Side-looking radar analysis of Grand Canyon Arizona geomorpholog

Jefferis, L. H.

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
1II1ME M IN THE GRAND CANYON AREA,
NORTHERN ARIZONA — A RADAR ANALYSIS
CRES TECHNICAL REPORT 118-9
February 19$9
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LINEANLNTS IN THE GRAND CANYON AREA, NORTHERN ARIZONA-
A RADAR ANALYSIS
by
Lee H. jefferis
CRES Report No. 118 -9
The Remote Sensing Laboratory
February 1969
Supported by NASA Contract NAS 9-7175
ABSTRACT
A comparison of structural date obtained from side looking radar
(SLAR) imagery of the Grand Canyon area, northern Arizona with previously
published reports demonstrates the potential of radar imagery as a tool for
geologic reconnaissance studies. The study, designed to determine the
geologic causes for a pronounced lineament pattern on the radar image,
also provided a measure of reliability for the radar image interpretation,
particularly the size of structure which may be interpreted with confidence.
The radar lineaments of the Grand Canyon area- indicate the loca-
tion of faults in the deformed Precambrian and relatively undeformed
Paleozoic strata. The strong correspondence of radar lineaments with
known faults is indisputable and to a lesser but still significant degree
the joint pattern and the radar lineament pattern showed a close correla-
tion. A number of lineaments on SLAR imagery in areas where nc faults have
been mapped substantiates the previous suggestion of SLAR as a geologic
reconnaissance tool.
The length of a fault is an important factor in a radar image identi-
fication. In the study area, a fault of less than one mile in length is
difficult to identify as a geologic structure, while the increasing length
of a lineament lends creditability to a structural interpretation.
LINEAMENTS IN THE GRAND CANYON AREA, NORTHERN ARIZONA —
A RADAR ANALYSIS
CRES Report 118-9
by
Lee H. jefferis
INTRODUCTION
Airborne radar systems capable c ` producing continuous images of
the eaiih`s surface are presently being studied as exploration tools for
earth science investigations. Tt_e photo-like images obtained from side
looking airborne radar (SLAR) systems contain data which have proven use-
ful in the delineation of regional geologic structures, fracture patterns,
and, in some areas, lithologic boundaries.
The use of remote sensors for geologic studies is by no means a
new reconnaissance technique. Air photos have been used widely by
geologists as aids in geologic investigations for years. The use of imag-
ing radars as remote sensors is a relatively new development however, and
its potential i-i geologic research is currently being studied. Investigations
carried out to date indicate that radar imagery is an excellent source of
geologic data. At present, radar imagery is being studied in detail in
order to develop guidelines and techniques for accurate and reliable geo-
logic interpretations.
A number of characteristics inherent to a SLAR system tend to emphasize
many terrain features of interest to the geologist. The relatively coarse
resolution of radar systems (when compared to conventional aerial photo-
graphy) tends to emphasize the gross patterns of an area, while suppressing
undesirable natural and cultural data. In addition radar energy impinging
on the earth's surface at an angle produces areas of shadow (negligible
2return of radar energy) behind areas of elevated topography, and areas of
high magnitude return from surfaces orthogonal to the radar signal (Figure
1). This results in what is essentially a three-dimensional presentation
without the use of stereo techniques. Another factor is the synoptic view
of radar imagery allowing the visual integration of terrain features over a
considerable area of the earth's surface.
This paper summarizes a study concerned with an attempt to define
criteria for the recognition and interpretation of geologic structures on
radar imagery. The study was carried out on imagery of the Grand Canyon
area, northern Arizona, where initial inspections of the image and geologic
data indicated.the possibility of a good correlation between radar linea-
ments and geologic structures. The purpose of the study was to determine
if additional information could be gained from radar imagery which would
be useful in the interpretation of similar structures in other areas.
