

ure 8). Variation of velocity with pressure decreases as

pressure increases (Figure 7 and Figure 8). The difference

in velocity from 400 to 600 atm probably represents the pre-

cision of the traveltime measurements (i.e. of a frequency

counter) and inaccuracies of the velocity determinations.

Measurements of core lengths were repeatable to within

1% while travel time measurements were repeatable to within

4% at 600 atm. Velocity is as precise as the least precise

measurement involved in the velocity determination which is

the measurement of travel time. Velocities are therefore

precise to ±4% at 600 atm. Velocities determined at 600 atm

are used to calculate reflection coefficients.

DENSITY DETERMINATIONS

Specific gravities (Mendenhall and others, 1950) of the

Catoctin samples are listed in Table 1. A graph of velocity

versus density for samples with no apparent foliation

(epidosites) (Figure 10) shows that velocity is approximately

a linear function of density (e.g. Birch, 1961).


-"' ........

6.4

6.2

6.0

~ 5.8 -Q.

> 5.6

5.4

5.2

5.0

JBS 10Ce JB4-4G II~, llS, e J64-4 D llS,

JB4-3D e II~, e JD5-10Dl(S,

JB5-10C e JB4-3o..l .;, .Ls, e

e JB4-4G .L'S,

e JB4-4DJ. s,

9 JB5-10DlS1

2.6 2.8 3.0 3.2 3.4 DENSITY (g/cm3 )

Figure 9. Velocity versus density of Catoctin greenstones: Sample JBS-lOD is an epidotized, foliated volcanic breccia.


6.4 JB4-4A

6.2 e

JB5-12A e o · :rns-11A

6.0 -0

' 5.8 E .:.:: - eJB4-3C

Q. > 5.6

5.4

5.2

5.0 2.6 2.8 3.0 3.2 3.4

DENSITY (g/cm3)

Figure 10. Velocity versus epidosites


density of Catoctin

23

REFLECTION COEFFICIENTS

Normal incidence reflection coefficients were calcu-

lated at 600 atm for various juxtapositions of Catoctin For-

ma ti on li thologies. Results are tabulated in Appendix B.

Most significant is the result that the highly epidotised

metamorphosed basalts and sandstones, samples JB4-4A,

JBS-llA, JBS-3C, and JBS-SD are associated with reflection

coefficients of magnitudes greater than or equal to 0.1. An

absolute value of 0.1 or greater indicates a "good" reflector

(Waters, 1981).

Pressure versus acoustic impedance perpendicular and

parallel to foliation of the greenstones (Figure 11) and

highly epidotized samples (epidosites) (Figure 12) indicate

that maximum constrasts result from the juxtaposition of the

Catoctin greenstones against the epidosites. A large con-

trast exists between acoustic impedance of sample JB4-3C and

acoustic impedance parallel to foliation of the greenstone

samples. Large contrasts occur between the acoustic

impedance of samples JB4-4A, JBS-llA, and JBS-12A and acous-

tic impedance perpendicular to foliation of the greenstone

samples; the reflection coefficient between sample JB4-4A and

sample JBS-lOC _1__S 1 is -0.08. Acoustic impedance constrasts

within the epidosites between sample JB4-3C, a metsandstone,

and samples JB4-4A, JBS-llA, and JBS-12A, the amygdaloidal metabasalts, are the largest observed; the reflection coef-


- 21 "' I ('II

E 20 () ........ ~

JB4-4G fl<;, : <:?-. ,.._, .

0 ~11~,

,... 19 ~ - •JB4-3DllS, i JBS-tOC 11s-;! w (.) z 18 <( JB4-30J.<;, • c S _ JB4-4D.le' w ~5, c.. 17 ~

(.)

~ 16 l ~ 15 __. ____ ....._ __ _._ ____ w

200 300 400 500 600 PRESSURE (atm)

Figure 11. Acoustic impedance versus pressure of Catoctin greenstones


-; 21 I

N. i::s4-4A .JBS-11A • E 0 20 ' E

,.._ <:r>

0 19 ,... -w· 0 z 18 Jss-so __. ~

<t ~ c w Q, 17 :E 0 - 16 JB4-3C t-CJ) :::> 0 0 15 <t 200 300 400 500 600

PRESSURE (atm)

Figure 12. Acoustic impedance versus pressure of Catoctin epidosites


ficient between samples JB4-3C and JB4-4A is 0.12.

Acoustic impedance constrasts resulting in reflection

coefficients also result from anisotropy (Figure 11).

Juxtaposition of acoustic impedance parallel to foliation

against acoustic impedance perpendicular to foliation for

sample JB4-4D gives a reflection coefficient of 0.06.

Anisotropy factors, A, of samples for which velocities were

available parallel and perpendicular to the foliation were

calculated according to the method of Uhrig and Van Melle

(1955). Per cent anisotropy was calculated using the method

of Christensen (1965). Data are listed in Table 2. From the

data given in the reflection coefficient table (Table 3 on

page 65) and the anisotropy table (Table 2), it may be con-

cluded that anisotropy is a secondary effect leading to re-

flections.


Table 2. Anisotropy of Catoctin Formation

PRESSURE 200ATM 400ATM 600ATM

SAMPLE A %ANIS A %ANIS A %ANIS

3D 1.05 5% 1.05 5 1.05 5

4D 1.06 8 1.10 10 1.10 10

4G 1.10 9 1.10 9 1.09 9

lOC 1.08 8 1.07 7 1.07 7

lOD 1.12 12 1.11 10 1.09 9

A=ANISOTROPY FACTOR=Vp II S1/V p.L S1

'1.,ANIS='1.,ANISOTROPY=Vp II S1 -v,J. Si/ { [ vf II S1+Vp.L S1 ]/2)


THIN BED THEORETICAL MODELS

Twenty-four fold NSF-2 data were acquired near

Charlottesville, Virginia using a 10-80 Hz Vibroseis sweep.

A narrower 14-56 Hz Klauder wavelet was chosen for modeling,

however, because the observed frequency content of Catoctin

reflections on NSF-2 data was more band-limited than the

source sweep (Figure 2). Computer modeling of thin bed se-

quences was done to obtain synthetic seismograms which might

simulate the reflection character observed on segment NSF-2.

