Convergence, block rotation, and structural interference across

Geological Society of AmericaSpecial Paper 365

2002

279

Convergence, block rotation, and structural interferenceacross the Peninsular-Transverse Ranges boundary,

eastern Santa Monica Mountains, California

Andrew J. Meigs*Department of Geosciences, Oregon State University, Corvallis, Oregon 97331, USA

Michael E. Oskin*Division of Geological and Planetary Sciences, California Institute of Technology,

Pasadena, California 91125, USA

ABSTRACT

Active deformation in southern California occurs in two discrete structural prov-inces. To the south of �34�N latitude, the Peninsular Ranges structural province ischaracterized by northwest-trending strike-slip faulting, northwest motion of crustalblocks relative to stable North America, and negligible vertical-axis block rotation. Incontrast, the Transverse Ranges province to the north of �34�N latitude is charac-terized by west-trending oblique-slip faulting and a significant component of north-south crustal shortening contemporaneous with northwestward motion and vertical-axis block rotation relative to stable North America. A structurally complex transitionzone between N33�45� and N34�15� latitude defines the boundary separating these twoprovinces. Bedrock and geomorphic relationships in the eastern Santa Monica Moun-tains document the sequential development of part of this boundary region. At thelongitude of downtown Los Angeles, the Malibu Coast–Santa Monica–Hollywoodfault system and the Elysian Park fault systems have accommodated the bulk of thedifferential motion in the boundary zone between the two provinces over the last 2.5–5 m.y. Structural evolution of the boundary zone was dictated by the progressiveincrease in displacement and lateral propagation of each fault system, differentialvertical-axis rotation of the Transverse Ranges block relative to the Peninsular Rangesblock, and a decrease in the obliquity of convergence with time. This interactiontransferred a portion of the Elysian Park anticline, an anticline developed in associ-ation with the Elysian Park fault system, to the hanging wall of the Hollywood fault.Net slip across the boundary zone north of downtown Los Angeles is limited to 1.7–2.5 km of dip-slip, to 1.5 km of strike-slip, and 2.3–2.9 km of oblique-slip during thepast 2.5–5 m.y. These low values imply that the southern boundary of the TransverseRanges has remained largely coupled to the adjacent Peninsular Ranges structuralprovince during compression. Using a 5 Ma age for initiation of growth of the SantaMonica Mountains and Elysian Park anticlines enables minimum rates of 0.3–0.5 mm/yr, 0.3 mm/yr, and 0.5–0.6 mm/yr for the dip-slip, strike-slip, and oblique-slip com-ponents of motion, respectively. A 2.5 Ma age of initiation of the Elysian Park anticlinewould double these rates. A new tectonic model for the structural evolution of the

Meigs, A.J., and Oskin, M.E., 2002, Convergence, block rotation, and structural interference across the Peninsular-Transverse Ranges boundary, eastern SantaMonica Mountains, California, in Barth, A., ed., Contributions to Crustal Evolution of the Southwestern United States: Boulder, Colorado, Geological Societyof America Special Paper 365, p. 279–293.

*E-mail: [email protected]; [email protected]

A.J. Meigs and M.E. Oskin280

boundary zone based on the sequence of structural overprinting reconciles apparentlydiscrepant geologic, paleoseismic, and geodetic data, data suggesting that the bound-ary zone is dominated by long-term strike-slip, intermediate-term oblique-slip, andshort-term dip-slip displacement.

Peninsular Ranges

W. Transverse Ranges

Sierra Nevada

San Gabriel Mountains

Fig. 3

SJE

NI

PVSC

G

SA

SA

MSH

Pacific Ocean

Mojave block

36°

35°

34°

33°

116°117°118°119°120°121°36°

35°

34°

33°

Longitude

SMC

Figure 1. Generalized tectonic map of southern California (modified from Bourne et al., 1998; Hor-nafius et al., 1986; Jackson and Molnar, 1990). Principal crustal blocks include the Peninsular Rangesstructural province, western Transverse Ranges, San Gabriel Mountains, and the Sierra Nevada. Faultsare the Malibu Coast–Santa Monica–Hollywood (MSH), Sierra Madre–Cucamonga (SMC), San An-dreas (SA), San Jacinto (SJ), Elsinore (E), Newport–Inglewood (NI), Palos Verdes (PV), and SantaCruz Island (SC). The rotation of the western Transverse Ranges is indicated by the looping arrow.Note that the western portion of the Peninsular Ranges structural province includes the highly ex-tended Borderlands region, one of several tectonic and geologic differences between the eastern andwestern portions of this province (Crouch and Suppe, 1993; Wright, 1991). The Peninsular Rangesprovince is defined as a tectonic province dominated by northwest-trending strike-slip faulting. Figure3 is indicated by a box.

INTRODUCTION

Continental transcurrent plate boundaries are often char-acterized by diffuse zones of deformation within which the rela-tive motion between the plates is accommodated by dip- andstrike-slip fault displacement and vertical-axis block rotation(McKenzie and Jackson, 1983). Structural development ofsouthern California in the Neogene associated with Pacific-North America plate motion provides one of the best docu-mented examples of this mode of crustal deformation (e.g.,Hornafius et al., 1986; Jackson and Molnar, 1990; Luyendyk,1991; Molnar and Gipson, 1994). Major structures in southernCalifornia define two discrete provinces. To the south of �34�Nlatitude, the Peninsular Ranges province is characterized bynorthwest-trending strike-slip faulting, northwest motion ofcrustal blocks relative to stable North America, minor short-ening perpendicular to the strike of major faults, and negligiblevertical-axis block rotation (Bourne et al., 1998) (Fig. 1). Mo-

tion of the Peninsular Ranges relative to North America is to-ward the northwest (�320�) and the rate increases with distancewest from the southern San Andreas fault. In contrast, theTransverse Ranges province to the north of �34�N latitude ischaracterized by west-trending oblique-slip faulting and a sig-nificant component of north-south crustal shortening (Fig. 1)(Jackson and Molnar, 1990; Molnar and Gipson, 1994). Paleo-magnetic data demonstrate �90� clockwise rotation of theTransverse Ranges since the early Miocene (Fig. 2) (Hornafiuset al., 1986; Luyendyk, 1991; Terres and Luyendyk, 1985).Thus, the motion of the Transverse Ranges relative to stableNorth America is a combination of northwestward translationand vertical-axis block rotation (Fig. 2) (Hornafius et al., 1986;Ingersoll and Rumelhart, 1999; Luyendyk, 1991; Nicholson etal., 1994).

