Neotectonics of the

San Andreas Fault System - Basin and Range Province

Juncture

NASA Grant NAG 5-177

Final Report

1 May 1981 - 15 March 1986

Submitted by:

Principal Investigator: Dr. John E. Estes

Professor of Geography

Co-Principal Investigator: Dr. John C. Crowell

Professor of Geology

Project Manager: Mr. Robert E. Crippen

Remote Sensing Research Unit

University of California

Santa Barbara, California 93106

7NASA-CR-176562) " BEOTECTCNICS OF THE SAN N86-2C996

ANDREAS .FAULT SYSTEM: BASIN AND BANGE

PROVINCE JUNCTURE Final Beport,, 1 .Hay 19S1

(California Univ.) "" -

V

1
Neotectonics of the

San Andreas Fault System - Basin and Range Province

Juncture

Introduction

This final report briefly summarizes research at the

University of California, Santa Barbara, on National

Aeronautics and Space Administration Grant NAG 5-177. As

part of the NASA Geodynamics Program, the general objective

of our study has been an improved understanding of the

tectonic interplay of the southern San Andreas fault system

and the Basin and Range province in the vicinity of the

Eastern Transverse Ranges of Southern California (Figure 1).

A parallel objective has been to determine the utility

of remotely sensed imagery and other spatial data in the

analysis of neotectonic patterns. A wide variety of

techniques, some standard and some experimental, have been

used and it is believed that the findings of this research

will be of value both to the earth scientist interested in

our study site and to others who might beneficially apply

some of the methodologies developed here to other sites.

Several parts of this research are being continued and will

be published in as-of-yet undetermined media. Publications

to date are listed at the end of this report. A detailed

and comprehensive report of the findings of this research

will be found in the dissertation of R.E. Crippen (1986).

Data Resources and Preprocessing

Several data sets were merged into a Geographic

Information System (CIS) format for comparative analyses and

extraction of synergetic information. These include (1)

digital elevation data, (2) aeromagnetic data, (3) gravity

data, (4) earthquake focus data, (5) Heat Capacity Mapping

Mission imagery, and (6) Landsat-2 Multispectral Scanner

(MSS) imagery. Each was formatted into a north-south,

west-east grid of pixels of 10-minute (N-S) and 12-minute

(W-E) spacing. This format preserved (actually oversampled)

the resolution of the HCMM and geophysical data and resulted

in images (360 lines by 450 samples) of pixels approximately

308 meters square. The digital elevation and MSS data were

also formatted at 2 1/2 minutes (N-S) by 3 minutes (W-E) to

preserve their higher spatial information (about 77 m) for

more detailed studies. Additional data sets of irregular or

incomplete coverage, not included in the GIS, are (1)

large-scale topographic maps, (2) Seasat radar imagery, (3)

aerial photographic imagery, and (4) Landsat-4 and Landsat-5

Thematic Mapper (TM) imagery.
CALIFORNIA

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Figure 1

STUDY AREA

LOCATION

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Selected Towns,

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Each data set required its own special preprocessing.

Two examples are: (1) one-fourth of the digital elevation

data required conversion from UTM to arc-second format, some

bad data lines needed replacement by interpolated values,

and below sea-level values needed several corrections (NCIC

digitization algorithms were not designed to properly handle

negative elevations), and (2) each of four aeromagnetic data

sets had to be assigned a scale-offset additive term so that

their merger would result in continuity across quadrant

boundaries.

Background information on geologic mappings, tectonic

models, and relevant methodologies were compiled into a

computerized, keyword-indexed bibliography of over 600

references (Crippen, 1986).

Field studies were necessary at several sites.

Techniques Summary

Geomorphometrics Research

A quantitative landform analysis technique, shown to be

effective in delineating neotectonic features (Crippen,

1983), was further developed and applied to the digital

elevation data set. The technique uses a measure of the

local correlation of elevation and relief to detect

deviations from fluvial geomorphic concavity. Linear

correlation is consistent with the logarithmic character of

longitudinal stream profiles and has been found to be a

close approximation to the general morphology of undisturbed

alluviated areas. Deviations from strong positive

elevation-relief correlation indicate disruption of common

fluvial morphology by non-fluvial (presumably neotectonic)

influences.

