1

XCORRELATION OF SEISMIC REFLECTION DATA WITH SEISMICITYOVER THE RAMAPO, NEW JERSEY, FAULT ZONE,

byRichard M.„D'Angelo

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 Sciencein

Geophysics

APPROVED:

J. K. Costain, Chairman L. Glover, III

[gg).2,"E. si Robinson N. M. Ratcliffe Uk“

July 24, 1985

Blacksburg, Virginia

1

4»?{ CORRELATION OF SEISMIC REFLECTION DATA WITH SEISMICITY

OVER THE RAMAPO, NEW JERSEY, FAULT ZONE

Richard M. D'Angelo

J. K. Costain, ChairmanGeophysics

(ABSTRACT)

Reflection seismic data, mylonite reflectivity, gravity

data, and earthquake hypocenters have been integrated into a

possible explanation for seismicity in the Ramapo fault area.

Seven reflection seismic lines were processed using vari-

ations in sorting and residual statics. Single VIBROSEIS

sweeps were treated as separate sourcepoints. Compressional

velocities and densities were determined in the laboratory. »

Reflection coefficients and gravity models provide evidence

for reflections from mylonite zones. Earthquake hypocenters

were projected into the vertical seismic sections. The re-

sults suggest a correlation between rock volumes containing

hypocenters and rock volumes containing mylonite zones. The

seismic line furthest from the Taconic suture displays fewer

hypocenters and mylonites, in agreement with an assumed model

of mylonite development possibly associated with obduction

of continental crust. The mylonite zones in the basement may

serve as local areas of crustal weakness for seismic activity

occurring in the area.

I

AQKNOWLEDGEMENTS

The reflection seismic data were collected by VirginiaTech as part of a cooperative project with the U.S.Geological Survey, Drs. N. Ratcliffe and J.K. Costain, Prin-cipal Investigators. Partial summer support during 1984-1985was provided by Arco Exploration and Sohio Petroleum Company.Dr. Nick Ratcliffe of the USGS is greatly appreciated for hisefforts in obtaining the USGS funds and for the core samplesand other valuable geologic information he provided.

Acknowledgements iii

TABLE OE CONTENTS

INTRODUCTION ..................... 1

PREVIOUS WORK .................... 2

Geology ..................... 2

Seismicity .................... 4

REFLECTION SEISMIC DATA ACQUISITION AND PROCESSING . . 6

Data Acquisition ................. 6

Data Processing ................. 8

DISCUSSION ...................... 13

Processing .................... 13

Velocities, densities, and reflection coefficients 24

Gravity data ................... 32

Earthquake data ................. 38

CONCLUSIONS ..................... 43

REFERENCES ...................... 48

APPENDIX A. LOCATIONS OF RAMAPO LINES ........ 53

APPENDIX B. STANDARD PROCESSING ROUTINE ....... 58

Table of Contents iv

l

APPENDIX C. EARTHQUAKE EPICENTRAL/HYPOCENTRAL DATA . . 61

APPENDIX D. REFLECTION SEISMIC SECTIONS .......63

APPENDIX E. . .‘...................78

VITA .........................83

Table of Contents V

1 _ _ _ _.

LISI 0F LLLUSTRATIONS

Figure 1. Location map of the seismic lines with thegeology of the Ramapo fault zone ..... 3

Figure 2. Effect of CDP line orientation on Line 3 . 15

Figure 3. Summed single-sweep processing vs. standardprocessing for Line 1 ........... 16

Figure 4. Part of Line 4 before (a) and after (b) ap-plication of residual statics corrections . 18

Figure 5. Line 7 with time-variant ARS ....... 19

Figure 6. Fence diagram with line drawings of the seis-mic sections ............... 21

Figure 7. Single-sweep processing vs. standard process-ing for Line 3 ........_ ...... 22

Figure 8. Line 5 single—sweep section ........ 23

Figure 9. Summed single-sweep processing vs. standardprocessing for Line 3 ........... 25

Figure 10. Summed single-sweep processing vs. standard ·processing for Line 5 ........... 26

Figure 11. P-wave velocities (km/s) of core samples atvarious lithostatic pressures ....... 30

Figure 12. Subsurface loading model ......... 34

Figure 13. Seismic lines and the general trend of thesteep gradient of the Bouguer gravity anomalyfield ................... 35

Figure 14. Bouguer gravity anomaly map, observed andcalculated gravity profiles, and the crustalmodel ................... 37

Figure 15. Seismic lines, Bouguer gravity gradient, andearthquake epicenters ........... 39

Figure 16. Hypocenters associated with mylonite re-flections on Line 1 ............·41

Figure 17. Hypocenters associated with mylonite re-flections on Lines 25 and 4 ........ 42

List of Illustrations vi

1

Table 1. Data recording parameters for the seismic

lines ................-. . 7 pTable 2. Rattlesnake Hill(RH) and Letchworth(L) core

samples ........... , ..... 28

Table 3. Reflection coefficients at various

pressures. ............... 30

List of Tables vii _

INTRODUCTION

The Ramapo fault zone in the northeastern United StatesV

is a portion of an extensive network of northeast trending

border faults which generally separate crystalline

Proterozoic gneisses and schists to the northwest and

Triassic sedimentary rocks to the southeast. According to

Ratcliffe (1971) these faults were initially active during

the Grenville Orogeny (1 bya) and probably have been reacti—

vated several times through geologic history until the

Jurassic (150 mya). Analysis of seismic data has related

earthquake locations to the surficial features of the Ramapo

fault zone (Page et al, 1968). Interest in better definition

of the seismotectonics of this region was spurred by the-

construction of the Indian Point Nuclear Generating Station

south of Peekskill, N.Y., immediately adjacent to a ummber

fault of the Ramapo fault zone (Ossman, unpubl.).

During 1983 zuui 1984, seven reflection seismic lines

were collected by Virginia Tech and the U.S.G.S. in eastern

Pennsylvania, northern N.J., and southwest N.Y. (Figure 1).

Additionally, velocity and density determinations were made

on core samples, and modeling of gravity data was done to

interpret the seismic reflections.

1

Z¤

EREYLOUS WOR§

GEOLOGY

The Ramapo Fault proper extends linearly from Peapack,

N.J., about 80 Ian northeast to Stony Point, N.Y., on the

Hudson River (Ratcliffe, 1971). The entire fault system,

including splays and branches along strike at both ends of

the main normal fault, expands 150 to 175 km. The main ex-

tensions are the Canopus Fault system northeast of the Hudson

River, and the Flemington-Furlong fault system to the south-

west. The trend of the system is approximately N 40° E

(Figure 1).

To the northwest of the faults lie primarily Precambrian-

gneisses (in part the New Jersey and Hudson Highlands) and

Cambrian-Ordovician metamorphosed rocks of the Manhatten

Prong (Figure 1). This terrane is folded into northeast

trending ridges which commonly contain Paleozoic sediments

in their intermontane valleys. Also, several mafic intru-

sives occur ranging i11 age from Late Precambrian to Late IOrdovician-Early Silurian (Ossman, unpubl.). To the south-

east, the faults of the Ramapo system generally boundI

Triassic-Jurassic basin sediments, e.g., the half graben

Newark Basin. Many of these Mesozoic basins contain diabase Iintrusives, such as the Palisades sill. I

2 I

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Figure 1 . Location map of the sei smic lines with thegeology of the Ramapo fault zone: Sei smiclines are numbered and the geologic data isfrom the 1978 USGS Tectonic Lithofacies Mapof the Appalachian Orogen (compiled by HaroldWilliams).

3 .