When relative plate motion is accommodated by a broadzone of shear that includes regions undergoing vertical-axisblock rotation, complex slip histories for faults within and

Convergence, block rotation, and structural interference 281

6 mm/yr

fp = 3

fn = 5.2

6 mm/yr

6 mm/yrfn = 5.8

fp = 1.5

fp/fn =0.6

fp/fn =0

fp/fn =0.25

500 km PR

SN

TRSAF

500 km

PR

SN

TRSAF

5 Ma

2.5 Ma

0 Ma

Plate configuration velocity space parallel/normal ratiofa

ult n

orm

al (

fn; m

m/y

r)

fault parallel (fp; mm/yr)

2.5 Ma5.0 Ma

7.25 Ma

0 2 4 6 8 10

0

2

4

6

8

10

assume 6 /My rotation rateassume steady plate direction/rateassume 6 mm/yr N-S TR-PR velocity

A.

B.

C.

D.

Figure 2. Model relating plate configu-ration and velocity to the ratio of fault-parallel (fp)-fault-normal (fn) motionon the Malibu Coast–Santa Monica–Hollywood fault system (plate configu-rations Nicholson et al., 1994). Snap-shots of the velocity and ratio are givenfor 5 Ma (A), 2.5 Ma (B), and the pres-ent (C). The Malibu Coast–Santa Mon-ica–Hollywood fault system is general-ized as a line to illustrate the fp-fn ratioin plan view changes systematically inthe face of steady block rotation (6�/m.y.) and plate motion (D). PR—Pen-insular Ranges; SAF—San Andreasfault; SN—Sierra Nevada, TR—Tran-verse Ranges.

bounding the rotated domain are likely (Wright, 1991). Simplegeometrical models demonstrate that the sense of displacementon block- and domain-bounding faults depends on the relativeplate-motion vector, rotation rate, sense of rotation (clockwiseor counterclockwise), and degree of coupling to the shear cou-ple boundary (Dickinson, 1995; Ingersoll and Rumelhart, 1999;Jackson and Molnar, 1990; Molnar and Gipson, 1994). More-over, rotation of both the blocks and their bounding faults isexplicitly required (McKenzie and Jackson, 1983; McKenzieand Jackson, 1986). Consequently, the ratio of dip- to strike-slip on block- and domain-bounding faults will vary as a func-tion of the orientation of faults with respect to the plate motionvector and depends on the extent to which the edge of the do-main is coupled to adjacent nonrotating domains and to theshear boundaries.

Geodetic data and slip vectors of earthquakes indicate thatinternal deformation of the Transverse Ranges is marked atpresent by a significant component of north-south shortening

and thickening (Argus et al., 1999; Jackson and Molnar, 1990;Molnar and Gipson, 1994), although the magnitude of that com-ponent of motion is unclear (Bawden et al., 2001). A compar-ison of rates of rotation from geodetic data with paleomagneticdata suggest that the rotation rate of the Transverse Ranges hasvaried little over the past 15 m.y. (6� � 2�/m.y.) (Molnar andGipson, 1994). Plate reconstructions indicate that both the di-rection and the rate of Pacific-North American motion havebeen steady over the past 7 m.y. (Atwater and Stock, 1998).Relatively constant rates of rotation of the Transverse Rangesand plate motion imply that the partitioning between dip- andstrike-slip displacement on faults within the boundary regionbetween the Transverse and Peninsular Ranges must havechanged systematically over the past 7 m.y. (Fig. 2).

The Malibu Coast–Santa Monica–Hollywood fault systemis part of a system of active folds and faults that define thesouthern structural boundary between the Transverse and Pen-insular Ranges provinces (Figs. 1 and 3) (Wright, 1991). Re-


7A

2 km

Figure 4CP Hollywood

Lake

101

101

134

134

5

XMt. Hollywood

X

GPa

SMa

BC

5

He

B.

7B

Hw

EPa

GPs

bpcp

10 km

He

LA basin

134

10

110

LA

405

101

R

VER

EPa

SMa

SMa

BC

SM

Hw

WBH

NIMC

GPa

Figure 3B

A.

Santa Monica Bay5 N

405

EBHaWa

SM

Map units

Mz. - Paleogene

Miocene volc.

Mz - pC crystallinerocks

Mid. to Upper Miocene

Pliocene - Quat.

Modern depositional plain

Outline of abandonedPleist. surface

freeway

contactsynclineanticline

faultreverse strike-slip

River

Map symbols

LCM

Figure 3. A: Geologic map of the eastern Santa Monica Mountains and Elysian Hills. B: Detailed map of the GriffithPark–Mount Hollywood region showing truncation of northwest trending structures by He and the loss of displacementon Hw into the core of SMa. Cross sections depicted in Figure 7 are indicated by the straight lines labeled 7a and 7b.Folds are the Elysian Park anticline (EPa), the Santa Monica Mountains anticline (SMa), the Griffith Park syncline-anticline pair (GPs, Gpa, respectively), the Wilshire arch (Wa), the Las Cienegas monocline (LCM), and the east BeverlyHills anticline (EBHa). Faults include the Benedict Canyon fault (BC), the Verdugo-Eagle Rock fault (VER), theRaymond fault (R), the individual segments of the Malibu Coast–Santa Monica–Hollywood fault system (Malibu Coastfault [MC], the Santa Monica fault [SM]), the Hollywood fault, western segment [Hw], the Hollywood fault, easternsegment [He]), the west Beverly Hills lineament (WBH), and the Newport–Inglewood fault (NI). The branch point ofHe and Hw is marked bp. The Camino Palmero paleoseismic site of Dolan et al. (1997, 2000) is marked cp. Freewaysare denoted by numbers and selected surface streets are denoted by name. LA marks the position of downtown LosAngeles. Modified from (Dibblee, 1989, 1991a, 1991b, 1992; Dolan and Sieh, 1992b; Dolan et al., 1997; Hoots, 1931;Hummon et al., 1994; Jennings and Strand, 1969; Lamar, 1970; Schneider et al., 1996).


gional tectonic reconstructions suggest that the long-term his-tory of the Malibu Coast–Santa Monica–Hollywood fault ischaracterized by left-lateral displacement from 15 to 60 kmsince early to late Miocene time (Lamar, 1970; Truex, 1976;Yeats, 1968; Yeats, 1976). Contrasting tectonic models of themid-Pliocene to late Quaternary displacement on the MalibuCoast–Santa Monica–Hollywood fault argue for negligible lat-eral motion of the Transverse Ranges relative to the PeninsularRanges (Wright, 1991) and for significant left-lateral motion(Walls et al., 1998).

