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No AccessGEOPHYSICSVolume 83, Issue 3

Visualizing effects of anisotropy on seismic moments and their potency-tensor isotropic equivalent

Authors:
https://doi.org/10.1190/geo2017-0442.1

ABSTRACT

Radiation patterns of earthquakes contain important information on tectonic strain responsible for seismic events. However, elastic anisotropy may significantly impact these patterns. We systematically investigate and visualize the effect of anisotropy on the radiation patterns of microseismic events. For visualization, we use a vertical-transverse-isotropic (VTI) medium. We distinguish between two different effects: the anisotropy in the source and the anisotropy on the propagation path. Source anisotropy mathematically comes from the matrix multiplication of the anisotropic stiffness tensor with the source strain expressed by the potency tensor. We analyze this effect using the corresponding radiation pattern and the moment tensor decomposition. Propagation anisotropy mathematically comes from the deviation between the polarization and the propagation direction of a quasi P-wave in an anisotropic medium. We investigate both effects separately by either assuming the source to be anisotropic and the propagation to be isotropic or vice versa. We find that both effects have a significant impact on the radiation pattern of a pure-slip source. Finally, we develop an alternative visualization of source mechanisms by plotting beach balls proportional to their potency tensors. For this, we multiply the potency tensor with an isotropic elasticity tensor having the equivalent shear modulus μ and λ=0. In this way, we visualize the tectonic deformation in the source, independently of the rock anisotropy.

REFERENCES

  • Červený, V., 2001, Seismic ray theory: Cambridge University Press.CrossrefGoogle Scholar
  • Chapman, C. H., 2004, Fundamentals of seismic wave propagation: Cambridge University Press.CrossrefGoogle Scholar
  • Chapman, C. H., and W. S. Leaney, 2012, A new moment-tensor decomposition for seismic events in anisotropic media: Geophysical Journal International, 188, 343–370, doi: 10.1111/j.1365-246X.2011.05265.x.GJINEA0956-540XCrossrefWeb of ScienceGoogle Scholar
  • Fedorov, F. I., 1968, Elastic waves in crystals: Springer Science + Business Media.CrossrefGoogle Scholar
  • Hudson, J., R. Pearce, and R. Rogers, 1989, Source type plot for inversion of the moment tensor: Journal of Geophysical Research, 94, 765–774, doi: 10.1029/JB094iB01p00765.JGREA20148-0227CrossrefWeb of ScienceGoogle Scholar
  • Knopoff, L., and M. Randall, 1970, The compensated linear-vector dipole: A possible mechanism for deep earthquakes: Journal of Geophysical Research, 75, 4957–4963, doi: 10.1029/JB075i026p04957.JGREA20148-0227CrossrefWeb of ScienceGoogle Scholar
  • Leaney, S., and C. Chapman, 2010, Microseismic sources in anisotropic media: 72nd Annual International Conference and Exhibition, EAGE, Extended Abstracts, F015.CrossrefGoogle Scholar
  • Rice, J. R., 1980, The mechanics of earthquake rupture: Elsevier/North Holland.Google Scholar
  • Segall, P., 2010, Earthquake and volcano deformation: Princeton University Press.CrossrefGoogle Scholar
  • Shapiro, S. A., 2015, Fluid-induced seismicity: Cambridge University Press.CrossrefGoogle Scholar
  • Tape, W., and C. Tape, 2013, The classical model for moment tensors: Geophysical Journal International, 195, 1701–1720, doi: 10.1093/gji/ggt302.GJINEA0956-540XCrossrefWeb of ScienceGoogle Scholar
  • Thomsen, L., 1986, Weak elastic anisotropy: Geophysics, 51, 1954–1966, doi: 10.1190/1.1442051.GPYSA70016-8033AbstractWeb of ScienceGoogle Scholar
  • Tsvankin, I., 1997, Anisotropic parameters and p-wave velocity for orthorhombic media: Geophysics, 62, 1292–1309, doi: 10.1190/1.1444231.GPYSA70016-8033AbstractWeb of ScienceGoogle Scholar
  • Vavryčuk, V., 2005, Focal mechanisms in anisotropic media: Geophysical Journal International, 161, 334–346, doi: 10.1111/j.1365-246X.2005.02585.x.GJINEA0956-540XCrossrefWeb of ScienceGoogle Scholar
  • Vavryčuk, V., 2015, Moment tensor decomposition revisited: Journal of Seismology, 19, 231–252, doi: 10.1007/s10950-014-9463-y.DXUEF71383-4649CrossrefWeb of ScienceGoogle Scholar
  • Yu, X., S. Leaney, J. Rutledge, and C. Chapman, 2016, Multievent moment-tensor inversion for ill-conditioned geometries: Geophysics, 81, no. 2, KS11–KS24, doi: 10.1190/geo2015-0074.1.GPYSA70016-8033AbstractWeb of ScienceGoogle Scholar
  • Zhu, L., and Y. Ben-Zion, 2013, Parametrization of general seismic potency and moment tensors for source inversion of seismic waveform data: Geophysical Journal International, 194, 839–843, doi: 10.1093/gji/ggt137.GJINEA0956-540XCrossrefWeb of ScienceGoogle Scholar