1

Ratcliffe (1976, 1980) recognized two distinct types of

faults i11 the Ramapo system. One is representative of

semiductile shear faulting related to major compressive

tectonic events; the other is characterized by more brittle

fracture (Ossman, unpubl.). The former are older thrust

faults associated with mylonite zones, whereas the latter are

younger normal or dip slip faults associated with cataclastic

fabrics.

The southeast dip of the Ramapo fault and associated

faults has been measured by drill hol—e data (Ratcliffe,

1980). In general, the dips are consistently steeper toward

the northeast, ranging from about 45° SE near Riverdale,

N.J., to about 70° SE at Stony Point, N.Y.

SEISMICITYl ~

Although the historic record of felt earthquakes in the

study area extends back some 250 yrs, only during the last

20 yrs have epicentral locations become accurate enough to

be tentatively correlated with geologic structures (Kafka,

1983). Several authors (Kafka, 1983, Kafka et al, 1982,

Aggarwal and Sykes, 1978, and Page et al, 1968) suggested

that current minor seismic activity may be associated with

the Ramapo fault and other exposed northeast trending faults.

Some epicenters in the study area appear to be associated

with the Ramapo system, occuring within 5 km of a fault with

4

surface expression (Ossman, unpubl.). However, few earth-

quakes in the Ramapo fault system area have been convincingly

correlated with mapped faults (Fischer, 1981).

Furthermore, the improvement 511 the determination of

focal mechanisms made possible by the increased density of

seismic monitoring stations has indicated that recent

seismicity is occurring on northwest—trending fractures (Yang

and Aggarwal, 1981, and Ossman, unpubl.). Therefore, al-

though some epicenters do occur with an apparent spatial re-

lationship to the faults of the Ramapo system and may

·indicate movement along these faults, there is a scatter of

events throughout the region, and focal mechanism solutions

are inconsistent. ”In addition, no fault displacement or

other geologically recent deformation has been observed on

faults in the Ramapo fault zone (Ratcliffe, 1980).l

5

T

REFLECTLON SEISMIC DATA ACQUISITIGN AND PROCESSING

DATA ACQUISITION

All RAMAPO lines were acquired by personnel from the

Regional Geophysics Laboratory (RGL) of the Geological Sci-

ences Department at Virginia Tech using a single Failing

Y-1100 P-wave vibrator. Min—Max 10-Hz geophones were used

in Chebychev weighted 20-element arrays in conjunction with

qan MDS-10 48-channel digital recording system with field

summing capability. Figure 1 is a location map of the seven

lines and Table 1 shows the recording parameters for the

lines. Additional recording parameters are given in Appendix

A.i

Data acquisition in this densely populated urban corri-

dor is difficult. For example, during the data collection

along Line 5, cultural obstacles necessitated the shooting

of several consecutive vibrator sweeps at the same location.

The inconsistent manner in which these data were collected

caused many of the CDPs to contain several traces with the

same offset, falsely* biasing the data. These repeated

common-offset traces were edited out during processing.

6

1

Table 1. Data recording parameters for the seismic lines———-----———-————-——-———----......................___________________________________________

LINLHAME LLNEJ. LINEZ LINE} LIEBE LINKS. 1.11115.6 LINE].

DIRECTION SHOT SE to NV SE to NV N to S SE to NV SE to NV NV to SE SE to NV

‘FOLD 12 12 12 12 24 12;24 12;24

CDP SPACING (m) 34.5 34.5 34.5 34.5 17.25 34.5 34.5

NUMBER OF SHOTS 234 42 73 330 113 186;63 35;146

LINE LENGTH (KH) 32.3 6.5 10.1 45.5 3.9 30.3 15.0

GROUP INTERVAL (m) 69 69 69 69 34.5 69 69

PATTERN (offend) PULL PULL PULL PUSH PULL;PUSH PULL PUSH

NEAR/PAR OFFSETS (m) 417/3684 417/3684 417/3684 348/3614 variable 348/3614 348/3614

NUMBER OF VIBRATORS 1 1 1 1 1 1 1

GROUP INTERVAL (m) 138 138 138 138 34.5 138;69 138;69

ARRAY LENGTH (m) 69 69 69 69 69 69 69 -

SVEEPS/VP (sum?) 16;12(no) 12 (no) 12 (no) 16;12(no) l6;8 (no) 16 (yes) 16 (yes)_

SWEEP FREQUENCY (Hz) 14 to 56 14 to 56 14 to 56 14 to 56 14 to 56 14 to 56 14 to 56

SWEEP LENGTH (sec) 24;30;27 27 27 27 Z7 24 24

RECORDING TIME (sec) 29;35;32 32 32 32 32 29 29

DATA LENGTH (sec) 5 5 5 5 5 5 5

SAMPLE RATE (sec) 0.002 0.002 0.002 0.002 0.002 0.002 0.002

c

7

l

DATA PROCESSING '

All processing was done at the RGL on a Digital Equip-

ment Corporation (DEC) VAX ll/780 computer, Floating Point

Systems (FPS) 12OB array processor, and Digicon DISCO seismic

software. All lines have undergone the same standard proc-

essing routine as described in Appendix B. In addition, se-

veral unusual techniques were used. For example, the effects

of different CDP line orientations and the application of

iterative automatic residual statics and time-variant auto-

matic residual statics were investigated. Furthermore, Lines

1, 2, 3, and 5 were subject to single-sweep processing.

CDP LINE ORIENTATION

During CDP sorting the effects of different CDP line1

orientations were investigated„ Ln a normal common-depth-

point (CDP) sort, a line of CDP stations (surface locations)_

is defined that is coincident with the source-receiver

stations but with a spacing half that of the latter. Each

trace is then assigned to the CDP station nearest to the g

source-receiver midpoint location„ This is done under the

assumption that all energy on the trace was reflected from a

subsurface point located at the source-receiver midpoint.

All traces assigned to a CDP station are then gathered 1

(sorted) and summed (stacked) to form a single trace which

(using the above assumption) contains all the recorded energy

Vwhich was reflected from beneath the CDP station. This as-

sumption is reasonable for horizontal reflectors; for dipping

events it is not valid.

In the case of an inclined interface and a straight

line, energy reflected from different parts of the reflector

will be included in the CDP gather, but the reflection time

will still vary systematically as a function of offset. The

result is that the reflector will be imaged at an arti-

ficially high stacking Velocity (Levin, 1971).

Where crooked roads and dipping interfaces are encount-

ered, reflections from different depths along the inclined

reflector are again collected into the same stacking gather.

Unfortunately, because of erratic road geometry (and result-

ing erratic apparent reflector dip), the reflection time will

not be a simple function of its source-receiver offset and4

the reflector will not be imaged at any stacking Velocity.

ha the RAMAPO lines the roads were mostly crooked. To

properly image dipping reflectors, a method of gathering the

data parallel to geologic strike was employed. .A CDP line

was defined perpendicular to geologic strike, and the data

were gathered perpendicular to this line. Thus, the data

were essentially projected onto the contrived CDP line and

each CDP gather contained all the traces with midpoints at

the same relative dip locations.

This process acts as a dip filter for which only inter-

faces with a dip direction near that of the CDP line will be

9

1

properly imaged. This filtering effect is also present in a

normal CDP sort; however, the erratic CDP line caused the dip

filter to change direction depending upon the road direction,

often within one receiver array length. The projection

technique merely allows a choice of dip direction (it must

be nearly the same direction as the line, however, to keep a

reasonable fold and line length).

RESIDUAL STATICSC

Static corrections were found to be a major problem on

all of the Ramapo lines. Datum static corrections, followed

by extensive surface consistent residual static corrections

were applied to the data. The residual statics were computed

in an iterative manner; a velocity function was chosen, res-

idual statics applied, then often another velocity analysis·

was done and the velocity function revismd if necessary.

