slip rate studies along the sierra madre-cucamonga fault system using geomorphic and 10 be...
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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