Geologic interpretation of side-looking radar imagery using aerial photographs of Californi

Brown, R. D., Jr.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19700029577 2020-03-11T22:52:43+00:00Z
IV;
IZAL RE'*"'.	 RCE
P OGRAM
AGE APPLICATIONS
OGRAIVIS
A
TiECHNI^,:,1,L LIETTER NASA
N 0QQQ 3
;o ^ A SSIO
4JC	 AGES)
C7` (N<ASA CR OR TMX OR AD NUMBER)
(THRU)
ODE)3
(CATEGORY)
US, Geologies' Su
&partment of the Int' r
UNITED STATES
_>.9
►^ o	 DEPARTMENT OF THE INTERIOR Technical Letter
GEOLOGICAL SURVEY
	 NASA-45
^ ,•o	 WASHINGTON, D.C. 20242
	
August 1966
Dr. Peter C. Badgley
Chief, Natural Resources Program
Cffice of Space Science and Applications
Code SAR, NASA Headquarters
Washington, D.C. 2054E
Dear Peter:
Transmitted herewith are 2 copies of:
TECHNICAL LETTER NASA-45
GEOLOGIC EVALUATION OF RADAR IMAGERY:
SAN ANDREAS FAULT ZONE FROM STEVENS CREEK,
I Y	 ROCK SAN MATEO COUNTYSANTA CLARA COUNT TO MUSSEL 	 ,	 , CALIFORNIA*
by
Robert D. Brown Jr.**
Sincerely yours,
William A. Fischer
Research Coordinator
Earth Orbiter Program
I
*Work performed under NASA Contract No. R-09-020-015
t
-"U.S. Geological Survey, Wlenle Park, California
1
It
UNITED STATES
DEPARTMENT OF THE INTERIOR
GEOLOGICAL  SURVEY
TECHNICAL LETTER NASA-45
GEOLOGIC EVALUATION OF RADAR IMAGERY:
SAN ANDREAS FAULT ZONE FROM STEVENS CREEK,
SANTA CLARA COUNTY TO MUSSEL ROCK, SAN MATEO COUNTY, CALIFORNIA*
by
Robert D. Brown, Jr.**
August 1966
These data are preliminary and should
not be quoted without permission
Prepared by the Geological Survey.
for the National Aeronautics and
Space Administration (NASA)
*Work performed under NASA Contract No. R-09-020-015
**U.S. Geological Survey, Menlo Park, California
Photo copies of illustrations are available for viewing at the
following places:
Author(s); Discipline Coordinators; NASA Data Bank (Houston); Remote
Sensing Evaluation and Coordination Staff (RESECS) and the J.S.
Geological Survey Libraries (Denver, Menlo, Washington).
w,
d
IT
,r
G,a
r
ii
i^
E
i
.r
i
Geologic evaluation of radar imagery:
San Andreas Fault Zone from Stevens Creek,
Santa Clara County to Mussel Rock, San Mateo County, California
by
Robert D. Brown, Jr.
INTRODUCTION
Side-looking radar imagery along the San Andreas Fault Zone provides
a useful test of the radar technique and of its applicability to geologic
problems.
The San Andreas Fault Zone is a major tectonic feature 600 miles or
more in length. It trends generally northwestward from the Gulf of
California in northern Mexico to Point Arena on the northern California
coasts Rocks of profoundly different character and age are found in
Juxtaposition on opposing sides of the fault zone, and geologic evidence
shows that the block southwest of it has moved northwestward relative to
its counterpart across the fault zone. Although the total displacement
and the antiquity of the fault zone are both uncertain, available
geologic evidence suggests a total horizontal displacement of more than
150 miles and a record of movement extending about 60 million years into
the past. The largest documented historic displacement in the San Andreas
Fault Zone--21 feet--occurred near the head of Tomales Bay north of
San Francisco during the 1906 earthquake, but slow creep of opposing
blocks, amounting to a few tenths of an inch per year, has been observed
and measured at a numrer of localities along the zone, and on related
faults branching from it.
r
1
(^I
I:I
1'
i
t
k
x
4
Fracturing within the fault zone is distributed along a series of nearly
parallel or anastomosing faults that vary in age of movement and in amount
of total relative displacement. This complex zone of movement varies in
