Imaging Deep Fault Structure: StrikeSlip Restraining and Releasing Bends

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Imaging Deep Fault Structure Strike-Slip
Restraining and Releasing Bends

• Mark R. Legg Legg Geophysical
• Marc J. Kamerling Venoco
• Chris Goldfinger Oregon State
• Jason Chaytor Oregon State
• Debra Einstein-Leight UC Irvine
• Herman D. Wang Northwestern Univ.

WGCEP 15-16 March 2006
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Seismic Hazard Assessment from a Data Processing
Viewpoint
Filtering
RULE 1 Preserve the SIGNAL!!!
Discontinuities are SIGNAL!
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Tectonic Evolution of Southern California
Strike-Slip Fault Bends

• Restraining Bends are common along southern
  California strike-slip faults
• Several Examples will be shown from the
  Borderland
• Restraining Bend geometry is unfavorable
  according to mechanical models
• Segall and Pollard, Mechanics of Discontinuous
  Faults (1980)
• Why are there so many prominent restraining bends
  in southern California?

Geological Society of London
Sept 28 Oct 1, 2005
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Major Strike-Slip Earthquakes

• Two largest earthquakes in California history
  occurred along strike-slip Restraining Bends
• 1857 Fort Tejon (M7.9)
• 1906 San Francisco (M7.8)
• Initiation and/or termination of these major
  fault ruptures occurred at strike-slip Releasing
  Bends (Pull-Apart Basins)
• Cajon Pass (1857) Cholame Valley?
• Golden Gate (1906)

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Which Seismic Gap is Next to Rupture?
Major Faults in California
Seismicity(Mgt4) 1932-1998
1906
San Gregorio
1872
Owens Valley
San Andreas
1857
Garlock
1812,1857
1812
California Continental Borderland
San Jacinto
Elsinore
Imperial
S D Trough
San Clemente
Cerro Prieto
Epicenters from SCSN
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Major Southern California Faults
Big Bend
San Bernardino Mtns
Sta Catalina Isl
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Character of Southern California Strike-Slip
Fault Bends

• Right-slip faulting is characterized by
  left-stepping en echelon fault patterns
• Wilcox, Harding, Seely, Wrench Fault Tectonics,
  (1973)
• Southern California right-slip faults show a
  distinct right-stepping en echelon pattern
• Similar to the Gulf of California Transform Fault
  System
• Releasing Bends and Pull-Apart Basins are
  associated with every restraining bend
• Transpressional fault sections link
  Transtensional fault sections
• Right-Stepping Transform faults link
  Left-Stepping Spreading Centers

Geological Society of London
Sept 28 Oct 1, 2005
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Los Angeles
Inner Borderland Rift
Right-Stepping, en echelon pattern of major
right-slip faults (San Clemente Catalina faults)
Catalina fault.
North-Trending South San Clemente Basin Rift
Rhombochasm w/Nascent Seafloor Spreading
San Clemente f.z.
San Diego
San Diego Trough
Volcano
Left-Stepping en echelon Volcanoes linked by
Right-Stepping en echelon Transform Faults
South San Clemente Basin
San Clemente f.z.
Volcano
San Diego Trough IB Rift Axis follow ancient
subduction trends
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Tectonic Evolution of Southern California
Strike-Slip Fault Bends
CONCLUSIONS
Changing relative plate motion vectors and
Re-activation of pre-existing structural fabric
are responsible for the abundance of Restraining
Releasing Bends along southern California
strike-slip faults
Understanding the Regional Tectonic Evolution is
Necessary to Predict Fault Structure at Depth
where Seismogenic Fault Interactions Occur
Geological Society of London
Sept 28 Oct 1, 2005
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Tectonic Evolution of Southern California
Strike-Slip Fault Bends

• Examples of Prominent Southern California
  Restraining Releasing Bends
• Focus on California Continental Borderland
• Well-defined seafloor tectonic geomorphology
• High-resolution subsurface imaging
• Neogene Locus of PAC-NOAM transform plate motion
• Deformation and fault activity persists today