The AN/APQ-97 side looking airborne radar system which produced
the radar image used in the study was developed by the U. S. Army Elec-
tronics Command. It is a real aperture radar system operating in the K-
band region of the electromagnetic spectrum. The area was flown by
Westinghouse Corporation under contract to the National Aeronautics and
Space Administration.
GEOLOGIC SUMMARY OF THE GRAND CANYON %REA
Introduction
The study was conducted in an area of approximately 325 square
kilometers located in the Grand Canyon area of north-central Arizona
(Figure 2) . This region in the southwestern portion of the Colorado Plateau
is a maturely dissected area underlain by nearly horizontal Paleozoic
sedimentary rocks overlying an intensely deformed Precambrian basement
sequence.
The study area lies within the region traversed by the Grand Canyon
of the Colorado Fever and its tributaries, and occupies a position between
3the Kaibab and Coconino uplifts of the Colorado Plateau. Approximately
1, 500 meters of relief exists between the steep-walled major canyons of
the area and the adjacent plateaus. Precambrian sedimentary rocks under-
lie the major portion of the study area, while Precambrian sedimentary and
meta-sedimentary rocks are exposed in the lower portions of the Grand
Canyon.Mesozoic rocks are not found within the study area.
Stratigraphic Summary
The Precambrian rocks of the study area belong to the Archean and
Algonkian systems, and are believed to be over 12,000 meters thick, (Maxon,
1966) . The Archean rocks are highly deformed metasediments consisting
in large part of schists and quartzites, while the Algonkian sedimentary
section is only moderately deformed. Rocks of both systems have been
intruded by granitic dikes (Figure 3). Paleozoic rocks of the area consist
of approximately 1, 200 meters of nearly horizontal, interbedded limestones,
sandstones, and shales. The Paleozoic section rests unconformably on the
Precambrian basement described above. The Paleozoic stratigraphy of the
Grant: !canyon area is summarized in Figure 3.
Structural Features
A southwest dipping homocline (average dip of 1.5') of the Paleozoic
sequence is the major structural feature of the Grand Canyon area. However
monoclinal folds, normal faults, joints, Precambrian dikes, and Precam-
brian schistosity all contribute to well-developed NE-SW and NW-SE
structural trends within the region.
Archean structures are indicative of extremely intense orogenic
activity. The Archean schists are characterized by broad isocli..al folds
trending northeast-southwest, having near-vertical schistosity and bedding.
jointing in the Archean section is nearly vertical and trends NW-SE. The
Algonkian strata are neither highly faulted nor folded yet represent the
deformation by stresses from the same directions as those which deformed
the Archean rocks.
4Paleozoic rocks of the study area reflect the stresses of the Late
Cretaceous to mid Tertiary Laramide orogeny. The Colorado Plateau area
was only gently deformed during the Laramide orogeny, however the stresses
were responsible for the development of local faults and monoclinal flexures.
Hodgson (1961) summarized the relationship between the fracture
pattern in the Precambrian and-the Paleozoic rocks:
"The major fracture trends, established in the basement
complex in Precambrian time, whether joints or faults
have persisted through time and through a fairly thick
section of Paleozoic... sedimentary rocks. This per-
sistence of the major elements of a Precambrian
fracture pattern in younger rocks suggests strongly
that the direction of jointing in younger rocks has
been directly controlled or strongly influenced by
these early fractures and the Precambrian pattern
has been imposed consistently on each successive
sedimentary rock unit." -
Thus the NW-SE and NF-SW fracture trends appear to have been
strongly defined in the Precambrian rocks, and were subsequently impressed
on the gently deformed overlying sedimentary rocks, resulting in a section
which was fractured in a uniform manner.
THE GEOLOGIC EVALUATION OF THE RADAR IMAGE
Introduction
Initial inspection of the radar image (Figure 4) of the study area
suggested that considerable structural data were available. The most
notable features of the image within the eroded canyon area are prominent
NW-SE and NE-SW trending lineament sets These lineaments sets are
expressed as the narrow straight portions of the Grand Canyon and many
of its tributaries.
