Quaternary convergence rate across the Sunland fault and related folds, near Sunland, California

1
Quaternary convergence rate across the Sunland
fault and related folds, near Sunland, California
Shelby Dawson Department of Geological
Sciences California State University,
Northridge Dr. Doug Yule, advisor
2
Significance
Study area

• Part of the Sierra Madre fault system
• 1971 Mw 6.6 San Fernando
• 1994 Mw 6.7 Northridge
• Located where Sierra Madre (SMAF) splays into
  multiple strands

3
The Problem

• Convergence rates across individual structures
  are not well constrained
• Regional uplift 2.5-4 km since lt5 Ma. (Meigs et
  al., 2002)
• Uplift rate 0.5-1.3 mm/year
• Seismic hazard

Sunland fault
4
Study Area
5
Background
1000 m
Sunland
6
Saugus-Towsley Contact?
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Saugus Formation
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Cross Section

• Pink purple Precambrian to Cretaceous
  crystalline rocks
• Sedimentary overlap sequence includes Miocene
  marine to Pliocene-Pleistocene nonmarine deposits
• Age of some units not well constrained

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Horizontal Shortening Across Fault Folds
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Total uplift Across Fault Folds
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Convergence on the Sunland Fault

• Slip on fault 440 m
• Uplift (z) 170 m
• Shortening (S) 410 m

• Uplift on folds 630 m
• Shortening 690 m

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Conclusions for Sunland Fault Folds

• Convergence rates since 1.8 Ma
• uplift 800 m / 1.8 m.y. ? 0.4
  mm/yrshortening 1100 m /1.8 m.y. ? 0.6
  mm/yr

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Implications for Sunland Fault Folds

1. Accounts for 20-30 of the total 2.5-4 km uplift
   within the northern anticlinorium
2. At shallow levels, folding is the primary
   mechanism for convergence fault motion
   secondary
3. Recurrence for 1971 San Fernando-type earthquakes
   (using average uplift of 2 m per earthquake) 2
   m 0.4 mm/yr 5000 years

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Acknowledgements
Special thanks to my advisor, Dr. Doug Yule, for
making time for me in his busy schedule. Its
been a privilege. Thanks to Dr. Richard Squires
for explaining to me the complexities of the San
Fernando and Ventura basins and for his
enthusiastic attempt to identify my fossils.
Finally, thanks to Dr. Carol Shubin and Jennifer
Wright for their encouragement and support
through the NASA CSUN JPL PAIR program, and for
compelling me to finish my project in a timely
fashion.
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References
Argus, D. F., and Gordon, R. G., 2001, Present
tectonic motion across the Coast Ranges and San
Andreas fault system in central California
Geological Society of America Bulletin, Vol.
113, p. 1580-1592 Dibblee, T. W., 1991, Geologic
map of the Sunland and Burbank (north ½)
quadrangles, Los Angeles County, California
Dibblee Geological Foundation, Map DF-32 Meigs,
A. J., 1997, Sequential development of selected
Pyrenean thrust faults Journal of Structural
Geology, Vol. 19, p. 481-502 Meigs, A., Yule, D.,
Blythe, A., and Burbank, D., 2003, Implications
of distributed crustal deformation for
exhumation in a portion of a transpressional
plate boundary, Western Transverse Ranges,
Southern California Quaternary International,
101-102, p. 169-177 Rockwell, T.K., Keller, E.
A., and Dembroff, G. R., 1988, Quaternary rate of
folding of the Ventura Avenue anticline,
western Transverse Ranges, southern California
Geological Society of America Bulletin, v. 100,
p. 850-858 Rubin, C. M., Lindvall, S. C., and
Rockwell, T. K., 1998, Evidence for large
earthquakes in metropolitan Los Angeles
Science, Vol. 281, p. 398-404 Shen, Z. K.,
Jackson, D. D. and Ge, B. X., 1996, Crustal
deformation across and beyond the Los Angeles
Basin from geodetic measurements Journal of
Geophysical Sciences, Vol. 101, Issue 12, p.
957-980