A thin bed was defined by Marangakis and others (1985)

as one whose two-way time thickness is less than the tuning

thickness, T/2, of the incident wavelet where T is the domi-

nant period of the wavelet. A tapered Vibroseis sweep of

14-56 Hz has a dominant period of 26 ms and a corresponding

dominant frequency (defined as the inverse of the dominant

period) of 38 Hz (Figure 13). The tuning thickness, T/2, for

the chosen Vibrosei s sweep is 13 ms ( Sengbush and others,

1961). A bed with thickness less than T/2 (13 ms) is herein

a thin bed.

At tuning thickness, the reflection begins to take on

the shape of the first derivative of the source wavelet

(Sengbush and others, 1961). Reflections from beds less than

X/8 thick where X is the dominant wavelength in the thin bed,

are essentially first derivatives of the incident wavelet

Thin Bed Theoretical Models 29

2.0

1 . 5

1 . 0 w 0.5 0

~ r-_J 0 .0 Q_ 2 -0.5 <(

-1. 0

- 1 . 5

-2.0 0 40 80 120

TIME (MS)

Figure 13. Synthetic 14-56 Hz Klauder wavelet


(Widess, 1973). The reflection from a thin bed is thus ei-

ther a first derivative waveform or is beginning to take on

the shape of a first derivative of the incident wavelet.

Generally, for zero-phase incident wavelets, beds less

than tuning thickness are not resolvable into the top re-

flection and the bottom reflection by conventional methods

(Kallweit and Wood, 1982; Widess, 1973). The resolution

limit of the zero-phase Klauder wavelet is defined as = T/2

(Kallwei t and Wood, 1982), Figure 14. Two spikes of equal

magnitude and the same polarity are progressively separated

in time by 2 ms ( 1 sample interval) . At 14 ms separation,

reflections from each spike are resolved, Figure 14(h). At

12 ms, the reflections interfere, Figure 14(g)).

The thin bed model also illustrates the Klauder waveform

resolution limit which corresponds to tuning thickness. Re-

flections from the top and bottom of a thin bed are not re-

solved at tuning thickness, as illustrated in Figure 15. A

dipole is a pair of reflection coefficients of opposite po-

larity and represents a thin bed. Maximum reflection ampli-

tude occurs at approximately 14-16 ms dipole thickness,

Figure lS(g),(h).

Consider the tuning of reflections from two dipoles of

the same polarity, Figure 16 and Figure 17. For an increas-

ing dipole separation and a constant bed thickness of 6 ms,

Figure 16, maximum constructive inter£ erence results when


.~ D 12'S

FREQUENCY (Hz) o~a~·~.~ 1zs. a 1zs. o 1a

-t i Ill

i ~

0 -

I I

0 -

I ! :

Ca) (b) Cc)

.~ .~ !\/\ 0 125. 0 ,.,Y,';v';,~

FREQUENCY (Hz) 1~ 0 1zs. 0 -

-t i .. i ~

8 -

f I

(f) (g) (h)

0 -

r 8 -

= I

(d)

.~ 0 1.S

F I I

(I)

F=

!

<·~

Figure 14. Resolution limit of 14-56 Hz wavelet: (a) Source wavelet amplitude spectrum, re-flection, and reflectivity series; (b)-(i) amplitude spectrum, reflection and re-flection coefficients of model; spike sepa-ration is 2 ms in (b) and is incremented by 2 ms per figure.


r-1 ~ /~ ~ /.1~~ 111111~1' 0 '"' 0 L?'S. 0 '"' 0 '"' 0 '"' FREQUENCY (Hz)

a -

i= a - a - a -

a : j. - t -.. I T i Ill

i I !.

I g - !

8 I :i - 8 - 8 -a -

I l a -

l a -

- -

l I - -------

~ - ~ - ~ - ~ - ~ -(a) (b) (c) (d) (e)

~ _,--~ J .... fl~, ~ Cr~ 0 '"' 0 !.:'S

FREQUENCY (Hz) 0 0 ::."'!!. 0 :;";;.

a: ~ a : j, 0: j a - J a -

1= ~ -==7 - 2

=~~~ =· ~ =~- ~.:-::( .. { r - i' I

i i I .. i I !. I

I

i 5 u 8 - il

a -

T T T -i--

I ! t - ;, ~ u ~ - CJ) (I) (g) (h) (I)

Figure 15. Tuning thickness: (a) Source wavelet ampli-tude spectrum, reflection, and reflectivity series; (b )- ( j) amplitude spectrum, re-flection, and reflection coefficients of model; bed thickness is 2 ms in (b) and is incremented by 2 ms per figure.


.~ a 121> FREQUENCY (Hz)

0 -

-4 i -Ill -

i : !.

0 -

~ 0 IZS

0 -

0 -

- - 8 - -8 -8 - . -0 0

- ~ =--=i= =r= I r I

---= i I I I

I i

I ' i I

I

I i

i N - 8 -I!!

(e) (f)

t '

"' - -

l'l - 8 -(c) (d) Ca) (b)

dj~~~~~~ o ·~ o ia o 1a a 1~ a 1~ o 1~ FREQUENCY (Hz)

0 - 0 -

-4 -i -"' -i : !.

0 -

-8 -

---;-

0 -

- -. 8 - 0 -0

-=t= =i= :----I - -.-

1

~ -

! ; I !

(g) (h)

-"' -l'l

I

!

-"' -l'l

(j)

I I

i !

- -"' - ill -., 0 0

(k) (I)

Figure 16. Tuning of reflections for two dipoles of same polarity: effect of increasing dipole sepa-ration for a constant bed thickness of 6 ms; (a) Source wavelet amplitude, reflection, and reflection coefficient; (b )- ( J) ampli-tude spectrum, reflection, and reflection coefficients of model; bed thickness is 2 ms in (b) and is and is incremented by 2 ms per figure.


beds are 12 ms, T/2, apart, Figure 16(h). For increasing bed

thickness and a constant dipole separation of 6 ms,

Figure 17, maximum constructive interference results when

each thin bed is at tuning thickness c~ 12 ms).