5Methods of Study
The study was divided into two phases; the first involved detailed
examination and interpretation of the radar image of the area; the second
phase consisted of compilation and evaluation of the published geological
investigations from the study area. Reliability and extent of the radar
data were determined from a careful comparison of the two sets of data.
Faults, folds, and joint patterns from geologic maps and other publications .
were compared visually with the lineament trends obtained from the radar
image. Rose diagrams were constructed relating lineament trends to the
known fracture patterns of the area.
Geologic Field Data
Although geologic field data for the ,,Wdy was gathered solely from
published reports, it was of sufficient quantity and detail to provide a
sound basis for evaluation of the radar image.
Maxson!s (1966) geologic map of the Bright Angel Quadrangle was
used to locate the known faults of the study area. Hodgson's (1961)
publication concerning jointing and fracturing was used to compare linea-
ment trends with the known fracture patterns. Published reports by Maxson
and Campbell (1933) and Van Gundy (1946) provided additional geologic
data.
Results
Image A of Figure 5 indicates the results of the lineament analy-
sis within the study area. Parallel to subparallel lineaments sets are
recorded with NE and SW orientation.Lineaments indicated on the image
range from nearly one cm. to over 8 cros. in length, representing struc-
tures on the ground ranging from 1 1/2 kilometers to over 16 kilometers in
length. Image B of Figure 5 shows the major mapped faults indicated
on Ma.xson's (1966) map of Bright Angel Quadrangle. Of the 18 prominent
faults (all over 3 kilometers in length) selected for comparison with the
radar data, 15 were interpreted as geologic structures on the initial SLAB
6interpretation. The 3 apped-faults which had not been found on the radar
imagery were 
nYeradar
1 expressed topographically, and consequently were
not emphasizee radar image. All three rf the faults which had been
overlooked on 	 image were in areas of extremely high - low contrast
of radar return in steep walled canyons. Any subtle contrasts which might
exist across the faults are most likely masked.
In addition to the major faults, numerous smaller faults are present
in the narrow inner gorge of the Grand Canyon. These were not discern-
able on the radar image due to either (1) extensive shadowing or (2) ex-
tremely high magnitude return caused by the steep walls of the inner canyon
which were oziented normal to the incident energy.
A comparison of images A and S of Figure 5 indicates over 25 radar
lineaments are present where no faults or fractures have been mapped.by
field workers. The radar lineaments may represent faults which occupy the
eroded canyon bottoms, and which have not been discovered by ordinary
geologic field methods, or alternatively the lineaments may be a surface
representation of joint concentrations along a line where no large offsets
of strata are present to indicate fracturing to field workers. In either case
a fracture pattern is indicated on the SLAB image and is a logical location
for field checks.
The rose diagram (Figure 6) summarizing radar lineament data from
the Canyon study area indicates the lengths of lineaments with respect to
their orientation. Figure 7 diagrams joints of the same area as mapped by
Hodgson (1961), but on the basis of direction and frequency of joints rather
than the length of a joint.
A comparison of these two data indicates field study of the joints
provides more comprehensive detailed data on the fracture pattern of an
area, whereas the radar interpretation emphasizes the gross pattern. How-
ever both rose diagrams show concentrations of lineaments or joints in
NE-SW and NW-SE directions.
The monoclinal folds, Precambrian schistosity and Precambrian dikes
which have been mapped by field workers were not identified on initial
7examination of Cie image and in fact were not identifiable through compari-
sons of the image with published field data. However in most cases the
schistosity trend and dikes were not recorded on the image due to the con-
finement of exposures of Precambrian rocks to the shadowed zones in the
inner gorge. In addition no radar data were found to aid in the identification
of the monoclinal folds of the area. Whereas monoclinal folds are known
to parallel a number of the lineament (fault) controlle,0 canyons, no apnarent
differences were detected between faulted canyons with and those without
adjacent monoclinal folds.