width from a few tens of feet to several thousand feet. Because of its
width and complexity, it is termed the San Andreas Fault Zone, and is
distinguished from the San Andreas Fault--the surface trace of most recent
(in many places, historic) movement. A distinction is also made between
the San Andreas Fault Zone, a relatively narrow linear feature, and the
San Andreas system, which includes major faults that branch from or cross
the San Andreas Fault at acute angles, and that extend tens or scores of
miles from the San Andreas Fault Zone. The faults which comprise the
San Andreas system are genetically and geographically related to the
San Andreas Fault Zone and are thought to be a product of the same crustal
forces as those which caused displacement along that fault zone.
General evaluation of ,radar imagery for geologic interpretation: Side-
looking radar imagery can be interpreted geologically in much the same
fashion as conventional black and white photography. The effect obtained
is that of photographs taken at low sun angles. Radar, unlike conventional
photography, is unimpaired by cloud cover or haze, and relatively clear
images are obtainable under varying atmospheric conditions. The screening
effect of vegetation, which in conventional black and white photography
masks detail in rocks at the surface and in topography, is greatly reduced
or eliminated in the radar images Radar imagery along the San 4ndreas
Fault Zone seems to enhance the photographic contrast between unconsolidated
geologic units and bedrock; thusq alluvium, lacustrine deposits, landslide
2
r•
a
y*
c
i
j!
rI'
debris, and similar units appear dark in tone, and contrast sharply with
more consolidated bedrock units. Different kinds of bedrock units, however,
are indistinguishable on the radar imagery except where such units engender
t	
a characteristic form of topographic expression. On the whole, radar imagery
compares favorably with conventional black and white photography in resolution,
contrast, and ease of geologic interpretation. The side-looking angle
accentuates topographic features, particularly linear features that are
parallel or oblique to the line of flight.
4
r
s
i
From the sample examined here, the polarized, radar image (figure IA)
seems most useful. The depolarized image is a helpful supplement, however,
and in this geologic study it was found to be particularly valuable in
screening out signal reflections from culture along densely populated parts
of the San Francisco Peninsula. Note, for example, areas "a" and "b" on
figure 2 9
 which correspond to unusually bright areas on figure IA. These
two bright areas and other smaller bright spots scattered along the lowlands
bordering San Francisco Bay seem to represent signal reflections from
clusters of similar structures or from individual structures. Both areas
appear normally illuminated in figure 1B 9
 and, in general, figure 1B tends
to subdue cultural detail without appreciable loss of detail in topography.
Because of the lower contrast of the depolarized print, some tone differences
are more easily detected in it than in the polarized print, a characteristic
which renders the depolarized print useful for some kinds of geologic
interpretation.
3
yi
I
7
Interpretation 0 Stevens Creek to Mussel Rock.- Figures IA and 1B show
polarized and depolarized views respectively of a 27--mile-long segment along
the San Andreas Fault Zone. The area shown is about 10 miles wide. Figure 2,
drawn from figure lAt illustrates the kinds of geologic information that
can be derived from radar imagery.
The most obviouseola is feature is a long, narrow trench ,formed9	 g	 gy
	
