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Regional Survey of Structural Properties 

and Cementation Patterns of Fault Zones

in the Northern Part of the Albuquerque

Basin, New Mexico—Implications for

Ground-Water Flow

By Scott A. Minor and Mark R. Hudson

Professional Paper 1719

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2006

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report. 

Minor, S.A., and Hudson, M.R., 2006, Regional survey of structural properties and cementation patterns of fault zones 

in the northern part of the Albuquerque Basin, New Mexico—Implications for ground-water flow: U.S. Geological 

Survey Professional Paper 1719, 28 p. 

1411309138

Suggested citation:
iii

Contents

Abstract ...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Geographic and Geologic Setting...............................................................................................................2

Fault Zone Characterization.........................................................................................................................5

Fault Orientation and Kinematics.......................................................................................................7

Fault Displacement and Paleodepth..................................................................................................9

Width of Architectural Components in Fault Zones........................................................................9

Architectural Index of Fault Zones ..................................................................................................10

Correlation Between Width and Displacement.............................................................................11

Influence of Lithology.........................................................................................................................13

Fault Core Compositions...........................................................................................................13

Width of Fault Zones .................................................................................................................13

Fractures in Damage Zones.....................................................................................................17

Cementation in Fault Zones...............................................................................................................19

 Mineralogy and Regional Distribution....................................................................................19

 Distribution Within Fault Zones ...............................................................................................22

Hydrologic Implications..............................................................................................................................23

Conclusions...................................................................................................................................................24

Acknowledgments.......................................................................................................................................25

References Cited..........................................................................................................................................25

Figures

1. Tectonic map of segment of middle Rio Grande rift................................................................3

2. Generalized geologic map of the northern Albuquerque and Santo Domingo 

structural basins ..........................................................................................................................4 

3. Photograph of fault zone exposed in arroyo south of Jemez River, northern 

Albuquerque Basin ......................................................................................................................6 

4. Diagram of generalized fault zone showing main architectural components ...................6 

5. Rose diagram showing frequency of orientation and slip geometry of faults in 

basins studied ..............................................................................................................................8 

6. Scatter diagram of widths of damage zones in hanging wall versus widths in 

 footwall.........................................................................................................................................10 

7. Histogram showing frequency distribution of widths of fault cores .................................11 

8. Scatter diagram of total width of fault zone versus architectural index of 

fault zone .....................................................................................................................................12

9. Scatter diagrams of widths of total fault zone and core versus dip separation .............12 

10. Pie diagram showing percentages of various compositions observed in 

 fault cores ....................................................................................................................................13

11. Photograph of road cut in Santa Ana fault zone showing extension fractures ..............14

12. Histograms showing frequency distributions of fault zone widths versus category 

of dominant lithology .................................................................................................................15 
13. Diagram of mean width of four fault zone components versus dominant lithology .......16

14. Diagram of best-fit lines showing relation between width of damage zone and

 dip separation for four categories of lithology .....................................................................16

15. Photograph of inner part of footwall damage zone, Santo Domingo Basin......................18

16. Histogram showing frequency distribution of fracture type versus dominant 

lithology ........................................................................................................................................18

17. Map of study basins showing spatial patterns of carbonate and silica fault 

zone cements .............................................................................................................................20

18. Photograph of asymmetrically cemented Santa Ana fault zone, Santo Domingo 

Basin .............................................................................................................................................21

19. Photograph of inner part of hanging-wall damage zone, Santo Domingo Basin.............21

20. Histogram showing frequency distribution of two fault zone cements versus 

 lithology and position in fault zones ........................................................................................23

Tables

1. Types of measurements and qualitative observations made at fault exposures ..............7

2. Statistical results of measured and computed fault zone parameters................................8 

m meter, meters

km kilometer, kilometers

Abbreviated terms used in this report

XRD X-ray diffraction

Fa Fault zone architectural index 

Whwdz Width of hanging-wall damage zone

Wfwdz Width of footwall damage zone 

Wt Total width of fault zone

R2 Coefficient-of-determination correlation factor

iv

Multiply By To obtain

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

 Conversion Factors and Abbreviations

Abbreviated units used in this report
Abstract

Motivated by the need to document and evaluate the 

types and variability of fault zone properties that potentially 

affect aquifer systems in basins of the middle Rio Grande rift, 

we systematically characterized structural and cementation 

properties of exposed fault zones at 176 sites in the northern 

Albuquerque Basin. A statistical analysis of measurements 

and observations evaluated four aspects of the fault zones: (1) 

attitude and displacement, (2) cement, (3) lithology of the host 

rock or sediment, and (4) character and width of distinctive 

structural architectural components at the outcrop scale. Three 

structural architectural components of the fault zones were 

observed: (1) outer damage zones related to fault growth; these 

zones typically contain deformation bands, shear fractures, 

and open extensional fractures, which strike subparallel to 

the fault and may promote ground-water flow along the fault 

zone; (2) inner mixed zones composed of variably entrained, 

disrupted, and dismembered blocks of host sediment; and (3) 

central fault cores that accommodate most shear strain and 

in which persistent low- permeability clay-rich rocks likely 

impede the flow of water across the fault. The lithology of the 

host rock or sediment influences the structure of the fault zone 

and the width of its components. Different grain-size distributions and degrees of induration of the host materials produce 

differences in material strength that lead to variations in width, 

degree, and style of fracturing and other fault-related deformation. In addition, lithology of the host sediment appears to 

strongly control the distribution of cement in fault zones.

Most faults strike north to north-northeast and dip 55°–

77° east or west, toward the basin center. Most faults exhibit 

normal slip, and many of these faults have been reactivated 

by normal-oblique and strike slip. Although measured fault 

displacements have a broad range, from 0.9 to 4,000 m, most 

are <100 m, and fault zones appear to have formed mainly at 

depths less than 1,000 m. Fault zone widths do not exceed 40 

m (median width = 15.5 m). The mean width of fault cores 

(0.1 m) is nearly one order of magnitude less than that of 

Regional Survey of Structural Properties and 

Cementation Patterns of Fault Zones in the 

Northern Part of the Albuquerque Basin, 

New Mexico—Implications for Ground-Water Flow

By Scott A. Minor and Mark R. Hudson

mixed zones (0.75 m) and two orders of magnitude less than 

that of damage zones (9.7 m). 

Cements, a proxy for localized flow of ancient ground 

water, are common along fault zones in the basin. Silica 

cements are limited to faults that are near and strike north 

to northwest toward the Jemez volcanic field north of the 

basin, whereas carbonate fault cements are widely distributed. 

Coarse sediments (gravel and sand) host the greatest concentrations of cement within fault zones. Cements fill some 

extension fractures and, to a lesser degree, are concentrated 

along shear fractures and deformation bands within inner 

damage zones. Cements are commonly concentrated in mixed 

zones and inner damage zones on one side of a fault and thus 

are asymmetrically distributed within a fault zone, but cement 

does not consistently lie on the basinward side of faults. From 

observed spatial patterns of asymmetrically distributed fault 

zone cements, we infer that ancient ground-water flow was 

commonly localized along, and bounded by, faults in the 

basin.

It is apparent from our study that the Albuquerque 

Basin contains a high concentration of faults. The geometry 

of, internal structure of, and cement and clay distribution in 

fault zones have created and will continue to create considerable heterogeneity of permeability within the basin aquifers. 

The characteristics and statistical range of fault zone features 

appear to be predictable and consistent throughout the basin; 

this predictability can be used in ground-water flow simulations that consider the influence of faults.

Keywords: Albuquerque Basin, cementation, fault zones, 

ground-water flow, lithology, structure

Introduction

Since the middle 1990s much research has focused on the 

detailed physical, structural, and fluid-flow properties of fault 

zones in a large variety of geologic materials and environments. We now better understand the complex interplay of 
Geographic and Geologic Setting

The Albuquerque composite basin in north-central New 

Mexico encompasses three structural subbasins—from north 

to south, the Santo Domingo, northern Albuquerque (also 

known as Calabacillas), and Belen subbasins—that form part 

of the extensive Rio Grande rift (fig. 1). Fault zones in the 

Santo Domingo and northern Albuquerque subbasins (hereafter referred to simply as “basins”) are the focus of this study. 

This segment of the Rio Grande rift is characterized by a 

series of structurally linked, north-trending, right-stepping, 

en-echelon extensional basins that formed mainly during the 

Neogene (fig. 1) (Kelley, 1982; Chapin and Cather, 1994). 

The Santo Domingo Basin is structurally connected with the 

next rift basin to the northeast, the Española Basin, by the 

La Bajada constriction, a relatively narrow and partly buried 

structural trough (fig. 1) (Minor and others, in press). The 

northern Albuquerque, Santo Domingo, and Española Basins 

are mostly filled with Neogene and Quaternary eolian, fluvial, 

alluvial, and playa sediments of the Santa Fe Group, although 

intercalated volcanic deposits markedly increase in volume 

within the northern Santo Domingo and western Española 

Basins toward the Jemez and Cerros del Rio volcanic fields 

(Smith and others, 2001; Dethier and others, in press; Thompson and others, in press). Intrabasin growth faults are common, reflecting syn-rift deposition of the basin fill (May and 

Russell, 1994; Connell and others, 1999; Minor and others, in 

press). 

In the Albuquerque Basin area, the rift flanks expose 

Precambrian crystalline rocks and unconformably overlying 

upper Paleozoic and Mesozoic sedimentary rocks that have 

undergone various degrees of Laramide deformation (fig. 2). 

Syn- and post-Laramide Eocene sedimentary rocks (Galisteo 

Formation) and Eocene and Oligocene volcanic (Espinaso 

 Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico 

protolith, displacement history, diagenesis, fluid pressure, 

stress state, and other factors that control spatial and temporal variations of structural architecture, permeability, and 

hydraulic properties in fault zones. Most of these studies have 

been based on field observations of individual fault zones (for 

example, Chester and Logan, 1986; Caine and others, 1996; 

Evans and others, 1997; Heynekamp and others, 1999) or 

on theoretical and numerical models of idealized fault zones 

partially constrained by field data (for example, Haneberg, 

1995; Zhang and Sanderson, 1996; Caine and Forster, 1999). 

Studies of fault-related fluid flow at regional scales, which 

have been conducted mainly to identify fault-related hydrocarbon seals, have relied chiefly on subsurface geophysical and 

drill-hole data (for example, Maclay and Small, 1983; Knott, 

1993; Gibson, 1994). Field-based fault characterization studies 

of regional or basin-wide scope are rare, particularly those that 

address fault zones as discrete hydrogeologic elements rather 

than simply as juxtapositions of different hydrostratigraphic 

units. Also uncommon are fluid-flow studies of fault zones 

in poorly lithified, high-porosity basin-fill sediments such 

as those that commonly compose basin aquifers of the arid 

southwestern United States (Goodwin and others, 1999). One 

such study of the Sand Hill fault in the northern Albuquerque 

Basin (Heynekamp and others, 1999) revealed hydrogeologic 

properties in the fault zone that differ substantially from those 

determined for faults in well-indurated or crystalline rock.

Our regional study of moderate to large (that is, displacement of mostly 10–2,000 m) fault zones in the northern part 

of the Albuquerque Basin (see fig. 1) is the first attempt to 

characterize the structural, physical, and cementation properties of faults throughout a broad part of this important basin 

aquifer, which provides water for more than half a million 

people in the Albuquerque metropolitan area. We have systematically observed and measured various fault zone properties 

in numerous widely scattered exposures in the erosionally 

dissected northern part of the basin to compare and contrast 

fault properties under a range of geologic conditions. Fault 

zone properties that bear on hydrologic history and the influence of faults on ground-water flow are emphasized; they 

include patterns of fault zone cementation that indicate ancient 

ground-water flow paths (for example, Heynekamp and others, 1999). Early ground-water flow models of the aggregate 

Albuquerque aquifer basin (fig. 1) treated intrabasin faults as 

ideal zones of constant, relatively low, horizontal hydraulic 

conductivity, and fault-induced changes in vertical conductivity were ignored (Kernodle and others, 1995). In this paper 

we document substantial statistical and spatial variations in 

fault zone properties and, by implication, permeability, which 

could be integrated into future ground-water flow models of 

the Albuquerque Basin. Results of this study also increase our 

knowledge of structural properties and strain evolution of fault 

zones in variably consolidated sediments, which are common 

in other extensional aquifer basins. 

