Abstract
In the determination of focal mechanism and rupture process of earthquake sources by using moment tensor inversion technique, it is difficult to guarantee the focal depth used in calculating the Green’s functions (theoretical focal depth) is exactly equal to the real focal depth. The difference between the theoretical and real focal depths, i. e., the focal depth error, will affect the moment tensor inversion to some extent. Using synthetic seismograms, the effect of the focal depth error on moment tensor inversion for three basic types of faults is discussed systematically. For the normal and thrust fault, the focal depth error mainly affects the explosive (EP) component and the compensated linear vector dipole (CLVD) component. In the case that the theoretical focal depth is greater than the real focal depth, the focal depth error causes a false positive EP component and a false negative CLVD component for the normal fault. However, it produces a false negative EP component and a false positive CLVD component for the thrust fault. The absolute values of the false EP and CLVD components for both normal fault and thrust fault cases increase with increasing focal depth error. In the case that the theoretical focal depth is smaller than the real focal depth, the focal depth error causes a false negative EP component and a false positive CLVD component for the normal fault. However, it produces a false positive EP component and a false negative CLVD component for the thrust fault. Similarly, the absolute values of the false EP and CLVD components for both normal fault and thrust fault cases increase with increasing focal depth error. For a pure strike-slip fault the focal depth error mainly affects the shape of source the function, unlike for the normal and thrust faults. The source time functions have artificially extended tails when either the theoretical focal depth is greater or smaller than the real focal depth. The numerical experiments show that the focal depth error less than 20 km has no significant effect on the overall focal mechanism of the earthquake. In addition, the effect of the focal depth error on the inversion result is slighter in case that the theoretical focal depth is greater than the real focal depth than in the case that the theoretical focal depth is smaller than the real focal depth.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Kennett B T N, 1983. Seismic Wave Propagation in Stratified Media. Cambridge: Cambridge University Press, 342
Ni J C, Chen, Y T, Wang M et al., 1991. Moment tensor inversion of some aftershocks of April 18, 1985, Luquan, Yunnan, China, earthquake. Acta Seismologica Sinica (Chinese edition): 13: 412–419; Acta Seismologica Sinca (English edition), 5 (3): 459–467, 1992
Bech S L and Christensen D H, 1991. Rupture process of the February 4, 1965, Rat islands earthquake, J Geophys Res, 96 (B2): 2 205–2 221
Christensen D and Ruff L, 1985. Analysis of the trade-off between hypocentral depth and source time function. Bull Seism Soc Amer, 75: 1 637–1 656
Dziewonski A M, Franzen J E and Woodhouse J H, 1983. Centroid-moment tensor solutions for April–June, 1983. Phys Earth Planet Interi, 33: 243–249
Johnson D E and Langston C A 1984. The effect of assumed source structure on inversion of earthquake source parameters: the eastern Hispaniola earthquake of 14 September, 1981. Bull Seism Soc Amer, 74: 2 115–2 143
Sipkin S A, 1982. Estimation of earthquake source parameters by the inversion of waveform data: synthetic waveforms. Phys Earth Planet Interior, 30: 242–259
Sipkin S A, 1986a. Estimation of earthquake source parameters by the inversion of waveform data: global seismicity, 1981–1983. Bull Seism Soc Amer, 76(6): 1 515–1 541
Sipkin S A, 1986b. Interpretation of non double-couple earthquake source mechanism derived from moment tensor inversion. J Geophys Res, 91: 531–547
Silency J, Panza G F and Campus P, 1992. Waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model. Geophys J Intl, 109: 259–274
Stump B W, and Johnson, J R, 1977. The determination of source properties by the linear inversion of seismograms. Bull Seism Soc Amer, 67: 1487–1502
Velasco A A, Lay T and Zhang J, 1993. Long-period surface wave inversion for source parameters of the 18 October, 1989 Loma Prieta earthquake. Phys Earth Planet Interior, 76: 43–66
Wallace T C, Velasco A, Zhang J et al., 1991. A broadband seimological investigation of the 1989 Loma Prieta, California, earthquake: evidence for deep, slow slip? Bull Seism Soc Amer, 81: 1 622–1 646
Ward S N, 1982. Earthquake mechanism and tsunami generation: the Kurile islands earthquake of 13. October, 1963. Bull Seism Soc Amer, 72: 759–777
Author information
Authors and Affiliations
Additional information
Contribution No. 97 A0068, Institute of Geophysics, State Seismological Bureau, Beijing, China.
About this article
Cite this article
Xu, LS., Chen, YT. The effect of focal depth error on moment tensor inversion. Acta Seimol. Sin. 10, 571–580 (1997). https://doi.org/10.1007/s11589-997-0020-4
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/s11589-997-0020-4