Figure 2 displays the spatial pattern of

elevation-relief correlations. The darker tones indicate

areas of poor correlation. Extensive anomalies are present

in the Surprise Spring area (34°18'N, 116°13'W) where

numerous faults cross alluviated terrain. The anomalies in

the San Bernardino, Little San Bernardino, and San Jacinto

Mountains appear to border areas of upland surfaces and

other products of neotectonic movements.

The limitation of his technique in this particular

study was the vertical resolution of the original elevation

data. The data were created by digitizing 200-foot contour

1:250,000 scale maps. The technique is good at detecting

gentle warps across alluviated areas. However, most such

features are lost at this crude resolution. The method will

have increased value as new high-resolution digital

elevation models become increasingly available.
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were useful in identifying regional geomorphic patterns. A

slope image was created to provide a quantitative measure of

this variable that is commonly correlated with zones of

tectonic activity.

Gravity and Aeromagnetic Studies

Bouguer gravity data and aeromagnetic data (Figures 5

and 6) were produced both as brightness images and as

contour images. Various mergers of these images with each

other and with the elevation and spectral images, allowed

inferences regarding major subsurface crustal trends

(discussed below). When brightness images were combined

with contour images, the pattern of data highs and lows was

clearly evident (brightness image), as were the data

gradients (contour image). This was significantly superior

to the individual use of the images and vastly superior to

the use of the original maps.

Earthquake Focus Studies

A "seismic-depth" image (Figure 4) was produced to

provide a three-dimensional view of earthquake epicenters

(locations), depths (color), and magnitudes (brightness).

Direct comparison of this image with spectral, topographic,

and geophysical images allowed us to evaluate the

significance of some lineaments. The shortness of the

seismic record is a limiting factor to this approach.

Aerial Photographic Mapping

An analysis of our study area, using low and high

altitude aerial photography, has revealed a number of fault

traces that were not previously mapped. These traces

include: (1) an extension of the Johnson Valley fault

southward along the eastern margin of the San Bernardino

Mountains (west of Landers); (2) a continuation of the

Calico fault southward to connect with an unnamed previously

mapped fault (west of Deadman Lake); (3) numerous kilometer

to five-kilometer long traces within the Central Mojave

shear system and along the Pinto Mountain fault zone; and

(4) various scattered short fault traces within and marginal

to the Eastern Transverse Ranges.

Orbital Imagery Analysis

Digital processing of our orbital imagery data has

resulted in the recognition of several features of possible

neotectonic significance. The most intriging of these are
numerous north-northwest trending lineaments that are

oblique to the major northwest trending faults of the

Central Mojave shear system. These features, seen on Seasat

imagery, could constitute synthetic faults of the simple

right shear model. Co-seismic faulting in recent years in

this area has occurred on previously unmapped faults having

this trend.

Some of the cross-valley Seasat lineaments do not

correspond to any surficial features found in aerial

photography or in the field. A cooperative effort with the

Radar Imaging Team at NASA-JPL to study the occurrence of

these lineaments has produced significant results (Blom et

al., 1984). Radar imaging of subsurface features had only

been clearly documented in one previous study. However,

evidence found in Means Valley (figure 7, 34°27'N, 116°31'W)

supports the presence of shallow-buried structural dihedral

reflectors oriented perpendicular to the radar look

direction. Some of these appear to be pediment-dike

combinations, but in areas of deep alluvial cover, an

alternative (perhaps neotectonic) explanation would be

necessary. Evidence in support of a faulting explanation

for many lineaments is the distinct correlation of their

presence within the Central Mojave Shear System, and not in

similar valleys (in the same imagery) outside the shear

system.