Figure 1. (facing page) Segment of middle Rio Grande rift; 

extent, topographic expression (gray background shading), and 

principal structural borders of the contiguous Santo Domingo, 

northern Albuquerque, and Española Basins and of La Bajada 

constriction are shown. Area of figure 2, which contains study 

area, is outlined. Prominent geologic and physiographic features 

labeled in pale blue (basins and embayments), dark blue (La 

Bajada constriction), pink (volcanic fields and Valles caldera), 

and purple (mountains) text. Note that La Bajada constriction 

overlaps northeastern part of Santo Domingo Basin and southwest part of Española Basin. Pliocene basaltic volcanic fields: 

Cerros del Rio (CDRVF) and Santa Ana Mesa (SAMVF). Faults 

labeled as follows: EZ, East Ziana horst; HB, Hagan Bench; JZ, 

Jemez; LB, La Bajada; PB, Pico Butte; PJ, Pajarito; PL, Placitas; 

RC, Rincon; SA, Santa Ana; SF, San Francisco; SI, Sile; SY, San 

Ysidro; TM, Tamaya; TT, Tetilla; VV, Valley View; WZ, West Ziana 

horst. Box shows area of figure with respect to structural subbasins of the Albuquerque composite basin. Small inset map shows 

location of Albuquerque Basin relative to Rio Grande rift.
Geographic and Geologic Setting 

CO

NM

N

Area

of

figure

City of

Albuquerque

Rio Puerco

Rio Grande

Albuquerque

composite basin

Santo

Domingo

subbasin

Northern

Albuquerque

subbasin

Sandia Mtns

Belen

subbasin

Española

Basin

Area of

figure

Jemez River

RIO GRANDE RIFT

EXPLANATION

Northern Albuquerque

 and Espanola rift basins ~

Santo Domingo rift basin

La Bajada constriction

Pliocene basaltic 

 volcanic fields

Principal basin border structures

Fault—Exposed; ball on

 downthrown side

Fault—Concealed and

 geophysically expressed;

 ball on downthrown side

Axis of monoclinal ramp—

 Concealed; arrow toward

 lower limb

35°45`

35°15`

106°45` 106°15`

0 7 14 KILOMETERS

0 15 30 KILOMETERS

C D R V F

 L A B A J A D A

 

C O N S T R I C T I O N

Jemez River

Rio Grande SA

LB

Rio Grande

SF

PJ

E S PA N O L A

B A S I N

~

S A N T O D O M I N G O

B A S I N

N O R T H E R N

A L B U Q U E R Q U E

B A S I N

VA L L E S

C A L D E R A

PJ

LB

SA

PB

EZ

SY

JZ

VV

HB

RC

SF

SI

TT

Jemez River

Rio Grande

Santa Fe River

S A M V F

H A G A N

E M B A Y M E N T

S A N D I A

M T N S

J E M E Z M O U N T A I N S

Area of

figure 2

WZ

TM

Z I A N A

H O R S T

PL

VV

J E M E Z

V O L C A N I C

F I E L D

Galisteo

Creek
Figure 2. Northern Albuquerque and Santo Domingo structural basins; sites of observed faults are marked. Most sites expose map-scale faults cutunits of Santa Fe Group. Mapped geology is based mainly on regional compilations of Anderson and Jones (1996) and Kelly (1977) but also on recent maps from numerous sources. Dotted (buried) faults coincide with geophysical lineaments from various sources that are described by Hudson and oies are based on isostatic residual gravity data of Grauch and others (1999). LB, La Bajada fault; PJ, Pajarito fault; SA, Santa Ana fault; SF, San Franc

Tb

Tv

Qbt

QTa

Qa

Tb

Tb













p

p

Tls

Tps

Tls

Tls

Tls

Tls

Tls

Tls

Tms

Tms

Tms

Tms

Tms Tms

Tms

Tms

QTus

QTus

QTus

QTus

QTus

QTa

QTa

Northern

 Albuquerque

 Basin

Qa QTa QTa

Qb

Qb

Qa Valley alluvium

Quaternary bas

Bandelier Tuff

Older alluvial d

Upper Santa Fe 

Pliocene basalt

Miocene Jemez 

Middle Santa F

Lower Santa Fe 

Oliogcene-Eoce rocks

Mesozoic-Paleo

Precambrian ba

Major fault—Ba

Buried fault or  lineament—

Approximate b

Qa

Qa

Qa

Qb

Qbt

Qb

HS

Tb

Tv

Tps

Tps

LB

SF

LB

SA

SH

SF

PJ

Rio Grande

Rio Grand

R

e

io Puerco

Jemez

River

106°15 ́

14 KILOMETERS

106°45 ́

35°45 ́35°15 ́

p



EXPLA

0 7

Albuquerque

Fault observatio

Basin

Santo

Domingo
Fault Zone Characterization 

Formation) rocks unconformably overlie these older rocks 

where they are locally preserved along the basin margins. 

Miocene and younger sediments deposited within the Albuquerque Basin are differentiated into three main lithostratigraphic units: the lower, middle, and upper Santa Fe Group 

(fig. 2) (for example, Hawley and others, 1995). These units, 

ranging from about 25 to 1 Ma, generally become less indurated and coarser grained up section owing to a basin drainage system that evolved from closed to integrated. However, 

marked lateral facies changes exist owing to the effects of 

growth faulting (for example, May and Russell, 1994; Hawley 

and others, 1995; Connell and others, 1999; Smith and others, 

2001). Composite thickness of deposits of the Santa Fe Group 

typically ranges from less than 1,200 m along the basin flanks 

to 3,300–4,300 m within the basin depocenters (for example, 

May and Russell, 1994; Grauch and others, 1999; Grauch 

and others, in press). Poorly lithified, post-7-Ma strata of the 

middle and upper Santa Fe Group, which contain abundant 

sand and gravel deposited by the ancestral Rio Grande (for 

example, Dethier and others, in press), form the main waterproducing hydrostratigraphic unit within the basin (Hawley 

and others, 1995).

Structurally, most basins composing the middle Rio 

Grande rift are asymmetrical half grabens in which intrabasinal strata and normal faults generally have opposing dips 

that are perpendicular to the rift basin trend (for example, 

Chapin and Cather, 1994; Russell and Snelson, 1994). In the 

northern Albuquerque Basin, sedimentary rocks are mostly 

tilted gently to the east and bounded on the east by major 

west-dipping normal faults, including the large-displacement 

Rincon fault whose footwall is expressed by the precipitous 

front of the Sandia Mountains (fig. 1). The stratal and fault 

dips of the Española half-graben basin (on the opposite, or 

northeast, side of the Santo Domingo Basin) are reversed relative to those of the northern Albuquerque Basin (Kelley, 1982; 

Chapin and Cather, 1994).

Compared with the northern Albuquerque and Española 

Basins, the intervening Santo Domingo Basin possesses a 

more symmetrical, antiformal fault block geometry with 

west-dipping normal faults and gentle eastward stratal tilts in 

the eastern part of the basin and opposing fault and stratal tilts 

in the western part (fig. 2) (Smith and others, 2001; Minor 

and others, in press). Down-to-west faults, including those 

of the basin-bounding La Bajada and San Francisco fault 

systems, gradually increase in abundance and throw toward 

the east and south (northern Albuquerque) sides of the basin, 

whereas down-to-east faults such as the marginal Santa Ana 

fault increase in abundance and throw toward the west and 

north (Española) sides (figs. 1 and 2) (Minor and others, in 

press). Between the basin margins and center, the dominance 

of one dip direction is gradually replaced by overlapping 

or interleaved faults that dip in both directions. Faults form 

a symmetrical, concentric pattern in map view within the 

Santo Domingo Basin; the pattern is centered on the area of 

Pliocene basalt flows of the San Felipe volcanic field in the 

central part of the basin (figs. 1 and 2) (Minor and others, 

in press). Isostatic residual gravity data (Grauch and others, 

1999; Grauch and others, in press) indicate that the center of 

this circular fault pattern coincides with the deepest part of 

the basin. Given the unique symmetrical structural geometry 

of the basin and its clear structural links to the adjacent rift 

basins, the entire Santo Domingo Basin can be effectively 

viewed as a broad tectonic transfer zone that relays extensional strain between the adjoining, opposing-polarity, northern Albuquerque and Española Basins (Minor and others, in 

press; compare with Smith and others, 2001).

Fault Zone Characterization

A field campaign in the Santo Domingo and northern 

Albuquerque Basins geologically characterized fault zones 

mappable at 1:24,000 scale. Field observations emphasized 

fault zone parameters that potentially bear on the hydraulic 

properties of faults in the subsurface of the basins. Within 

or bordering the basins, outcrops that expose the entire 

cross-sectional extent of fault zones were targeted to obtain 

complete, structurally and spatially related, suites of measurements (fig. 3). However, partially exposed fault zones 

were also investigated to provide data for some fault zone 

parameters. Care was taken to select fault exposures in a 

variety of structural, stratigraphic, and lithologic settings to 

investigate possible variations of fault properties owing to 

changes in geologic conditions.

Fault zone observations were made at 176 sites within 

the Albuquerque Basin area. Nearly all of these exposures 

(n=170) are located in the northern Albuquerque and Santo 

Domingo structural basins where erosional dissection of 

faulted basin-fill sediments is most pronounced (fig. 2). 

About two thirds of these sites (n=112) are located within 

or along the edges of the Santo Domingo Basin. Six fault 

sites are located at rare, exceptional fault zone outcrops 

in the southwestern part of the Albuquerque Basin (fig. 

1). Depending on the degree of structural complexity and 

exposure, as many as 19 different fault zone measurements 

and observations were recorded at each fault site (table 1 and 

fig. 4). Where exposures allowed, measurements were taken 

of well-developed fault-plane orientations in the core and 

associated slickenline rake values, dip separations of offset 

contacts or beds, and the cross-sectional widths of the various 

fault zone components (table 1 and fig. 4). The slip sense (or 

senses) of measured faults was determined chiefly by use 

of stratigraphic offsets but also by use of secondary fracture 

criteria (for example, Petit, 1987). Qualitative observations 

were made of the damage-zone fracture types and geometries, the structural fabric and constituents of fault cores, the 

mineralogy and structural position of fault zone cements, the 

dominant lithology of wallrocks, and the shape of prominent 

fault-core slip surfaces (table 1).

Following earlier terminology used to describe fault 

zones (for example, Sibson, 1977; Chester and Logan, 1986; 
 Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

Figure 3. Representative fault zone 

exposed in an arroyo south of Jemez 

River, northern Albuquerque Basin; 

various fault zone features are labeled. 

Footwall damage zone here consists 

mostly of sandstone cut by deformation bands that are not readily visible 

in photograph. Note variable width of 

clay core. Solid white lines, boundaries between fault-zone components; 

dashed white line, gradational boundary; opposed arrows indicate slip 

sense of main and mesoscale faults.

Figure 4. Generalized fault zone model showing architectural components and damage zone fracture types and geometries that 

were recorded at observation sites. Graphical definition of various fault zone component widths shown in lower left: Wt, width of 

total fault zone; Whwdz, width of hanging-wall damage zone; Whwmz, width of hanging-wall mixed zone; Wc, width of fault core; 

Wfwmz, width of footwall mixed zone; Wfwdz, width of footwall damage zone.