From Figure 16 and Figure 17, we may conclude that beds

at tuning thickness or tuning thickness apart may tune to

give large amplitude reflections. Maximum amplitude re-

flections result from the constructive interference of beds

at tuning thickness. The composite reflection from two

dipoles of the same polarity has either a first derivative

or ringing waveform, depending on the bed thicknesses and

dipole separation.

Consider now two dipoles of opposite polarity with an

increasing dipole separation and a constant bed thickness of

6 ms thickness, Figure 18. Up to 16 ms thickness, the in-

crease in dipole separation widens the central lobe of the

reflection until resolution is apparent at 18 ms dipole sep-

aration, Figure 18(j). Dipole separations of 2-8 ms lead to

maximum constructive interference of thin bed reflections and

a well-formed Klauder wavelet.

If dipole thickness is increased and dipole separation

is held constant at 6 ms, Figure 19, the central lobe on the

reflection widens as the beds become thicker, as in the pre-

vious example, Figure 18. The composite thin bed reflections


.~~~ ~ ~~ O l~ O lZS 0 ll'S. 0 !ZS 0 IZS FREQUENCY (Hz)

0 -

... -i "' -i : !.. :

0 -

=

(b)

= I ! I

(c)

-~ -

-8 - 8 -0 -

I r I ! I I I

~ - I ~ -

(d) (e) (f)

JJ~~LAL~~~L a IZS a IZS 0 12S 0 !ZS 0 IZS 0 I~

FREQUENCY (Hz)

... -i -Ill -

i : !.. =

- =r-r I

-~ -

(g)

Figure 17.

0 -

- --c i

-N -

"' 0

(h)

--0 0

___,___

r N -i'i

co

o;t -. -

0 0

r !

-N -i'i

(J)

- -8 - 8 -

~ - ---,

I I= ! I

I I

- -~ - ~ -

(k) (I)

Tuning of reflections from two dipoles of same polarity: effect of increasing bed thickness for constant dipole separation of 6 ms. (a) Source wavelet amplitude spectrum, reflection, and reflectivity series; (b)-(1) amplitude spectrum, reflection, and re-flection coefficients of model; bed thick-ness is 2 ms in (b) and is incremented by 2 ms per figure.


r-\ 111111~ a 1a

FREQUENCY _(Hz) 0 -

-4 i -"' i ?.

(a)

£.':y~

o~~

lT . - I 8

(b)

. -8 . -

8 . -8

0 -

T -T ~ - ~ -

Cc) (d)

0 -

__ T _ T ~ ~

(e) (f)

Dfl.~ f.W~. J\0~~ ('y~ (\A 0 1"5. 0 :::.-s 0

rl1111~ .-'T •••• ~

FREQUENCY (Hz) IZ':i. 0 •-'!> 0 l<"S 0

0 -

~ 0 - 0 - 0 - 0 -- ~ - .3. __ l __},. 0 -

~ - - --

T - - - --4 ·~, -

i -

~ ~ -

-~~ -

-~ -.. - -:::> "7> - -=--:-~ - f ? -

i -

f - ?

- I f

r ?. - I

I - i I

! I I I i ( ! I - - - i 8 '· i -

8 " 8 ..

g u -" 0

T -l. T l r =+= -- -

i I i

I !

l I .. N •. i.'l " " " " (h) J• ;,; ,, '" (g) (I) 0

(k) 0

(j) (I)

Figure 18. Tuning of reflections from two dipoles of opposite polarity: effect of changing dipole separation for beds of 6 ms thickness. (a) Source wavelet amplitude spectrum, re-flection, and reflectivity series; (b )- ( i) amplitude spectrum, reflection, and re-flection coefficients of model; dipole sepa-ration is 2 ms in (b) and is incremented by 2 ms per figure.

Thin Bed Theoretical Models

1,.,;

37

I~ ~~~~ 0 I~ 0 I~ a I~ 0 I~ a 1~

FREQUENCY (Hz) 0 -

-4 -ii: : m

a = !. -

(a)

0 : ==r= I I

(c)