To document the degree of coupling between the rotatingand nonrotating domains of southern California, we investigatethe Pliocene-Quaternary slip history of the Hollywood fault,which forms the eastern end of the Malibu Coast–SantaMonica–Hollywood fault system (Fig. 3). The hanging wall ofthe Hollywood fault is the eastern end of Santa Monica Moun-tains anticline, an east-trending fault-propagation fold (Davisand Namson, 1994). The footwall of the Hollywood fault is theElysian Park anticline, a northwest-trending fault-propagationfold developed in the boundary region between the Peninsularand Transverse Ranges provinces (Oskin et al., 2000). Transferof a portion of the Elysian Park anticline to the hanging wallof the Malibu Coast–Santa Monica–Hollywood fault system isargued from structural and map observations. On the basis ofthe structural chronology interpreted from these relationships,a new model for development of the two anticlines and the faultsystem in response to the differential motion of the TransverseRanges relative to the Peninsular Ranges is proposed. Bedrockgeologic relationships constrain net displacements of 1.5 � 0.2km of strike-slip and 1.7–2.5 km of dip slip on the Hollywoodfault during the past 2.5–5 m.y. Geomorphic observations arealso consistent with less than 1 km of left slip across the bound-ary zone during the Quaternary. Both data sets suggest that thesouthern boundary of the Transverse Ranges has remained rela-tively coupled to the adjacent Peninsular Ranges for at least thepast 2.5 m.y. Offsets of pre-Pliocene stratigraphic units used toargue for significant left slip across the boundary zone musthave developed prior to the current contractional regime. Themodel reconciles apparently discrepant geologic, paleoseismic,and geodetic data that suggest that the boundary zone is dom-inated by long-term strike-slip, intermediate-term oblique-slip,and short-term dip-slip displacement, respectively.

PRINCIPAL STRUCTURES IN THE TRANSVERSE-PENINSULAR RANGES BOUNDARY ZONE NEARDOWNTOWN LOS ANGELES

A semicontinuous fault system marks the southern bound-ary of the Transverse Ranges (Fig. 1) (Hornafius et al., 1986;Luyendyk, 1991). The Sierra Madre–Cucamonga fault systemdefines the southern boundary from �118�W longitude east tothe San Andreas fault (Terres and Luyendyk, 1985). To the westof �118�, the Malibu Coast–Santa Monica–Hollywood faultsystem comprises a series of individual fault segments that ex-

tend to the west, offshore into the Santa Barbara Channel (Hor-nafius et al., 1986; Luyendyk, 1991; Seeber and Sorlien, 2000).In detail, the boundary region west of �118� is a zone of dis-tributed deformation including oblique-slip reverse faults andassociated folds described collectively as the Santa MonicaMountains anticlinorium (Fig. 3). At the northern end of theLos Angeles basin, the Santa Monica Mountains anticlinoriumcomprises the Santa Monica Mountains anticline, the Wilshirearch, and the Santa Monica and Hollywood faults.

Several parallel, northwest-trending zones of transcurrentdeformation divide the Peninsular Ranges (Fig. 1). These zonesare deflected westward and become zones of oblique conver-gence as they approach the Transverse Ranges boundary. TheElysian Park anticlinorium comprises a series of uplifts thatextend northwest of the Elsinore fault trend to form the north-east edge of the Los Angeles basin (Fig. 3). The principal struc-tures of the Elysian Park anticlinorium near downtown Los An-geles are the Elysian Park anticline and the Las Cienegasmonocline (Davis et al., 1989; Davis and Namson, 1994; Dolanet al., 1995; Schneider et al., 1996; Wright, 1991). Considerableattention has focused on the Elysian Park anticlinorium becausethe 1987 Whittier Narrows earthquake likely occurred on theblind fault system at depth beneath the anticlinorium to thesoutheast of the study area (Allmendinger and Shaw, 2000;Davis et al., 1989; Hauksson and Jones, 1989; Lin and Stein,1989; Shaw and Shearer, 1999).

The Santa Monica Mountains anticlinorium and the Ely-sian Park anticlinorium converge in a structurally complex re-gion to the west and northwest of downtown Los Angeles inthe eastern Santa Monica Mountains and Elysian Hills (Fig. 3).Folds and faults in the eastern Santa Monica Mountains andElysian hills trend either east or northwest (Fig. 3A) (Dibblee,1991a, 1991b; Hoots, 1931). East-trending structures are theSanta Monica Mountains anticline and the Hollywood fault(east-northeast trending); the Hollywood fault coincides withthe sharp, linear topographic break and a discontinuous seriesof scarps that define the southern mountain front (Fig. 3B)(Dibblee, 1982, 1991a, 1991b; Dolan and Sieh, 1992b; Dolanet al., 1997; Hoots, 1931). Upper Mesozoic Santa Monica slateintruded by a suite of late Mesozoic plutons and unconformablyoverlain by the Miocene Topanga and Modelo formations areexposed in the core and on the flanks of the anticline. Growthstrata in the east Beverly Hills oil field indicate initial growthof the Santa Monica Mountains anticlinorium by ca. 5 Ma(Schneider et al., 1996; Tsutsumi et al., 2001; Wright, 1991).

Northwest-trending folds are crosscut by the Hollywoodfault. North of the Hollywood fault, in the easternmost SantaMonica Mountains, the Griffith Park anticline-syncline pair isexposed between Cahuenga Pass and the Los Angeles River(Fig. 3B). The Griffith Park anticline is defined by the trend ofa structural culmination, expressed at the surface by folded lateMesozoic granitic rocks unconformably overlain by the Mio-cene Topanga and Modelo Formations. The axis of the GriffithPark anticline plunges northwest. In detail, a series of low-


amplitude, short-wavelength folds are present across the crestof the culmination (Dibblee, 1982). Cahuenga Pass is a struc-tural low between the Griffith Park and Santa Monica Moun-tains anticlines, which coincides with the axis of the GriffithPark syncline. Middle Miocene strata (the Topanga Formation)are structurally and stratigraphically continuous between theSanta Monica and Griffith Park anticlines and lie unconform-ably on crystalline basement (Fig. 3) (Hoots, 1931). An acuteangle is formed between the two anticlines (Fig. 3).

The Elysian Park anticline is the principal bedrock structureto the south, in the footwall of the Hollywood fault (Fig. 3A).The anticline extends �20 km to the southeast from the pointwhere it intersects the eastern segment of the Hollywood fault inthe Elysian Hills (Fig. 3). A northwesterly trend characterizes theaxial trace of the fold. Numerous low-amplitude, short-wave-length folds, whose structural trends are subparallel to the pri-mary axis, characterize the surface expression of the fold (Lamar,1970; Oskin et al., 2000; Wright, 1991). Folded Middle to upperMiocene Puente Formation (equivalent to the Modelo Forma-tion), and younger strata are exposed at the surface (Lamar,1970). Along the crest of the Elysian Park anticline, Puente For-mation strata unconformably overlie basement rocks that are in-ferred to be the Santa Monica Slate (Lamar, 1970; Tsutsumi,1996; Tsutsumi et al., 2001; Wright, 1991). Puente Formationoverlies Topanga Formation on the limbs of the anticline (Daviset al., 1989; Wright, 1991). A disconformity at the base of Fer-nando Formation exposures in downtown Los Angeles may in-dicate initiation of development of the Elysian Park anticline(Soper and Grant, 1932). Development of the anticline ismarked stratigraphically by an angular unconformity developedbetween the Lower Fernando (Repetto) and Upper Fernando(Pico) Formations (Soper, 1943). Age estimates for the base ofthe Lower and Upper Fernando Formation are ca. 5 Ma and 2.5Ma, respectively (Blake, 1991). Active growth of the ElysianPark anticline is indicated by deformed Quaternary fluvial ter-races (Bullard and Lettis, 1993; Oskin et al., 2000).