Whwdz

Wc Wt Wfwmz

Whwmz

Wfwdz

Outer boundary of damage zone

Extension fracture

Cross fracture or other fracture

Mixed zone

Core

Synthetic mesoscale fault or

 deformation band

Antithetic mesoscale fault or

 deformation band

Slip direction of block

Hanging-wall

block

Footwall block

EXPLANATION

Hanging-wall

damage zone

Extension

fracture

Synthetic

mesofault

Footwall damage

zone

Clay core

Antithetic

mesofault

Hanging-wall mixed zone
Caine and others, 1996), we define the core as a relatively 

narrow central zone of concentrated shear strain manifested 

by cataclastic particulate flow (Rawling and Goodwin, 2003) 

and shear on discrete, closely spaced slip surfaces. We then 

define the enveloping hanging-wall and footwall damage 

zones as tabular rock volumes containing subsidiary faults, 

extension (that is, opening-mode) fractures, deformation 

bands (Antonellini and Aydin, 1994), veins, and drag folds 

that decrease in abundance away from the core (fig. 4). Part 

of the way through our field campaign we embraced the 

concept of the mixed zone as a third component of fault zone 

architecture; it is commonly developed in poorly indurated 

sediments such as those composing basin-fill deposits of the 

Santa Fe Group (Heynekamp and others, 1999). Mixed zones 

were originally defined as relatively narrow zones of tectonic 

entrainment and mixing, marked by rotated, attenuated, and 

dismembered bedding and by mixing of sediments at scales 

ranging from beds down to individual grains; such zones 

commonly flank and grade into the fault core (fig. 4) (Mozley 

and Goodwin, 1995; Heynekamp and others, 1999; Rawling and others, 2001). Although we commonly recognized 

core-flanking zones that contained entrained, disrupted beds 

Fault Zone Characterization 

that exhibit many of the features described for mixed zones, 

we rarely observed bed- to grain-scale mixing in outcrop. We 

typically observed discrete slip surfaces parallel to the fault 

core that bound both the inner and outer sides of mixed zones, 

but the mixed zones appear to have greater affinities with the 

core owing to their prominent bulk shear-strain and cataclastic 

particulate-flow fabric (Rawling and Goodwin, 2003). 

Owing to the broad extent of the study area, large 

number of targeted fault sites, and time constraints, qualitative field observations emphasized the dominant structural, 

diagenetic, and lithologic aspects of the fault zones that most 

likely influence the hydrologic properties of the fault zones. 

Dominant fractures and structures in damage zones were 

documented (fig. 4) and their relative abundance noted. Most 

cemented zones along faults were described in terms of their 

footwall or hanging-wall location and their relative degree of 

development (that is, weak, moderate, or strong). Cements 

were tentatively identified as either carbonate or silica in 

the field; identities were confirmed or refined later by x-ray 

diffraction (XRD) analyses (S.J. Sutley, written commun., 

1999). The dominant (that is, most voluminous) lithologic 

components were recorded separately for the footwall and 

hanging-wall blocks. Standard lithologic classifications used 

were gravel, conglomerate, breccia, sandstone, siltstone, mudstone, lava, and tuff. Where lithologically diverse interbedded 

sediments were observed in a single fault-block exposure, the 

relative abundance of the dominant sedimentary components 

was estimated. 

Fault Orientation and Kinematics

The orientation, slip direction (or directions), and slip

sense (or senses) of fault-core slip surfaces were systematically recorded in the study area to investigate their possible 

correlation with observed fault zone parameters or cementation patterns.

In the Santo Domingo and northern Albuquerque Basins, 

most measured fault surfaces strike north to north-northeast 

(mean 008°), subparallel to the dominant strike of mapped 

faults (figs. 2 and 5, table 2). Most fault surfaces dip between 

55° and 77° (mean 66°), but faults dip as shallowly as 23° and 

a few are subvertical (table 2). There is a moderate clustering 

of relatively shallow dips (≤55°) along eastern and northern 

border faults of the Santo Domingo Basin, and a similar 

clustering of steep dips (≥80°) along north-northeast-striking 

faults near the northwestern border of the basin. Collectively 

the observed fault surfaces dip equally to the east and west. 

In any one area, however, dips are commonly unidirectional 

toward the basin center, which largely reflects the relatively 

symmetrical fault geometry of the Santo Domingo Basin. 

Most observed fault surfaces are approximately planar at 

the outcrop scale, but several slip surfaces of mainly larger 

displacement (that is, >100 m) faults exhibit large undulatory 

mullions that trend subparallel to the principal slip direction 

and create curvilinear fault traces.

Table 1. Types of measurements and qualitative observations 

made at fault exposures.

[Measurement abbreviations in parentheses are the same as those in figure 4 

and table 2]

Measured fault zone attributes

 Fault attitude, slip measurements

 Strike

 Dip

 Rake of principal slickenline (rake1)

 Rake of overprinted, younger slickenline (rake2)

 Slip sense

 Dip separation

Widths of architectural components of fault zones

 Hanging-wall damage zone (Whwdz)

 Hanging-wall mixed zone (Whwmz)

 Fault core (Wc) or aggregate core (Wc + Wmz)

 Footwall mixed zone (Wfwmz)

 Footwall damage zone (Wfwdz)

Qualitative fault zone observations

Core characteristics

 Composition

 Structural fabric

 Shape of principal slip surface or surfaces

Damage zone structural fabric

 Hanging-wall damage zone fault or fracture type and 

 geometry

 Footwall damage zone fault or fracture type and geometry

Cement characteristics

 Mineralogy of cement

 Distribution of cement relative to fault zone components

Wallrock lithology

 Dominant lithology of hanging-wall block

 Dominant lithology of footwall block
 Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

 Table 2. Statistical results of measured and computed fault zone parameters.

 [n, number; S.D., standard deviation; Min., minimum; Max., maximum]

Parameters n Mean Median Mode S.D. Min. Max. Range

Measured1

 Strike2 170 7.8 (188) 5 (185) 10 (190) 25.9 001 359 360

 Dip 166 62.2 68.0 70.0 10.9 23 90 67

Rake1

3 158 74.4 80.0 85.0 16.3 1 89 88

Rake2

4 32 52.4 55.0 50.0 19.8 5 85 80

Dip separation 148 275 67 10 552 0.9 4,000 4,000

Whwdz 111 9.8 6.1 3.0 13.2 0 100 100

Whwmz 99 0.7 0.3 0 1.2 0 7.0 7.0

Wc 101 0.10 0.05 0.05 0.15 0.002 0.91 0.91

Wfwmz 102 0.8 0.3 0 1.6 0 13.7 13.7

Wfwdz 131 9.6 6.0 4.0 11.0 0 60 60 

Computed 

Wt 111 18.9 15.5 32.1 16.5 0.7 90.1 89.4

Wc + Wmz 129 1.23 0.68 0.10 1.79 0 14.7 14.7

Fa

5

 104 0.92 0.94 0.94 0.08 0.66 0.99 0.34

Whwdz/Wfwdz 105 2.49 0.91 1.00 6.47 0 60 60

1

All width terms defined in figure 4 and in text, and all width and separation values in meters.

2

Strike statistics computed after converting measurements from 360° azimuthal values to 180° bidirectional values;

parentheses indicate opposing bidirectional values.

3

Rake values of primary slickenlines.

4

Rake values of secondary, mostly overprinted, slickenlines.

5

Fa = (Whwdz + Wfwdz)/Wt.

Figure 5. Frequency of orientation 

and slip geometry of faults in basins 

studied. Percentage next to each 

diagram indicates relative maximum 

radius, and numbers in bold are 

mean strike, dip, and rake values. 

Faults dominantly strike north (mean 

008°), dip moderately (mean 66°) east 

or west, and have normal slip sense 

(mean rake 72°). Overprinted and 

generally lower rake slickenlines 

(mean 52°) indicate normal-oblique 

slip reactivation of many faults. N, 

north; n, number.

10 percent

90

45

0

7 percent 23 percent

90

52 Overprinted

0

26

percent

Sinistral

12 percent

n=170

n=195

N

N

Strike Dip

Rake or slip sense Rake

Dextral

Normal

66

72

008

Dip direction

Measured1

Strike2

Dip

Rake1

3

Rake2

4

Dip separation

Whwdz

Whwmz

Wc

Wfwmz

Wfwdz

Computed1

Wt

Parameters
Fault rake, which is the angle made by a slickenline (that 

is, a striation formed during slip and preserved on an exposed 

fault surface) and the fault strike line, averages about 75°, and 

half of the measured rakes equal or exceed 80° (see table 2, 

rake1). These data, together with the consistent normal senses 

of slip revealed mainly by offset stratigraphic units, indicate 

that most of the faults are normal-slip faults. However, 

normal-oblique-slip (30° < rake ≤60°) or, less commonly, 

strike-slip (rake ≤30°) slickenlines are present on about 25 

percent of the fault surfaces (see table 2, rake2). On most of 

these, the moderate- to low-rake striae (mean 52°) crosscut 

older high-rake normal-slip striae (mean 66°). We interpret this 

relation in the study area as indicating reactivation of a substantial number of normal faults by oblique strike-slip motion. 

Sinistral and dextral slip components are equally common 

(fig. 5). Although strike-slip sense has no obvious statistical 

correlation with fault strike, local spatial domains do possess 

either dextral slip components (for example, northwest margin 

of Santo Domingo Basin) or sinistral slip components (for 

example, southeastern border faults of Santo Domingo Basin) 

that are dominant on faults within a certain strike range.

Fault Displacement and Paleodepth

Determinations of fault displacements or dip separations 

are important not only because they can be used to predict fault 

juxtaposition of hydrostratigraphic units in the subsurface, but 

they can also be compared to or correlated with other measured fault zone parameters such as width (Maclay and Small, 

1983; Hull, 1988; Knipe, 1993; Knott, 1993; Caine and others, 

1996). Previous studies suggest that faults can contribute substantially to the heterogeneity and anisotropy of permeability 

in intrabasinal sediments and that they do so through a broad 

range of displacements that can be less than 1 m (for example, 

Knott, 1993; Caine and others, 1996; Sigda and others, 1999). 

Thus, we measured structural parameters of fault zones having 

a wide range of displacements to investigate possible structural 

correlations with slip magnitude.

Many of our dip-separation estimates are minimum 

approximations of true fault displacements, in part because of 

the uncertain vertical position of offset stratigraphic contacts that are buried or eroded on one or both sides of large 

faults and in part because a majority of the faults show small 

components of lateral movement in addition to normal dip slip 

(see below). Also, because growth faulting played a major role 

in the development of the rift basins, fault offsets measured 

at the surface likely are somewhat less than the true dip-slip 

movement of footwall rocks in the fault zone. Nonetheless, the 

separations are considered to be reasonable approximations 

of displacement for use in correlation with other fault zone 

properties, because most of the faults studied record similar 

dip-slip and growth-sedimentation histories.

Dip separations measured on faults range from 0.9 to 

4,000 m and average 275 m (table 2). Well over half of the 

observed faults, however, have dip separations less than 100 

m. Faults having dip separations greater than 200 m, such as 

the central parts of the San Francisco, La Bajada, and Sand 

Hill faults, are concentrated near the borders of the Santo 

Domingo and northern Albuquerque Basins, whereas smaller 

displacement faults are more widely distributed throughout 

the basins (fig. 2). Dip-slip displacement along faults diminishes along strike toward fault terminations as increasing 

amounts of extensional strain were accommodated by adjacent overlapping or en-echelon faults of the same or opposing 

dip direction.

The range and distribution of dip separations observed 

in these basins constrain the depths at which now-exposed 

fault zone features formed; these constraints, in turn, give 

clues about stress conditions during faulting. It is more difficult to estimate paleodepths of larger displacement fault 

zones, owing to large contrasts in paleodepth of juxtaposed 

fault blocks in such zones, and these contrasts may be more 

pronounced near growth faults. Also, the stratigraphic levels 

represented by rocks and deposits that are in fault juxtaposition provide clues about paleodepths, but uncertainties in 

stratigraphic thicknesses and amounts of erosional stripping 

before and during faulting add to the difficulty of obtaining 

accurate depth estimates. Owing to these pitfalls, we make 

only general estimates of faulting depths. Prebasin rocks 

exposed in the footwalls of large-displacement, basinbounding faults (for example, southern San Francisco fault, 

fig. 2) may have been displaced upward from depths as great 

as 4,000 m, whereas hanging-wall components of these fault 

zones probably formed at depths much less than 1,000 m. 

Both the footwall and hanging-wall com-ponents of smaller 

displacement fault zones exposed in the basin interiors are 

estimated to have formed mostly at depths ranging from about 

1,000 m to less than 10 m. 

