An elusive blind-thrust fault beneath metropolitan Los Angeles

Science

Volumn 283, Issue 5407, 1999, Pages 1516-1518

  Shaw, John H ^a   Shearer, Peter M ^b  

^a HARVARD UNIVERSITY   (United States)

^b UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

PETROLEUM;

CRUSTAL STRUCTURE; SEISMIC REFLECTION; SEISMICITY; THRUST;

ARTICLE; EARTHQUAKE; FORECASTING; GEOGRAPHY; GEOLOGY; PRIORITY JOURNAL; UNITED STATES; VELOCITY; WAVEFORM;

UNITED STATES;

EID: 0033525585     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.283.5407.1516     Document Type: Article

References (24)

1. Scientists of the U.S. Geological Survey and the Southern California Earthquake Center, Science 266, 389 (1994).
2. C. M. Rubin, S. C. Lindvall, T. K. Rockwell, ibid. 281, 398 (1998).
3. R. S. Stein and G. Ekstrom, J. Geophys. Res. 97, 4865 (1992).
4. J. Shaw and J. Suppe, ibid. 101, 8623 (1996).
5. T. L. Davis, J. Namson, R. F. Yerkes, ibid. 94, 9644 (1989).
6. J. Suppe, Am. J. Sci. 283, 684 (1983).
7. _ and D. A. Medwedeff, Ecologae Geol. Helv. 83/3, 409 (1990).
8. R. F. Yerkes, U.S. Geol. Surv. Prof. Pap. 420-C (1972).
9. T. L. Wright, in Active Margin Basins, K. T. Biddle, Ed., Am. Assoc. Pet. Geol. Mem. 52, 35 (1991).
10. R. S. Yeats and G. J. Huftile, Southern California Earthquake Center 1996 Annual Report, (Southern California Earthquake Center, Los Angeles, CA, 1997), vol. II, pp. C75-C79.
11. J. Suppe, G. T. Chou, S. C. Hook, in Thrust Tectonics, K. R. McKlay, Ed. (Chapman & Hall, London, 1992), pp. 105-121.
12. The seismic profile presented in Fig. 1 underwent a standard processing routine including normal moveout correction and wave equation migration (Kirchoff F/K domain). The interpreted fault plane is highlighted in red and was selected in a user-defined area by its dip and lateral coherence. Various additional processing steps aimed at reducing noise and eliminating dipping artifacts were applied to the line (not shown), including frequency-wave number (FK) filters and frequency (FX) deconvotution. These steps failed to remove the north-dipping reflections interpreted to represent the fault surface.
13. The Elysian Park fault system forms the overlying Santa Monica Mountains anticlinorium (5). Both the fault and the anticlinorium have a northwest-southeast orientation (4, 5) that is distinct from the east-west-striking nodal planes of the 1987 Whittier Narrows mainshock (14) and the mapped segments of the Southern Puente Hills blind-thrust system (Fig. 2). Moreover, the Puente Hills fault system lies on top of folds formed above the Elysian Park system (Fig. 1). Thus, we contend that the Elysian Park and Puente Hills fault systems are distinct from one another.
14. E. Hauksson and L. Jones, J. Geophys. Res. 94, 9569 (1989).
15. P. M. Shearer, ibid. 102, 8269 (1997).
16. K. B. Richards-Dinger and P. M. Shearer, Eos (Fall Meeting Suppl.) 78, F445 (1997).
17. Fault areas are taken below 5-km depth, which we consider to be the minimum depth of significant moment release in large earthquakes. Shallower thresholds can be considered with the use of the fault map in Fig. 2.
18. D. L. Wells and K. J. Coppersmith, Bull. Seismol. Soc. Am. 84, 974 (1994).
19. J. F. Dolan et al., Science 267, 199 (1995).
20. Minimum and maximum slip rates are determined on the basis of geologic and geodetic constraints. The geometry of folded growth strata in the Santa Fe Spring structures indicates that at least 800 m of slip occurred on the underlying blind thrust in the Quaternary, with the use of the methods of Suppe et al. (11) and Shaw and Suppe (4). Use of the maximum age of Quaternary strata (1.6. million years ago) yields a minimum slip rate of 0.5 mm/year. Maximum slip rate (2.0 mm/year) is taken as the portion of the shortening (7.5 to 9.5 mm/year) (21, 22) measured by geodesy across the Los Angeles basin that remains unaccounted for on previously recognized fault systems (23).
21. Y. Bock et al., J. Geophys. Res. 102, 18013 (1997).
22. Y. Bock and S. Williams, Eos 78, 293 (1997).
23. C. Walls et al., Nature 394, 356 (1998).
24. This research was funded by the Southern California Earthquake Center and data were provided by Texaco. We thank F. Bilotti, K. Bishop, K. Richards-Dinger, J. Dolan, G. Ekström, K. Mueller, and P. Süss for contributions to this work.