-N -<D 0

=i= I l

(d)

~~~~~. 0 125 a !LS. 0 lZS a IZS 0

FREQUENCY (Hz)

io~t m -a • -

- I 8 -

~ : ( (f)

-8

-"' -<D 0

(g)

-g

-"' -<D 0

= --i !

(h)

0 0

-

-"' -<D 0

_j=

(I)

-N -<D 0

CJ)

Figure 19. Tuning of reflections from two dipoles of opposite polarity: effect of changing bed thickness for constant dipole separation of 6 ms. (a) Source wavelet amplitude spectrum, reflection, and ref lecti vi ty series; ( b) - ( j) amplitude spectrum, reflection, and re-flection coefficient of model; bed thickness is 2 ms in (b) and is incremented by 2 ms per figure.


from either increasing dipole separation or increasing bed

thickness have approximately the same well-formed Klauder

waveform reflection for beds less than tuning thickness. The

two-dipole model with dipoles of opposite polarity and dipole

separation of 2 ms is chosen to develop a multiple thin bed

model.

The time series summation of the reflectivity function

for a sequence of thin and thick beds may be found from its

reflectivity expression. Consider an 8 dipole reflectivity

series with 4 dipoles of opposite polarity in the repeating

unit (Figure 20). This 8 dipole reflectivity expansion (16

reflection coefficients) reduces to 7 reflection coefficients

when the separation between dipoles goes to zero

(Figure 20). A thin bed model with 8 thin beds of uniform

thickness has the same time series representation as a a

simplified thin bed model with 6 beds of varying thicknesses.

To a first approximation, the simplified multiple thin

bed model (Figure 20) with dipole separation of zero may be

written as the summation of four series:

<.o I'\ r(t)=!(-1) [(-6(t-4nt)+26(t-(4n+l)t) -26(t-(4n+3)t) ,, "'(;)

+6(t-(4n+4)t)]

where t is the two-way travel time through the bed (dipole

thickness).


TIME (me) ·

-0.12 -o 8 0 .12 10

2 - ·10 0.24 8 2

-20 20

- 30 -0.24

10 -40

-50

-so

-10

-so

-90

(al (b)

Figure 20. Thin bed models: (a) Multiple thin bed model;(b) Simplified thin bed model with six beds.


A term by term expansion of this series gives:

r(t)=(-1) 0 [o(t)+26(t-t)-26(t-3t) +6(t-4t)]

+(-1) 1 [-6(t-4t)+26(t-5t)-26(t-7t) +6(t-8t)]

+(-1) 2 [-o(t-81)+2o(t-91) -2o(t-111)+o(t-121)J

+(-1) 3 [-o(t-121) +2o(t-13t)-2o(t-15•)+o(t-16t)J

+ . . .

which is the reflectivity expression for the multiple thin

bed model. Because the thin bed model and the simplified

thin bed model have the same time series expression, they are

convolutionally equivalent.

The series simulating beds of tuning thickness may be

generalized for any wavelet as:

~ n r(t)=E(-1) [(-6((t-4nt)+26(t-((T/2)n+l)•)

n~

-2o(t-((T/2)n+3)t)+o(t-((T/2)n+4)t)]

where T is the dominant period of the wavelet.

Reflections corresponding to the series expansions for

the terms n=O through n=2 for beds 8 ms thick and 2 ms apart,

Figure 21, result from constructive interference of re-

flections from two or more thin beds. This can be seen more

clearly by comparison of the multiple thin bed model with its

convolutional equivalent, the simplified thin bed model,


I~ ... L 0 12S 125 O IZS: FREQUENCY (Hz)

·-4 -I: -m i -!. -

-8 - -8 - 8 - - - -- 8 - 8 - 8 -

I 0 -

T 0 - -..__ 0 - r= 0 - == 0 - --- - - --, - I - - __,_ - =:/--

I - - -- - -I

i I =r= I - - - == I i I - I

I I

- I N - N -ill <D

(a) 0 (b)

I I I I ! ! i -

N - - I N

- i ~

- - N - -<D <D <D

(c) 0 (d) 0 (e) 0 (f)

Figure 21. Multiple thin bed model: (a) Source wavelet amplitude spectrum, reflection, and reflectivity for a single interface; (b) am-plitude spectrum, reflection, and reflection coefficients of thin bed model-reflection approximates first derivative waveform; ( c) four dipole model - approximation to 3-point model; (d) series expansion for n=O term; (e) n=l; (f) n=2.


~~ l .. L 0 l~ 0 I~ 125 0 I.ZS FREQUENCY (Hz)

0 - 0 - 0 -

-t -i m -i !. -

0 -

I JT JT Jr JI :T a> m en ~ m

(a) 0 (b) 0 (c) 0 (d) (e) 0 (f) N -

~

Figure 22. Simplified thin bed model: Convolutional equivalent of multiple thin bed model. (a) source wavelet amplitude spectrum, re-flection, and reflectivity for a single interface; (b) amplitude spectrum, re-flection and reflection coefficients of thin bed; (c) three-point model arrived at by re-ducing dipole separation of four-dipole model in multiple thin bed model; (d) n=O term - tuning of two thin bed reflections; (e) n=l term; (f) n=2 term.


.~~~lfL1.~ ~REQUENCY l~z) a '"" a '"" a '"" o 125

-4 -i -!!! . -3 -!. :

0 0

-0 0

- -8

" I :IT :1 T : T : T 00 ~ ID 00 00

o (a) (b) a (c) o (d) o (e)

Figure 23. Multiple thin bed model for t~T/2: beds at tuning thickness result in very large ampli-tude reflections. (a) Source wavelet ampli-tude spectrum, reflection, and reflectivity series; (b) tuned first derivative waveform; ( c) tuned 3-point model approximation; ( d) n=O term; (e) n=l term. Note that individual reflections in ( d) and ( e) are resolvable into first derivative waveforms from thin beds and Klauder waveform from 3-point model approximation.


Figure 22. From the simplified thin bed model, Figure 22(d),

we see that the four-dipole model in Figure 2l(d) approxi-

mates two dipoles of the same polarity 20 ms apart. The re-

flections from the two beds constructively interfere to give

a large amplitude reflection with first derivative charac-

teristics (e.g. Figure 16(k)). A two-dipole series approxi-

mates a 3-point reflectivity series which results in a

reflection with a Klauder waveform, Figure 21 ( c) . As more

thin beds are added to the time series, the reflections take

on a reverberating character.

First derivative and Klauder waveforms are distinguish-

able in models for the n=O through n=2 terms of the series

expression of the multiple thin bed model, Figure 22. For

