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Deformation in the lower crust and downward extent of the San Andreas Fault as revealed by teleseismic waveforms

Abstract

High resolution images of crustal structure across the San Andreas Fault (SAF) were obtained by using the common conversion point stacking of teleseismic P-to-S converted waves recorded during the Los Angeles Region Seismic Experiments (LARSE-I and II). In the upper crust, several sedimentary basins were delineated in the images, including the San Fernando and the Santa Clarita Basins. The San Fernando Basin reaches a depth of 8 km under the northern edge of the San Fernando Valley. On the LARSE-I profile, the downward projection of the SAF truncates several lower crustal interfaces including the Moho on both sides. The Moho is vertically offset by as much as 8 km. Along the LARSE-II profile, the impedance contrast and slope of the Moho are seen to change across the fault. These results indicate that the fault penetrates into the lower crust and probably uppermost mantle as a narrow (<10 km) feature. The Moho beneath the San Gabriel Mountains is shallower (26 km) than under the San Gabriel Valley to the south and the Mojave Desert to the north, suggesting that the mountain ranges were lifted en masse by horizontal compression. On the northeast side of the SAF, the Mojave Desert has a sharp and essentially flat Moho at a depth of 32 km. The lower crustal structure beneath the San Fernando and Santa Clarita Valleys along the LARSE-II profile south of the SAF is complicated as indicated by the large undulation and low impedance contrast of the Moho. These observations suggest that the deformation in the lower crust is localized and often concentrates near boundaries of crustal blocks or beneath those places which have experienced intensive faulting and deformation in the upper crust.

References

  1. Bourne, S., P. England, and B. Parsons, The motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike-slip faults, Nature, 391(6668), 655–659, 1998.

  2. Brocher, T., J. McCarthy, P. Hart, W. Holbrook, K. Furlong, T. McEvilly, J. Hole, and S. Klemperer, Seismic evidence for a lower crustal detachment beneath San Francisco Bay, California, Science, 265(5177), 1436–1439, 1994.

  3. Dueker, K. and A. Sheehan, Mantle discontinuity structure from midpoint stacks of converted P to S waves across the Yellowstone hotspot track, J. Geophys. Res., 102(B4), 8313–8327, 1997.

  4. Froidevaux, C., Basin and Range large-scale tectonics: constraints from gravity and reflection seismology, J. Geophys. Res., 91, 3625–3632, 1986.

  5. Fuis, G. S., T. Ryberg, N. J. Godfrey, D. A. Okaya, and J. M. Murphy, Crustal structure and tectonics from the Los Angeles basin to the Mojave Desert, southern California, Geology, 29, 15–18, 2001a.

  6. Fuis, G. S., T. Ryberg, N. J. Godfrey, D. A. Okaya, and J. M. Murphy, Crustal structure and tectonics from the Los Angeles basin to the Mojave Desert, southern California, Geology, 29, 15–18, 2001b.

  7. Fuis, G. S., T. Ryberg, W. J. Lutter, E. Hauksson, K. B. Richards-Dinger, T. G. Hildenbrand, V. E. Langenheim, J. M. Murphy, and D. A. Okaya, Deep structure in the region of the San Fernando and Santa Clarita Valleys, southern California, from LARSE II seismic imaging, earthquake relocation, and magnetic modeling—a progress report, Eos. Trans. AGU, 82 (47), Fall Meet. Suppl., Abstract S12E-05, 2001c.

  8. Furlong, K., W. Hugo, and G. Zandt, Geometry and evolution of the San Andreas Fault Zone in northern California, J. Geophys. Res., 94(B3), 3100–3110, 1989.

  9. Hadley, D. and H. Kanamori, Seismic structure of the Transverse Ranges, California, Geol. Soc. Am. Bull., 88, 1469–1478, 1977.

  10. Hauksson, E., Crustal structure and seismicity distribution adjacent to the Pacific and North America plate boundary in southern California, J. Geophys. Res., 105, 13875–13903, 2000.

  11. Henstock, T., A. Levander, and J. Hole, Deformation in the lower crust of the San Andreas Fault System in northern California, Science, 278(5338), 650–653, 1997.

  12. Holbrook, W., T. Brocher, U. TenBrink, and J. Hole, Crustal structure of a transform plate boundary: San Francisco Bay and the central California continental margin, J. Geophys. Res., 101(B10), 22311–22334, 1996.

  13. Jones, C. H. and R. A. Phinney, Seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern Sierra-Nevada and vicinity, California, J. Geophys. Res., 103, 10065–10090, 1998.