Width of Architectural Components in 

Fault Zones 

Previous modeling and field studies have demonstrated 

the importance of the dimensions of architectural components 

of fault zones for predicting variations in fault permeability as 

well as bulk values of fault zone permeability (for example, 

Caine and others, 1996; Caine and Forster, 1999; Heynekamp 

and others, 1999). The widths of fault zones are valuable 

parameters in numerical models of fluid flow along faults 

and in estimates of transmissivities of fault zones (Maclay 

and Small, 1983; Haneberg, 1995; Caine and Forster, 1999; 

Rawling and others, 2001). Differences in widths can also 

be correlated with differences in protolith; such correlations 

can be related to changes in deformation mode and mechanical strength within the fault zones (for example, Chester and 

Logan, 1986; Antonellini and Aydin, 1995; Caine and others, 

1996; Heynekamp and others, 1999).

The cross-sectional widths of all exposed damage zones, 

mixed zones, and cores were measured at each fault site and, 

where all of the component widths could be determined, the 

total fault zone width was computed from their sum (fig. 4). 

The outer edges of measured damage zones were 

Fault Zone Characterization 
10 Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

designated where the density of subsidiary faults and fractures 

was estimated to diminish to ambient, or background, levels 

(Caine and others, 1996). The degree of fracturing abruptly 

decreases at the margins of many damage zones such that 

they could be confidently located, whereas the outer edges of 

some other damage zones could not be determined owing to 

incomplete exposure or poor definition. At 62 percent of the 

sites visited, the full cross-sectional width of fault zones is 

exposed (that is, the complete width of damage zone is visible 

on both sides of the fault zone) and was measured. Although 

the initial 19 percent of our measurements of fault zone width 

did not differentiate between mixed zones and cores, these 

measurements were chiefly made in moderately indurated to 

well-indurated protoliths that do not readily accommodate the 

particulate flow that is typical of mixed zones (Rawling and 

Goodwin, 2003). The widths of damage zones, mixed zones, 

and cores were generally measured to the nearest 0.1, 0.01, 

and 0.001 m, respectively. Width values were averaged at sites 

where the width of a fault zone component varies considerably 

in a single exposure.

The frequency of the 111 measured total widths of fault 

zone decreases nearly exponentially with increasing width 

(coefficient-of-determination correlation factor R2 = 0.86). Most 

fault zones in the basins are less than 40 m wide, and nearly 

half of the zones are less than 15 m wide (table 2). Frequency 

distributions of the widths of hanging-wall and footwall 

damage zones similarly decay roughly exponentially with 

increasing width. Although average widths of damage zones 

are nearly identical in hanging-wall blocks (mean width 9.8 

m, median width 6.1 m) and footwall blocks (mean width 

9.6 m, median width 6.0 m) (table 2), individual ratios of the 

width of hanging-wall damage zone to the width of footwall 

damage zone differ considerably. A diagram of widths of 

hanging-wall versus footwall damage zones (fig. 6) indicates 

considerable scatter in this ratio and illustrates that widths of 

damage zones are strongly unequal in several fault zones. A 

slightly greater percentage (57 percent) of fault zones have a 

wider footwall damage zone; the median ratio of damage zone 

width is 0.91. Antonellini and Aydin (1995) observed wider 

footwall damage zones in fault zones cutting indurated but 

porous sandstones in Utah. The slight statistical imbalance in 

the width of fault damage zones in the Santo Domingo and 

northern Albuquerque Basins may reflect greater cumulative 

shear strain and associated widening of damage zones in the 

footwalls of growth faults, although Heynekamp and others (1999) documented generally narrower footwall damage 

zones and mixed zones along the Sand Hill growth fault in the 

northern Albuquerque Basin. As the widths of mixed zones 

increase, frequency decreases exponentially (R2 = 0.84), and 

the average widths of mixed zones are virtually the same in 

the hanging-wall and footwall blocks (mean ~0.75 m and 

median 0.3 m in both cases) (table 2). As widths of fault cores 

increase, frequency decreases abruptly in a roughly exponential manner (R2

 = 0.68) (fig. 7). Widths of half of the measured 

cores are less than 5 cm, and the mean width of cores (10 cm) 

is nearly one order of magnitude narrower than the average 

width of mixed zones and two orders of magnitude narrower 

than the average width of damage zones (table 2). Thus, cores 

typically make up a very small proportion (0.5 percent) of the 

total width of fault zones in the studied basins.

No strong spatial patterns in width of fault zone components are apparent in either basin. Instead, at intermediate 

to basin-wide scales, values of width are heterogeneous. One 

notable exception are concentrations of relatively wide (>15 

m) fault zones within or bordering sedimentary rocks of the 

lower Santa Fe Group in the western part of the study area. 

The significance of this spatial pattern is discussed below in 

the context of lithologic controls on fault zone properties.

Architectural Index of Fault Zones

Caine and others (1996) introduced a numerical index 

that is a measure of the architectural style of the fault zone 

and the degree to which a fault zone may act as a conduit or 

barrier to fluid flow. This index, referred to as the “fault zone 

architectural index” (Fa), was defined by Caine and others 

(1996) as

where Whwdz and Wfwdz are the widths of the hanging-wall and

footwall damage zones, respectively, and Wt is the total width 

of the fault zone. This architectural index, which was developed for fault zones in well-indurated protoliths, does not 

consider mixed zones. To compute Fa values in this study we 

0

10

20

30

40

50

60

0 10 20 30 40 50 60

FOOTWALL DAMAGE ZONE WIDTH, IN METERS

HANGING-WALL DAMAGE ZONE WIDTH, IN METERS

x = y

Wfwdz > Whwdz

(57 percent)

Whwdz > Wfwdz

(43 percent)

Figure 6. Widths of damage zones in hanging-wall block 

(Whwdz) versus width in footwall block (Wfwdz) for individual 

fault zones. Footwall damage zones are wider in 57 percent 

of fault zones observed. Points that plot on line labeled x = 

y represent fault zones in which hanging-wall and footwall 

damage zones are of equal width.

Fa = (Whwdz +Wfwdz) / Wt
Fault Zone Characterization 11

included mixed zones as part of an “aggregate core,” owing to 

the close structural affinity of the mixed zones with the adjacent fault core. Values of Fa can range from 0 to 1 depending 

on the width of the aggregate core relative to the width of 

the damage zones. Most (73 percent) Fa values computed for 

fault zones in the Santo Domingo and northern Albuquerque 

Basins exceed 0.9 (mean 0.92) and only 4 percent of the 

values are less than 0.75. These results indicate that relatively thin aggregate cores (average of 8 percent of fault zone 

width) characterize the fault zones. Thus, the fault zones in 

bulk should act as conduits for along-fault fluid flow, if one 

assumes that the damage zones are zones of increased permeability owing to open fracture networks commonly associated with them (Caine and others, 1996). The validity of this 

assumption is discussed below in the section on hydrologic 

implications. A scatter diagram of Fa versus total width of 

the fault zone (Wt) (fig. 8) highlights the predominantly high 

(>0.9) Fa values and shows that the range of fault zone widths 

increases with increasing dominance of the damage zone (that 

is, with increasing Fa), which reflects the commonly broad, 

distributed nature of fracturing in damage zones. However, it 

is apparent that some fault zones in which the damage zones 

are dominant have narrow widths similar to the widths of 

fault zones with more substantial cores. Such variations in 

fault zone architecture likely reflect differences in mechanical 

behavior of the diverse wall-rock lithologies and variations in 

fault displacement history. 

Fault zones with lower Fa values (that is, <0.9) appear 

to be concentrated in the central parts of the basins within 

less-indurated middle and upper basin-fill deposits of the 

Santa Fe Group (fig. 2). This spatial association, together with 

the previously noted concentration of relatively wide fault 

zones within older intrabasin sedimentary rocks, suggests that 

lithology, and especially the overall degree of induration or 

stiffness of the protoliths, exerts some control on the relative 

dimensions of the fault zone components.

Correlation Between Width and Displacement 

Total fault zone and aggregate-core widths were compared with dip separation to investigate the possible influence of fault displacement on fault zone widths (fig. 9A, B). 

Both sets of width data possess very weak linear correlation 

with the log of dip separation (R2 for Wt and Wc+Wmz = 0.17 

and 0.05, respectively). Similarly, the principal core widths 

(Wc) correlate poorly (R2 = 0.05). Thus, although the widths 

of architectural components in a fault zone may increase 

slightly with increasing displacement, other factors must more 

strongly influence the widths of fault zones (fig. 9) (compare 

with Evans, 1990). No correlation was observed between 

computed Fa values and dip separation, which implies that, 

with increasing fault displacement, the width of the core does 

not change at a significantly different rate than the width of 

the damage zones.

Our results contrast with those of several other studies 

that reported a positive correlation between displacement and 

total fault zone width (for example, Hull, 1988; Knott, 1993) 

or core gouge width (for example, Engelder, 1974; Scholz, 

1990) throughout a similar range of displacement. Most of 

these studies, however, used “mixed” fault data compiled 

from several different tectonic settings, protoliths, and fault 

slip modes, which brings into question the reliability of the 

correlations (Evans, 1990). Consistent with our study, poor 

correlations of total width of the fault zone or width of core 

gouge with displacement have been found in a variety of geologic environments for individual faults or fault populations 

developed in similar protoliths (Chester and Logan, 1986; 

Blenkinsop, 1989; Evans, 1990). The poor correspondence 

between width and displacement in these earlier studies was 

mainly attributed to strain softening and strain localization 

resulting from strength contrasts caused by lithologic variations in the wallrocks and by relatively weak core gouge 

zones. Blenkinsop (1989) also inferred that irregular fault 

n = 101

Mean = 0.1 m

Median = 0.05 m

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

FAULT CORE WIDTH, IN METERS

0

10

20

30

40

50

60

70

FREQUENCY

Figure 7. Fault core widths. In this and 

subsequent histograms x-axis labels show 

maximum value within each data bin. Note 

that most fault cores are less than 0.1 m 

wide.
12  Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

Figure 9. Total width of fault zone and width 

of aggregate core, both versus dip separation. 

Lines (of form y = c ln x+b) of best fit (leastsquares regression) to data and associated 

coefficient-of-determination correlation 

factors (R2) are also shown. A, Total fault zone 

width versus separation. Poor correlation indicates that there is no simple relation between 

displacement and width. B, Width of aggregate 

core (mixed zones + core) versus separation. 

Diagram similarly indicates weak correlation. 

Broad range of widths for a given separation 

suggests that additional factors are important.

Figure 8. Total width of fault zone versus 

architectural index of fault zone (Fa). Fa is 

the ratio of the sum of widths of fault damage zones to total width of fault zone (Caine 

and others, 1996). Fa can range from 0 to 1. 

For most faults measured in this study area, 

Fa >0.9 indicates that most width of fault 

zones comprises damage zones. Although 

range of fault zone widths increases with 

increasing damage-zone dominance (that 

is, with increasing Fa), some fault zones in 

which damage zones dominate (or cores 

are deficient) are narrow.

0

1 10 100 1,000 10,000

DIP SEPARATION, IN METERS

10

20

30

40

50

60

70

80

TOTAL FAULT ZONE WIDTH, IN METERS

A

 R2 = 0.17

0.1 1 10 100 1,000 10,000

 R2 = 0.05

0

1

2

3

4

5

6

7

DIP SEPARATION, IN METERS

AGGREGATE CORE WIDTH, IN METERS

B

20

40

60

80

0.7 0.8 0.9 1.0

Fa

TOTAL FAULT ZONE WIDTH, IN METERS 

0

0.6
shapes and geometries can cause pronounced variations in 

width along a single fault zone. We noted such variations in 

width at several scales of observation along some fault zones 

in the study basins (fig. 3), and Heynekamp and others (1999) 

observed similar relations for mixed zones along the Sand Hill 

fault.