This sequence was repeated several times, usually three or

four, on most lines to optimize the statics used for the

final sections by accumulating the calculated values after

each run.

An unconventional time·variant residual statics calcu-

lation also was applied to some of the lines, a procedure

beyond the capability of the DIGICON software, by processing

the data twice, first applying ARS to the shallow part of the

section and a second time by applying ARS to the deeper part

of the section. The two output data sets were muted to

10

'zero-out' the portion not subjected to the ARS routine, and

then summed, resulting in a complete section that has had

different automatic residual statics computed for the shallow

and the deep portions. «

SINGLE-SWEEPPROCESSINGThe

standard reflection seismic data acquisition tech-

nique used involves the summation of commonly 16 or 12

VIBROSEIS sweeps symmetrically located around a common shot— point. This summation occurs in the field or after corre-

lation and is disadvantageous because the structural~detail

along· Ehe summation distance is lost. However, for single-

sweep processing, the individual sweeps are not summed, but

are recorded separately and continue through the entire

processing sequence as separate sources. By recording andl

processing the sweeps individually, greater lateral resol-

ution is apparent in the final section (Belcher, unpubl.).

This procedure was applied to Lines 1, 2, 3, and 5.

During single-sweep processing each VIBROSEIS sweep is

treated as a separate shot point with the receiver array held

constant for each 'family' of 16 or 12 sweeps. Thus, al-

though the distance the reflection line covers remains the

same, the effective length of the section is increased by a

factor of 16 or 12. The appearance of reflectors is dis-

torted as dipping beds are stretched out severely and appear

flat.

11

Station locations for the individual sweeps are in-

terpolated by assuming the sweeps are spaced at constant in-

tervals equal to the station spacing (69 m) divided by the

number of sweeps per shot point (16 or 12). Therefore, the

CDP spacing for the single-sweep sections is about 2.2 m for

16 sweeps/shot and about 2.6 m for 12 sweeps/shot; the shot

spacing is approximately twice this value.

12

DISCUSSION

PROCESSING

Common depth point sorting along crooked survey lines

results in stacked sections with highly variable fold cover-

age. Thus, best-fit modified-crooked CDP sort lines often

are defined along crooked survey lines. However, because the

orientation of the CDP-line can act as a dip filter, several

different CDP-line orientations were used to sort each of the

Ramapo lines and the resultant stacked sections were com-

pared.

The Ramapo lines are oriented generally NW—SE, approxi-

mately perpendicular to surface geologic strike. The stackedl

sections of the lines submitted to standard processing appear

in Appendix D. All have been sorted using a modified-crooked

CDP-line definition and plotted with no vertical exagger-

ation. A difference in the stacked section caused by

CDP-line orientation was observed for Line 3. 'Unlike the

other lines, Line 3 is oriented oblique to surface geologic

strike. Thus, the best-fit modified-crooked CDP-line also

is oriented oblique to surface geologic strike. A straight

CDP-line oriented perpendicular to geologic strike was de-

finmd for this data in order to sort traces from common

depths on a dipping reflector. The stacked section shows a

13

M

different perspective of the border fault and Triassic basin

than the original section (Figure 2).

Less significant differences (if any) were observed for '

the other lines. For example, Line 6 has an abrupt change

in direction as it crosses the surface trace of the border

fault. This orientation was considered a possible reason for

the lack of coherent reflected energy from the subsurface

fault plane on the modified-crooked line section. However,

when sorted along a straight CDP-line perpendicular to the

surface trace of the fault, the resulting stacked section

still did not contain reflections from the buried fault plane

(Appendix E).

The single-sweep data also were processed using differ-

ent CDP-line orientations. Crooked-line, modified-crooked

line, and straight-line CDP sorts were performed on the data.l

As opposed to the standard data, the straight CDP-line de-

fined perpendicular to strike was observed to produce a

single-sweep stacked section with the best coherency and most

constant fold coverage. Therefore, the single-sweep sections

also offer a different perspective of the data. For example,

part of Line 1 was processed single-sweep and then summed

after processing for comparison on the same scale with the

standard data (Figure 3). Note the possible indication of a

fault on the summed single-sweep section which is not present

on the standard data. This observation may be due to either

14

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Figure 3 . Summed single-sweep processing vs . standardprocessing for Line 1: (a) Part of Line 1processed by single-sweep and summed. Notepossible fault location marked by arrow thatis not apparent on the standard section ofLine 1 (b) and the increased coherency of re-flection ' I' on the single—sweep data. (Un-migrated and no vertical exaggeration.)

16

the different orientations of the CDP lines or to the process

of single—sweep processing.

Automatic residual statics (ARS) calculations are ap-

plied to correct for shifts in the data that are not removedby datum statics corrections. Static shifts were limited to

20 ms. These corrections were especially valuable due to the _

low fold coverage (12 to 24) and low signal-to-noise ratio

of these data. ha particular, deep coherent energy from6

within the crystalline basement was greatly enhanced by the

application of ARS. A good example of this effect can be

observed on the data from Line 4 plotted before and after ARS

calculations (Figure 4). Note the increased coherency of the ·

reflections after application of residual statics calcu-

lations. Line 4 is located largely over Precambrian crys-

talline rocks and required three iterations of the ARS4

routine to obtain this improvement. Similar reflection en-

hancement is observed on data from Line 6 (Appendix E).

Line 7 (Figure 5) and Line 25 (Appendix E) were subject

to time-variant residual statics corrections also resulting

in enhancement of reflections from within the basement. This

process enables corrective shifts to be applied to deep re-flections without degrading the coherency of shallower re-

flections.

The presence of signal coherency within the crystalline1

basement rocks is evident to some degree on all of the Ramapo

lines (Figure 6). The application of residual static cor-

17

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18 _

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. I •

and no vert1cal exaggerat1¤n.)

rections improved this coherency. However, it was observed

that for this data the ARS software will not cause alignment

of reflection amplitudes (coherency) where signal coherency

is not already present. That is, the residual static cor-

rections affect enhancement of preexisting coherency in the

data but do not produce artificial coherency where none pre-

viously exists.

Single-sweep processing was performed on Lines 2, 3, 5

and part of Line l. Reflections from the bottom of the basin

on Line 3 (Figure 7) appear offset indicating small, near-

vertical (about 80°) thrust(?) faults in the basement. Evi-

dence for these faults is not apparent on the standard

section of Line 3. Also on Line 3 near surface reflections,

possibly indicating another shallow basin, were observed on

the single-sweep data (Appendix E) but not on the standard_

data.

Similarly, improved geologic information was available

from the single-sweep sections of the other lines. For ex-

ample, a reflection on the single-sweep section of Line 5

(Figure 8) has much greater lateral continuity and coherency

than is observed on the standard section. In fact, on the

single-sweep section. this reflection. resembles the inter-

preted mylonite(?) reflections observed on the other lines,

discussed later.

All of the single-sweep stacked sections were summed

after complete processing for further comparison with the

20

. xÄ: ä \am4.% •-————•

ll!01s.¤¤

I.%

l.%2.%\ —

3.% 44.% 3m

9%‘

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2% wo am am 100°·°° am ‘ xu2.u Ä\^zuam

\ ~ am Ü\4 aa° F «i‘¤„ ‘·°° T.„—* ‘ \S·°° V, s.a¤

Figure 6. Fence diagram with line drawings of the seis-mic sections: All sections are at the samescale with no vertical exaggeration. Verticalaxes are two-way travel times in seconds andhorizontal axes are surface stations. Dashed ’lines represent border fault reflections.Some reflections from within the basins areinterpreted— to be from igneous intrusives(labeled 'I'). Unlabeled reflections arein-terpretedto be from mylonite(?) zones.

21 _

II

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22 .