Each of the principal structures in the eastern Santa MonicaMountains and Elysian Hills is apparently truncated by the Hol-lywood fault. Map relationships between the fault and bedrockstructures to the north, in the hanging wall, suggest that thefault consists of discrete western and eastern segments (Hw andHe, respectively; Fig. 3B). The western segment (Hw) trendsnortheast, is subparallel to the trend of the Santa Monica Moun-tains anticline, and apparently loses displacement eastward intothe core of the anticline (Fig. 3B). In contrast, the eastern seg-ment (He), which defines the easternmost 8 kilometers of themountain front, trends east-northeast and cuts the Griffith Parkanticline-syncline pair and the Elysian Park anticline at a highangle. Truncation of these folds by the He is implied by thelarge angle between the folds and fault, and the observation thatneither anticline has an obvious counterpart immediately acrossthe fault trace. Paleoseismic data indicate that the Hollywoodand the Santa Monica fault to the west are active (Fig. 3A)(Dolan and Pratt, 1997; Dolan et al., 1997, 2000a)

BEDROCK AND GEOMORPHIC CONSTRAINTSON HOLLYWOOD FAULT OFFSET

Eastern segment of the Hollywood fault

Net slip and slip sense for the Malibu Coast–SantaMonica–Hollywood fault system reflect successive episodes oftranstension and transpression accompanying the rotation of theTransverse Ranges in the Cenozoic (Ingersoll and Rumelhart,1999; Luyendyk, 1991). Post-Oligocene left-lateral offset onthe fault system of �60 km has been inferred from stratigraphicdata and from apparent offsets in pre-Cenozoic basement struc-ture (Lamar, 1970; Truex, 1976; Yeats, 1968; Yeats, 1976). Off-set of the Tarzana submarine fan (Redin, 1991) suggests 15–16km of left-lateral separation on the Malibu Coast–SantaMonica–Hollywood fault system since late Mohnian time (8–6.5 Ma) (Blake 1991). Quaternary slip sense and offset for thefault system are best constrained for the Malibu Coast segmentin the west (Fig. 3) (Birkeland, 1972; Dibblee, 1982; Dolan andSieh, 1992b; Dolan et al., 1995, 1997; Hoots, 1931; Johnson etal., 1996; McGill, 1989). In contrast, paleoseismologic datafrom the Santa Monica and Hollywood fault segments constrainonly the dip-slip component of displacement (Dolan and Pratt,1997; Dolan et al., 1997, 2000a).

Structural relationships in the eastern Santa Monica Moun-tains and Elysian hills contain information on the net fault-slipsense and magnitude on the eastern Hollywood fault segmentover the past 2.5–5 m.y. (the time scale of Santa Monica andElysian Park anticline growth). The apparent truncation of theElysian Park and Griffith Park anticlines at the eastern Holly-wood fault suggest that they may be the same fold offset acrossthe Hollywood fault. Each of the folds has a similar northwesttrend in map view, folds rocks of similar age, and forms anacute angle with the Santa Monica Mountains anticline (Fig.3). This correlation enables tentative use of the fold for esti-mation of the strike- and dip-slip components and rates of dis-placement since 5 or 2.5 Ma. To use the fold axis as a piercingpoint to estimate the dip-slip component of fault slip, three ob-servations are required: (1) the trend and plunge of the hingeline in the hanging wall and footwall of the fault (the line ofinflection between fold limbs at the crest of a fold defines thehinge line), (2) the depth or elevation of a hinge line from acommon structural or stratigraphic level in each piece of thefold, and (3) the fault dip angle. The hinge line defines thepiercing point, which when projected up or down plunge ontothe plane of the fault, allows the dip-slip component of dis-placement to be measured. Lateral separation is revealed bymap relationships (Fig. 3). Net slip can thus be determined fromindependent measures of each component of separation.

Left separation of the anticline along the eastern segmentof the Hollywood fault is �1.5 � 0.2 km, with the uncertaintya function of position of the axial trace of the anticline (Fig. 4and Table 1). A contact between the basement and Miocenevolcanic rocks is also offset across the fault in a left sense.


Figure 4. Constraints and offset valuesacross the Hw and He. Units and labelsdescriptions are given on Figure 3.

TABLE 1. SLIP AMOUNT AND RATE VERSUS FAULT ANGLE FOR He

Slip sense Slip(km)

Rate(mm/yr)*

Rate(mm/yr)*

Slip(km)

Rate(mm/yr)*

Rate(mm/yr)*

Slip(km)

Rate(mm/yr)*

Rate(mm/yr)*

Average slip(km)

Average rate(mm/yr)*

Average rate(mm/yr)*

Duration (m.y.) 5 2.5 5 2.5 5 2.5 5 2.5

400 m depth to basementFault angle 50 70 90Strike slip 1.5 0.3 0.6Dip slip 3.4 0.7 1.4 2.1 0.4 0.8 1.7 0.3 0.7 1.9 0.4 0.8Oblique slip 3.7 0.7 1.5 2.6 0.5 1.0 2.3 0.5 0.9 2.4 0.5 1.0

800 m depth to basementFault angle 50 70 90Strike slip 1.5 0.3 0.6Dip slip 4.0 0.8 1.6 2.5 0.5 1.0 2.1 0.4 0.8 2.3 0.5 0.9Oblique slip 4.3 0.9 1.7 2.9 0.6 1.2 2.6 0.5 1.0 2.7 0.5 1.1

Note: Fault angles are in degrees.*mm/yr � km/m.y.

Lateral separation measured from this contact at the groundsurface is less (850 m) than that of the fold axis. This differencemay be a function of partitioning of slip between the individualsplays comprising the eastern segment in detail (i.e., where the850-m offset reflects displacement across only the northernstrand of the eastern segment; Fig. 4).

The trend and plunge of the Griffith Park and Elysian Parkfold axes were determined via stereographic projection of thepole to the best-fitting great circle of poles to bedding attitudesfrom the Hollywood and Los Angeles geologic maps (28�,N65W, n � 108; 6�, N53W, n � 152, respectively; Fig. 5)(Dibblee, 1989, 1991b). Hollywood fault dip angle was esti-mated to be between 70� and 90� based on observed dip at thesurface and in the shallow subsurface (Dibblee, 1982, 1991b;Dolan and Sieh, 1992a; Dolan et al., 1997; Hoots, 1931; Lamar,1970; McGill, 1989). Elevation of the basement-cover contactin the Griffith Park anticline was determined in the field northof the fault (Dibblee, 1991b). Structural and stratigraphic datasuggest that the sediment-basement contact is at a depth of�400 to 800 m in the subsurface at the crest of the ElysianPark anticline in the Elysian Hills (Blake, 1991; Davis et al.,1989; Dibblee, 1982, 1989, 1991b; Division of Oil and Gas,1991; Hoots, 1931; Lamar, 1970; Wright, 1991; Yeats andBeall, 1991).