'	 within intensely fractured rocks of the San Andreas Fault Zone. This
trench is occupied by San Andreas Lake and Crystal Springs Reservoir.
	
#y	 That it is a major tectonic feature is well demonstrated in figure lA by
the contrast in relief, sand forms, and drainage on opposite sides of it.
The most recent tectonic movements along 'the trench (and hence also along
the fault zone which it expresses) are relatively young, for well established
drainages terminate at the trench or turn abruptly and flow along it.
Detailed examination of imagery of the southern part of the trench,
using low magnifications,
e.
recent; evidence of this
examples of recent stream
drainage systems.
Two faults which are
in the radar imagery by t
San Mateo Fault, branches
shows that some movement is geologically very
is shown by sag ponds, offset stream channels,
piracy, and shutter-ridges which block entrenched
part of the San Andreas system can be identified
heir physiographic expression. One of these, the
northwesterly from the San Andreas Fault Zone
near' the north end of Crystal Springs Reservoir, and its trace follows the
course of San Mateo Creek. The other, the Pilarcitos Fault, extends -from
r
San Pedro Valley on the pacific Ocean to Stevens Greek, and the fault
trace marks a distinct topographic line along the upper part of ,Pilarcitos
Creek and along the upper part of the southwestern slope of Cahi,l Ridge.
_a	 4
rt;
r
.r
r
F Q
^T
"i
J*
The Pilarcitos Fault, like the San Andreas Fault Zone, separates rocks
of markedly different lithology, and some geologic evidence supports the
contention that this fault was once the major break, in the San Andreas
system. Some of this evidence is suggested by detail visible on the radar
imagery. For example, along the northwestern part of the fault, the upland
mass that constitutes Montara Mountain (quartz diorite and granodiorite) is
,juxtaposed against a deeply dissected terrain that is underlain by relatively
weak and relatively heterogeneous cataclastic rocks, greenstone, and chert.
The topographic lineation that marks the Pilarcitos Fault clearly separates
the massif of Montara Mountain from weaker and less resistant rocks to the
northeast A similar juxtaposition of rock types is shown in Cahil Ridge.
a few males to the southeast. There, relatively indurated and erosion-
resisU nt sandstone along the crest and northeast slope of the ridge is
in faul t,: contact with softer, more easily eroded shale southwest of the fault.
Can the radar imagery, the moderately dissected upland of Cahil Ridge is
	 t
easily distinguished from deeply eroded rocks across the fault to the
southwest. This distinction is accentuated by a southwest-facing escarp-
ment, somewhat modified by erosion, which rises from the Pilarcitos Fault
toward the summit of Cahil Ridge.
Bedrock units can seldom be positively identified by either conventional
black and white photography or by radar imagery, but radar--like conventional
photography--can be used to delineate bedrock units with characteristic
structural forms, or with characteristic physical or chemical properties
provided those properties are reflected in some manner by the land surface.
	 Y
Thus, in the previous section, differences in the resistance to erosion of
juxtaposed rock units helped define several fault traces. A crude and
generalized geologic map can be derived from the radar imagery, using
k
5
J#
topographic form as an index to underlying rock units. For example, in
	
T
	
figures IA and 1F at least three rock units can be recognized and roughly
delinea teds 1) a rock mass ( granodior ,ite and quartz diorite) that is
	
ter,
	 highly resistant to erosion and which forms the prominent mass of Montara
Mountain, II) a widespread heterogeneous unit, moderately to deeply dissected
	
Y	 by erosion, which underlies most of the hilly area on figure 1A, and III) a
relatively unconsolidated rock unit fringing the shores of San Francisco
Bay and filling the Lower end of San Pedro Valley; this unit is typically
^n
expressed by lowland areas. Geologic data from field investigations show
that each of these three units is a composite of several rock°.types which
pan be separately delineated by geologic field. methods. The composite
nature of unit II is discernible in the radar imagery, but the contrasts
in expression of the several components are too poorly defined to permit
a further subdivision. The high quality of the radar imagery makes it
set- likely that similar imagerys at a lower altitude, could provide the
basis for a more detailed geologic map.
6
i
rt
NAO
^t
I
kl i
m
V)
E
r`N
^ou
Y
Ql
FaU
C
Q^
(n
O
YU
O
a
a
N
a
C
O
R.
OU
N
..r
U
C
10
H
L4
C
W
O
t
a
m
H
J
4J
o v
t a,
CL N
H H
^0 ^0
0 C
Cl
1Q
N
H
7
N
H
m
O
a
v
Y
NU
Qr
v
(n
n
N
Y
U
O
v
V)
c
C
R.
O
U
N
..r
u
C
H
L4
C
m
O
.0
a
^o
ti
rn
O
O
ta
H
O
CY
01
it
7
Q`
LL
I	 A
x
f
NA
E
4
P.
V
h
v
Q
It
Q
A
(1) m
.,4
,roHO .m
C
O ••
.c J
4J
o c
.-4 -F4
^d)U)13
U
13 •O
ao
• H
W
C H
roW X
•
¢eaa^
c O V
Oa m
(DU)U)4JU)
Acv
c
aw
E 3
v ^ a
O N ► 4
U) 
C 
v
U r-i O
.r4	 4J
O = Q)
^10N
1
N
a^
Lc.
F
}
r
t^
I I.
lb
^y
s
0 ^	 I>
o
	
/	 _WI Io
N^^ a
ol
^,A
, ►
	
l	 ^	 u
Jr ^
1 0	 ^ f^	 1\
10 v I	 ^^	 H
0\ lo bc
Q	
^e	
(^ N1 th; ^a
W 4^ or^^ o
.c lo
	 v I °c 1lz
	
^	 IQ ^	 J1 l
	
0%6	 j	 h;
uh	 1 1/a tl 0
Id	 t	 ",	
W 
Lr


Geological evaluation of radar imagery - San Andreas fault zone from Stevens Creek, Santa Clara County to Mussel Rock, San Mateo County, California

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server