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

Shelby DawsonShelby DawsonDepartment of Geological SciencesDepartment of Geological SciencesCalifornia State University, NorthridgeCalifornia State University, NorthridgeDr. Doug Yule, advisorDr. Doug Yule, advisor

SignificanceSignificance

► 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 ProblemThe Problem

► Convergence rates across individual structures are not well Convergence rates across individual structures are not well constrainedconstrained Regional uplift ~2.5-4 km since <5 Ma. (Meigs et al., 2002)Regional uplift ~2.5-4 km since <5 Ma. (Meigs et al., 2002) Uplift rate ~0.5-1.3 mm/yearUplift rate ~0.5-1.3 mm/year

► Seismic hazardSeismic hazard

Sunland

fault

Study AreaStudy Area

BackgroundBackground

1000 m

Sunland

N 30

° E

Saugus-Towsley Contact?Saugus-Towsley Contact?

Saugus FormationSaugus Formation

Cross SectionCross Section

► Pink & purple: Precambrian to Cretaceous crystalline rocksPink & purple: Precambrian to Cretaceous crystalline rocks► Sedimentary overlap sequence includes Miocene marine to Sedimentary overlap sequence includes Miocene marine to

Pliocene-Pleistocene nonmarine depositsPliocene-Pleistocene nonmarine deposits► Age of some units not well constrainedAge of some units not well constrained

Horizontal Shortening Across Fault & Horizontal Shortening Across Fault & FoldsFolds

Total horizontal Total horizontal shortening: ~1100 mshortening: ~1100 m

Total uplift Across Fault & FoldsTotal uplift Across Fault & Folds

Total uplift: Total uplift: ~800 m~800 m

Convergence on the Sunland FaultConvergence on the Sunland Fault

Szslip

► Slip on fault: ~440 mSlip on fault: ~440 m► Uplift (z): ~170 mUplift (z): ~170 m► Shortening (S): ~410 mShortening (S): ~410 m

► Uplift on folds: ~630 mUplift on folds: ~630 m► Shortening: ~690 mShortening: ~690 m

Conclusions for Sunland Fault & FoldsConclusions for Sunland Fault & Folds

Convergence rates since ~1.8 Ma:Convergence rates since ~1.8 Ma:

uplift =uplift = 800 m / 1.8 m.y. 800 m / 1.8 m.y. → → ~0.4 mm/yr~0.4 mm/yr

shortening =shortening = 1100 m /1.8 m.y. 1100 m /1.8 m.y. → → ~0.6 mm/yr~0.6 mm/yr

Implications for Sunland Fault & FoldsImplications for Sunland Fault & Folds

1.1. Accounts for ~20-30% of the total Accounts for ~20-30% of the total 2.5-4 km uplift within the northern 2.5-4 km uplift within the northern anticlinoriumanticlinorium

2.2. At shallow levels, folding is the At shallow levels, folding is the primary mechanism for primary mechanism for convergence; fault motion convergence; fault motion secondarysecondary

3.3. RecurrenceRecurrence for 1971 San Fernando- for 1971 San Fernando-type earthquakes (using average type earthquakes (using average uplift of 2 m per earthquake):uplift of 2 m per earthquake):

2 m 2 m ÷ 0.4 mm/yr = ÷ 0.4 mm/yr = 5000 5000 yearsyears

AcknowledgementsAcknowledgementsSpecial thanks to my advisor, Dr. Doug Yule, for making time for me Special thanks to my advisor, Dr. Doug Yule, for making time for me

in his busy schedule. It’s been a privilege. in his busy schedule. It’s been a privilege. Thanks to Dr. Richard Squires for explaining to me the complexities Thanks to Dr. Richard Squires for explaining to me the complexities

of the San Fernando and Ventura basins and for his enthusiastic of the San Fernando and Ventura basins and for his enthusiastic attempt to identify my fossils. attempt to identify my fossils.

Finally, thanks to Dr. Carol Shubin and Jennifer Wright for their Finally, thanks to Dr. Carol Shubin and Jennifer Wright for their encouragement and support through the NASA CSUN JPL PAIR encouragement and support through the NASA CSUN JPL PAIR program, and for compelling me to finish my project in a timely program, and for compelling me to finish my project in a timely fashion. fashion.

ReferencesReferencesArgus, D. F., and Gordon, R. G., 2001, Present tectonic motion across the Coast Ranges Argus, D. F., and Gordon, R. G., 2001, Present tectonic motion across the Coast Ranges

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