Dip-slip displacement estimated by projection of the hingeline at the basement-cover contact to its intersection with thefault plane is sensitive to plunge, fault dip, and depth and ele-vation of the contact in the footwall and hanging wall, respec-tively (Fig. 6 and Table 1). The minimum and maximum dis-placements, given a fault plane dip of 70� or 90� and footwalldepth to the basement-cover contact of �400 m, are then �1.7 and 2.1 km (Table 1), respectively. If the footwall depth tothe basement-cover contact is �800 m, then the minimum andmaximum displacement are � 2.1 and 2.5 km, respectively.The estimate of the dip slip component is higher for a moreshallowly dipping fault (50�; Table 1). Minimum (90� fault dip,�400 m depth), and maximum (70�, �800 m depth), leftoblique-slip derived from this analysis are 2.3 and 2.9 km (Ta-ble 1). Strike-slip displacement is thus roughly half the dip-slipdisplacement.

Linear projection of the hinge line of the Griffith Park anti-cline at the basement-cover contact to the Hollywood fault (Fig.6), introduces uncertainty that is difficult to quantify. The dif-ference in plunge between the Griffith Park anticline axis (28�)and the Elysian Park anticline axis (6�) is not accounted for inour estimation. Factors that may contribute to the difference inplunge across the Hollywood fault include (1) the fault geom-etry at depth (i.e., whether it is curviplanar (concave-up) or


Figure 5. Equal area stereonet plot ofpoles to bedding and the best-fit greatcircle for the Elysian Park and GriffithPark anticlines.

Figure 6. Estimates of dip-slip fault dis-placement across He. Paleoseismologicand geologic data suggest that the dip ofthe He ranges from 70� to 90� (Dibblee,1982, 1991a, 1991b; Dolan and Sieh,1992b; Dolan et al., 1997; Hoots, 1931).The hinge line used to measure offset istaken at the structural level of the base-ment/cover contact. Uncertainty in dip-slip displacement is discussed in thetext. White circles mark offset on the 70�fault plane, black circles mark offset onthe 90� plane. The 50� fault dip gives thehighest values for dip-slip displacementand displacement rate (Table 1), but isinconsistent with published data.

9050 70

0

-2

-4

2

4

kilo

met

ers

v = h

intersection ofGriffith Parkanticline axis

(28 plunge)w/He

1.7 km2.1 km

NW (294 ) SE (118 )

approximate topography

Separation on 70 faultSeparation on 90 fault

2.1 km

2.5 km

consists of multiple planar segments of varying dip), (2) thepossible noncylindrical nature of the Elysian Park fold, and(3) tilting of Topanga strata prior to folding. Displacementacross a fault characterized by multiple planar fault segmentswith variable dip or by a curviplanar, listric geometry will resultin progressive tilting and rotation of the hanging wall aboutsubhorizontal axes (Medwedeff and Suppe, 1997; Seeber andSorlien, 2000). Variable dip of the Hollywood fault at depth isconsistent with the interpretation that the Malibu Coast–SantaMonica–Hollywood fault system is listric farther west (Seeberand Sorlien, 2000), and with interpretations that the fault is asplay off a blind thrust underlying the Santa Monica Mountainsanticlinorium (Davis and Namson, 1994; Davis et al., 1996).An originally noncylindrical fold implies that high displace-ment gradients on the underlying blind Elysian Park fault have

existed during fold growth, or that the hinge lines are curvi-linear or irregular. Folding in this area involves basement rockswith significant preexisting structural relief and complexity(Davis et al., 1989, 1991a, 1991b; Wright, 1991), which impliesthat the cylindrical-fold assumption may be an oversimplifica-tion. Evidence for an earlier period of tilting of Topanga-agestrata is indicated by deposition of Puente or Modelo directlyon basement on the east side of the Griffith Park anticline(Dibblee, 1989). In each of these cases, linear projection of thehinge line represents a minimum estimate of the dip-slip com-ponent of displacement, depending on the dip of the fault andthe extent of overthrusting by the hanging wall.

Left slip on the eastern Hollywood fault can also be seenin a pair of offset bedrock stream channels (Fig. 4). A three-reach drainage basin south of Mount Hollywood coalesces into


a single channel at the fault. A second, smaller catchment liesto the east of the adjacent larger catchment. To the south andeast across the fault, two beheaded stream channels cross theElysian Hills. The extent of dissection and development ofthese channels suggests that they formed in association with acatchment larger than any available within the Elysian Hills.The pairs of streams on each side of the fault have parallelcourses and each pair is separated by an interfluve developedin crystalline rock. It seems probable that the stream pairs rep-resent the same streams offset in a left sense by the easternsegment of the Hollywood fault. A strike-slip displacement of575 � 75 m is indicated from measurement of valley walls ofeach channel and the centerline of the interfluve. To the west,a third channel developed along the contact between crystallinebasement and overlying volcanic rocks is offset in a consistentsense and amount across the fault (850 m; Fig. 4).

A topographic scarp reflecting the dip-slip component oflate Quaternary fault slip is partially developed on the southernflank of the eastern Santa Monica Mountains. An �90-m-hightopographic ramp that parallels the eastern segment of the Hol-lywood fault is inferred to be a fault scarp (Dolan et al., 1997).Shallow subsurface geologic data from this scarp reveal jux-taposition of hanging-wall basement rocks over upper Quater-nary footwall strata (Dolan et al., 1997). Elsewhere along themountain front, youthful fault scarps are not well preserved,although topographic relief of the range front exceeds 600 m.Erosion rates in the Santa Monica Mountains have been esti-mated to be �0.5 mm/yr (Meigs et al., 1999). If uplift rates arecomparable to erosion rates, then late Quaternary scarps gen-erated during individual earthquakes may have been removedby erosion between events.

In order to translate estimates of slip magnitude into esti-mates of slip rate, age constraints on the displacements must beestablished. Data that constrain directly the age of any portionof the Malibu Coast–Santa Monica–Hollywood fault systemhave not been identified (Dibblee, 1982; Dolan et al., 1997;Hoots, 1931; Lamar, 1970; Wright, 1991; Yeats, 1968; Yeats,1976; Yeats and Beall, 1991). Several indirect age estimatessuggest a long history of left slip on the fault system. More than60 km of post-Oligocene left slip across the boundary regionbetween the Peninsular and Transverse Ranges provinces hasbeen inferred (Lamar, 1970; Truex, 1976; Yeats, 1968; Yeats,1976), although the constraints on total offset are not well es-tablished. Correlation of basement rock types and Paleoceneredbeds exposed in the Santa Monica Mountains, the PuenteHills, and the Santa Ana Mountains suggests 26–40 km leftlateral displacement since the early Miocene (Tsutsumi, 1996).This slip was probably distributed across the boundary regionbecause no single fault or fault system can account for total theinferred offset (Tsutsumi, 1996). Much of the left slip may haveaccompanied the period of block rotation between 18 and 12Ma (Ingersoll and Rumelhart, 1999). Estimates of offset of thelate Miocene Tarzana fan by 15–16 km across the MalibuCoast–Santa Monica–Hollywood fault system are made on the

basis of correlation of facies in the Modelo Formation in theSanta Monica Mountains with facies in the Puente Formationexposed in the Elysian Park anticline (Redin, 1991; Sullwold,1960). This correlation provides the best published evidencefor significant left slip of the Hollywood fault since late Mio-cene time. If the Griffith Park and Elysian Park anticlines arecorrelative, then the magnitude and timing of displacementalong the Hollywood fault synchronous with or occurring afterformation of these two folds can be established (i.e., Plioceneto Holocene time). The age of the folds, therefore, brackets aninterval of time over which slip accumulated and allows thelong-term slip rate to be estimated.