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1.Figure8. Line 5 single-sweep section: Note the strong‘ continuous reflection marked by the arrows.Doming of traces around CDP 1310 due to ir-regular data collection. (Unmigrated)

23 V

\

standard sections. The increased coherency and increased

signal-to-noise ratio on the single-sweep data of Line 1 is

especially well illustrated in this manner. For example,

reflection 'I° on Line 1 is a more laterally continuous event

on the single-sweep data than on the data stacked in the

conventional manner (Figure 3). This same enhancement of·

reflections is observed on other summed single-sweep sections

(Figure 9 and Figure 10).

VELCCITIES, DENSITIES, AND REFLECTION COEFFICIENTS

Reflections from the border faults and intrusives within

the Triassic basins have been interpreted by their corre-

lation with surface geology (Figure 6). Interpretation ofl

the reflections from deep within the basement is supportede

by the following analysis. Density and ultrasonic velocity

determinations were made on core samples (Table 2) from the

U.S.G.S. drill-hole at Rattlesnake Hill near Riegelsville,

Pennsylvania (proximal to Line 7, Figure 13) and the

Letchworth #HZ drill-hole near Annsville, New York (proximal

to Line 25). The dip of the mylonitic fabric in the

Rattlesnake Hill core was between 20° and 30°, whereas it was

about 70° in the Letchworth core. P-wave velocities were

measured parallel to the axis of the core, except for sample

L2 for which the velocity was measured perpendicular to the

mylonitic foliation„ Velocity determinations were made at

24

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Figure 9. Summed single-sweep processing vs. standardprocessing for Line 3: (a) Summed single-sweep data of Line 3 and (b) part of standardsection. (Unmigrated and no vertical exagger—ation)

25 .

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(a I -I 1I' °° I **1I I

Figure 10. Summéd S1nql€•'SW€€p prOC€SSlng VS. standardprocesszmg for L1ne 5: (a) Summed s1ngle—sweep data of L1ne 5 and (b) co1:·respond1ngpart of standard sect1on of L1ne 25. (Unm1-qratéd and no V€rtlCal €Xagg€rat10n)

lithostatic pressures between 500 PSI and 9000 PSI. Density

and Velocity determinations were performed twice. The den-

sities (Table 2) and p-wave Velocities ( Figure 11) are close

to published Values for similar rock types (Jones and Nur,

1984, and Telford at al, 1976). Because of tüua small size

of the sample used to measure the Velocity· of' p-waves

propogating perpendicular to foliation (sample L2), the error

in these Values is about 11%, i.e., as much as plus or minus

500 m/s. Velocities for waves traveling parallel to the

mineral foliation could not be measured because the samples

shattered along the foliation planes under relatively low

pressures (<500 PSI). Reflection coefficients (Table 3) were

calculated assuming a normal incidence raypath (Neidell,

1984),

P2V2°p1V1A

--------- (cos 6)P2V2+P1V1

where 9= 90° is the angle of incidence of the raypath. The

high reflection coefficients (absolue Value) between the

mylonitic and non—mylonitic rock layers (>O.1) may be indic-

ative of reflections from mylonite zones. Reflection coef-

ficients of 0.14 and 0.125 are good reflectors (Neidell,

1984).

Specificallyy for seismic energy propogating through

homogeneous undeformed basement adjacent to a deformed

mylonitic zone with a propogation direction perpendicular to

the foliation. in the mylonites, a large enough acoustic

27

impedance contrast would exist to cause a detectable seismic

reflection. Therefore, the reflections from deep within the

basement are asserted to be from mylonite zones. Another

proposed explanation for these reflections is basaltic in-

trusives. However, the type of basaltic formations necessary

are not observed on the surface as is the widespread occur-

rence of mylonite and shear zone outcrops.

Table 2. Rattlesnake Hill(RH) and Letchworth(L) core sampleswith depths of occurrence in meters and measureddensities in gm/cm’ (errors < 0.5%).

SAMPLE-DEPTH LITHOLOGY DENSITY

RHl-3l hornblende gneiss 2.73

RH2-116 mylonitic hornblende gneiss 2.67 _

RH3-126 dolomite/dolomitic limestone 2.88

RH4-202 mylonitic limestone 2.80

RH5-251 homogeneous gneiss ,2.67

L1-159 homogeneous granite 2.68 .L2—41 mylonitic granite(?) 2.63

2 8

7.0

I; o o ¢

oo6.6

U) 6.0\ . x * *E . . *+ + XX I; 6 6 1_ X + + *>— 6.6 " ¥F; +

Y RH1RH2 XBj ¤H3<>R Y —I > 6.0 [*;;,1

L2 0·

04.6 O l O

-0

4.0i

0 2000 4000 6000 6000 10000' F?°6E66lJ1R’E, 66I

Figure ll. P·wave velocities (km/s) of core samples atvarious lithostatic pressures: An approxi-mately 3% to 4% error is inherent, i.e. , plusor minus 200 m/s. Somewhat higher for sampleL2 (see text).

29 I

1

Table 3. Reflection coefficients at various pressures.

com: soo 1000 3000 sooo 7000 6000·SAMPLE psx ps: psx psx psx psxpm

-‘ · -0.001 -0.003 -0.004 -0.00s -0.006 -0.006

0.160 0.127 0.127 0.127 0.126 0.123 0M

-------0.123 -0.110 -0.10s -0.10s -0.10s -0.1030.010 -0.000 -0.010 -0.000 -0.006 -0.000M15

--0.170 -0.16s -0.145 -0.145 -0.140 -0.128L2

-

30

NGRAVITY DATA

Additionally, evidence for the possibility of re-

flections from uwlonite zones is derived from analysis of· gravity data in the study area. The origin of the gravity

field over orogenic terranes has been the subject of many

papers (Turcotte and Schubert, 1982, Watts, 1981, Simpson et

al, 1981, Griscom, 1963, Zietz et al, 1963, Airy, 1855, and

Pratt, 1855). The Bouguer gravity anomalies observed over

the Appalachian and other mountain systems such as the Alps

and Himalayas consist of a large-amplitude positive and neg-

ative gravity anomaly. Brooks (1970) related the anomaly

couple to the overthrusting of one crustal plate onto an-

other. In his interpretation the outer gravity high is re-

lated to the lithospheric flexural bulge (the topography) andl

the outer gravity low is related to the basement deformation

caused by the surface load. Karner and Watts (1982) de-

scribed a modified version of such a model which includes the

effects of subsurface loading.

Karner and Watts (1982) suggest that any load acting on

the lithosphere will be associated with a positive gravity

anomaly, i.e., undercompensation. Therefore, a second inner

gravity high in the Bouguer anomaly profile over the

Appalachians not related to the lithospheric flexural bulge

may indicate the existence of some other load acting upon the

lithosphere 511 addition 1x1 the surface topography. They

31

I

propose that the observation that the peneplanation of the

Appalachians has not resulted in the destruction of its

molasse basin is evidence for the existence of a subsurface

load that is not expressed in the topography. Thus, the va-

lidity of their model rests on the assumption of a surface

loading (fold/thrust belts) as well as a subsurface loading

(obducted blocks/flakes). It is the subsurface crustal loads

which may be responsible for the additional inner positive,

anomaly observed on the Bouguer gravity profiles over the

Appalachians.

The model of Karner and Watts (1982) consists of the

obduction of continental crust onto a broken elastic plate

(Figure 12). The model implies that the strongly asymmetric

negative component of the anomaly is related to the deformed

basement and the symmetric positive component is associatedl

with subsurface crustal loads. This simple model agrees well

with observed data over the Appalachians (Karner and Watts,

1982). The gravity anomalies over the Himalayas and Alps

also can be described by flexure due to surface and subsur-

face loads (Karner and Watts, 1982). With regard to the

present study, the edge of the obducted broken plate is co-

incidental with the steep gravity gradient of the inner pos-

itive anomaly. Therefore, the edge of the broken plate and

thus, the Taconic suture zone may be delimited by the ob-

served inner gravity anomaly high.