Influence of Lithology

Lithologic composition and its variation within rocks 

that host fault zones can profoundly influence the mechanical properties, structural architecture, and deformational and 

diagenetic histories of fault zones, which in turn can strongly 

influence their permeability structure (for example, Chester 

and Logan, 1986; Evans, 1990; Knipe, 1993; Antonellini and 

Aydin, 1995; Caine and others, 1996; Caine and Forster, 1999; 

Heynekamp and others, 1999; Rawling and others, 2001; 

Doughty, 2003). Below, fault core compositions, fault zone 

widths, and damage zone fracture types are statistically compared with the nature of footwall and hanging-wall protoliths 

to assess lithologic controls on these parameters in the study 

area. Also, damage-zone widths are compared to dip separations within various protolith categories.

Fault Core Compositions

A majority of fault cores observed in the study area (68 

percent) consists of sheared and foliated clay with variable but 

subordinate amounts of silt, sand and, more rarely, pebbles 

(figs. 3 and 10). On the basis of mesoscopic observations, 

nearly pure clay composes entire exposed cores in nearly half 

(45 percent) of the fault zones (fig. 10). These clays are typically brown to reddish brown, although the clay also takes on 

shades of green and gray and rarely is black. XRD analyses of 

a few clay samples from cores suggest that montmorillonite is 

the dominant mineral component (S.J. Sutley, written commun., 1999). Mudstone-rich sedimentary layers within several 

fault zones are clearly dragged and smeared into the cores; 

locally the cores thicken and taper in a manner similar to that 

described by other workers in the basin (Goodwin and others, 

1999; Heynekamp and others, 1999; Doughty, 2003). These 

observations, and independent geochemical evidence (Caine 

and others, 2004), suggest that mechanically assimilated clay 

minerals derived from clay-rich sedimentary protoliths are 

a major component of the fault cores, particularly in poorly 

lithified sediments. However, finely comminuted sedimentary grains probably also contribute to the clay cores (for 

example, Knipe, 1993; Heynekamp and others, 1999; Vrolijk 

and van der Pluijm, 1999). Sheared and foliated siliciclastic 

sand (or sandstone) and gravel lacking substantial amounts of 

clay compose 25 percent of the fault cores, whereas variably 

sheared and brecciated vein, volcanic, and well-indurated 

sedimentary rock make up the remaining 7 percent (fig. 10). 

These coarser grained, relatively heterogeneous cores likely 

reflect dominantly coarser grained and mechanically stronger 

protoliths that lack significant amounts of clay and mudstone 

(for example, fig. 11). Discrete slip surfaces are common both 

within and bordering the cores, regardless of their composition, similar to slip surfaces described for the Sand Hill fault 

zone (Heynekamp and others, 1999) and fault zones elsewhere 

(for example, Chester and Logan, 1986; Caine and others, 

1996). Clay-rich cores are common in nearly all faulted protoliths throughout the Santo Domingo and northern Albuquerque 

Basins. In contrast, sand-rich cores appear to be more common in sandstone-dominant rocks of the lower Santa Fe Group 

exposed in the western parts of the basins, and sheared and 

brecciated volcanic rock cores are concentrated in the northern 

part of the Santo Domingo Basin where tuffs and lavas of the 

Jemez volcanic field are prevalent (fig. 2). 

Width of Fault Zones

To investigate possible lithologic influences on fault 

zone widths in the Santo Domingo and northern Albuquerque 

Basins, the frequency distributions and mean values of the 

widths of fault zone components in several different lithologic categories were plotted together to allow direct comparison (figs. 12 and 13). Protoliths in which gravel and sand 

(or sandstone) dominate have the narrowest damage zones 

(mostly <20 m), whereas damage zones in “bedrock” (that is, 

well-indurated tuff, lava, and pre-Santa Fe Group sedimentary 

rocks) have the broadest range of widths (fig. 12A). Although 

the widths of damage zones in dominantly clay (or mudstone) 

and silt (or siltstone) are concentrated at the narrow end of 

the distribution range, a few damage zones in fine-grained 

protoliths are relatively wide (>45 m) (fig. 12A). The mean 

width of damage zones changes depending on the lithology of 

the host rock or sediment (fig. 13): the width of damage zones 

increases as the dominant grain size in sedimentary protoliths 

Fault Zone Characterization 13

Figure 10. Percentages of various compositions observed in 

fault cores at 141 sites.

Breccia

(7 percent) Clay

(45 percent)

Clay mixed with

coarser sediments

(23 percent)

Sheared

sand/gravel

(25 percent)
decreases, and damage zones in bedrock are considerably 

wider than average. The mean widths of damage zones are 

notably greater in the hanging-wall block than in the footwall 

in protoliths in which clay (or mudstone) and silt (or siltstone) 

dominate and in bedrock (fig. 13). The widths of mixed zones 

differ little as a function of dominant grain size (figs. 12B and 

13). The relative percentage of narrow (<0.5 m) mixed zones 

in which clay (or mudstone) and silt (or siltstone) dominate is 

slightly greater than is true in the other lithologies, whereas 

the relative percentage of wide (>3 m) mixed zones in bedrock 

is notably greater (fig. 12B). Also, the mean width of mixed 

zones is slightly greater in bedrock than in the other lithologic categories (fig. 13). Distributions of fault core width are 

affected little by the different lithologic categories (fig. 12C). 

The importance of any correlation between core width and 

lithology is unclear, given two uncertainties: the relative contributions of contrasting hanging-wall and footwall protoliths, 

and the likelihood that protoliths presently juxtaposed along a 

core may have had less influence on that core’s development 

than protoliths at higher or lower stratigraphic levels.

Our results suggest that the widths of architectural 

components in a fault zone generally increase as the grain size 

in sedimentary protoliths decreases, although there appears 

to be a disproportionately greater number of the narrowest 

mixed zones and cores in or adjacent to protoliths rich in clay 

(or mudstone) and silt (or siltstone). These findings partially 

contrast with those of previous investigations, which found that 

the individual and aggregate widths of fault zone components 

generally decrease with decreasing grain size or increasing 

clay content of the protolith owing to strain-softening effects 

(for example, Antonellini and Aydin, 1995; Caine and others, 

1996; Heynekamp and others, 1999).

In the Santo Domingo and northern Albuquerque Basins, 

weakening and localization of strain in clay-rich protoliths 

could explain the development of the narrowest mixed zones 

and cores in very fine grained protoliths (Heynekamp and 

others, 1999), but it does not explain the overall widening 

of fault zones observed in finer grained protoliths (fig. 13). 

Heynekamp and others (1999) observed local fault zone widening in poorly lithified, fine-grained sediments along the Sand 

Hill fault. Comparisons of best-fit linear (log) regression diagrams of damage zone width versus dip separation for each of 

the protolith categories (fig. 14) suggest that, as displacement 

accumulated along faults, fault zones tended to become wider 

and, by implication, to experience greater strain hardening 

as the dominant grain size decreased. Such comparisons also 

suggest that as grain size of protoliths decreased, fault zones 

widened at progressively greater rates. These inferences are 

supported by the progressive increase in correlation factors 

(R2) and the increase in slope of the best-fit lines as the grain 

Figure 11. Road-cut exposure of Santa Ana fault zone, northern part 

of Santo Domingo Basin. Extension fractures concentrated in cemented 

sandstone layers in footwall damage zone. Extension fractures oriented 

about 45° with respect to principal fault core, which consists of sheared 

sand. Pick in lower right part of view is about 0.75 m long. Opposed 

arrows indicate sense of slip.

14  Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

Hanging-wall

mixed zone

Extension

fracture

Core

Footwall

damage

zone
Fault Zone Characterization 15

size of protoliths decreases. These diagrams also reveal that, 

in all protolith categories except gravel to sand (or sandstone), the width of damage zones in the hanging-wall block 

increases, with respect to displacement, at a greater rate 

than does that width in the footwall block. Wider fault zones 

and greater degrees of strain hardening in many of the finer 

grained sedimentary host rocks and deposits in the study 

basins may reflect that, at the outcrop scale, these protoliths 

are lithified or cemented to widely varying degrees and 

contain compositionally distinct, comparatively strong interbeds. For example, a few well-cemented sandstone interbeds 

within an otherwise poorly lithified mudstone sequence may 

exert the greatest control on the overall width of a damage 

zone. Poorly lithified sand-dominant protoliths, such as are 

common within the upper basin-fill deposits of the Santa Fe 

Group, may be much weaker and more apt to localize strain 

than stiffer and more compacted mudstones and siltstones 

of similar age. The contrasts in strength between sand and 

well-consolidated or -cemented sandstones may be 

considerable, such that narrow fault zones have a greater 

tendency to form in poorly lithified sand than in indurated 

sandstone.

Our observation that damage zones in gravel-rich and 

conglomeratic sedimentary protoliths tend to be relatively 

narrow, and similar relations noted elsewhere by Chester and 

Logan (1986), suggests that brittle strain in such materials 

is largely accommodated by broadly distributed, small-scale 

(microscopic?) extension and shear fractures within the sedimentary clasts or matrix or both (for example, Eidelman and 

Reches, 1992). Such small-scale, diffuse deformation, if it exists, 

may extend outward beyond the zones of damage detected in the 

field such that damage zones in gravel-rich and conglomeratic 

protoliths may be wider than our measurements record. Alternatively, protoliths with abundant large clasts may inhibit widening 

of damage zones by absorbing or localizing shear strain within a 

relatively small volume of material. 

Figure 12. Frequency distributions (relative percentages) of fault zone widths with respect to categories of 

dominant lithology. A, Width of damage zones; note preponderance of narrow widths in gravel and sand (or 

sandstone) protoliths that contrast with wide distribution of widths in mudstone and in bedrock. B, Width of 

mixed zones; note relatively wide bedrock mixed zones. C, Width of fault cores; lithology assigned for each 

value of core width reflects the protolith of only one of the juxtaposed fault blocks. In order to construct 

these diagrams, values of fault zone width were counted more than once in the common case in which the 

fault block protolith consists of two or more categories of sedimentary material in subequal proportions (for 

example, interbedded sandstone and mudstone).

DAMAGE ZONE WIDTH, IN METERS

0

10

20

30

40

50

60

70

5 10 15 20 25 30 35 40 45 50 >50

FREQUENCY, IN PERCENT FREQUENCY, IN PERCENT

n = 53 (Grav-ss), 177 (Ss), 

46 (Muds-slts), 31 (Bedrock) 

0

10

20

30

40

50

60

70

80

0.5 1 1.5 2 2.5 3 >3

MIXED ZONE WIDTH, IN METERS

0.05 0.1 0.15 0.2 >0.2

CORE WIDTH, IN METERS A

B

C

Grav-ss—Gravel to sand or sandstone 

Ss—Sand or sandstone

Muds-slts—Clay or mudstone to

 silt or siltstone

Bedrock—Volcanic and prebasin-fill 

 well-indurated rocks

Dominant Lithology 

EXPLANATION 

n = 50 (Grav-ss), 127 (Ss), 

32 (Muds-slts), 19 (Bedrock) 

n = 64 (Grav-ss), 176 (Ss), 

43 (Muds-slts), 25 (Bedrock) 

FREQUENCY, IN PERCENT

0

10

20

30

40

50

60

70

80
16  Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

A majority of the widest damage and mixed zones are in 

“bedrock” protoliths (figs. 12 and 13). These protoliths typically consist of well-indurated or well-cemented, competent, 

stiff rocks. Additionally, the width of hanging-wall damage 

zones increases abruptly and has a relatively strong correlation as dip separation increases in bedrock protoliths (fig. 14). 

These bedrock properties suggest that strain-hardening mechanisms were the principle cause of fault zone widening detected 

Hanging-wall damage zone

Hanging-wall mixed zone

Footwall damage zone

Footwall mixed zone

EXPLANATION

5

10

15

20

25

MEAN WIDTH, IN METERS

Grav-ss Ss Muds-slts Bedrock

DOMINANT LITHOLOGY

Figure 13. Mean width of four fault 

zone components versus dominant 

lithology. Mean width of damage zone 

increases as grain size decreases in 

basin-fill sedimentary protoliths and is 

greatest in bedrock. In any one lithologic category, mean width of hanging-wall damage zone is greater than 

mean width of footwall damage zone. 

Grav-ss, gravel to sand or sandstone; 

Muds-slts, clay or mudstone to silt or 

siltstone; Ss, sand or sandstone.

