PPT - California State University, Northridge

Quaternary convergence rate
across the Sunland fault and
related folds, near Sunland,
Shelby Dawson
Department of Geological Sciences
California State University, Northridge
Dr. Doug Yule, advisor
► 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
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
Study Area
1000 m
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 &
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
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
Accounts for ~20-30% of the total
2.5-4 km uplift within the northern
At shallow levels, folding is the
primary mechanism for
convergence; fault motion
Recurrence for 1971 San Fernandotype earthquakes (using average
uplift of 2 m per earthquake):
2 m ÷ 0.4 mm/yr = 5000 years
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
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(north ½) quadrangles, Los Angeles County, California: Dibblee Geological
Foundation, Map DF-32
Meigs, A. J., 1997, Sequential development of selected Pyrenean thrust faults:
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