32

Gf0v•|y onqmdy

ov"' OvlerI

;„„¢,

IO

IModec Of Henne

ISu¤su«1occ lood-oql I l

ouqe botgn I MIUVCI MQ"···" .· —“"_

II \ I I

II

‘ ‘I I

•; • ••;,’\

ll , "• •‘ I I \ \ \, •' •

4 • I'

I C. — — _ _‘_ gg .

O I .· _ . A. z¥’ -. a4 ‘hm .

I *

3.4

40EL}

‘ IOv•vtrwuge‘Ienqm

Figure 12. Subsurface loading model: Calculated grav-ity effect and flexure profile for subsurfaceloading using a broken plate. Densities aregiven. (From Karner and Watts, 1982)

33

l\

4

{ J. 3

Ä/

*X ß-” ‘

i(

Figure 13. Seismic lines and the general trend of thesteep gradient of the Bouguer gravity anomalyfield: The seismic lines are numbered andline 'G' marks the area of the inflection inthe gravity gradient from the 1982 SEG grav-ity map of the U.S. The approximate locationof the Rattlesnake Hill drill-hole is indi-cated by point 'RH'.

34 3

The steepest part of the gradient in the Appalachian

Bouguer gravity field from the 1982 SEG gravity anomaly map

of the U.S. is located just east of all of the Ramapo lines

except Line 4 (Figure 13). Assuming the gravity gradient

does mark the suture zone formed during the Taconic orogeny,

then it is evident that the suture zone and thus the basement

to the east will not be imaged on six of the seven vertical

seismic sections. Yet, the absence of the suture zone does

not preclude the appearence of related ductile deformation

zones (mylonite zones) on any of the seismic lines. For ex-

ample, a Bouguer gravity anomaly profile parallel to Line 1

has been modeled using a modification of the Karner and Watts

(1982) model (Figure 14). Here the model reflects the

peneplanation of the Appalachians and crustal deformation is

shown to be the primary cause of the observedl

positive/negative anomaly couple.

Line 1 is located between the maximum negative and pos-

itive values of the gravity profile, proximal to the proposed

suture zone in the crustal model. Therefore, mylonite zones

parallel to the Taconic suture could extend into the crustal

subsurface in the area of the seismic lines. Notice that if

the gravity gradient in Figure 13 does indicate the general

location of the suture, then the seismic lines get further

away from the suture toward the southwest.

35

us- 1

mnvuvv Anouuv um

O

. , Il /‘_/ ~ Ä

1"

26 °"’ O( O‘

4Ä IP*·5OKfT\*(

20+ aoucusn csuvnvv 7FANOMALY PROFILES /

MGO

-20\\ /’ -·

-40 / —iob••rv•dI——c•IcuI•t•d—6O

O KM YO0 200 300 400

KM 2.8 •ue\uv\• 2.840 Ä

\/,,’34

Figure 14. Bouguer gravity anomaly map, observed andcalculated gravity profiles, and the crustalmodel: The model is similar to the Karnerand Watts (1982) model (Figure 12) excepthere the surface is eroded down into thecrust. Topographic irregularities are ig-nored. Gbserved gravity data from the 1982SEG gravity map of the U.S. Extent of Line1 on the model is shown by the arrows.

36 .

EARTHQUAKE DATA

Earthquake events in the study area during the period

October 1, 1975 to September 30, 1983 have been collected

from the Northeastern. U.S. Seismic Network Bulletins of

Seismicity of the Northeastern U.S. (Nos. 1. to 32). The

dates and time of occurrence, latitude and longitude coordi-

nates, depths (km), magnitudes, and ERH/ERZ values for these

events are listed in Appendix C. For information concerning

the seismic instrumentation, velocity models, and magnitude

formulae used in obtaining these data see Kafka (1983) and

Ossman (unpubl.). The earthquake epicenters have been plot-

ted along with the seismic reflection lines and the steep‘ gradient in the Appalachian gravity anomaly (Figure 15).

Hypocenters were projected onto the vertical seismic sections4

along geologic strike (Appendix D), which is approximately

perpendicular to all the lines except Line 3. Horizontal and

vertical error bars defining a 95% confidence of location

ellipse have been included where the data were available.

For events located halfway between two lines, their

hypocenters were projected onto both lines. Several earth-

quakes also were plotted onto both Lines 25 and 3 because

they could be projected onto both lines. No epicenters are

located near Line 7 which is farthest from the Taconic

suture.

37

.0.0é LS!0• a. Ü ·

—¤öoälg 'xL |

Vx \ ·1 .1. 02 °Q ääi Ö ÄC l 1

I

l\l\/’:.6.· -• Ä; K/‘ —/Jx .¤·*?'° ‘ *7 6sx,/""'

‘·’

· J x<°$“°•l„7so 0 L 1/I 1

{J••Ex

l 7ß

os . ; *.1.0. .4 L ff

ä A_)

Figure 15. Seismic lines, Bouguer gravity gradient, andearthquake epicenters: Epicenters are in-dicated by solid circles and focal depths aregiven in km.

38 1

In general, the seismic activity is located within the

crystalline basement on the seismic sections. Few earth-

quakes have locations within the Triassic basins or along the

border faults. In addition, there is a volumetric corre-

lation of the mylonite(?) reflections with the earthquake

hypocenters. This relationship is apparent to some extent

on all of the seismic lines.

For example, on Line 1 several hypocenters occur within

reflections interpreted to be from mylonite zones and other

hypocenters are located in-line with other possible mylonite

zone reflections (Figure 16). Line 25 (Figure 17) contains

a similar correspondence of mylonite reflections and earth-

quake hypocenters. Line 4, located largely over crystalline

rocks, has few reflections. However the few deep relatively

strong reflections that are observed do have an associatione

with earthquake hypocenters projected onto the section (Fig-

ure 17). This apparent correlation of earthquake hypocenters

with reflections interpreted to be from mylonite zonesmayimply

that regional stresses are initiating brittle fracture

along zones of crustal weakness associated with ancient

ductile deformation zones.

39

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Qr' ‘YV,-6:2-;%::5 IIc—.•·**#*=2—«—.:.II&;:%>@~•gos:•g.-:-:„~I-<;·§;-:»·:;-e—,. ‘ .¤.. "

,• -0,.;. . •’

'·E'”·$~1+?3·r?·:Ä?°#:=-I·‘i€••·_Ä~TE·{‘~$:-TE':·_~ 'g . -0 „;_.:~?*•!J·Z$??·¢--

MI

Flqüfé 17. HYPOCGITCGIS aßSOClat€d Wlth mylOI'11 E I6fl€Ct1OHS on L1nes 25 and 4: Parts of L1ne25 (a) and L1ne 4 (b) w1th I€fl€Ct1OHS 1n-terpreted to be from mylonite zones labeledTM,

alld plotted as Open circlesw1th ERH/ERZ bars 1ncluded. (Unm1grated andHO V€I‘tiCal exaggerati OI1 )

CONCLUSIONSU

Reflection seismic data have been processed using vari-

ous orientations of the common·depth-point sorting line. The

vertical sections produced afforded different perspectives

of the geology. Generally, the resultant sections were only

· slightly modified from one another, perhaps due to the fact

that almost all of the survey lines were oriented approxi-

mately perpendicular to strike.

In the case of Line 3, which was not aligned perpendic-

ular to strike, significant variations in the final section

were produced by altering the orientation of the CDP line.

Therefore, in certain situations the use of different CDP

lines during sorting can be an important method to increasee

the geologic information in the data.

