Slip Rate Studies Along the Sierra Madre-Cucamonga Fault System Using Geomorphic and 10Be Cosmogenic

Surface Exposure Age Constraints

Active Faults in the Los Angeles Active Faults in the Los Angeles RegionRegion

Geodetic vs Geologic RatesGeodetic vs Geologic Rates

Geodetic (GPS) shortening rates Geodetic (GPS) shortening rates ~6 mm/yr between JPL and USC (Argus et al., ~6 mm/yr between JPL and USC (Argus et al.,

1999)1999) How much slip on Sierra Madre fault system?How much slip on Sierra Madre fault system? What is the magnitude of strain, and how is What is the magnitude of strain, and how is

strain partitioned across the L.A. basin?strain partitioned across the L.A. basin? Two competing modelsTwo competing models

Crustal escape model (Walls et al., 1998)Crustal escape model (Walls et al., 1998) Crustal thickening model (Argus et al., 1999; Crustal thickening model (Argus et al., 1999;

Bawden 2001)Bawden 2001)

Previous Slip Rate StudiesPrevious Slip Rate Studies

Escape Tectonics vs Crustal ThickeningEscape Tectonics vs Crustal Thickening > 50% of N-S contraction is > 50% of N-S contraction is

accommodated by E-W accommodated by E-W extensionextension

N-S contraction rates 7-9 mm/yrN-S contraction rates 7-9 mm/yr E-W extension rates ~6 mm/yrE-W extension rates ~6 mm/yr Does not consider viscoelastic Does not consider viscoelastic

effects of the SAF and SJFeffects of the SAF and SJF

Walls et al. (1998)Walls et al. (1998) Argus et al. (1999)Argus et al. (1999) N-S contraction is almost entirely N-S contraction is almost entirely

accommodated by crustal thickeningaccommodated by crustal thickening N-S contraction rates 5.8 ± 1.9 mm/yrN-S contraction rates 5.8 ± 1.9 mm/yr E-W extension 0-2 mm/yrE-W extension 0-2 mm/yr Removes viscoelastic effects of the Removes viscoelastic effects of the

SAF and SJFSAF and SJF

Two Study AreasTwo Study Areas

Tectonic Geomorphic Analysis and Tectonic Geomorphic Analysis and MappingMapping

Fault scarps, fluvial terraces and fan Fault scarps, fluvial terraces and fan surfaces were identified and mapped using surfaces were identified and mapped using aerial photography and digital topography.aerial photography and digital topography.

Measuring Uplift of Geomorphic Measuring Uplift of Geomorphic SurfacesSurfaces

Construct topographic profiles across Construct topographic profiles across

surfaces and fault scarpssurfaces and fault scarps Total station surveysTotal station surveys 5-20 ft contour maps5-20 ft contour maps

Measure vertical separation (uplift) of Measure vertical separation (uplift) of

surfacessurfaces

Uplift, Shortening, and Dip-Slip Uplift, Shortening, and Dip-Slip RatesRates

Formation of Uplifted and Formation of Uplifted and Abandoned Fluvial Terrace Abandoned Fluvial Terrace

SurfacesSurfaces

Cosmogenic Nuclide FormationCosmogenic Nuclide Formation Cosmic rays consisting of neutrons, Cosmic rays consisting of neutrons,

protons and muons strike and penetrate protons and muons strike and penetrate rocks at the earths surface.rocks at the earths surface. The cosmic rays interact The cosmic rays interact

with Si and O in quartz to with Si and O in quartz to

produce produce 1010Be and Be and 2626Al Al

nuclides.nuclides.

Cosmogenic Surface Exposure Cosmogenic Surface Exposure AgesAges

Western Sierra Madre Fault Western Sierra Madre Fault SystemSystem

Pacoima Wash TerracesPacoima Wash Terraces

Abandoned terracesAbandoned terraces Q1-Q6Q1-Q6

1971 rupture1971 rupture Three older fault scarpsThree older fault scarps Qt4 surfaceQt4 surface

Moderately preservedModerately preserved Fine-course gravel with Fine-course gravel with

discontinuous overbank discontinuous overbank deposits and 20-30 cm deposits and 20-30 cm soil development [seems soil development [seems thin]thin]

Agricultural modificationAgricultural modification

Qt4 Surface ProfileQt4 Surface Profile Total vertical separation of Qt4 surface Total vertical separation of Qt4 surface

across 3 fault sacross 3 fault scarps = 27 carps = 27 ± 2 m± 2 m

View of Qt4 SurfaceView of Qt4 Surface

Sampling of Qt4 SurfaceSampling of Qt4 Surface

Processed 5 individual subsurface samplesProcessed 5 individual subsurface samples