CONCLUSIONS
Comparison of radar derived structural data with published field data
of the Grand Canyon area .amonstrates the potential of radar imagery as a
tool for geologic, fracture reconnaissance studies. In addition some of
the limitations of SLAR for structural studies are damonstrated.
(1)A strong positive correlation exists between the major lineament
patterns of the radar image and the major normal faults of the study area.
Although the jointing pattern shows strong parallelism with the radar linea-
ments, the correlation with faults is indisputable. It is therefore con-
cluded that the NE-SW and NW-SE trending faults are responsible for the
prominent structural grain as shown by the radar lineaments, and the
correlation of joints with the lineaments indicates the close relationship
between the directions-of jointing and faulting.
(2) The lineaments interpreted as faults or joints yet not mapped -;
such on the geologic maps are the locations of possible structures, and
therefore excellent leads for further field checks. Radar imagery thus pro-
vides a reliable source of reconnaissance data, even in areas where con-
siderable geologic exploration and mapping have been accomplished.
(3) In this area of considerable relief, the look-direction of the
SLAR system (the direction normal to the flight direction) has an effect on
the quantity and quality of the information available on radar imagery
8(MacDotald, 1969) . Since the radar data were obtained on a flight path
parallel to the inner gage of the Grand Canyon, virtually no data were
available from the area where Precambrian rocks are exposed.
(4) The interpretation of geologic structures on a SLAR image is a
function of the scale of the image, and the size of the structural feature.
Lineaments on the study image with a length less than approximately 1.5
kilometers were generally difficult to interpret due to their irregular appear-
ance. However if a longer lineament is studied in increments of 1.5 kuo-
meters, many portions appear as irregular features. Thus it is concluded
that the interpretation of the short lineaments is of questionable reliability,
and the increasing length of a lineament lends creditability to a structural
interpretation.
9REFERENCES
Hodgson, R. A. , 1961, Reconnaissance of jointing in Bright Angel
Area, Grand Canyon, Arizona, Bull. Amer. Assoc.
Petroleum Geoi. , Vol. 45, no. 1, pp. 95-105.
MacDonald, H. C . , In Press, Influence of Radar Look-Direction on
the Detection of Selected Geologic Features: Sixth
Symposium on Remote Sensing of Environment, University
Of Michigan, Ann Arbor, Michigan.
Maxson, J. H. , 1961, Geologic History of the Bright Angel Quadrangle,
Arizona, Text of Accompanying Geologic Map; Grand Canyon
Necural History Association.
Maxson, J. H. and Cambell, 1933, Faulting in the Bright Angel Quadrangle,
Arizona: Proc . Geol . Soc . America, p. 301.
Van Gundy, C. E . , 1946,  Faulting in East Part of Grand Canyon of
Arizona; Bull. Amer. Assoc. Petroleum Geol., v. 30,
pp. 1599-1909.
10
RADAR ANTENNA
x
A
LAND SURFACE	 `^	 a
RADAR
SHADOW
FIGURE, Effect of irregular terrain on incident radar energy. Peak
at X masks opposite valley wall below point Y, resulting
in radar shadow zone as shown. Areas t*arked with an A
are approximately orthogonal to the incident energy and
consequently return a large proportion of the incident energy
toward the antenna. Curved lines mark positions of advancing
wave fronts of the radar energy.
11
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Figure 3. Generalized stratigraphic su,•nmary of the
Grand Canyon area. From Maxson, 1961.
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figure 4 . SLAR image of the Grand canyon area.
14
figure 5, Image A, Radar lineaments of the Granct Canyon studv .n,3.
f figure 5, Image B, Mayor mapped faults of the Grand C,i:1: :. •:r, .j.
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RECONNAISSANCE STRUCTURE MAP, BRIGHT ANGEL AREA,
GRAND CANYON, ARIZONAQ obert, A HodgSon
1960
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CONTGURS TOP RErWALL LS
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Figure 7. Jointing data from the Grand Canyon area.
From Hodgson, 1961.


Lineaments in the Grand Canyon area, northern Arizona - A radar analysis

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