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
Significance
► 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
Study
area
The Problem
► Convergence
rates across individual structures are not
well constrained
 Regional uplift ~2.5-4 km since <5 Ma. (Meigs et al., 2002)
 Uplift rate ~0.5-1.3 mm/year
► Seismic
hazard
Sunland
fault
Study Area
Background
1000 m
Sunland
Saugus-Towsley Contact?
Saugus Formation
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
Horizontal Shortening Across Fault &
Folds
Total horizontal
shortening: ~1100 m
Total uplift Across Fault & Folds
Total uplift:
~800 m
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
S
z
Conclusions for Sunland Fault & Folds
Convergence rates since ~1.8 Ma:
uplift = 800 m / 1.8 m.y.
→ ~0.4 mm/yr
shortening = 1100 m /1.8 m.y.
→ ~0.6 mm/yr
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 Fernandotype earthquakes (using average
uplift of 2 m per earthquake):
2 m ÷ 0.4 mm/yr = 5000 years
Acknowledgements
Special thanks to my advisor, Dr. Doug Yule, for making time for me
in his busy schedule. It’s 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.
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:
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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