Age of the Griffith Park anticline cannot be determineddirectly because no growth strata are preserved on the limbs ofthe fold. The youngest rocks exposed on the limbs of the anti-cline are Modelo Formation exposed on the southeastern limb(Fig. 3), although the contact with the basement has beenmapped as both a depositional contact and a fault (Dibblee,1991b; Hoots, 1931). Topanga strata are structurally continuousacross a syncline (the Griffith Park syncline), formed betweenthe Griffith Park and Santa Monica Mountains anticlines (Fig.3). Thus, the age of the Griffith Park syncline, and by inference,the age of the anticline, are equivalent to the Santa MonicaMountains anticline. Growth strata and fault-stratal crosscuttingrelationships indicate initial contractional growth of the SantaMonica Mountains anticlinorium by 5 Ma, possibly as early asca. 6 Ma (Schneider et al., 1996; Tsutsumi et al., 2001; Wright,1991). Initiation of growth of the Elysian Park anticlinoriumoccurred during deposition of the Lower Fernando (Repetto)Formation (5–2.5 Ma) (Schneider et al., 1996; Soper and Grant,1932; Wright, 1991). When these age relationships are com-bined with the crosscutting relationship between the Hollywoodfault and hanging-wall and footwall folds, 2.5–5 Ma is a rea-sonable maximum age for offset of folds across the fault. If theoffsets are younger, then fault displacement rate would begreater by a factor of 2 (Table 1).

Combining the net dip-, strike-, and oblique-slip and a5 Ma maximum age for the eastern Hollywood fault allows theaverage slip rate over the past 2.5–5 m.y. to be calculated (Table1). Minimum and maximum dip-slip displacement rates, givenuncertainties discussed above, are 0.3 and 0.5 mm/yr, respec-tively. These end members are calculated for a fault dip of 90�and �400 m depth to the basement-cover contact at the crestof the Elysian Park anticline (minimum) and a fault dip of 70�and �800 m depth (maximum). Strike-slip displacement rateis 0.3–0.6 mm/yr. Combined, these bracket the oblique-slip rateto between 0.5 and 0.6 mm/yr. Because the amount of strike-slip is reasonably well constrained, uncertainty in the oblique-slip reflects primarily the large uncertainty in dip-slip and ageof initiation of fold growth. The rates are higher for shallowerfault dip angles and for younger ages of initiation (50�, 2.5 Ma,respectively; Table 1). If correct, then the strike-slip displace-ment rate indicates that the stream network in the eastern SantaMonica Mountains developed in the early Pleistocene (offset *


Figure 7. Fault-parallel serial cross sec-tions depicting bedrock structure to thenorth-northeast (A) and south-southeast(B) of Hw. Dip data are from unpub-lished field observations and publishedmaps (Dibblee, 1982, 1991a, 1991b;Hoots, 1931; Lamar, 1970). C: The topof the Miocene volcanic sequence ex-tracted from hanging-wall section A(thick, gray line) and footwall section B(thick, black line) to illustrate the sepa-ration across and uplift on the Hw.

-1200

400

0

-400

-800

400

0

-400

-800

-1200

met

ers

55 55 23 49 40 2610

33 34 4057

SSW

1 km

meters

4657

5364 36

25 3623 33 15

WSW SSE

B.

A.

SMa

Uplift syncline base: 0.390 km

top Miocene volcanic sequencefootwall Hw (section A)

hanging wall Hw (section B)

Lateral separation:Topanga/volcanic syncline axis contact: 1.5 km 0.365 km

C.

SMa GPa

GPa

NNW

average rate�1 � �0.575 km * (0.3–0.6 km/m.y.)�1 � 1.0–1.9 Ma). Independent age determination for formation of thedrainages would independently bracket displacement rate onthe eastern Hollywood fault.

Western segment of the Hollywood fault

In contrast to the eastern segment, bedrock contacts andstructure across the eastern end of the western segment ofthe Hollywood fault exhibit right separation (Figs. 3 and 4).The magnitude of that separation decreases eastward from thebranch point of the eastern and western segments (point bp,Fig. 3B). A contact between Miocene volcanic rocks and over-lying sedimentary strata is separated by �1450 m (Figs. 4 and7). To the east, separation of �365 m is suggested by the offsetof the Griffith Park synclinal axis across the fault. Stratigraphicseparation across the fault appears to decrease toward zerowithin Miocene strata to the east of the intersection of the faultand the Griffith Park syncline. Upper Pleistocene-Holocenesoils cut by the Hollywood fault show a similar right sense,although with a normal dip-slip component, across the western

segment (Dolan et al., 1997, 2000b). Cross sections parallel tothe fault point to �400 m of hanging-wall uplift of the base ofthe Griffith Park syncline relative to the footwall near the east-ern end of the western segment (Fig. 7).

Existing paleoseismologic data document a large dip-slipcomponent of displacement on the western Hollywood fault(Dolan et al., 1997, 2000b). However, evidence of lateral mo-tion is equivocal. North-side-down normal faulting revealed lo-cally in excavations across the fault is the principal observationused to argue for lateral displacement (point cp, Fig. 3B). Atthe same excavation, right separation of a soil horizon (Dolanet al., 1997) provides support for the inferred lateral displace-ment. In an attempt to reconcile these observations with datasuggesting large left slip regionally (Redin, 1991; Truex, 1976;Yeats, 1968; Yeats, 1976), normal faulting and right separationwere attributed to releasing bends at minor northeast-trendingsteps along the surface trace of the fault (Dolan et al., 1997).