beds of tuning thickness in the multiple thin bed model, the

individual thin bed reflections are resolvable (Figure 23).

Constructive inter£ erence of multiple thin bed reflections

results in large amplitude reflections.

As the spike separation in a dipole decreases, convo-

lution of the wavelet with the dipole results in differen-

tiation of the wavelet and and a shift in the amplitude

spectrum toward high frequencies. Peaks in the amplitude

spectra of the thin bed model reflections occur at f requen-

cies which correspond to the periodicities of the dipoles

used in the models. Dipole periodicity is 1/t where t is the

two-way time thickness (Marangakis and others, 1985). Side

lobes in the amplitude spectra result from complex frequency


domain addition of amplitude spectra of reflectivity func-

tions. The number of side lobes increases as thin beds are

added to the time series, Figure 21 and Figure 22. Addition

of the complex amplitude spectra of reflectivity functions

of the multiple thin bed model results in amplitude spectra

similar to spectra of reverberations in that they are tuned

at a specific frequency.

RESULTS

Computer modeling of thin beds shows that reflections

from a thin bed slightly less than tuning thickness

Figure 15, approximates the first derivative of the wavelet.

However, these thin bed reflections themselves may construc-

tively interfere to form "tuned'' first derivative reflections

which are larger in amplitude than either the incident

wavelet or the reflection from a single tuned thin bed ,Fig-

ure 13 and Figure 15(c). Modeling of multiple thin beds is

extended to the Catoctin Formation using the reflection co-

efficients determined in this study and stratigraphic infor-

mation supplied by R. Badger (Figure 5).

Exact thin bed models of Catoctin reflectivity are con-

structed based on the stratigraphy of the geologic sections

of R. Badger (pers. comm., 1985), Figure 24 and Figure 29,

and from reflection coefficients determined in this study.

Variations on these models are constructed to illustrate re-


f lection character of other possible thin bed models for the

Catoctin Formation. Homogeneous layers of the samples chosen

are assumed. Lateral and vertical velocity variations pres-

ent in outcrop and in the subsurface are not represented in

these models.

The beds in the stratigraphic sections shown in

Figure 24 and Figure 29 are acoustically thin beds. For a

dominant frequency of 38 Hz and a compressional velocity of

6000 m/s, the dominant wavelength is approximately 157 m.

The Catoctin model beds are less than 30 m thick or less than

X/4 thick, so they are acoustically thin beds.

The reflection from the exact time model of section A,

Figure 24, is a small amplitude reflection. Individual thin

bed reflections have destructively interfered in this model.

Reflections from models based on variations of section A with

layers removed and replaced, Figure 25, Figure 26,

Figure 27, and Figure 28, are generally smaller amplitude

than the source wavelet also. However, the reflection from

the model in Figure 28 is a well-formed Klauder wavelet of

amplitude slightly less than the source wavelet. Construe-

tive interference of thin bed reflections from this model has

resulted in a waveform similar to the waveform of reflections

from within the Catoctin Formation on seismic profile NSF-2.

The reflection from the exact outcrop model of section

B is a large amplitude reflection with a slighl ty ringy or

reverberating appearance, Figure 29. Variations on section


OEPTH (m)

o-------- JB5-10C 6010 mis

60

JB4-3C 5710 mis JB4-30 5969 mis JB4-3B 5126mla JB4-30 5969 mis JB4-3B 5128 mis

-"1:.::::::::z::C:::::~ JB5-10C 6010 mis . JB4-3B 5128 mla

JB5-10C 6450 mis

JB5-100 6212 mla

JB5-10C 601<lml1

JB4-3B 5128 mis JB5-10C 6010 mis JB4-38 5128 mis JB4-30 6281 mis JB5'-100 6212 mis

JB5-10C 6010 mis

(a)

-o cC, -,___.~ c15 -0.0'1 0-0'i - 5

-o.O'l o.o'-J -o o'1 0.08

-0-0'1

(b)

-10

-15 o.os

-20

0 -

"" -0 0

0 -

... -.. 0

-=== I '

Figure 24. Catoctin thin bed model constructed from section A: (a) Original depth model; (b) corresponding time series ;(c) amplitude spectrum, reflection, and ref lee ti vi ty se-ries.


~' 0 IZB

DEPTH (m)

0

50

(a)

JB4-30 5969 mis

JB5-1or. 6212mls

JB4-4G 5924 mis

JB4-3C 5710mls

J84-40 6369 mis

-o.o:; -o.

(b)

·nflo\e(ms) -0

o.o'f -')

r~o o.o

-15

-w

0 -

.. -0 0

0 -

N -.. 0

?

-<=--I I

!

(c)

Figure 25. Section A without beds <l ms and with beds replaced: (a) depth model of A without beds <l ms thick; JBS-lOC and JBS-lOD of Figure 24 replaced by JB4-4G and JB4-3C; (b) corresponding ref lecti vi ty series; ( c) am-plitude spectrum, reflection, and reflectivity series.


DEPTH (m) 0 ______ .,

40

J84-30 5969 mis

JB5-100 6212 mis

JB4-3C 5710 mis

J84-40 6389 mis

-o.o~

(b)

,~. 0 1~

-o 0 -

o.o'i -5 o.o~

-10

... -8

0 -

N -... 0

(c)

Figure 26. Section A - previous figure without layer JB4-4G: (a) same depth model as Figure 25 without JB4-4G; (b) corresponding reflectivity series; (c) amplitude spectrum, reflection, and reflectivity series.


DEPTH (m)

JB4-30 5969 mis

JB5-10f"I 6212 mis

J64-3C 5710 m/a

-o.o~

JB5-10C 6010 mis

-o.o'-l JBS-100 6212 mis

-104-30 5969 mis

(a) t'l>J

I\ t-\i;: (Y't"'-J

-o

o.a-1 -~ Q.0'.:

- IO

-1? .o.o··

-'lD

~C~-r-r .. 0

0 -

.. -0 0

0 -

N -,,. 0

12S

1 )

--=-

(c)

Figure 27. Section A - previous figure with layers re-peated and replaced: (a) Same depth model as Figure 26 with JB4-4D replaced by JBS-lOC and with layers JB4-3D and JBS-lOD repeated; (b) corresponding time series; (c) amplitude spectrum, reflection, and reflectivity se-ries.


DEPTH (m) o-r-----.. JB4-30

rL ii Mt~

I ' I t t 1 t I I 1r;'";\.I

0 ti;