Figure 14. Best-fit (least-squares regression) lines (of form y = c ln x+b) of damage zone 

width versus dip separation in four categories 

of lithology in hanging-wall and footwall blocks. 

Numbers next to lines represent associated R2

values. Lithologic categories based on dominant 

grain size. With decreasing dominant grain size 

in the protolith, correlation generally improves 

and width of damage zone increases at a 

progressively greater rate relative to displacement (that is, slope of line steepens). Except 

for one category (gravel to sand or sandstone), 

width increases at a greater rate in hanging-wall 

block.

1 10 100 1,000 10,000

DIP SEPARATION, IN METERS

0

10

20

30

40

50

60

DAMAGE ZONE WIDTH, IN METERS

Footwall

0.08

0.01

0.03

0.14

0.14

0.35

0.36

0.57

Bedrock; volcanic or prebasin-fill 

 well-indurated rocks (n=12)

Bedrock; volcanic or prebasin-fill 

 well-indurated rocks (n=16)

Clay or mudstone to silt or 

 siltstone (n=18)

Clay or mudstone to silt or 

 siltstone (n=23)

Sand or sandstone (n=69) Sand or sandstone (n=87)

Gravel to sand or sandstone 

 (n=24)

Gravel to sand or sandstone 

 (n=21)

Hanging wall

EXPLANATION
fractures commonly have minute apertures unfilled by secondary minerals, but it is not known to what degree these fracture 

openings reflect near-surface relaxation of lithostatic loads 

and become closed at depth. Observed mesoscale synthetic 

and antithetic shear fractures are discrete, small-displacement 

(<1–10 m) slip surfaces that are commonly polished and contain slickenlines that trend more or less parallel to striae on the 

main fault surface (fig. 15). Deformation bands, which consist 

of narrow zones (commonly <5 mm) of sand grains comminuted and compacted by cataclasis (Antonellini and Aydin, 

1994), are usually observed in sandstones where they typically stand out in positive relief. The synthetic and antithetic 

shear fractures and deformation bands are oriented subparallel 

and at high angles (50°–70°), respectively, to the principal 

fault surface and can therefore be viewed as conjugate (that 

is, Andersonian) subsidiary faults (figs. 4 and 15). However, 

some of these mesoscale structures geometrically resemble, 

and probably formed as, Riedel and anti-Riedel shear fractures (for example, Petit, 1987). Extension and shear fractures 

that strike obliquely or at very high angles to the main fault 

surface, and that do not clearly belong to the other fracture 

sets, were classified as cross or oblique fractures (compare 

with Caine and Forster, 1999). With the possible exception of 

cross fractures, the abundance of damage zone fractures and 

the amount of shear displacement exhibited by mesoscale slip 

surfaces generally increase toward the central fault core (figs. 

4, 11, and 15).

Synthetic shear fractures and deformation bands are the 

most common types of fractures observed in damage zones 

in the basins regardless of protolith, although antithetic shear 

fractures and deformation bands and subvertical extension 

fractures are also prevalent (fig. 16). Fracture type in a damage zone correlates only weakly with lithology. All three of 

the most common fracture types appear to be somewhat rarer 

in gravel-dominant protoliths, where strain may be accommodated by some mechanism other than mesoscale fracturing (see earlier discussion) (fig. 16). Extension fractures are 

somewhat more common in bedrock and in protoliths rich in 

mudstone and siltstone (fig. 16). The former association is 

expected given the typically greater lithification, competency 

and, presumably, shear strength in the prebasin-fill rocks and 

in the volcanic rocks. Such properties should have promoted 

tensile, opening-mode, failure at the low confining pressures 

at which most of these rocks were faulted; perhaps relatively 

competent, stiff beds or intervals in protoliths rich in mudstone 

and siltstone failed in a similar mode. Cross and oblique fractures, although rarely observed in general, are fairly common 

in bedrock protoliths. Their relative abundance in bedrock 

may reflect an increased likelihood of older, variably oriented 

fractures in the prebasin-fill rock units (compare with Caine 

and Forster, 1999).

Our field observations document that, within individual 

damage zones, changes in lithology can locally influence the 

type and abundance of fractures at the suboutcrop scale. This 

influence is especially strong in deformation bands, which 

form dominantly in sandstone beds, and in extension 

Fault Zone Characterization 17

in the bedrock protoliths (for example, Chester and Logan, 

1986). Antonellini and Aydin (1994, 1995) recognized strain 

hardening as a process in faulted, porous, but indurated sandstones by which deformation bands within fault zones form 

and widen as displacement increases. Such a process may 

also explain the earlier mentioned concentrations of comparatively wide fault zones in sedimentary rocks of the lower 

Santa Fe Group in the western part of the study area. These 

rocks include abundant, partially indurated, sandstone layers that commonly host deformation bands in fault zones (for 

example, Heynekamp and others, 1999). The large width of 

many “mixed zones” in bedrock protoliths is attributed to fault 

entrainment of numerous large, competent blocks of rock that 

have resisted significant internal shearing and cataclasis owing 

to their relative strength. A lack of clear tectonic mixing at the 

outcrop scale in bedrock fault zones is consistent with prior 

observations that mixed zones, as zones of pervasive mixing at 

a range of scales, are mainly limited to poorly indurated, highporosity sediments (Goodwin and others, 1999; Heynekamp 

and others, 1999; Rawling and others, 2001). 

The diagrams and frequency distributions of fault zone 

width (figs. 6, 8, and 12) reveal that the fault zone components have finite, limited ranges of width regardless of their 

dominant protoliths. Furthermore, in most protolith categories 

the rate at which the width of fault zones increases is slightly 

lower, with respect to fault displacement, in the footwall damage zone (fig. 14) despite the greater amount of cumulative 

strain in most footwall fault rocks. These observations suggest 

that a characteristic strain threshold may be associated with 

a given wall-rock protolith, beyond which strain-softening 

mechanisms dominate strain-hardening mechanisms and fault 

zones no longer widen. 

Fractures in Damage Zones

Fractures and associated structures in damage zones can 

strongly influence the heterogeneity and anisotropy of permeability of fault zones (for example, Chester and Logan, 1986; 

Caine and others, 1996; Evans and others, 1997; Caine and 

Forster, 1999). We routinely observed the dominant types and 

geometry of fractures in damage zones to qualitatively assess 

if they differ with lithology and to infer their effect on the 

permeability structure of the fault zone. Four main categories 

of fractures were recognized in the fault zones: (1) openingmode, or extension, fractures; (2) synthetic mesoscale shear 

fractures (that is, slip surfaces) and deformation bands; (3) 

antithetic mesoscale shear fractures and deformation bands; 

and (4) cross, or oblique, fractures (fig. 4). Local zones of 

breccia were also noted. Extension fractures typically strike 

subparallel to the main fault surface and are subvertical, such 

that they commonly make angles of 30°–50° with the main 

fault slip surface (figs. 4 and 11). These fractures tend to 

concentrate in relatively competent, indurated, or cemented 

sedimentary beds and in lavas. As is true with other types of 

damage zone fractures, extension fractures appear to increase 

in abundance towards fault cores. In outcrop, extension 
18  Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

Figure 15. Inner part of footwall damage zone exposed near eastern border of Santo 

Domingo Basin showing synthetic (S) and antithetic (A) shear fractures and differentially 

cemented sandstone layers; cement is carbonate. Principal fault surface is just out of view 

on left, and high-rake (dip-slip) slickenlines are visible on mesoscale slip surface on right side 

(highlighted by dashed lines). Pick in left center of photograph is about 0.75 m long.

Figure 16. Frequency distribution of fracture type in damage zone versus dominant lithology. 

Frequencies represent percentage of damage zones, in a given lithology, containing feature 

indicated. Most common fracture types are synthetic mesoscale faults or deformation bands 

(Syn flt/db), antithetic mesoscale faults or deformation bands (Anti flt/db), and extension fractures (Ext frac). Cross frac, cross fractures; No frac, no fractures. Fracture types illustrated in 

figure 4.

0

20

40

60

80

Synflt/db Antiflt/db Cross frac Extfrac Breccia Nofrac

FRACTURE TYPE IN DAMAGE ZONE

FREQUENCY, IN PERCENT

Gravel to sand or sandstone (n=76)

Sand or sandstone (n=197)

Clay or mudstone to silt or siltstone (n=47)

Bedrock; volcanic or prebasin-fill well-indurated rocks (n=44)

EXPLANATION

S

S

S S

A

A

A
Fault Zone Characterization 19

fractures, which concentrate in relatively competent, indurated, or cemented sedimentary beds (fig. 11) and in lavas.

Earlier field and modeling studies of fault zones in 

moderately lithified to well-lithified and indurated rocks 

recognized that networks of interconnected slip surfaces and 

extension fractures that contain finite apertures can increase 

the permeability of damage zones relative to the permeability of host rock and core (for example, Chester and Logan, 

1986; Caine and others, 1996; Evans and others, 1997; 

Caine and Forster, 1999). Fault zones observed in this study 

that juxtapose or bound bedrock protoliths, especially near 

the margins of the study basins (fig. 2), may similarly have 

increased permeability within their damage zones as a result 

of open slip surfaces and fractures. In contrast, shear fractures 

and deformation bands in high-porosity, poorly lithified or 

unconsolidated sediments are generally thought to reduce permeability in damage zones owing to shear-induced cataclastic 

grain-size reduction and compaction along such structures 

(Antonellini and Aydin, 1994, 1995; Goodwin and others, 

1999; Heynekamp and others, 1999; Sigda and others, 1999). 

The presence in the study basins of extension fractures in all 

lithologic categories (fig. 16), however, suggests that permeability may increase along fractures in some of the damage 

zones—even those in poorly or moderately lithified basin-fill 

sediment. Indeed, secondary mineral veins and cemented 

zones observed along many such fractures (see discussion 

below) attest to past movement of mineralizing fluids along 

the structures, even though the fractures have since been 

sealed by the vein materials. In damage zones containing 

extension fractures that have not been cemented, permeability 

should be greater in directions parallel to the fractures and 

to the principal fault core (Sibson, 1996; Caine and Forster, 

1999).

Cementation in Fault Zones 

Secondary cementation and mineralization are widely 

recognized as being spatially associated with faults as a 

direct consequence of concentrated fluid flow or strong fluid 

pressure gradients (or both) along or across fault zones (for 

example, Chester and Logan, 1986; Sibson, 1990; Parry and 

others, 1991; Knipe, 1993; Mozley and Goodwin, 1995; 

Caine and Forster, 1999). Furthermore, it has been shown that 

the permeability of fault zones is considerably reduced where 

the zones are cemented and, thus, that faults can evolve from 

zones of high permeability into zones of low permeability (for 

example, Knipe, 1993; Mozley and Goodwin, 1995; Caine 

and Forster, 1999). If we assume that fault zone cements 

indicate focused flow of ancient fluids, then past variations in 

permeability and fluid flux within individual fault zones and 

across faulted basin aquifers can be inferred from the spatial 

distribution of fault zone cements. We systematically recorded 

the basic mineralogy and distribution of cements relative to 

architectural components observed in fault zones in the study 

basins, and we mapped the along-strike extent of cements 

along the traces of fault zones.

Mineralogy and Regional Distribution

Two principal mineral cements, silica and carbonate, 

are recognized in the study area. Silica cements are limited 

to fault zones in the north part of the Santo Domingo Basin 

mainly north of the Jemez River and west of the Rio Grande, 

where they increase in frequency and intensity northward 

toward the Jemez volcanic field (figs. 1 and 17). Commonly, 

silica-cemented fault zones form prominent topographic ribs 

or ridges. An exceptional example is the silica-cemented 

footwall block of the Santa Ana fault zone, which forms a 

conspicuous ridge as wide as 100 m that can be traced for 

more than 15 km northward into Jemez volcanic rocks (figs. 

17 and 18) (Chamberlin, 1999; Grauch and others, 2001). 