Residual statics corrections have been demonstrated to

considerably enhance the coherency of seismic reflections.

These calculations normally require a high signal-to-noise

ratio in the data, however even with the relatively low

signal-to-noise ratio, the reflection coherency was improved

by using an iterative approach to the residual statics cor-

rections. After calculating and applying static corrections

the stacking velocity function was reevaluated and residual

statics corrections were recalculated. This process was re-

peated until a nmximum level of reflection coherency was

42

I 4achieved. Often the results included reflections only barely

discernible, if at all, in the original data and greatly en-

hanced the seismic sections and therefore the interpretation

of the geologic structure.

Single-sweep processing proved to be a valuable proce-

dure for increasing* the geological detail of ‘the seismic

data. In particular, local reflections which extend over

only a few CDP traces on the original section and thus go

unnoticed, become extended over many more CDP traces on the

single-sweep section. The results from Line 3 exemplify this 4

effect where small near vertical faults in the basin floor,

not apparent on the standard section, became evident on the

single-sweep section.

Even when new geologic detail is not‘produced, the

overall coherency and signal-to—noise ratio is improved byl l

single-sweep processing. For example, reflections cxu the

summed single-sweep data appear more laterally continuous

than on the standard section„ Additionally, the signal—to-

noise ratio is noticeably higher even when new geologic in-

formation is lacking. Evidently, it is beneficial to apply

all steps of the processing routine to each sweep individ-

ually and then sum, rather than sum sweeps in the field be-

fore processing.

whether or not single-sweep processing is appropriate

and cost-efficient as a standard procedure depends largely

upon the specific purposes of the reflection seismic survey

43

and the degree of geologic complexity encountered. If large

volumes of data are involved, for example in petroleum in-

dustry exploration, the value of single-sweep processing may

not outweigh its expense and time requirements. However, for

smaller academic surveys in which the volume of data is less

and the geology is more complex, such as in tectonic regimes,

single-sweep processing could prove to be worth the time and

effort.

Reflection coefficient values calculated from determi-

nations of rock velocities under pressure and modeling of .

gravity data have provided supporting evidence for re-

flections originating from mylonite zones. For waves trav-

eling perpendicular to the mineral foliation in the

anisotropic mylonites, the contrast in the acoustic impedance

between the mylonites and the adjacent isotropic basement·

granite is enough to generate a detectable p-wave reflection.

Deep reflections from within the crystalline basement on the

Ramapo lines are interpreted to originate from interfaces

between. mylonitic and granitic rocks. Furthermore, the

mylonites indicate areas of ancient ductile deformation in

the crust which now may be zones of crustal weakness.

Earthquake hypocenters projected along geologic strike

onto the reflection seismic sections have a distinct associ-

ation with the mylonite reflections. This relationship seems

especially significant because the earthquake Ähypocenters

generally lack any correlation with the Triassic basins or

44

I

the brittle border faults. Furthermore, Fischer (1981)

stated that movement on the Ramapo fault ceased during Middle

to Upper Cretaceous time and Ratcliffe (1980) found zu> evi-

dence for recent movement in cores taken across the fault.

Therefore, it is proposed that stresses in the region may be

relieved by brittle fracture along ancient zones of ductile

deformation which now are weak zones in the crust marked by‘ mylonitic rocks. Ratcliffe (1980) similarly suggested that

current seismic activity may be more strongly controlled by

deeply-buried ductile deformation zones than by brittle sur-

face fractures.

During laboratory determinations of Velocity, the

mylonite rock samples were found to have planes of weakness

parallel to the mineral foliation along which the rock sam-

ples fractured under· relatively lxnv pressures. -PerhapsV

stresses in the earth oriented parallel to these planes of

mineral foliation similarly could initiate brittle fracture

along the mylonite zones generating the low magnitude earth-

quakes common in the study area. This theory requires a

horizontal compressive stress (ci) generally greater than

lithostatic stress because,

¤1=Iv/(1·v)1¤z „for a gravity-loaded model, where v is Poisson's ratio and

oz is lithostatic stress.

V 45

I

FUTURE WORK: Ongoing research concerning the occurrence

of seismicity in the northeastern U.S. should include the

continued integration of geologic, seismic reflection,

earthquake, and pmtential field data„ Reflection seismic

data coverage could be extended to the east over the location

of the Taconic suture with additional lines in other lo-

cations along the Ramapo fault zone. Earthquake data could

be improved upon by increasing the density of seismic moni-

toring stations to obtain. more confident epicentral and

hypocentral locations. At present, accurate focal depth de- .

termination is only possible when at least one station is

located close enough to the event that the epicentral dis-

tance is less than about twice the depth of the event (Kafka,

1983). Detailed analysis of focal mechanism solutions may

lead to a better understanding of the orientation and sources!-

of the stress field in the region.

46

' 1

REFERENCESl

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· ern New Jersey: Science, no. 200, p. 425.

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Anderson, J. and Dorman, J., 1973, Local geological effectson short-period Rayleigh waves around New York City:Bull. Seis. Soc. Amer., v. 63, p. 1487-1497.

Belcher, S.W., 1984, Spatial resolution by single sweep re-cording and processing: Masters Thesis, VirginiaPolytechnic Institute and State University.

Brooks, M., 1970, Positive Bouguer anomalies in some orogenicbelts: Geol. Mag., v. 111, p. 399-400.

Coruh„ C. and Costain, J.K., 1983, Noise attenuation byVIBROSEIS whitening (VSW) processing: Geophysics, v. 48 -p. 543-554.

Dames and Moore, 1977, Geotechnical investigation of theRamapo fault system in the region of the Indian Pointgenerating station, Appendix D: Geophysical investi-gations : report to Consolidated Edison of New York,Inc., v. 1, Cranford, New Jersey.

Dorman, J. and Ewing, M., 1962, Numerical inversion of seis-mic surface wave dispersion data and crust—mantle struc-ture in the New York-Pennsylvania area, Jour. Geophys.Res., v. 67, p. 5227-5241.

Epstein, J.B., D'Agostino, J.P., Drake, A.A.Jr., andLampiris, N., 1967, Preliminary log of drill hole nearRiegesville, Pennsylvania: Bureau of Topographic andGeologic Survey, Dept. of Internal Affairs, Harrisburg,Pa., 17120.

Fischer, J.A., 1981, Capability of the Ramapo fault system,in Earthquakes and earthquake engineering: the easternUnited States, v. ]„ J.E. Beavers, editor, Ann ArborScience, Inc.

47

I

Fountain, D.M., Hurich, C.A., and Smithson, S.B., 1984,Seismic reflectivity of mylonite zones in the crust:Geology, V. 12, p. 195-198.

Fountain, D.M., and Salisbury, M.H., 1981, Exposed cross-sections through the continental crust: Implications forcrustal structure, petrology and evolution: EarthPlanet. Sci. Lett., v. 56, p. 263-277.

Gibb, R.A., and Thomas, M.D., 1976, Gravity signature offossil plate boundaries in the Canadian Shield: Nature,V. 262, p. 199-200.

Griscom, A., 1963, Tectonic significance of the Bouguergravity field of the Appalachian system: abstract, Geo.Soc. Amer. Spec. Papers, V. 73, p. 163-164.

Harwood, D.S., and Zietz, I., 1974, Configuration ofPrecambrian rocks in southeastern New York and adjacentNew England from aeromagnetic <5ata: Geol. Soc. Amer.Bull., v. 85, p. 181-188.

James, D.E., Smith, T.J., and Steinhart, J.S., 1968, Crustalstructure of the middle Atlantic states, Jour. Geophys.Res., V. 73, p. 1983-2008.