Surveyed site for Surveyed site for

suitable samplessuitable samples Collected 3 initial Collected 3 initial

samples in depth samples in depth profileprofile

Subsurface depths:Subsurface depths: PW-1 = 1.09 mPW-1 = 1.09 m PW-2 = 0.70 mPW-2 = 0.70 m PW-3 = 0.33 mPW-3 = 0.33 m

Qt4 Model Surface agesQt4 Model Surface ages

Depth Corrected Ages

Sample ID

10Be model age

PW-1 33,239 ± 1564

PW-2 31,196 ± 1287

PW-3 31,024 ± 1073

PW-B 69,825 ± 3055

PW-C 64,720 ± 2143

Results - Qt4 SurfaceResults - Qt4 Surface Total uplift = 27 Total uplift = 27 ± 2 m± 2 m

Measured from topographic profileMeasured from topographic profile 1010Be Model surface age = 31,561 ± 729 yrBe Model surface age = 31,561 ± 729 yr

Weighted mean age corrected for depth/latitude/altitudeWeighted mean age corrected for depth/latitude/altitude Assumes zero erosion and zero inheritanceAssumes zero erosion and zero inheritance

Uplift rate = 0.9 ± 0.1 mm/yrUplift rate = 0.9 ± 0.1 mm/yr Horizontal Shortening rate = 0.9 ± 0.3 mm/yrHorizontal Shortening rate = 0.9 ± 0.3 mm/yr Dip Slip rate = 1.2 ± 0.4 mm/yrDip Slip rate = 1.2 ± 0.4 mm/yr

Using estimated fault dip of 45 ± 10°Using estimated fault dip of 45 ± 10° Oblique slip rate = 1.2 ± 0.4 mm/yrOblique slip rate = 1.2 ± 0.4 mm/yr

Using estimated 45 ± 10 ° rake from a 1:1 ratio of left Using estimated 45 ± 10 ° rake from a 1:1 ratio of left oblique motion during the 1971 San Fernando oblique motion during the 1971 San Fernando earthquakeearthquake

Lopez Canyon SurfaceLopez Canyon Surface

Lopez Canyon SurfaceLopez Canyon Surface

Abandoned alluvial Abandoned alluvial surfacesurface

Two fault scarpsTwo fault scarps Scarps 4 and 5Scarps 4 and 5

Limited preservation Limited preservation of remnants (along of remnants (along ridges) in highly ridges) in highly dissected surfacedissected surface

Surveyed Surveyed TopographicTopographic Profiles Profiles

Uplift across scarp 5 = 8.5 ± Uplift across scarp 5 = 8.5 ± 0.5 m0.5 m

Uplift across scarp 4 = 7.0 ± 0.5 mUplift across scarp 4 = 7.0 ± 0.5 m

Cumulative Cumulative

offset across offset across

both scarps =both scarps =

15.5 ± 0.7 m15.5 ± 0.7 m

Lopez Canyon Surface AgesLopez Canyon Surface Ages

Processed 4 surface samplesProcessed 4 surface samples

Lat./Alt. Corrected Ages

Sample ID

10Be model age

LC-129,029 ±

884

LC-233,443 ±

1009

LC-333,181 ±

943

LC-424,273 ±

851

Results - Lopez Canyon Results - Lopez Canyon Surface Surface

Total offset = 15.5 Total offset = 15.5 ± 0.7 m± 0.7 m Measured from topographic profiles.Measured from topographic profiles.

1010Be Model surface age = 29,540 ± 458 yrBe Model surface age = 29,540 ± 458 yr Weighted mean age corrected for latitude/altitudeWeighted mean age corrected for latitude/altitude

Assumes zero erosion and zero inheritance.Assumes zero erosion and zero inheritance.

Uplift rate = 0.5 ± 0.1 mm/yrUplift rate = 0.5 ± 0.1 mm/yr

Horizontal Shortening rate = 0.6 ± 0.2 mm/yrHorizontal Shortening rate = 0.6 ± 0.2 mm/yr

Dip Slip rate = 0.8 ± 0.3 mm/yrDip Slip rate = 0.8 ± 0.3 mm/yr Using measured fault dip in exposure of 40 ± 10°Using measured fault dip in exposure of 40 ± 10°

Wilson Canyon Fan SurfaceWilson Canyon Fan Surface

Wilson Canyon Fan SurfaceWilson Canyon Fan Surface

Abandoned fan Abandoned fan surfacesurface

Uplifted from modern Uplifted from modern valley floorvalley floor

Remnants of surface Remnants of surface preserved along ridge preserved along ridge lineslines

