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

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 M w 6.6 San Fernando

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

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  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 • 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

  3. 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

  4. Study Area

  5. N 30° E Background 1000 m Sunland

  6. Saugus-Towsley Contact?

  7. Saugus Formation

  8. 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

  9. Total horizontal shortening: ~1100 m Horizontal Shortening Across Fault & Folds

  10. Total uplift: ~800 m Total uplift Across Fault & Folds

  11. S z slip 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

  12. 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

  13. Implications for Sunland Fault & Folds • Accounts for ~20-30% of the total 2.5-4 km uplift within the northern anticlinorium • At shallow levels, folding is the primary mechanism for convergence; fault motion secondary • Recurrence for 1971 San Fernando-type earthquakes (using average uplift of 2 m per earthquake): 2 m ÷ 0.4 mm/yr = 5000 years

  14. 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.

  15. 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

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