Silica cements include microcrystalline cristobalite, microcrystalline tridymite, and opaline and chalcedonic silica, 

which are locally accompanied by hydrous manganese oxides 

and, rarely, barite or heulandite (S.J. Sutley, written commun., 

1999). On the basis of the mineralogy and spatial restriction 

of the silica cements we infer that the cements precipitated 

from hydrothermal fluids flowing southward, presumably 

down ancient hydraulic gradients, and upward along faults 

projecting from magmatic centers within the Jemez volcanic 

field. Chamberlin (1999) came to a similar conclusion for 

silicified faults near the southern edge of the volcanic field, 

and furthermore he spatially and temporally linked the silica 

cementation to 10–7 Ma volcanic centers.

Carbonate cements, mostly micritic and less commonly 

sparry calcite, are much more widely distributed than silica 

cements in both the Santo Domingo and northern Albuquerque Basins (fig. 17) (for example, Mozley and Goodwin, 

1995; Heynekamp and others, 1999). Fault zone sandstones 

that are strongly cemented with carbonate commonly stand 

out in positive topographic relief. Carbonate cements are also 

expressed as spherical to spherulitic concretions that weather 

into balls as much as several centimeters in diameter (fig. 

19), but elongate carbonate concretions such as those used by 

Mozley and Goodwin (1995) to infer orientations of ancient 

ground-water flow were rarely observed. Although the source 

(or sources) of the carbonate cements is unknown, their basinwide distribution (fig. 17) suggests that they were not derived 

from a single, spatially restricted, ground-water flow system.

Both carbonate and silica cements are present along 

some faults in the northern part of the study area (fig. 17), and 

contact and crosscutting relations indicate that the carbonate 

mostly precipitated later than the silica (figs. 18 and 19). The 

most strongly carbonate-cemented fault zones lie south of the 

area of silica cementation in the southern Santo Domingo and 

northern Albuquerque Basins (fig. 17). 
20 Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

Figure 17. Spatial patterns of carbonate and silica cements that are asymmetrically distributed in fault zones. Silica cement is 

restricted to northern Santo Domingo Basin along faults near Jemez volcanic field, whereas carbonate cement is distributed throughout basins. Asymmetries of cementation along faults show no systematic pattern relative to basin positions or predevelopment directions of ground-water flow (wide gray arrows). Flow directions derived from Bexfield and Anderholm (2000). Black solid line, exposed 

fault; black dotted line, buried fault; ball, on apparent downthrown side. Faults labeled as follows: EZ, East Ziana horst; HB, Hagan 

Bench; JM, Jemez; LB, La Bajada; PB, Pico Butte; PJ, Pajarito; PL, Placitas; RC, Rincon; SA, Santa Ana; SF, San Francisco; SH, Sand 

Hill; SI, Sile; SP, South Pajarito; SY, San Ysidro; TM, Tamaya; TT, Tetilla; VV, Valley View; WZ, West Ziana horst.

0 10 20 KILOMETERS

Santo Domingo

Northern Albuquerque

Basin

SF

PJ

LB

HB

PL

RC

SA

JZ

TT

PB

EZ

VV

TM

SI

SF

SH

Espanola

Basin

~

Rio Grande

Rio Grande

Jemez River

Rio Puerco

SF

LB

SY

WZ

PB

TM

RC

Sandia Mountains

Jemez

TT?

PJ?

SP

SA

VV

Jemez Volcanic Field

Mountains

Basin

Approximate predevelopment

 ground-water flow direction

EXPLANATION

West carbonate cement

East carbonate cement

West silica cement

East silica cement

Albuquerque

106°45` 35°45`

35°15`

106°15`
Fault Zone Characterization  21

Figure 18. Asymmetrically 

cemented Santa Ana fault zone (see 

fault labeled SA in fig. 17) exposed 

in large arroyo in Santo Domingo 

Basin, looking southwest. Footwall 

block of fault consists of sandstone 

of lower Santa Fe Group, strongly 

silica cemented, whereas hangingwall block consists of interbedded 

mudstone, siltstone, and sandstone 

of upper Santa Fe Group, very weakly 

carbonate cemented. Principal fault 

surface, which contains large steeply 

plunging mullions, is exposed across 

right side of photograph. White line, 

fault trace; opposed arrows, sense of 

fault movement. Height of view about 

30 m.

Figure 19. Inner part of hanging-wall damage zone, along fault 

near northwestern border of Santo Domingo Basin. Fine network 

of silica-cemented synthetic and antithetic shear fractures, deformation bands, and extension fractures all stand out in positive 

relief. Concretionary carbonate balls visible between fractures 

provide evidence of later compartmentalized flow of carbonaterich fluids between silica-cemented fractures. Pick head in lower 

left is about 0.2 m wide.

Silica-cemented

footwall block

Hanging-wall

block

Pr ni c pi al

sl pi

surface
cements occupy gravel- and sand-rich protoliths regardless of 

the cement mineralogy or asymmetry. This result is expected 

given that the permeability of Santa Fe Group basin-fill 

sediments typically increases as mean grain size increases 

(Detmer, 1995) and that the potential flux of cementing fluids 

passing through sediment generally increases with increasing 

sediment permeability. In footwall blocks, sand-rich protoliths 

more commonly host cements than do gravel-dominant protoliths, whereas in hanging-wall blocks, both protoliths equally 

host carbonate cements (fig. 20). This difference may reflect 

the fact that basin-fill strata of the Santa Fe Group generally 

have a finer average grain size at lower stratigraphic levels (for 

example, Connell and others, 1999), such that stratigraphically lower layers in the upthrown footwall blocks of largedisplacement faults are less likely to contain a large proportion of gravel. In most fault zones that juxtapose sedimentary 

protoliths, the dominant grain size on the cemented side of 

the fault is either coarser than (44 percent of observations) or 

similar to (48 percent of observations) the dominant grain size 

in the opposing fault block. These observations are partially 

consistent with previous interpretations of cementation patterns along the Sand Hill fault in the Albuquerque Basin that 

invoke across-fault, down-gradient flow of ancient groundwater where similar coarse-grained, hydraulically conductive 

sedimentary layers are juxtaposed (Mozley and Goodwin, 

1995; Heynekamp and others, 1999). An equally plausible 

explanation for asymmetrical cement distribution is that flow 

of cementing fluids was restricted to one side of fault zones 

owing to one or more sealing effects of lower permeability 

protoliths juxtaposed along the faults, of the low-permeability 

fault cores, or of older, mineralogically distinct, cemented 

zones on the opposite sides of faults (for example, Knipe, 

1993; Knott, 1993; Gibson, 1994; Knipe and others, 1998; 

Rawling and others, 2001; Caine and others, 2002). Such fault 

seals should reduce permeability in directions perpendicular 

to fault zones, whereas flow parallel to fault zones should be 

at least slightly increased in damage zones containing open 

fractures that strike parallel to the fault core such as along 

extension fractures and along some slip surfaces (fig. 4). Caine 

and others (1996) have described such fault zones in wellindurated rocks as having combined conduit-barrier permeability structures.

To address the validity of across-fault versus faultbounded or fault-localized fluid flow within the study basins, 

we mapped the sense of cement-distribution asymmetry along 

faults throughout the study area (fig. 17). This mapping indicates that domains of consistent cement asymmetry exist (for 

example, area of east-cemented fault zones near and including the Sand Hill fault) (see SH, fig. 17), but in other areas 

the asymmetry of cement locally alternates across a series of 

laterally adjacent fault blocks (fig. 17). For example, opposing silica-cement asymmetries characterize two strands of the 

San Francisco fault exposed in the eastern part of the Santo 

Domingo Basin (see SF, fig. 17); the eastern San Francisco 

fault strand and the aligned end of the oppositely dipping 

South Pajarito fault (labeled SP in fig. 17) to the north are both 

22  Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

Distribution Within Fault Zones

Silica and carbonate cements are restricted to, or are 

concentrated on, one side of the fault core in a majority of 

exposed fault zones (figs. 17 and 18). In many of these 

asymmetrically cemented fault zones, the cements are localized within one of the mixed zones and in sand-rich domains 

of fault cores. Some cements extend outward into the 

hanging-wall or footwall damage zone but, with the exception of areas of regional stratabound cementation, they rarely 

extend beyond the outer edge of the damage zone (figs. 15, 

18, and 19). Commonly, cements pervasively impregnate host 

sediments within fault zones. Microscopic observations of 

carbonate-cemented, shear-foliated sandstones from various mixed zones and fault cores reveal that the cements can 

compose more than 50 percent of the rock and completely 

envelope and isolate individual grains, which suggests high 

fluid flux and, perhaps, fluidization in these materials during 

mineral precipitation. Cements in some mixed and damage 

zones appear to be concentrated within or adjacent to deformation bands and mesoscale shear fractures (figs. 15 and 19), 

and veins of cementing minerals locally occupy extension 

fractures. Despite the grain-size reduction and consequent 

reduced permeability generally associated with deformation 

bands, cements have been reported within some deformation bands elsewhere, which have been attributed to dilatancy 

during shear and increase in porosity (Antonellini and Aydin, 

1994; Heynekamp and others, 1999). Future petrographic 

analysis is required to evaluate whether cements within the 

study basins are actually concentrated within or immediately 

adjacent to deformation bands. Cemented zones restricted to 

one side of a fault can be traced as far as 15 km along strike in 

fault zones, although along-strike reversals in cement asymmetry have been observed along a few faults in the eastern 

part of the Santo Domingo Basin (fig. 17). The restriction of 

strongly cemented domains to one side of fault zones throughout considerable strike lengths suggests that the asymmetries 

in cement distribution are owed primarily to fault-bounded 

and fault-localized fluid flow rather than to fortuitous juxtapositions of cemented and uncemented stratigraphic intervals. However, where protoliths have undergone formational 

diagenetic cementation, fault-controlled cement is difficult to 

distinguish from previously precipitated cement in beds that 

were entrained in the fault zone. Carbonate cements commonly are asymmetrically distributed in both hanging wall 

and footwall blocks, whereas concentrated silica cements are 

mostly restricted to stratigraphically lower (and perhaps at the 

time of cementation structurally deeper) footwall rocks (figs. 

17 and 18). The latter observation is consistent with deposition 

of most silica cement earlier in the growth-fault history of the 

northern Santo Domingo Basin (that is, 10–7 Ma?) (Chamberlin, 1999). 

To investigate lithologic controls on the distribution of 

cement in fault zones, we compared frequency histograms of 

silica and carbonate cement for various categories of hangingwall and footwall lithology (fig. 20). Virtually all fault zone 
Hydrologic Implications  23

silica cemented on their west sides, whereas the western San 

Francisco strand is cemented on its east side (fig. 17). Such 

closely spaced reversals in cement asymmetry strongly 

suggest that ancient flow was baffled or channeled by faults 

in such areas and that the regional hydraulic gradient was 

locally modified by faults that acted as both ground-water 

flow permeability conduits and barriers. Intrabasin patterns 

of cement asymmetry can also be compared with “modern” 

ground-water flow (that is, hydraulic-gradient) directions 

(fig. 17) estimated from predevelopment data on groundwater levels (Bexfield and Anderholm, 2000). Although these 

flow directions do not necessarily reflect past ground-water 

flow directions at the time that cement precipitated, they do 

indicate that regional flow is generally directed toward the 

position of the active Rio Grande. The distribution of ancestral Rio Grande deposits in the study basins indicates that the 

Rio Grande has not shifted laterally more than about 10 to 15 

km east or west of its modern channel since its establishment 

about 7 Ma (Hawley, 1996; Smith and Kuhle, 1998), and thus 

regional ground-water flow directions may not have changed 

much since inception of the Rio Grande. If we assume that the 

pre-development flow directions are reasonable approximations of ancient flow, then they suggest that both up-gradient 

and down-gradient sides of faults have been cemented (fig. 

17). Such a cementation pattern may have resulted from channelization and redirection of ground-water flow owing to lowpermeability fault seals and, perhaps, increased along-fault 

permeability in damage zones (compare with Caine and 

Forster, 1999). If so, appreciable across-fault flow was likely 

restricted to areas where fault seals were broken or poorly 

developed.

It is well known that regions of localized fluid flow 

within fault zones can evolve into flow barriers owing to 

cementation that diminishes permeability of the flow medium 

(for example, Sibson, 1987, 1990; Parry and others, 1991; 

Knipe, 1993; Mozley and Goodwin, 1995; Caine and Forster, 

1999). A few faults in the northern Santo Domingo Basin 

contain separate zones of silica and carbonate cement on 

opposite sides of their respective fault zones (for example, 

see SF strands in fig. 17), which suggests that some cemented 

zones have acted as seals to later ground-water flow (fig. 