Landsat MSS enhancement methods have included principal

components analysis, ratio image combinations, high-pass

filtering and various experimental techniques. The first

two (MSS) or three (TM) principal component images have been

particularly useful in the depiction of neotectonic

displacements of Quaternary deposits. A remapping of the

locations, extents, and ages of some faults was warrented.

Thematic mapper imagery clearly reveals the expression

of the Blue Cut fault in the Holocene alluvium of Pinto

Basin (figure 7, 33°55'N, 115°45'W) (Crippen and Spencer,

1984). Several previous field investigations failed to

detect the fault trace, apparently due to its subtle and

irregular character. Field studies guided by the TM imagery

confirmed the geomorphic expression of the fault, which

controls the irradiance and indirectly controls the

reflectance properties of the terrain. The curvilinear

fault trace is most prominently displayed in the

long-wavelength reflectance (non-photographic infrared)

channels. Multispectral color composite images further

clarify the geomorphic features.

Two new quantitative techniques were developed during

this study that will have widespread use in a variety of

remote sensing applications. One is a method of band

selection to maximize spectral information content in color

composite displays of band data (Crippen et al., 1986). The
method uses a matrix of bi-spectral correlation coefficients

for an n-band image. A spectral information index, ranging

from 0 to 1, is derived, for each combination of three bands.

The combination with the highest index is the combination

with the most overall spectral information. Results show

that for almost any ground cover, the 1,4,7 combination is

preferable for Landsat TM reflectance data and that the

true-color combination (1,2,3) is the worst.

The other new technique is a method of adjusting

radiance data for band ratioing. Adjustments are needed to

reduce the influence of extrinsic inputs to image data,

namely atmospheric path radiance and sensor calibration

offsets. Ratioing was used to enhance the spectral contrast

of surface materials in order to detect discontinuities of

possible neotectonic origin. In simple terms, the method

determines bi-spectral regression lines for homogeneous

areas in rugged terrain. These lines are projected in pairs

to intersection points. Ideally, the coordinates of these

points must equal the measurements for zero ground radiance

since that is the only condition under which spectrally

different materials can have the same radiance values.

Tests show that the method is successful in determining

radiance correction values that result in maximum removal of

the topographic effect in ratio images. The method has

several advantages over other data adjustment techniques

(Crippen, 1986).

Merged Data Analyses

Several combinations of the GIS data sets were used in

order to evaluate geologic and geophysical features. This

was especially useful for comparing the spatial patterns of

surficial features (lineaments, elevation, slope, tonal

anomalies) with features that are more indicative of

subsurface characteristics (geomagnetic and gravity

anomalies, earthquake foci).

Tectonics Summary

Southern California may be the most complex continental

crustal region in North America. Recent geophysical studies

have led to the development of new neotectonic models, most

of which include partial decoupling (on detachment faults)

within the crust. Deformation in the upper crust here

consists primarily of brittle fracturing, probably driven by

ductile flow (with small-scale convection) below the

detachment surface. Our study has served primarily to

define the character and extent of surface manifestations of

recent tectonic activity so as to place constraints upon

various components of those models.
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Fault traces mapped within the Central Mojave shear

system appear to define a southward bending of the

southeasterly trending system within the western half of the

study area. Most of the offsets in the shear system are

believed to be largely right-lateral. Vertical components

of slip are inconsistent although up-on-the-east dominates

in the southern region as the western blocks sag and the

eastern blocks compress with the termination of the

right-lateral shear system against the Pinto Mountain fault.

Figure 7 displays our current update of the locations of

faults of known or inferred Quaternary movement throughout

the study area.