10 5969 m/s

JBS-100 20 6212 mis -o.o9

JB4-3C 5710 m/a

-0 0 -

1 o.o'i -5 0.0) I

-10 30

JB5-10C -o.os - 15 6010 mis

40 .. -0 0

..-...... JB4-JC 5710 m/e

(_~)

0 - -(b) -,

I "' - I .. 0

(<!)

Figure 28. Section A - previous figure with layers re-peated: (a) Sarne depth model as Figure 27 with layer JB4-3C repeated instead of layers JB4-3D and JBS-lOD repeated; (b) correspond-ing time series; (c) amplitude spectrum, re-flection, and reflectivity series.


DEPTH (m)

0

70

(a)

Figure 29.

JBS-SF

I''hrn S680 mis

JB4-4A 6238 mis TlME:l'.w.s) 0

_o 0 -

JBs-1oc t 6010 mla 0.10 _s -o Oi

JBS-11A o.os- lo I 6TS9mls

I -0.11 JBS-SF o.o? - IS

I -20 ,. -JBS-SO o.o~ 0

5979 mis -o.o8 0

-2~ 0 - ---=-I

JBS-SF 5680 mis

(b) "' -,. 0

Le)

Catoctin thin bed model constructed from section B: (a) Original depth model; (b) corresponding time series; (c) amplitude spectrum, reflection, and ref lecti vi ty se-ries.

126


DEPTH (m) 0

Figure 30.

(a)

JB4-30 5969 mis

JBS-11A 6159m/s

JBS-SO 5979 mis

-o.ob

-o o5

{b)

0 -

o.o"!_?

-10

-.&. -

8

0 -

( c.}

Section B - layers replaced and removed: (a) Sarne depth model as Figure 29 with layer JBS-lOC replaced by JBS-30, JBS-SF and JBS-lOD removed ( b) corresponding time se-ries; (c) amplitude spectrum, reflection, and reflectivity series.

Thin Bed Theoretical Models S4

DEPTH (m)

0

JB4-4A 6238 mis

JBS-10C 6010 mis

JBS-SF S680 mis

JBS-SO S979 mis

-0

5

D.05'"- lO

o.o:i - l5

fl I I I I I I I I I f I I 0 12!0

0 -

-~

.. -0 c

0 -

JBS-10() ___ _.... .............. _. //l.i l.; m/ s T

Figure 31.

(~) (ti)

N -.. 0

I I

(C)

Section B two layers removed: (a) Same depth model as Figure 29 with JBS-llA removed and JBS-lOD removed (b) corresponding time series; ( c) amplitude spectrum, reflection, and reflectivity series.


B arrived at by replacing, removing, or repeating layers in

section B result in reflections with a variety of waveforms,

Figure 30 and Figure 31.

Figure 31 is a large

derivative appearance.

The reflection from the model in

amplitude reflection with a first-

This first derivative waveform could

be interpreted as a single thin bed when, in fact, the re-

flection represents several beds.

Models based on the Catoctin outcrop information illus-

trate that constructive interference of reflections from

multiple thin beds results in large amplitude composite re-

flections. These composite reflections are characterized by

first derivative waveforms, Klauder-type waveforms, or ring-

ing signatures.


CONCLUSIONS

Reflections from within the Catoctin Formation of cen-

tral Virginia are due to constructive interference of re-

flections from acoustically thin, epidotized metabasalts and

metasediments inter layered with non-epidotized metabasal ts

and metasediments. Interbedded thin layers of rift volcanics

and rift sediments also provide acoustic impedance contrasts

from which reflections may originate. Individual thin bed

reflections constructively interfere to form large amplitude,

reverberating reflections similar to those seen on seimsic

reflection data in central Virginia.

Conclusions 57

REFERENCES

Backus, M. M., 1959, Water Reverberations-Their Nature and Elimination, Geophysics, Vol.24, February, p. 233.

Bally, A. W., 1981, Atlantic-Type Continental Margins in Geology of Passive Continental Margins, AAPG Education Course Note Series #19.

Birch, Francis, 1961, The Velocity of Compressional Waves in Rocks to 10 Kilobars, Part 2, Journal of Geophysical Re-search, Vol. 66, No. 7, p. 2199-2224.

Brun, J. P. and P. Choukroune, 1983, Normal Faulting, Block Tilting, and Decollement in a Stretched Crust, Tectonics, V. 2, No. 4, p. 345-356, August.

Christensen, N. I., 1965, Compressional Wave Velocities in Rocks at Pressures to 10 Kilobars, Journal of Geophysical Research, Vol. 70, p. 6147.

Coruh, C., Costain, J. K., Glover, Lynn III, Pratt, T. L., 1985, Sei smici ty and Seismic Reflection, Gravity, and Geology of Central Virginia Seismic Zone, Part 2, Re-flection Seismology.

Dobrin, Milton B., 1976, Introduction to Geophysical Pros-pecting, Third Edition, McGraw-Hill, New York.

Gathright, T. M., II, 1976, Geology of the Shenandoah Na-tional Park, Virginia: Virginia Division of Mineral Re-sources Bulletin 86, 93 p.

Kallweit, R. S. and L. C. Wood, 1982, The limits of resol-ution of zero-phase wavelets, Geophysics, Vol. 47, No. 7, p. 1035-1046.

Kolich, 1974, Master's Thesis, Virginia Polytechnic Institute and State University.

Marangakis, A. , Costain. J. K., and Coruh, C., 1985, Use of integrated energy spectra for thin-layer recognition, Short note, Geophysics, Vol. 50, No. 3, p. 495-500.

Mendenhall, C. E., Eve, A. S., Keys, D. A., and R. M. Sutton, 1950, College Physics, Third Edi ti on, D. C. Heath and Company, Boston.

References 58

Sengbush, R. L., Lawrence, P. L., and McDonal, F. J., 1961, Interpretation of Synthetic Seismograms, Geophysics, Vol. 26, No. 2, p. 138-157.

Sheriff, Robert E., 1973, Encyclopedic Dictionary of Explo-ration Geophysics, Society of Exploration Geophysicists, Tulsa, Oklahoma.

Uhrig, L. F., and F. A. Melle, 1955, Velocity Anisotropy in a Stratified Media, Geophysics, Vol. 20, No. 4, pp. 774-779.

Waters, Kenneth H., 1981, Reflection Seismology, A Tool For Energy Resource Exploration, John Wiley & Sons, New York.

Wehr, Frederick and Lynn Glover, III, 1985, Stratigraphy and tectonics of the Virginia-North Carolina Blue Ridge:Evolution of a late Proterozoic-early Paleozoic hinge zone, Geological Society of America Bulletin, v. 96, p. 285-295, March.

Widess, M. B., How thin is a Thin Bed?, Geophysics, Vol. 38, No. 6 (December 1973), p. 1176-1180.

References 59

APPENDIX A. CALIBRATION CURVES

Calibration curves used to determine the correction for