18). Perturbed predevelopment ground-water flow directions near the northern Santa Ana fault (SA, fig. 17) may 

result from redirected flow caused by the laterally extensive 

zones of silica cement that characterize faults in the area. If a 

fault zone is repeatedly deformed, perhaps because of many 

earthquake cycles, then cemented zones may episodically 

refracture and become conduits for flow (for example, Sibson, 

1987, 1990; Caine and Forster, 1999). Evidence of recurring 

fault cementation and fracturing in the study area is provided 

by numerous exposures of one or more generations of veins 

and cemented fractures that cut earlier cemented sediments 

within mixed zones (figs. 15 and 19). These relations indicate 

that some of the cemented fault zones alternately acted as 

seals and conduits for fluid flow, presumably owing to the 

effects of episodic fault deformation concentrated near the 

fault cores. 

Hydrologic Implications 

Our observations suggest several generalizations regarding past and present hydrologic behavior of fault zones in the 

study basins. Furthermore, these results provide a preliminary 

basis for assigning hydrologic properties to faults in groundwater flow models of the Albuquerque and other basins of the 

Rio Grande rift (for example, Bartolino and Cole, 2002).

Statistical averages of the various widths of architectural 

components in fault zones, such as those determined in the 

present study, can be used in estimates of fault zone transmissivity and in other parameters in numerical models of fluid 

flow along faults (for example, Maclay and Small, 1983; 

Haneberg, 1995; Caine and Forster, 1999). Our preliminary 

correlations of fault zone widths with protolith and displacement (figs. 12, 13, and 14) imply that knowledge of subsurface lithologic variations can be used to help predict down-dip 

variations in fault zone widths and hydrologic properties that 

depend on width. In the study basins, fault cores and adjacent 

mixed zones make up a small proportion of the total width 

of a fault zone. Many field, experimental, and numerical 

modeling studies have found that sheared and comminuted, 

ultrafine-grained gouge and clay in fault cores typically have 

very low permeabilities as compared with the surrounding 

fault zone components and host materials. Such core materials can form in a variety of poorly indurated to well-indurated 

protoliths and, thus, can form effective, areally extensive seals 

that obstruct fluid flow across a fault and create strongly 

Figure 20. Frequency distribution (relative percentages) of two 

fault zone cements with respect to dominant lithology and position 

within fault zones. Strong cementation is restricted to coarser 

grained sediments in both footwall and hanging-wall blocks. 

Dominant lithology: Grav-ss, gravel to sand or sandstone; Ss, sand 

or sandstone; Muds-slts, clay or mudstone to silt or siltstone; Bedrock, volcanic and prebasin-fill rocks that are well indurated.

0

10

20

30

40

50

60

70

80

Grav-ss Ss Muds-slts Bedrock

DOMINANT LITHOLOGY

FREQUENCY, IN PERCENT

Footwall carbonate cement (n=20)

Hanging-wall carbonate cement (n=21)

Footwall silica cement (n=24)

Cement distribution and type

EXPLANATION
24  Structure and Cementation of Fault Zones, Albuquerque Basin, New Mexico

anisotropic permeability along the fault zone (for example, 

Morrow and others, 1984; Chester and Logan, 1986; Knipe, 

1993; Caine and others, 1996; Evans and others, 1997; Knipe 

and others, 1998; Caine and Forster, 1999; Heynekamp and 

others, 1999; Caine and others, 2002). A majority of cores 

observed in the present study consists of sheared and foliated 

clay or finely comminuted sedimentary grains that presumably impart very low permeability, especially normal to the 

core. Thus, despite their relatively narrow widths, such 

undisturbed cores should act as seals that prevent fluid flow 

across faults and that contribute to anisotropic permeability 

within fault zones (for example, Knipe, 1993; Caine and Forster, 1999; Caine and others, 2002). 

The presence of extension fractures in damage zones in 

a variety of protoliths, including poorly lithified sediments, 

suggests that some damage zones are, or were, more permeable than their adjacent unfractured protolith. This conclusion 

is corroborated by field evidence of cements localized along 

extension fractures and, more rarely, along shear fractures. 

Fault zones in relatively lithified and indurated bedrock 

protoliths, such as those concentrated near the margins of the 

study basins, are most likely to have permeable open fractures 

within their damage zones (for example, Chester and Logan, 

1986; Caine and others, 1996; Evans and others, 1997; Caine 

and Forster, 1999). Damage zones should be more permeable 

in directions parallel to open extension fractures and synthetic 

and antithetic mesoscale faults, all of which typically strike 

parallel to the adjacent fault core (Sibson, 1996; Caine and 

Forster, 1999). Overall vertical permeability parallel to fault 

dip, however, might be reduced in damage zones that contain 

large concentrations of intersecting antithetic and synthetic 

shear fractures owing to the compartmental geometry created 

by them. In the study area, damage zones are wide relative 

to cores (that is, high Fa values); this relation and the observations mentioned above imply that intrabasin fault zones 

overall should promote subhorizontal ground-water flow 

parallel to their cores, although probably not to the degree that 

they should in bedrock on the rift margins (Caine and others, 

1996). 

Patterns of fault cementation (and by inference ancient 

flow) in the study basins can be used to predict the distribution and geometry of modern ground-water flow paths in 

fault zones. Flow should be concentrated within mixed zones 

and inner damage zones in gravel- and sand-rich protoliths, 

unless permeability has been greatly reduced by cementation. Localized ground-water flow that is parallel to a fault 

should dominate, whereas flow across a fault is likely only 

where sediments or rocks of similar or higher permeability 

are juxtaposed on the down-gradient side of faults that are 

either poorly sealed or perforated (for example, Mozley and 

Goodwin, 1995; Heynekamp and others, 1999; Doughty, 

2003). Flow localized along one side of a fault zone is probably favored where faults form effective seals owing to the 

juxtaposition of lower permeability protoliths or cemented 

zones on opposite sides of the faults, or where continuous 

low-permeability (for example, clay) fault cores are present 

(for example, Maclay and Small, 1983; Knipe, 1993; Knipe 

and others, 1998; Knott, 1993; Gibson, 1994). Independent 

evidence that faults in the basin impede across-fault flow and 

control the patterns of regional ground-water flow is provided 

by interferometric synthetic aperture radar (InSAR) images of 

the central Albuquerque Basin area, which indicate differential land-surface subsidence and recovery across known faults 

in areas of ground-water pumping (Heywood and others, 

2002).

Cemented parts of fault zones in the study basins that 

once localized fluid flow are now zones of low permeability 

unless the cements themselves have developed new open 

fractures. Strong cementation of fault zones that have not 

undergone refracturing has shifted the regions of highest relative permeability away from cemented zones and probably laterally toward the outer damage zone or, in some cases, to the 

other side of the fault zone. The long, continuous cemented 

zones visible along many of the exposed faults in the study 

area suggest that the modern basin aquifers may be compartmentalized or baffled by cement fault seals along considerable 

(>10 km) strike distances. Such partitioned flow in the study 

basins is corroborated by hydraulic discontinuities and perturbed predevelopment directions of hydraulic gradient along 

or near strongly cemented faults (Bexfield and Anderholm, 

2000) (fig. 17). Multiple generations of veins and cemented 

fractures imply that some cement seals on faults were refractured episodically, probably under transient elevated tectonic 

stress or fluid pressure, which allowed renewed fluid flow 

within the cemented zones (for example, Sibson, 1990; Parry 

and others, 1991). Studies in crystalline rock have shown 

that faults that are critically stressed and optimally oriented 

for failure in an ambient stress field have the highest permeabilities owing to incipient fracturing adjacent to such faults 

(Barton and others, 1995; Hickman and others, 1997). Some 

cemented faults in the study basins may similarly be at critically stressed states and may be undergoing fracturing such 

that their cemented zones no longer form effective groundwater seals. Evaluation of such conditions along faults in the 

study basins is beyond the scope of this study.

Conclusions

In this study we systematically characterized physical,

structural, and cementation properties of many fault zones in 

the Albuquerque aquifer basins to infer hydrologic properties 

of the faults and thus evaluate their potential effect on present 

ground-water flow. A statistical evaluation of four broad categories of fault zone measurements and observations indicates 

that the dominant host lithology, especially sediment grain 

size and degree of induration, influences the width of fault 

zones and distribution of cement. To a lesser degree, lithology 

also influences the types of fractures that develop in damage zones. These controls are attributed to strength contrasts 
References Cited  25

associated with different ranges of grain size in protoliths and 

with different degrees of induration that accommodate faultrelated strain in various ways. Such lithologic controls are 

corroborated by a poor correlation between fault zone widths 

and fault displacement when the protolith is not taken into 

account but by an improved correlation when it is. Fault cores 

are mostly composed of sheared and foliated clay that locally 

contains variable amounts of entrained and sheared silt, sand, 

and gravel. Although mostly relatively thin, clay cores locally 

thicken in proximity to clay- and silt-rich protoliths. Even the 

thinnest clay cores probably form effective fault seals where 

they continue for long distances along strike, owing to their 

very low relative permeability. Opening-mode fractures are 

common in inner damage zones, especially within moderately 

indurated basin-fill sediments. Cementation patterns indicate 

that past fluid flow was concentrated along these fractures 

and, to a lesser degree, along shear fractures and deformation bands. Such fractures, where not cemented, may increase 

fault-parallel ground-water flow along inner damage zones. 

Cement was precipitated along fault zones with no consistent basinward, down-gradient preference. On the basis of 

observed asymmetrical distributions of fault zone cements, 

we infer that intrabasin, fault-parallel, fault-localized groundwater flow was, and may continue to be, common.

Results from this study provide new constraints for 

ground-water flow models of the Albuquerque composite basin. Faults are abundant in the study basins and have 

geometries, internal structures and compositions, and cement 

distributions that have imparted, and will continue to impart, 

pervasive heterogeneity to permeability within the basin 

aquifers. Thus, characterization of faults as simple, uniform 

hydrologic entities, as has been done in earlier flow models, 

is oversimplified. However, exact prediction of fault zone 

properties at depth in the aquifer basin may prove difficult. 

One approach is to assign statistical averages of fault zone 

properties keyed to lithologic intervals determined in subsurface stratigraphic studies. Certainly faults should be modeled 

as barriers to across-fault flow in areas of strong, continuous 

cementation such as exist in the northern part of the Santo 

Domingo Basin. Results from this study may be applicable 

to other faulted basin aquifers, especially extensional basins 

characterized by normal-slip fault zones.

Acknowledgments

The peoples of the Cochiti, Santo Domingo, San Felipe, 

Santa Ana, Zia, and Jemez Pueblos are acknowledged for 

graciously granting us access to their tribal lands. Without 

their openness and cooperative spirit this study would not 

have been possible. Gary Smith, Andrika Kuhle, Frank Pazzaglia, Dan Koning, and Karl Karlstrom of the University 

of New Mexico, Steve Cather of the New Mexico Bureau of 

Mines and Mineral Resources, and David Dethier of Williams 

College kindly provided us preliminary copies of their 

geologic maps and identified the locations of key fault zone 

exposures. Steve Sutley of the U.S. Geological Survey 

generously made many XRD analyses of fault zone samples. 

Our research greatly benefited from discussions with Laurel 

Goodwin and Mick Heynekamp of the New Mexico Institute 

of Mining and Technology, Bill Haneberg and John Hawley of 

the New Mexico Bureau of Mines and Mineral Resources, and 

Jonathan Caine, Tien Grauch, David Sawyer, and Jim Cole of 

the U.S. Geological Survey. This paper was greatly improved 

by the excellent reviews of Jonathan Caine and Chris Potter.

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Published in the Central Region, Denver, Colorado

Manuscript approved for publication December 2, 2005

Graphics by Scott A. Minor

Photocomposition by Norma J. Maes

Edited by Mary-Margaret Coates (Contractor, ATA Services)
Printed on recycled paper

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