Southwest View of Wilson Canyon Southwest View of Wilson Canyon Fan Surface RemnantFan Surface Remnant

Topographic ProfileTopographic Profile

Uplift across fault scarp is 63.5 ± 5 mUplift across fault scarp is 63.5 ± 5 m

Hospital fault‘Wilson Canyon’ fault

Wilson Canyon Fan Surface AgesWilson Canyon Fan Surface Ages

Processed 6 surface samplesProcessed 6 surface samples

Lat./Alt. Corrected Ages

Sample ID

10Be model age

PW-13 52,071 ± 1435

PW-14 61,489 ± 1534

PW-15 49,265 ± 1705

PW-16 72,255 ± 1955

PW-17 41,688 ± 1082

PW-18 64,584 ± 2122

Wilson Canyon Fan Surface AgesWilson Canyon Fan Surface Ages

Older sample ages reflect significant soil development but still may Older sample ages reflect significant soil development but still may underestimate age of surface (?)underestimate age of surface (?)

Lat./Alt. Corrected Ages

Sample ID

10Be model age

PW-14 61489 ± 1534

PW-16 72255 ± 1955

PW-18 64584 ± 2122

W* Mean65,245 ±

1049

Results - Wilson Canyon FanResults - Wilson Canyon Fan Total Uplift = 63.5 Total Uplift = 63.5 ± 5 m± 5 m

1010Be Model surface age = 65,345 ± 1049 yrBe Model surface age = 65,345 ± 1049 yr

Weighted mean age corrected for latitude/altitudeWeighted mean age corrected for latitude/altitude

Assumes zero erosion and zero inheritance.Assumes zero erosion and zero inheritance.

Uplift rate = 1.0 ± 0.1 mm/yrUplift rate = 1.0 ± 0.1 mm/yr

Horizontal Shortening rate = 1.2 ± 0.7 mm/yrHorizontal Shortening rate = 1.2 ± 0.7 mm/yr

Dip Slip rate = 1.5 ± 0.9 mm/yrDip Slip rate = 1.5 ± 0.9 mm/yr

Using estimated fault dip of 40 ± 20°Using estimated fault dip of 40 ± 20°

Cumulative Shortening RateCumulative Shortening Rate

1.2 ± 0.7 mm/yr

0.6 ± 0.2 mm/yr

+ 0.9 ± 0.3 mm/yr

2.7 ± 0.8 mm/yr

Check math2.7 or 2.6 mm/yr?

Cucamonga Fault ZoneCucamonga Fault Zone

Day Canyon Fan Study SiteDay Canyon Fan Study Site

Modified from Matti and Morton (1987)

Oblique Aerial Photograph Oblique Aerial Photograph of Day Canyon Fan Surfaceof Day Canyon Fan Surface

Topographic Profile AnalysisTopographic Profile Analysis

Three profiles Three profiles across strand Cacross strand C

One profile across One profile across strand A and Bstrand A and B

All profiles were All profiles were constructed from constructed from total station surveystotal station surveys

Topographic Profile AnalysisTopographic Profile Analysis

Total uplift across profile A (QyfTotal uplift across profile A (Qyf1b1b)=5 ± 0.5 m)=5 ± 0.5 m

Topographic Profile AnalysisTopographic Profile Analysis

Total uplift across profile B (QyfTotal uplift across profile B (Qyf1a1a)=7 ± 0.5 m)=7 ± 0.5 m

Topographic Profile AnalysisTopographic Profile Analysis

Total uplift across profile C (QyfTotal uplift across profile C (Qyf1a1a)=12 ± 0.5 m)=12 ± 0.5 m

Topographic Profile AnalysisTopographic Profile Analysis Total offset across profile D (QyfTotal offset across profile D (Qyf1a1a)= 20 ± 0.5 m)= 20 ± 0.5 m Total offset across fan surface QyfTotal offset across fan surface Qyf1a1a = 34 ± 0.7 = 34 ± 0.7

Sampling of Day Canyon Fan Sampling of Day Canyon Fan SurfacesSurfaces

Fan surface QyfFan surface Qyf1b1b 5 south of strand C5 south of strand C

Fan surface QyfFan surface Qyf1a1a 6 south of strand C6 south of strand C 3 between A/B and C3 between A/B and C 4 north of strand A/B4 north of strand A/B 3 depth profile 3 depth profile

samples south of samples south of strand C strand C

Active washActive wash 3 between A/B and C3 between A/B and C

Sample Ages for QyfSample Ages for Qyf1b 1b Surface Surface (East)(East)