Bedrock relationships, in contrast, show right separationon the western segment of the Hollywood fault that decreasessystematically eastward toward the end of the fault (Fig. 3B).Other systematic changes to the east include diminishing ver-


SMa

SM

WBHEBHa

WaHw

N

B. 2.5 Ma

SMa..?EBHa

N

SMa

EPa

SMEBHa Wa

WBH

Hw

He

C. 500 Ka

N

SMa

EPa

EPa

SM EBHa WaWBH

Hw

He

D. Present

N

A. 5.0 Ma

EPaEPa

EPa

Figure 8. Proposed model for the development of the northern margin of the Los Angeles basin at 5 Ma (A), 2.5 Ma(B), 500 Ka (C), and the present (D). Active structures are black, whereas inactive and/or final positions of structuresare grayed. Structures include the Santa Monica Mountains anticline (SMa), the east Beverly Hills anticline (EBHa),the Wilshire Arch (Wa), the Elysian Park anticline (EPa), the Santa Monica fault (SM), the west Beverly Hills lineament(WBH), and the western and eastern segments of the Hollywood fault (Hw, He, respectively). Paleomagnetic and geodeticdata indicate that the hanging wall of the Hollywood fault has rotated �30� since 5 Ma, whereas no such data areavailable for the EPa (see text for discussion). Consequently, the trend of the EPa is held fixed in its present orientation.

tical separation across the fault and the eastward plunge andconcomitant decrease in structural and topographic relief of theSanta Monica Mountains anticline (Fig. 3). Together, these ob-servations suggest that dip-slip motion on the western Holly-wood fault has been accompanied by folding of the hangingwall and that a large displacement gradient exists along theeasternmost 2.5 km of the fault (0.6 km/km). The right sepa-ration likely reflects dip-slip motion accompanied by eastwardfault-tip propagation. Thus, right slip inferred for the westernsegment and left slip across the eastern segment of the Holly-wood fault are not exclusive.

5 MA TO HOLOCENE INTERACTION BETWEENTHE SANTA MONICA AND ELYSIAN PARKANTICLINES

A map-view model for the development of a portion of theboundary region between the Transverse and Peninsular Rangesprovinces is proposed in order to synthesize our preferred in-terpretation of the interactions among the Santa Monica Moun-tains anticline, the Hollywood fault, and the Elysian Park anti-cline (Fig. 8). Present north is the frame of reference for themodel, which depicts the evolution of the boundary region overthe past five million years. A steady 6�/m.y. rotation rate of theboundary region is assumed (Molnar and Gipson, 1994). Struc-

tures depicted at 5 Ma are rotated 30� counterclockwise fromtheir present position. Rotation of the Santa Monica Mountainsis well constrained by paleomagnetic data (Hornafius et al.,1986). Intermediate stages at 2.5 and 0.5 Ma are presented toschematically illustrate the sequential development of the prin-cipal structures. Their temporal development is unconstrainedat the scale of these time steps, but the stages are included toprovide a sense of the structural orientation and developmentas the boundary zone evolved.

Growth of the Elysian Park and Santa Monica Mountainsanticlines began at ca. 5 Ma and resulted in the creation ofbathymetric highs that affected sediment dispersal patterns onthe northern margin of the Los Angeles basin (Fig. 8A) (Blake,1991; Schneider et al., 1996; Wright, 1991; Yeats and Beall,1991). The east Beverly Hills anticline and Wilshire arch com-prise the Santa Monica Mountains anticlinorium structural high(Figs. 8A and B) (Meigs et al., 1999). Along-strike propagationof each anticline is inferred to have accompanied increasingdisplacement on associated faults. Isolation of the Santa MonicaMountains anticline from the east Beverly Hills anticline andWilshire arch between 2.5 and 0.5 Ma is loosely constrainedby the inferred development of the Hollywood basin in the foot-wall of the Hollywood fault by 1 Ma (Fig. 8B) (Hummon etal., 1994).

Structural interference has resulted from eastward propa-


gation of the Santa Monica Mountains anticline toward thenorthwestward-propagating Elysian Park anticline. We inferthat the Hollywood fault was reactivated as a response to theinteraction due to lateral propagation of the anticlines (Fig. 8Band C). The �1.7–2.5 km of reverse slip on the Hollywoodfault is one consequence of that interference (Fig. 6 and Table1). Transfer of a portion of the Elysian Park anticline (the Grif-fith Park anticline), to the hanging wall of the Hollywood faultresulted from fault truncation of the northwestern end of theanticline. In this manner, the Hollywood fault acted as a trans-form fault that accommodated differential motion between thetwo structures. Eastward propagation of the south-vergent SantaMonica Mountains anticline into the southwest-vergent, north-west-propagating Elysian Park anticline should have resultedin right-lateral offset of the Elysian Park axis, similar to thedisplacement observed for the eastern tip of the western seg-ment of the Hollywood fault. However, simultaneous clockwiserotation of the Santa Monica Mountains resulted in net left slipacross the Hollywood fault. This interpretation assumes that thetwo anticlines overlapped structurally prior to truncation of theElysian Park anticline by the Hollywood fault (Fig. 8B and C).

DISCUSSION

Correlation of the Griffith Park and Elysian Park anticlinesis the key interpretation that allows the net displacement on theHollywood fault to be estimated (Fig. 4 and Table 1) and theevolutionary model to be constructed. These folds involve base-ment and cover rocks that record a complex tectonic historythat predates the time frame of this analysis. Thus, althougheach fold involves rocks of generally similar age, our interpre-tation rests on the observation that the two anticlines have simi-lar northwest trends (Figs. 3 and 5). Linking the two folds onthe basis of structural trend alone has an associated uncertainty.This uncertainty is unavoidable when crosscutting structuralfeatures are the sole basis of correlation. However, the north-west trend of these folds is clearly different from the east-trending Santa Monica Mountains anticline. The difference intrend, coupled with the observation that both the Elysian Parkand Griffith Park anticlines are truncated at a high angle by theHollywood fault, favors the inference that the Elysian Park andGriffith Park anticlines are correlative structures. Moreover,neither fold is related to the Santa Monica Mountains anticline.Unfortunately, growth strata that would establish the age of theGriffith Park anticline are not preserved. Determining whetherthe Elysian Park and Griffith Park anticlines grew over the sametime period would provide a key test of the hypothesis that theyare correlative.

Alternative models to that proposed in this study include:(1) That the Griffith Park anticline is an older structure unre-lated to the Elysian Park anticline and has been passively up-lifted by formation of the Santa Monica Mountains anticlineand displacement on the Hollywood fault; or (2) That the Ely-sian Park and Griffith anticlines formed contemporaneously, but

independently. Variations on alternative (2) include (a) that theGriffith Park anticline formed farther east than the present Ely-sian Park anticline (implying a larger Pliocene to Holocene lat-eral displacement than reported in Table 1), (b) that the GriffithPark anticline formed between the present position of the Ely-sian Park and the Griffith Park anticlines (implying a smallerPliocene to Holocene lateral displacement than reported in Ta-ble 1), or (c) that the Griffith Park and Elysian Park anticlinesare � 2.5 m.y. If (b) is more likely, then the upper estimate forslip and slip rate (2.9 km, 0.6 mm/yr) represent the maximumpost-Pliocene rate. If (a) or (c) are more likely, then the sliprates are even higher than the maximum rates reported in Table1. Although none of these alternatives can be ruled-out defini-tively, the �16 km offset of the Tarzana fan across the Holly-wood fault after 8 Ma (Redin, 1991; Wright, 1991), implies alateral slip rate of �2 mm/yr, higher than our rate, which isconsistent with either alternatives (a) or (c). Establishing theage of the channels offset across the Hollywood fault wouldprovide a test of these alternatives because the age would formthe basis of a rate estimate at a different time scale than thesestructural and stratigraphic constraints.