Jones, T.D., and Nur, A., 1984, The nature of seismic re- .flections from deep crustal fault zones: J. Geophys.Res., V. 89, p. 3153-3171.

Kafka, A.L., 1983, Earthquake hazard studies 511 New YorkState and adjacent areas: Final Report, April 1976-June1982, Lamont-Doherty* Geological Observatory report toU.S. Nuclear Regulatory Commission.

Kafka, A.L., Schlesinger-Miller, E.A., Barstow, N.L., Cramp,D., and Sykes, L.R., 1982, Earthquake xnagnitudes andseismicity in the New York City metropolitan area: Pre-print (To be submitted for publication to BSSA).

Karner, G.D., and Watts, A.B., 1983, Gravity anomalies andflexure of the lithosphere at mountain ranges: J.Geophys. Res., V. 88, p. 10449-10477

Karner, G.D., and Watts, A.B., 1982, On isostasy atAtlantic-type continental margins: J. Geophys. Res., V.87, p. 2923-2948. .

48

I

Karner, G.D., 1981, Global data bank system: Tech. Rep. 1,CU-1-81, v. 27, Lamont-Doherty Geol. Observ. of ColumbiaUniv., Palisades, N.Y.

Klemperer, S.L., and Brown, L., 1985, Simulations of noiserejection and mantissa-only recording: An experiment inhigh-amplitude noise reduction with. COCORP data:Geophysics, v. 50, p. 709-714.

Levin, F.K., 1971, Apparent velocity from dipping interfacereflections: Geophysics, v. 36, p. 510-516.

Neidell, N.S., 1984, Stratigraphic modeling and interpreta-tion: Geophysical principles and techniques: Amer.Assoc. Petrol. Geol. Education Course Note Series #13.

Nuttli, 0.W., 1973, Seismic wave attenuation and magnituderelations for eastern North America: J. Geophys. Res.,v. 78, p. 876-885.

Osberg, P.H., 1978, Synthesis of the geology of the north-eastern Appalachians, U.S.A., IGCP Project 27: Geol.Surv. Canada, Paper 78-13, 1377-147.

Ossman, R.M., 1984, Seismotectonics of southeastern New YorkState, Masters Thesis, The Pennsylvania State University.

Page, R.A., Molnar, P.H., and Oliver, J., 1968, Seismicity .in the vicinity of the Ramapo fault, New-Jersey-New York:Bull. Seis. Soc. Amer., v. 58, no. 2, p. 681-687.

Pratt, J.H., 1855, On the attraction of the Himalayan Moun-tains, and of the elevated regions beyond them, upon theplumb line in India: Philos. Trans. R. Soc., v. 145, p.53-100. .

_Ratcliffe, N.M., 1968, Contact relations of the Cortlandt

Complex at Stony Point, New York, and their regional im-plications: Geol. Soc. Amer. Bull., v. 79, p. 777-786.

Ratcliffe, N.M., and Shuart, S.G., 1970, The Rosetown complexand its bearing on the antiquity of the Ramapo faultsystem: Geol. Soc. Amer. Abstr., part 1, (northeast.sect.), p. 32-33.

Ratcliffe, N.M., 1971, The Ramapo fault system in New Yorkand adjacent New Jersey: a case of tectonic heredity:Geol. Soc. Amer. Bull., v. 82, p. 125-141.

49II

I

Ratcliffe, N.M., 1976, Final report on major fault systemsin the Vicinity of Tompkins Cove—Buchanan, New York: re-port for Woodward-Clyde Consultants, Wayne, New Jersey.

Ratcliffe, N.M., 1980, Brittle faults (Ramapo fault) andphyllonitic ductile shear zones in the basement rocks ofthe Ramapo seismic zone, New York and New Jersey, andtheir relationship to current seismicity: in. Fieldstudies of New Jersey geology and guide to field trips,Rutgers University, Newark, New Jersey.

Ratcliffe, N.M., 1982, Fault reactivation and seismicity inthe Ramapo seismic zone, New Yerk-New Jersey: Abstr.-Eqke. Notes, V. 53, p. 32. Sbar, M.L., Rynn, J.M.W.,Gumper, F.J., and Lahr, J.C., 1970, An earthquake se-quence and focal mechanism solution, Lake Hopatcong,northern New Jersey: Bull. Seis. Soc. Amer., V. 60, p.1231-1243.

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50

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51

(APPENDIX A. LOCATIONS OF RAMAPO LINES

RAMAPO LINE1 was acquired from 9/5/83 to 9/8/83 in

Somerville, New Jersey along state route 517 (Bound

Brook, Raritan, Gladstone, Califon, and Hackettstown USGS

7.5' quadrangles).

RAMAPO LINE2 was acquired from 9/9/83 to 9/10/83 in1 1

Rockland County, New York, near the city of Stoney Point

along state route 210 (Haverstraw, Thiells, and Popolopen

Lake USGS 7.5' quadrangles).

RAMAPO LINE3 was acquired from 9/11/83 to 9/12/83

also near the city of Stoney Point, New York, along theA

Palisades Interstate Parkway (Thiells and Popolopen Lake

USGS 7.5' quadrangles).

RAMAPO LINE4 was acquired from 10/25/83 to 11/4/83

starting near the New York/Connecticut state border going

Northwest along routes 121 and 6, Interstate 84, Storm

Mountain Road, routes 52 and Old 52, route 216, Phillips

Road, Sylvan Lake Road and Old Sylvan Lake Road,

Arthursburg Road, and Noxon Road (Peach Lake, Brewster,

Lake Carmel, Poughquag, Hopewell Junction, and Pleasant

Valley USGS 7.5' quadrangles).

52

l

RAMAPO LINE5 was acquired from 11/5/83 to 11/6/83

also near Stoney Point, New York, along route 21O over-

lapping part of RAMAPO LINE2 (Haverstraw and Thiells USGS

7.5' quadrangles).V

RAMAPO LINE6 was acquired from 11/8/84 to 11/13/84

in Passaic County, New Jersey, near the city of Patterson

along state route 23 (Eianklin, Newfoundland, PomptonJ

Plains, and Wanaque USGS 7.5' quadrangles).

RAMAPO LINE7 was acquired from 11/14/84 to 11/18/84

near Bethlehem and Riegelsville, Pennsylvania along state

route 412, Gallows Hill Road, route 212, Durham Road, and .

Raubville Road (Bedminster, Riegelsville, and Easton USGS

7.5' quadrangles).

53

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Begin Line 1 End Line 1B°uud Brddk Quad Hackettstown Quad

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Begin Line 25 End Line 25F Haverstraw Quad Popolopen Quad

54

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gew; gie 4 d aaa Lina 4eac a E Qua Pleasant Valley Quad

55

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64

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End Line 7Bedminster Quad

56

1

APPENDIX B, STANDARD PROCESSING ROUTINE

Demultiplexing and Correlation

First, normal demultiplexing was performed on the

data, followed by a modification to a normal correlation.

The unusual correlation technique was the application of

VIBROSEIS Whitening (VSW) (Coruh and Costain, 1983).

This process involves applying an automatic gain control

(AGC) to the data before correlation to balance the

spectral content of the record (whiten the data). This

process was applied to all the data with an AGC window

of 1.0 sec.

Normally the individual sweeps are summed in the

field or after correlation. IHowever, for single-sweepl

processing, the individual sweeps are not summed, but

continue through the entire processing sequence as sepa-

rate shots. This procedure was applied to Lines 1, 2,l

3, and 5.

Editing;

Hand-editing of the data consisted of deleting bad

shot records and traces with prevalent high or low fre-

quency noise. .

Geometry and Datum Statics;

57

ulÄ

The geometry for each line was defined directly from

the survey data and observer's notes.