New evidence of faulting within and marginal to the

Eastern Transverse Ranges has also been found. Additional

traces of the Blue Cut and Pinto Mountain faults were mapped

(discussed above). Also, evidence of minor faulting was

found at the eastern end of the Transverse Ranges at wide

angles to the east-west trends of the active faults within

the ranges. This may be significant. The central and

eastern Mojave Desert are known to differ in several

geophysical properties (compression/extension, heat flow,

vertical displacements). Their boundary extends south from

the eastern end of the Garlock fault to the eastern end of

the Transverse Ranges. As neotectonic models are further

developed, our evidence of on-going faulting activity here

may be significant in understanding the surfical

manifestations of crustal deformation along this important

geophysical boundary.

Seismic activity occurs primarily in the western half

of the study area. Deep earthquakes are limited (in the

seismic record) to the San Jacinto fault and the San

Gorgonio Pass segment of the San Andreas fault. Activity

occurs as far east as the eastern end of the Transverse

Ranges and in the easternmost Central Mojave Desert, but not

further east. This is generally consistent with the pattern

of recent faulting.

The gravity and aeromagnetic images indicate crustal

trends in a generally northwest-southeast pattern, even

across the Transverse Ranges. Seismic studies have

suggested that the Transverse Ranges are rootless and

bounded on their base by a detachment surface. The patterns

seen in these two images tend to support that contention.

Conclusion

Several new details regarding the surficial patterns of

neotectonic activity of the Eastern Transverse Ranges and

vicinity have been discovered. Additionally a number of

data display and analysis techniques have been developed.
11

These findings will be useful both in the continued

development of neotectonic models for Southern California

and for the future application of remote sensing

methodologies elsewhere.

NASA Technical Officer: Dr. Paul D. Lowman, Jr.

Geophysics Branch, Code 922

Goddard Space Flight Center

Greenbelt, Maryland 20771
12

Bibliographic Record

Abstract of presentation supported in part by NASA funding

of technique development:

Crippen, Robert E., 1983, A geomorphometric technique

for detecting the surficial expression of the White

Wolf fault across the southern San Joaquin Valley,

California: Geological Society of America,

Abstracts with Programs, v. 15, no. 5, p. 401.

Journal article on research initiated in this project and

supported in part by NASA funding:

Blom, Ronald G. , Robert E. Crippen, and Charles Elachi,

1984, Detection of subsurface features in Seasat radar

images of Means Valley, Mojave Desert, California:

Geology, v. 12, p. 346-349.

Abstract of research review presentation at NASA

Geodynamics Conference:

Crippen, R.E., J.C. Crowell, and J.E. Estes, 1984,

Neotectonics at the Juncture of the Southern San

Andreas and Central Mojave Shear Systems: EOS,

v. 65, no. 16, p. 195.

Abstract of presentation at the Annual Meeting of the

Geological Society of America:

Crippen, Robert E., and Amanda L. Spencer, 1984,

Landsat Thematic Mapper revealment of Blue Cut

fault, Pinto Basin, Eastern Transverse Ranges,

California: Geological Society of America,

Abstracts with Programs, v. 16, no. 6, p. 479.

Journal articles on remote sensing methodologies developed,

in part, with the support of NASA funding:

Crippen, Robert E., John E. Estes, and Earl J. Hajic,

1986, Band selection to maximize spectral information

content: Photogrammetric Engineering and Remote

Sensing, in preparation for submission.

Crippen, Robert E., 1986, The Regression Intersection

Method of adjusting image data for band ratioing:

Photogramnjetric Engineering and Remote Sensing,

submitted.
13

Symposium proceedings article on methodology developed, in

part, with the support of NASA funding:

Crippen, Robert E., 1986, The Regression Intersection

Method of adjusting image data for band ratioing:

ERIM Fifth Thematic Conference, Remote Sensing

for Exploration Geology (Reno), submitted.

Doctoral dissertaion supported largely by NASA funding:

Crippen, Robert E., 1986, Remote Sensing Investigation of

Neotectonic Activity in the Eastern Transverse Ranges

and Vicinity, Southern California: University of

California, Santa Barbara, in preparation.

It is anticipated that additional articles, particularly

regarding the neotectonic findings of this study, will

be completed and submitted for publication during the next

several months.