Steady rotation of the Transverse Ranges relative to thePeninsular Ranges requires that the ratio of dip to strike slip onthe Hollywood and other faults within the boundary regionchanged with time (Fig. 2). If the boundary between the Trans-verse and Peninsular Ranges provinces is depicted as a line,then the relative proportion of boundary-parallel versusboundary-normal motion can be estimated. Because the Trans-verse Ranges are presently east-west trending, the ratio ofboundary-parallel to -normal motion is predicted to be rela-tively small (Figs. 2C and D) (Argus et al., 1999; Jackson andMolnar, 1990; Molnar and Gipson, 1994). Restoration of theTransverse Ranges to their 5 Ma position and orientation (Nich-olson et al., 1994), rotates the boundary counterclockwise �30�and suggests an initial boundary-parallel to boundary-normalratio of 0.6 (Fig. 2A). Thus, this ratio would systematicallydecrease from 0.6–0 between 5 and 0 Ma as a function of therotation rate and fault orientation (Fig. 2D). The ratio is insen-sitive to the absolute magnitude of the displacements, whichdepends on the rate and direction of the velocity vector of theTransverse Ranges relative to the Peninsular Ranges. Bedrockoffsets presented here indicate that the ratio of parallel to nor-mal motion on the Hollywood fault is �0.5 or that dip-slipmotion has been greater than the strike-slip motion over thepast 2.5–5 m.y., consistent with the kinematic model. Availabledata lack sufficient temporal resolution to determine whetherthe sense of slip has changed systematically through time. How-ever, a changing ratio of strike to dip slip is consistent withavailable data if the drainage network offset laterally across theeastern segment is relatively old (Fig. 4), and if late Quaternaryslip is dominated by dip-slip displacement, as indicated by pa-leoseismologic data (Dolan et al., 1997, 2000b).

Long-term slip rates compare favorably with paleoseis-mologic and other data, which suggests that the Quaternary dip-


slip rate ranges from 0.25 to 0.4 mm/yr and that the strike-sliprate is probably similar (Dolan et al., 1997). Because of uncer-tainties in the slip estimates based on bedrock offsets, it is notpossible to determine whether the factor of 2–4 differences be-tween rates calculated from paleoseismologic and bedrock con-straints is significant (Table 1). Regardless, these low rates areconsistent with the inference that the Hollywood fault is char-acterized by long earthquake recurrence intervals (Dolan et al.,1997, 2000b). The dip-slip rate is consistent with the 0.6 mm/yr minimum rate estimated from deformed geomorphic surfacesto the west on the Santa Monica fault (Fig. 3) (Dolan et al.,2000a; Johnson et al., 1996). A low dip-slip rate for the Hol-lywood fault suggests that 3–4 mm/yr slip rates inferred fromcrustal cross sections of the blind thrust at depth beneath theSanta Monica Mountains (Davis et al., 1989; Davis and Nam-son, 1994) are too high by an order of magnitude (Dolan et al.,2000a; Johnson et al., 1996; Meigs et al., 1999). Moreover,these results are consistent with an emerging picture of rela-tively slow crestal uplift and dip-slip rates on blind faults andassociated folds in the northern Los Angeles basin (Meigs etal., 1999; Oskin et al., 2000; Schneider et al., 1996).

The limited left slip across the Hollywood fault indicatedby correlation of the Griffith Park and Elysian Park anticlinesimplies that the Transverse Ranges has remained relatively cou-pled to the Peninsular Ranges at the longitude of downtownLos Angeles since at least 2.5 Ma. If significant late Quaternaryleft slip has occurred on the boundary fault system (Walls etal., 1998), that motion must have occurred on faults other thanthe Hollywood fault. Alternatively, significant left slip mayhave occurred along the southern boundary of the TransverseRanges prior to 2.5–5 Ma.

CONCLUSIONS

Bedrock and geomorphic offsets in the eastern Santa Mon-ica Mountains and Elysian Hills provide the first suggestion ofthe magnitude of Pliocene and lateral left slip along the Hol-lywood fault. Displacement across the fault is most clearly doc-umented across its eastern segment, where the Elysian Parkanticline may be truncated by the fault, resulting in transfer ofa portion of the fold to the hanging wall. This key relationshipsuggests that the structural evolution of the boundary regioninvolved structural interference between the Elysian Park andSanta Monica Mountains anticlines as they propagated towardeach other. The Hollywood fault appears to have simulta-neously accommodated shortening and left-lateral differentialmotion across the boundary zone. The proposed truncation ofthe Elysian Park anticline by the Hollywood fault is also thekey relationship that enables the net dip-slip of 1.7–2.5 km,strike-slip of 1.5 km, and oblique slip of 2.3–2.9 km to bedetermined from bedrock relationships. Smaller left slip (575–850 m) is marked by stream channels beveled into the evolvingstructures. A strike-slip to dip-slip ratio of �0.5 implies greaterdip-slip than strike-slip motion since formation of the two an-

ticlines. Using a 5 Ma age for initiation of the Santa MonicaMountains and Elysian Park anticlines enables minimum ratesof 0.3–0.5 mm/yr, 0.3 mm/yr, and 0.5–0.6 mm/yr for the dip-slip, strike-slip, and oblique-slip components, respectively. Us-ing a 2.5 Ma age for initiation of the Elysian Park anticlinedoubles these rates. Slip-rate estimates presented here are con-sistent with rates determined using geomorphologic and paleo-seismologic data, and support characterization of oblique-slipfold-fault pairs in the northern Los Angeles basin as having lowfault slip-rates, low crestal uplift rates, and long recurrence in-tervals between major earthquakes. The low rate of strike-slipon the Hollywood fault is inconsistent with proposed significantlate Quaternary left slip on the southern boundary of the Trans-verse Ranges.

ACKNOWLEDGMENTS

Ramon Arrowsmith, Ray Ingersoll, Karl Mueller, Bob Yeats,and Doug Yule provided helpful, detailed reviews of this manu-script that helped to clarify and strengthen our arguments. KerrySieh, Jim Dolan, and Chris Sorlien are thanked for discussions.A.J.M. was supported by a Division of Geological and Plane-tary Sciences, California Institute of Technology PostdoctoralFellowship, a Southern California Earthquake Center Postdoc-toral Fellowship. This research was supported by the SouthernCalifornia Earthquake Center and grants from the NASA To-pography and Surface Change program to D. Burbank (NASA(NAG-5–2191), NASA (NAG-5–7646)). Stereonet programprovided by Rick Allmendinger. SCEC is funded by NSF Co-operative Agreement EAR-8920136 and USGS CooperativeAgreements 14-08-0001-A0899 and 1434-HQ-97AG01718.This is Southern California Earthquake Center paper 410.

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