Viscoelastic flow in the lower crust after the 1992 Landers, California, earthquake

Science

Volumn 282, Issue 5394, 1998, Pages 1689-1692

  Deng, Jishu ^a   Gurnis, Michael ^a   Kanamori, Hiroo ^a   Hauksson, Egill ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CRUSTAL DEFORMATION; LANDERS EARTHQUAKE 1992; POSTSEISMIC PROCESS; VISCOELASTICITY;

ARTICLE; EARTHQUAKE; EVOLUTION; FLOW MEASUREMENT; GEOGRAPHY; GEOLOGY; PRIORITY JOURNAL; THREE DIMENSIONAL IMAGING; UNITED STATES; VISCOELASTICITY;

UNITED STATES;

EID: 0032573556     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article

References (34)

1. K. Sieh et al., Science 260, 171 (1993).
2. G. Peltzer et al., ibid. 273, 1202 (1996).
3. W. J. Bosl and A. Nur, Eos 78, F491 (1997).
4. J. C. Savage and J. L. Svarc, J. Geophys. Res. 102, 7565 (1997).
5. D. Massonnet, W. Thatcher, H. Vadon, Nature 382, 612 (1996).
6. D. D. Jackson et al., Science 277, 1621 (1997).
7. Y. Bock et al., J. Geophys. Res. 102, 18013 (1997).
8. Z. K. Shen et al., Bull. Seismol. Soc. Am. 84, 780 (1994).
9. K. Heki, S. Miyazaki, H. Tsuji, Nature 386, 595 (1997).
10. A. Nur and G. Mavko, Science 183, 204 (1974).
11. J. B. Rundle, J. Geophys. Res. 83, 5937 (1978); W. Thatcher and J. Rundle, ibid. 89, 7631 (1984).
12. J. B. Rundle, J. Geophys. Res. 83, 5937 (1978); W. Thatcher and J. Rundle, ibid. 89, 7631 (1984).
13. H. J. Melosh and A. Raefsky, ibid. 88, 515 (1983); S. C. Cohen, ibid. 89, 4538 (1984).
14. H. J. Melosh and A. Raefsky, ibid. 88, 515 (1983); S. C. Cohen, ibid. 89, 4538 (1984).
15. F. F. Pollitz, ibid. 102, 17921 (1997).
16. J. C. Savage, ibid. 95, 4873 (1990).
17. C. J. Marone, C. H. Scholtz, R. Bilham, ibid. 96, 8441 (1991).
18. A. M. Dziewonski, C. Ekstrom, M. P. Salganik, Phys. Earth Planet. Inter. 77, 151 (1993).
19. C. J. Ammon, A. A. Velasco, T. Lay, Geophys. Res. Lett. 20, 97 (1993).
20. We note that the first-motion mechanism presented by Hauksson et al. (20) has a rake angle of 170° on a fault striking in N10°W. The mechanism solution of the second point source obtained by Qu et al. (28) (shown in Fig. 1), which is located near the southern end of the Emerson fault, has a rake angle of 153°, which involves even a larger dip-slip component than Hauksson et al.'s (20). Also several aftershocks near the Emerson fault show a significant thrust component (20). The aftershock distribution along the Emerson fault shown by figures 10a and 10b of (20) suggests a northeast dipping fault, which is qualitatively consistent with the solution of Qu et al. (28). F. Cotton and M. Campillo [Geophys. Res. Lett. 22, 1921 (1995)] showed that the Landers earthquake is almost pure strike-slip, but the rake angle varies considerably around 180° on the Emerson and Camp Rock faults. Their average rake angle is about 176°. Surface rupture measurements [For example, J. R. Arrowsmith and D. D. Rhodes, Bull. Seism. Soc. Am. 84, 511 (1994)] also showed some direct evidence of up to 2.5 m of vertical motion along a short segment of the Emerson fault. The various rake angles suggest that 7 to 45% of the seismic moment is released through dip-slip motion along the Emerson Fault segment, corresponding to 0.3 to 1.8 m of dip-slip displacement. In our calculations, we assume 0.7 m of dip-slip motion.