Datum statics were applied using the average ele-

vation of the line as the datum elevation and the average

direct wave velocity as the datum velocity.

CDP Sorting;

- CDP sorting was applied to the data often several

times using different CDP line orientations.

Velocity Analysis and Mute

A standard velocity analysis was performed on the

data using constant velocity stacks (CVAs). On several

lines, the velocity analysis was done in an iterative

fashion, alternating with the residual statics applica-_·

tions.

Mute functions were applied to the lines to elimi-

nate first breaks, refractions, and wavelet stretching.

Experimentations with several different mute patterns

were undertaken since many of the lines contained impor-

tant near surface reflections.

Residual Static Corrections

Datum statics, followed by extensive surface con-

sistent residual statics analyses were applied to the

data. The residual statics were computed in an iterative

58

1

manner; a Velocity function was chosen, residual statics

applied, then often another Velocity analysis was done

and the Velocity function revised if necessary. This

sequence was repeated several times (usually three or

four) on most lines to optimize the statics used for the

final sections by accumulating the calculated values af-

ter each run.

An unconventional time—variant residual staticscalculation also was applied to some of the lines.

Band·Pass Filtering

A band·pass filter of 14 to S6 Hz was applied.

Migration UPost—stack migration also was performed. The

U

single-sweep data were not migrated.

59

n

APEENDIL Q, EARTHQUAKE EPICENTRALg§XPOCENTRAL DATA

Yr MoDy Hr:M¤ Lat(Dg) Lo¤(Dg) Depth Mag ERH ERZ

1983 915 23:17 41.139 -74.230 9.1 1.5 0.7 0.781983 913 2:46 41.260 -73.958° 10.5 1.4 0.22 0.411983 913 3:53 41.260 -73.960 10.1 1.9 0.18 0.321983 6 1 9:50 40.872 -74.525 5.2 1.5 1.69 0.961983 426 19:36 41.533 -73.635 13.9 1.4 2.0 1.71983 4 7 20:34 41.672 -73.687 10.8 1.6 1.7 1.11983 226 19:59 41.552 -73.663 6.7 3.0 0.24 2.251983 219 5:45 40.648 -74.768 6.1 2.7 0.26 0.521983 121 21:21 40.955 -73.682 0.2 2.2 1.14 1.61982 916 6:36 41.118 -74.645 0.5 1.6 1.7 31.61982 818 4:30 41.127 -74.155 6.0 2.0 0.2 0.11982 6 2 3:27 41.745 -74.070 4.6 1.5 0.7 0.31981 621 5:04 41.070 -74.590· 8.5 1.81981 518 7:22 41.100 -74.200 8.7 2.2

° 1981 518 7:22 41.100 -74.200 11.8 2.31981 319 8:51 40.940 -74.360 9.6 1.9 419801212 23:04 41.310 -73.910 14.6 2.319801212 23:04 41.270 -73.830 10.8 1.719801015 17:02 41.250 -73.880 2.0 1.51980 927 0:48 41.540 -73.690 7.0 2.2 ~1980 9 4 4:30 41.120 -73.780 12.6 2.91980 8 2 17:21 40.440 -74.140 7.6 3.01980 520 21:33 41.350 -74.370 2.3 2.61980 512 1:38 41.280 -74.140 4.2 2.41980 5 7 4:32 41.020 -73.870 0.0 2.61980 5 2 19:02 40.240 -75.030 0.0 3.01980 5 2 15:23 40.160 -74.990 5.0 2.81980 425 0:23 41.350 -74.370 0.0 2.41980 325 18:54 40.970 -75.020 5.0 2.81980 117 10:13 41.300 -73.920 3.6 2.81980 117 10:12 41.290 -73.930 4.5 1.919791230 14:50 41.150 -73.690 7.0 2.3197912 1 16:14 41.350 -74.360 0.0 1.9197910 1 19:50 41.650 -73.920 5.0 0.01979 9 4 7:38 41.580 -73.540 8.0 1.11979 620 19:20 41.350 -74.380 0.0 0.01979 310 4:49 40.720 -74.500 3.0 3.11979 211 7:21 41.190 -73.750 11.0 2.01979 2 2 2:26 40.770 -74.660 0.0 1.91979 130 16:30 40.320 -74.260 5.0 3.51978 723 23:02 41.320 -73.930 2.0 2.11978 630 22:39 41.080 -74.200 6.0 1.81978 630 20:13 41.080 -74.200 5.0 2.7

60

I

1978 616 4:59 40.990 -74.570 0.0 0.01978 518 1:29 41.020 -74.340 6.0 1.51978 3 5 7:53 41.350 -74.150 5.0 2.11978 215 5:28 40.920 -74.430 6.0 1.61978 210 9:37 41.300 -73.990 9.0 0.01978 115 7:41 41.380 -73.950 3.0 0.01978 114 18:47 41.370 -73.940 4.0 0.01978 113 5:15 41.400 -73.970 0.0 0.019771226 16:54 40.810 -74.760 0.0 1.719771225 15:39 40.810 -74.760 0.0 1.519771224 10:25 40.810 -74.760 0.0 1.619771223 16:20 40.810 -74.760 0.0 1.419771223 4:55 40.820 -74.750 0.0 2.2197712 9 17:33 41.560 -73.880 5.0 2.3197712 6 8:34 40.810 -74.760 0.0 1.7197712 6 17:51 40.810 -74.760 0.0 1.6197712 4 23:50 40.810 -74.760 0.0 2.1197712 4 23:50 40.810 -74.760 0.0 1.819771127 13:57 41.020 -74.210 5.0 1.819771027 9:22 41.070 -74.590 6.0 1.519771014 9:53 41.560 -73.950 0.0 2.41977 917 18:47 41.200 -74.060' 1.0 0.01977 9 2 5:53 41.310 -73.920 3.0 2.41977 7 2 11:13 40.700 -74.930 7.0 2.31977 610 12:48 40.700 -74.890 6.0 1.11977 310 16:22 41.180 -74.150 6.0 2.21977 1 7 0:05 41.020 -74.510 19.0 0.0197612 7 4:55 40.770 -74.760 5.1 1.7 .197612 5 16:32 40.770 -74.760 3.4 1.819761028 1:13 40.890 -74.490 0.0 0.71976 922 9:04 41.290 -73.950 8.0 1.81976 820 22:08 41.110 -73.750 6.0 2.51976 312 10:28 40.950 -74.340 0.0 2.21976 311 21:07 40.960 -74.360 1.0 2.41976 3 6 4:14 41.160 -73.810 6.0 2.319751110 3:02 41.180 -74.380 5.0 1.8197511 2 4:09 41.670 -74.000 0.0 0.019751028 21:45 41.710 -73.720 0.0 0.019751024 7:43 41.590 -73.930 3.0 2.219751024 7:08 41.620 -73.980 5.0 2.0

61

JJ

APEENDIX D, REFLECTION SEISMIC SECTIONS

Unmigrated, and migrated reflection. seismic lines

from the Ramapo fault zone plotted with x¤> vertical ex-

aggeration (one to one scale). Open circles on the un-

migrated sections represent earthquake hypocenters. ERH

and ERZ bars are included for events with that informa-

tion. Detailed geologic interpretations of the re-

flection seismic lines is being undertaken by Nick

Ratcliffe of the U.S.G.S., Reston. Here the main re-

flections on the unmigrated seismic lines are labeled

according to the following classifications:

(1) Reflections from sedimentary/basement interfaces,

i.e., the Triassic basin bounding faults. Labeled'B'.(2)

Reflections from intrusive basaltic flows within

the sedimentary basins, e.g., the Palisades sill (Line

1). Labeled 'I'. J

(3) Reflections from within the crystalline basement

which are interpreted to be from mylonite(?) zones. La-

beled 'M'.

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