transit time through the steel and the electronics at pres-

sures of 200, 400, and 600 atmospheres are shown in

Figure 32, Figure 33, and Figure 34 respectively.

60

47 46

0 45 ~ 44 ~ 43 w ~ 42 t-u:: 4 1 > ~ 40 t-

39 38

6.0 7.0 8.0 9.0 10.0 CYLINDER HEIGHT, CM

Figure 32. Steel calibration curve for 200 atm

I I . 0

61

47 46 45

0 w 44 en ~ 43 .. . w :e 42 -I-.J 41 w > 40 < a: I- 39 e

38 6.0 7.0 8.0 9.0 10.0 11 . 0

CYLINDER HEIGHT, CM

Figure 33. Steel calibration curve for 400 atm

62

·47

46 0 45 w 0 44 ~ u.i 43 ! 42 .... w 41 > ~ 40 1-

39 38

6.0 •

7.0 8.0 9.0 10.0 CYLINDER HEIGHT, CM

Figure 34. Steel calibration curve for 600 atrn

11 . 0

63

APPENDIX B. REFLECTION COEFFICIENTS

64

Table 3 (Part 1 of 30). Catoctin Fe~lection Coefficients(600atm)

I

TOP LAYER Description

3B __L S1 Phyllite 38%0p,26%Chl,22%Q, 9%Ep,4%Sph,2%Cc (Phyllite)

BOTTOM LAYER Description R.C.

JB4-3C Meta sandstone -0.01 45%Ep, 45%Q+F,10%0p (Epidosite)

JB4-3D J_ S1 Schist 0.04 47%Ep,28%Chl, 14%Q,6%Cc,5%0p (Greenstone)

JB4-3D 11 s1 Schist 0.08 47%Ep,28%Chl, 14%Q,6%Cc,5%0p (Greenstone)

JB4-4A Metabasalt 0.12 50%Ep,17%Chl,17%Q+F 8%Cc,8%0p (Epidosite)

JB4-4D _L S1 Schist 0.03 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)

S1 REFERS TO MAJOR FOLIATION

II S1 =PROPAGATION II TO MAJOR FOLIATION

l_s 1=PROPAGATION _LTO MAJOR FOLIATION

65

Table 3 (Part 2 of 30). Catoctin Reflection Coefficients(600atm)

JB4-4D II S1 Schist 0.09 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)

JB4-4G J_ S1 Schist o.os 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)

JB4-4G II S1 Schist 0.09 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)

JBS-SD Metabasalt 0.06 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)

JBS-SF _L S1 Schist 43%Chl, 0.01 17%Q+F,15%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC _J_ S1 Schist 0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)

JBS-lOC II S1 Schist 0.08 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)



_L_ S1 =PROPAGATION J_ TO MAJOR FOLIATION

66


JBS-lOD _l_ S 1 Phyllite 0.05 45%Ep,34%0p,15%Q+F, 6%Cc (Volcanic Breccia)

JBS-lOD II S1 Phyllite 0.08 45%Ep,34%0p,15%Q+F, 6%Cc (Volcanic Breccia)

JBS-llA Amygdaloidal 0.11 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)

JB5-12A Amygdaloidal 0.09 metabasalt 45%0p,35%Q,20%Ep (Epidosite)


~S 1 =PROPAGATION ~ TO MAJOR FOLIATION

_L_ S1 =PROPAGATION _L TO MAJOR FOLIATION

67



JB4-3C Meta sandstone 45%Ep, 45%Q+F,10%0p (Epidosite)


JB4-3D _l_ S 1 Schist 0.05 47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)

JB4-3D II S1 Schist 0.08 47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)

JB4-4A Metabasalt 0.12 50%Ep I l 7%Chl I 17%Q+F,8%Cc,8%0p (Epidosite)

JB4-4D _J_ S1 Schist 0.04 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)




J_ S1 =PROPAGATION l_ TO MAJOR FOLIATION

68

Table 3 (Part S of 30). Catoctin Reflection Coefficients(600atm)

JB4-4G -~ S1 Schist o.os 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)


JBS-SD Metabasalt 0.06 38%Ep,29%Q+F, 23%0p,10%Cc (Volcanic Breccia)

JBS-SF _I S1 Schist 43%Chl I 0.01 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC J_ Si Schist o.os 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


JBS-lOD _J __ S1 Phyllite o.os 4S%Ep,34%0p,1S%Q+F, 6%Cc (Volcanic Breccia)



.J_S 1=PROPAGATION _l_TO MAJOR FOLIATION

69

Table 3 (Part 6 of 30). Catoctin Reflection Coefficients(600atrn)

JBS-lOD II S1 Phyllite 0.09 45%Ep,34%0p,15%Q+F, 6%Cc (Volcanic Breccia)

JBS-llA Arnygdaloidal 0.12 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)

JBS-12A Arnygdaloidal 0.10 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)


II S1 =PROPAGATION II TO MAJOR FOLIATION I ' ..LS 1 =PROPAGATION ...L TO MAJOR FOLIATION

70


TOP LAYER Description I JB4-3D _1_ S1 Schist

47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)


JB4-3D II s1 Schist 0.03 47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)

JB4-4A Metabasalt 0.07 50%Ep I l 7%Chl I

17%Q+F,8%Cc,8%0p (Epidosite)

JB4-4D J_ S1 Schist -0.01 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)

JB4-4D 11 s1 Schist 0.05 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)

I JB4-4G _L S1 Schist 0.01 45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)



.l_S 1=PROPAGATION j_ TO MAJOR FOLIATION

71


JB4-4G II S1 Schist o.os 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)


JBS-SF J_ S1 Schist 43%Chl, -0.04 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC j_ S1 Schist 0.00 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


JBS-lOD J_ S1 Phyllite 0.00 4S%Ep,34%0p,1S%Q+F, 6%Cc (Volcanic Breccia)

JBS-lOD II S1 Phyllite 0.04 4S%Ep,34%0p,1S%Q+F, 6%Cc (Volcanic Breccia)



J_ S1 =PROPAGATION j_ TO MAJOR FOLIATION

72



JB5-12A Arnygdaloidal 0.05 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)



J_ S 1 =PROPAGATION j_ TO MAJOR FOLIATION

73



JB4-3D II S1 Me ta sandstone 45%Ep, 45%Q+F,10%0p (Epidosite)


JB4-4A Metabasalt 0.04 50%Ep I 17%Chl I 17%Q+F,8%Cc,8%0p (Epidosite)

JB4-4D _l_ S1 Schist -0.04 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)


. JB4-4G -L S 1 Schist -0.03

45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)

JB4-4G II S1 Schist 0.02 45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)


l!S 1=PROPAGATION II TO MAJOR FOLIATION

_l_ S1 =PROPAGATION J_ TO MAJOR FOLIATION

74


JBS-SD Metabasalt -0.02 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)

JBS-SF J_ S1 Schist 43%Chl, -0.07 17%Q+F,1S%Sph, 14%0p,6%Ep,5%Cc (Greenstone)

JBS-lOC _L S1 Schist -0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)

JBS-lOC 11 s1 Schist 0.00 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)

JBS-lOD J_ S1 Phyllite -0.03 45%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)