21. We note that the first-motion mechanism presented by Hauksson et al. (20) has a rake angle of 170° on a fault striking in N10°W. The mechanism solution of the second point source obtained by Qu et al. (28) (shown in Fig. 1), which is located near the southern end of the Emerson fault, has a rake angle of 153°, which involves even a larger dip-slip component than Hauksson et al.'s (20). Also several aftershocks near the Emerson fault show a significant thrust component (20). The aftershock distribution along the Emerson fault shown by figures 10a and 10b of (20) suggests a northeast dipping fault, which is qualitatively consistent with the solution of Qu et al. (28). F. Cotton and M. Campillo [Geophys. Res. Lett. 22, 1921 (1995)] showed that the Landers earthquake is almost pure strike-slip, but the rake angle varies considerably around 180° on the Emerson and Camp Rock faults. Their average rake angle is about 176°. Surface rupture measurements [For example, J. R. Arrowsmith and D. D. Rhodes, Bull. Seism. Soc. Am. 84, 511 (1994)] also showed some direct evidence of up to 2.5 m of vertical motion along a short segment of the Emerson fault. The various rake angles suggest that 7 to 45% of the seismic moment is released through dip-slip motion along the Emerson Fault segment, corresponding to 0.3 to 1.8 m of dip-slip displacement. In our calculations, we assume 0.7 m of dip-slip motion.
22. Z. K. Shen et al., Eos Trans. AGU 78, 477 (1997).
23. E. Hauksson, et al., J. Geophys. Res. 98, 19835 (1993).
24. E. Hauksson, Bull. Seismol. Soc. Am. 84, 917 (1994).
25. D. J. Wald and T. H. Heaton, ibid., p. 668.
26. K. B. Richards-Dinger and P. M. Shearer, J. Geophys. Res. 102, 15211 (1997).
27. FEVER (Finite Element code for Visco-Elastic Rheology) is an object-oriented finite element software program developed by one of us (Deng). The code was implemented in C++ and systematically tested against many analytic solutions of linear and non-linear viscoelastic problems. The error of the numerical solution for almost alt of the tested cases is within 1% of the corresponding analytic result.
28. We fixed the upper boundary of the weak zone to be 15 km deep, and assume that the lower boundary of the weak layer is the Moho surface, constrained from the Moho-reflected PmP arrivals (23). A thicker weak zone to the west of the Johnson Valley fault (Moho is about 32 km deep) (23) leads to a larger uplift rate in that region, compared to models with uniform Moho depth (28 km).
29. P. S. Kaufman and L. H. Royden, J. Geophys. Res. 99, 15723 (1994).
30. L. E. Gilbert, C. H. Scholz, J. Beavan, ibid., p. 23975.
31. J. Qu, T. L. Teng, J. Wang, Bull. Seismol. Soc. Am. 84, 596 (1994).
32. Y. Okada, ibid. 82, 1018 (1992); L. Erikson, User's manual for DIS3D: A three-dimensional dislocation program with applications to faulting in the earth, thesis, Stanford University (1986).
33. Y. Okada, ibid. 82, 1018 (1992); L. Erikson, User's manual for DIS3D: A three-dimensional dislocation program with applications to faulting in the earth, thesis, Stanford University (1986).
34. We thank M. Simons for a critical review of the manuscript and G. Peltzer, J. Savage, C. Scholz, K. Sieh, M. Spiegelman, L. Sykes, T. L. Teng, W. Thatcher, and many people in the seismo lab for discussion. This research was supported by SCEC. SCEC is funded by NSF Cooperative Agreement EAR-8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. This is SCEC contribution 446 and contribution number 8574 of the Division of Geological and Planetary Sciences, California Institute of Technology.