  14. Kohler, M. D. and P. M. Davis, Crustal thickness variations in southern California from Los Angeles Region Seismic Experiment passive phase teleseismic travel times, Bull. Seismol. Soc. Am., 87, 1330–1344, 1997.

  15. Kosarev, G., R. Kind, S. Sobolev, X. Yuan, W. Hanka, and S. Oreshin, Seismic evidence for a detached Indian lithospheric mantle beneath Tibet, Science, 283(5406), 1306–1309, 1999.

  16. Lemiszki, P. and L. Brown, Variable crustal structure of strike-slip fault zones as observed on deep seismic-reflection profiles, Geol. Soc. Am. Bull., 100(5), 665–676, 1988.

  17. Li, A., K. Fischer, M. Wysession, and T. Clarke, Mantle discontinuities and temperature under the North American continental keel, Nature, 395(6698), 160–163, 1998.

  18. Lutter, W. J., G. S. Fuis, C. H. Thurber, and J. M. Murphy, Tomographic images of the upper crust from the Los Angeles basin to the Mojave Desert, California: Results from the Los Angeles Region Seismic Experiment, J. Geophys. Res., 104, 25543–25565, 1999.

  19. Lutter, W. J., T. Ryberg, G. S. Fuis, J. M. Murphy, and D. A. Okaya, Basin structure of the San Fernando and Santa Clarita Valleys and geometry of the Northridge and San Fernando faults as determined from Los Angeles Region Seismic Experiment, Phase II (LARSE II), Eos. Trans. AGU, 82 (47), Fall Meet. Suppl., Abstract S11A-0540, 2001.

  20. McBride, J. and L. Brown, Reanalysis of the COCORP deep seismic reflection profile across the San Andreas Fault, Parkfield, California, Bull. Seismol. Soc. Am., 76(6), 1668–1686, 1986.

  21. Molnar, P., Brace-Goetze strength profiles, the partitioning of strike-slip thrust faulting at zones of oblique convergence, and the stress-heat flow paradox of the San Andreas Fault, in Fault Mechanics and Transport Properties of Rocks, edited by B. Evans and T.-F. Wong, Academic Press Ltd., 1992.

  22. Namson, J. and T. Davis, Structural transect of the western Transverse Ranges, California—implications for lithospheric kinematics and seismic risk evaluation, Geol., 16(8), 675–679, 1988.

  23. Parsons, T., Seismic-reflection evidence that the Hayward fault extends into the lower crust of the San Francisco Bay Area, California, Bull. Seismol. Soc. Am., 88, 1212–1223, 1998.

  24. Prescott, W. H., The accommodation of relative motion at depth on the San Andreas Fault System in California, J. Geophys. Res., 86, 999–1004, 1981.

  25. Ryberg, T. and G. Fuis, The San Gabriel Mountains bright reflective zone: possible evidence of young mid-crustal thrust faulting in southern California, Tectonophys., 286(1–4), 31–46, 1998.

  26. Shen, Y., S. Solomon, I. Bjarnason, and C. Wolfe, Seismic evidence for a lower-mantle origin of the Iceland plume, Nature, 395(6697), 62–65, 1998.

  27. Stern, T. and J. McBride, Seismic exploration of continental strike-slip zones, Tectonophys., 286(1–4), 63–78, 1998.

  28. Taylor, S. and M. N. Toksoz, Measurement of interstation phase and group velocities and Q using Weiner filtering, Bull. Seismol. Soc. Am., 72, 73–91, 1982.

  29. Yeats, R. S., Quaternary flake tectonics of the California Transverse Ranges, Geol., 9, 16–20, 1981.

  30. Zhu, L., Crustal structure across the San Andreas Fault, southern California from teleseismic converted waves, Earth Planet. Sci. Lett., 179, 183–190, 2000.

  31. Zhu, L. and H. Kanamori, Moho depth variation in southern California from teleseismic receiver functions, J. Geophys. Res., 105, 2969–2980, 2000.

  32. Zuber, M., E. Parmentier, and R. C. Fletcher, Extension of continental lithosphere: a model for two scales of Basin and Range deformation, J. Geophys. Res., 91, 4826–4838, 1986.

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Correspondence to Lupei Zhu.

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Zhu, L. Deformation in the lower crust and downward extent of the San Andreas Fault as revealed by teleseismic waveforms. Earth Planet Sp 54, 1005–1010 (2002). https://doi.org/10.1186/BF03353293

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Keywords

  • Lower Crust
  • Crustal Structure
  • Moho Depth
  • Mojave Desert
  • Converted Wave