JBS-lOD II S1 Phyllite 0.01 45%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)




.L S 1 =PROPAGATION J_ TO MAJOR FOLIATION

75





J_ S1 =PROPAGATION J_ TO MAJOR FOLIATION

76



JB4-4A Metabasalt SO%Ep, 17%Chl,17%Q+F, 8%Cc,8%0p (Epidosite)


JB4-4D _;_ S 1 Schist -0.08 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)

JB4-4D 11 s1 Schist -0.03 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)

JB4-4G J_s1 Schist -0.07 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)

JB4-4G II S1 Schist -0.02 45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)



II s 1 =PROPAGATION II TO MAJOR FOLIATION

_L S1 =PROPAGATION J_ TO MAJOR FOLIATION

77


JBS-SF~ S1 Schist 43%Chl, -0.11 17%Q+F,1S%Sph, 14%0p,6%Ep,5%Cc (Greenstone)

JBS-lOC J.. S1 Schist -0.08 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)

JBS-lOC II S1 Schist -0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)

JBS-100 J_ S1 Phyllite -0.07 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)

JBS-100 i1S1 Phyllite -0.03 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)


JBS-12A Amygdaloidal -0.02 metabasalt 4S%0p,35%Q,20%Ep (Epidosite)


ijS 1=PROPAGATION ij TO MAJOR FOLIATION

J_S 1 =PROPAGATION _J_To MAJOR FOLIATION

78

Table 3 (Part lS of 30). Catoctin Reflection Coefficients(600atrn)


JB4-4D _l S1 Schist 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)


JB4-4D II S1 Schist 0.06 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)

JB4-4G l_ S1 Schist 0.02 4S%Chl,26%Sph, 21%Ep,4%Q+F,47.,Act (Greenstone)



JBS-SF J_ S1 Schist 43%Chl, -0.02 17%Q+F,1S%Sph, 14%0p,6%Ep,5%Cc (Greenstone)



J_ S1 =PROPAGATION _l_ TO MAJOR FOLIATION

79


JBS-lOC J_ S1 Schist 0.01 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


JBS-lOD J_ S1 Phyllite 0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)

JBS-lOD II S1 Phyllite 0.05 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)

JBS-llA Arnygdaloidal 0.08 rnetabasalt 42%Ep, 32%0p,26%Q+F (Epidosite)




J_ S 1 =PROPAGATION J_ TO MAJOR FOLIATION

80



JB4-4D 11 s1 Schist 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)


JB4-4G J_ S1 Schist -0.04 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)

JB4-4G 11 s1 Schist 0.01 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)


JBS-SF _l_ S1 Schist 43%Chl, -0.08 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC J_ S1 Schist -0.0S 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)



_l_ S 1 =PROPAGATION _l_ TO MAJOR FOLIATION

81



JBS-lOD J_ 81 Phyllite -0.04 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)

JBS-lOD 1181 Phyllite -0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)




~81=PROPAGATION ~ TO MAJOR FOLIATION

_L S1 =PROPAGATION _L TO MAJOR FOLIATION

82



JB4-4G_l_ S1 Schist 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)




JBS-SF J_ S1 Schist 43%Chl, -0.04 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC J_ S1 Schist -0.01 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)




j_ S1 =PROPAGATION J_ TO MAJOR FOLIATION

83


JBS-lOD _j_ S1 Phyllite 0.00 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)



JBS-12A Amygdaloidal 0.04 metabasalt 45%0p,35%Q,20%Ep (Epidosite)



_l_ S1 =PROPAGATION _L TO MAJOR FOLIATION

84



JB4-4G II S1 Schist 4S%Chl,26%Sph, 21%Ep,4%Q+F,4roAct (Greenstone)



JBS-SF _L S1 Schist 43%Chl I -0.09 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC J_ S 1 Schist -0.0S 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


JBS-lOD _l S1 Phyllite -0.0S 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)



_J__ S1 =PROPAGATION _J_ TO MAJOR FOLIATION

8S


JBS-lOD II S1 Phyllite -0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)





_!_S 1 =PROPAGATION _l TO MAJOR FOLIATION

86



JBS-SD Metabasalt 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)


JBS-SF J_ S1 Schist 43%Chl, -0.0S 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)

JBS-lOC J_S1 Schist -0.02 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


JBS-lOD _J_ S1 Phyllite -0.01 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)

JBS-lOD II S1 Phyllite 0.03 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)



J_ S 1 =PROPAGATION _l TO MAJOR FOLIATION

87






_l S1 =PROPAGATION j_ TO MAJOR FOLIATION

88

Table 3 (Part 2S of 30). Catoctin Reflection Coefficients(600atm)

TOP LAYER Description I JBS-SF _,_ S1 Schist 43%Chl I

17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)


JBS-lOC J_ S1 Schist 0.03 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


' JBS-lOD ~· S1 Phyllite 0.04 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)

JBS-lOD II S1 Phyllite 0.08 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)




J __ S 1 =PROPAGATION J_ TO MAJOR FOLIATION

89


JB5-12A Amygdaloidal 0.08 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)



__L 5 1 =PROPAGATION _l_To MAJOR FOLIATION

90



JBS-lOC _L S 1 Schist 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)



JBS-lOD _l_ S 1 Phyllite 0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)






_J_S 1=PROPAGATION j_ TO MAJOR FOLIATION

91



JBS-lOC II S1 Schist 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)


JBS-lOD J_ S1 Phyllite -0.03 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)

JBS-lOD i1S1 Phyllite 0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)





_l_S 1 =PROPAGATION j_ TO MAJOR FOLIATION

92



JBS-lOD l. S1 Phyllite 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)







_L S1 =PROPAGATION j_ TO MAJOR FOLIATION

93



JBS-lOD II S1 Phyllite 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)





~S1=PROPAGATION ~ TO MAJOR FOLIATION

_l_s1=PROPAGATION J_To MAJOR FOLIATION

94

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