Geological Society of London
Sept 28 Oct 1, 2005
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MAJOR STRIKE-SLIP FAULT SYSTEMS
Irregular and curved fault segments with offsets
and overlaps
Irregular traces inherited from complex tectonic
evolution and pre-existing structure
Fault bends, offsets and step-overs create local
areas of convergence or divergence with uplift or
subsidence
Moderate (Mgt5) earth-quakes of San Clemente Fault
System show Right-Slip Oblique-Reverse - 1986
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About 60 km top-to-bottom
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(No Transcript)
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Dextral Oblique-Reverse Faulting Analog
Right-Lateral Shear along Edge of Block-Glide
Landslide (San Onofre State Beach, CA)
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Geologic Reality may Overwhelm Geophysical
Imaging Capability
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Location of Seismic Profiles
SMCS-01
SMCS-06
SMCS-04
San Diego Trough f.z.
Sea Beam Swath SDT f.z. Pop-Up
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High-Resolution MCS Profile SMCS-04
San Clemente Fault
South San Clemente Basin
SW
twtt
1
Upthrusts
Oblique Fault
Oblique Faults
2
PEL
3
Multiple
4
sec
V.E.3.1X _at_ 1.5 km/s
San Diego Trough Fault
Descanso Plain
NE
twtt
1
Low-Angle Normal Fault
Strike-Slip Fault
PEL
2
3
Multiple
4
sec
V.E.2.3X _at_ 1.5 km/s
Migrated Time Sections
PEL late Quaternary Hemipelagic Layer
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High-Resolution MCS Profile SMCS-06
San Clemente Fault
San Diego Trough Fault
SW
NE
twtt
1
Oblique Faults
Strike-Slip Fault
2
3
Multiple
4
sec
V.E.3.5X _at_ 1.5 km/s
High-Resolution MCS Profile SMCS-01
SW
twtt
1
San Clemente Fault
Navy Fan
2
Oblique Faults
PEL
3
Migrated Time Sections
V.E.2.5X _at_ 1.5 km/s
4
sec
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Seafloor Morphology of Restraining Releasing
Bends
Crespi Knoll Miocene Volcano?
Restraining Bend
Pull-Apart Basin
Pull-Apart Basin

13 July, 1986 MS5.8
San Diego Trough Fault Zone
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USGS-114
twtt
0
Coronado Bank fault zone
San Diego Trough fault zone
2
Thirtymile Bank Detachment Fault
4
sec
Migrated Time Section
Data processing by Chris Sorlien
V.E.3.8X _at_ 1.5 km/s
Geological Society of London
Sept 28 Oct 1, 2005
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Shaded Relief Digital Elevation Model
Santa Catalina Island
Los Angeles Basin
Image provided by Jose Borrero, USC
V.E.15x
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Los Angeles
Santa Catalina Island and Vicinity
Palos Verdes Hills
Deflected Drainages
Lasuen Knoll
Locked Catalina Fault?
Crespi Knoll
Epicenters from Astiz Shearer, 2000
San Clemente Island
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Southeast Santa Cruz-Catalina Ridge
Complex structure near intersection of San
Clemente and Catalina faults Vertical strike-slip
faults with secondary high-angle reverse faults
and pop-up structures Analog to structure in
the Cajon Pass region where San Andreas fault
meets San Jacinto fault
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USGS-124
Santa Catalina Island Platform
twtt
0
San Pedro Basin Fault Zone
Catalina Fault Zone
2
4
sec
Migrated Time Section
Data processing by USGS (Eric Geist)
V.E.3.6X _at_ 1.5 km/s
Note Uplift occurs on BOTH sides of the Catalina
Fault!
Geological Society of London
Sept 28 Oct 1, 2005
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Sub-Vertical Strike-Slip FaultsTransform Faulting
Dont be Fooled by Apparent Normal or Reverse
Separation Right-Slip Exceeding 20 to 60 km has
Occurred along these Transform Faults
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Seven Segment Catalina Fault Model
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RESTRAINING BEND POP-UP STRUCTURES
Rhomboid Shape typifies Restraining Bend Pop-Ups
and Pull-Apart Basins or Rhombochasms
Catalina Tsunami Initial Condition Elastic
Dislocation Model Static Uplift
Analog Model Above Seafloor Example Below
10 m contours
lt About 5 km gt
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LARSE-1 (Line 1)
Preferred
Ten Brink et al. 2000
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LARSE-1 (Line 1)
Ten Brink et al. 2000