Samples collected south of fault strand CSamples collected south of fault strand C

Lat./Alt. Corrected Ages

I.D.10Be Model

Age

DC-1 27,233 ± 883

DC-2 26,411 ± 906

DC-3 28,578 ± 958

DC-4 23,457 ± 956

DC-5 22,111 ± 760

Sample Ages of QyfSample Ages of Qyf1a 1a Surface Surface (West)(West)

Weighted mean model surface age = 33,395 ± 332 yearsWeighted mean model surface age = 33,395 ± 332 years Excluding samples that plot outside the yellow boxExcluding samples that plot outside the yellow box

Results - Day Canyon FanResults - Day Canyon Fan Total uplift = 34 Total uplift = 34 ± 0.7 m (across 3 scarps)± 0.7 m (across 3 scarps)

1010Be Model surface age = 33,395 ± 332 yrBe Model surface age = 33,395 ± 332 yr Weighted mean age corrected for depth/latitude/altitudeWeighted mean age corrected for depth/latitude/altitude

Assumes zero erosion and zero inheritanceAssumes zero erosion and zero inheritance

Uplift rate = 1.1 ± 0.1 mm/yrUplift rate = 1.1 ± 0.1 mm/yr

Horizontal Shortening rate = 1.6 ± 0.3 mm/yrHorizontal Shortening rate = 1.6 ± 0.3 mm/yr

Dip Slip rate = 1.9 ± 0.35 mm/yrDip Slip rate = 1.9 ± 0.35 mm/yr Using measured fault dip of 32.5 ± 5° from Matti Using measured fault dip of 32.5 ± 5° from Matti et alet al. .

(1982)(1982)

Comparison With Previous Comparison With Previous StudyStudy

(Morton and Matti, 1987 or Dolan et al., 200???)(Morton and Matti, 1987 or Dolan et al., 200???) Geomorphic and soil chronologic Geomorphic and soil chronologic

studystudy 36 m of uplift (vs our 34 m) surface 36 m of uplift (vs our 34 m) surface

QyfQyf1a1a

Surface age of ~13 ka using soil Surface age of ~13 ka using soil comparisons with radiometrically dated comparisons with radiometrically dated soil at Cajon Passsoil at Cajon Pass

Slip rate ~4.0 - 5.5 mm/yrSlip rate ~4.0 - 5.5 mm/yr

Sources of strain Sources of strain accommodated by the accommodated by the Cucamonga fault zone.Cucamonga fault zone.

Regional north-south compressionRegional north-south compression Slip transfer from the San Jacinto Slip transfer from the San Jacinto

fault to San Andreas fault.fault to San Andreas fault.

????

Implications for a Lower Slip Implications for a Lower Slip RateRate

1) Strain distributed between the San 1) Strain distributed between the San Jacinto and San Andreas fault is Jacinto and San Andreas fault is almost entirely accommodated by almost entirely accommodated by interactions between smaller crustal interactions between smaller crustal blocks.blocks.

2) Only a small portion of the 2) Only a small portion of the geodetically observed contraction is geodetically observed contraction is accommodated by the Cucamonga accommodated by the Cucamonga fault.fault.

Slip Rates vs. Geodetic Slip Rates vs. Geodetic RatesRates

Based on geologic slip rates, the Sierra Based on geologic slip rates, the Sierra Madre-Cucamonga fault zone (SMCFZ) Madre-Cucamonga fault zone (SMCFZ) accommodates between 10% - 50% of the accommodates between 10% - 50% of the estimated geodetic contraction rate of 4.4 estimated geodetic contraction rate of 4.4 ± 0.8 mm/yr± 0.8 mm/yr

Where is the additional slip Where is the additional slip accommodated?accommodated? Active structures located within the L.A. basinActive structures located within the L.A. basin Distributed deformationDistributed deformation Additional fault strands located within the Additional fault strands located within the

SMCFZ.SMCFZ.

Active Faults in the Los Angeles Active Faults in the Los Angeles RegionRegion

ConclusionsConclusions

Western Sierra Madre fault zone Western Sierra Madre fault zone accommodates 2.7 ± 0.8 mm/yr of accommodates 2.7 ± 0.8 mm/yr of horizontal shorteninghorizontal shortening Excluding the Wilson Canyon faultExcluding the Wilson Canyon fault

Horiz. shortening rate = 1.5 ± 0.4 mm/yrHoriz. shortening rate = 1.5 ± 0.4 mm/yr

Cucamonga fault accommodates 1.6 Cucamonga fault accommodates 1.6 ± 0.3 mm/yr of horizontal shortening± 0.3 mm/yr of horizontal shortening