TY - JOUR
T1 - An implosive component to the source of the deep Sea of Okhotsk earthquake of 24 May 2013
T2 - Evidence from radial modes and CMT inversion
AU - Okal, Emile A.
AU - Saloor, Nooshin
AU - Kirby, Stephen H.
AU - Nettles, Meredith
N1 - Funding Information:
We thank Miaki Ishii for a catalog of splitting parameters for higher overtones, and an anonymous reviewer for constructive comments on an earlier version of the paper. CMT inversions at Columbia University were supported by the National Science Foundation under grant EAR-1639131 .
Funding Information:
We thank Miaki Ishii for a catalog of splitting parameters for higher overtones, and an anonymous reviewer for constructive comments on an earlier version of the paper. CMT inversions at Columbia University were supported by the National Science Foundation under grant EAR-1639131.
Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/8
Y1 - 2018/8
N2 - We study the spectral amplitudes of the first two Earth radial modes, 0S0 and 1S0, excited by the Sea of Okhotsk earthquake of 24 May 2013, the largest deep event ever recorded, in the search for an isotropic component to its source. In contrast to the case of the 1994 Bolivian earthquake, we detect an implosive component MI=-1.1×1027 dyn*cm, equivalent to 3% of the full scalar moment, but 14% of the lone deviatoric component exciting the Earth's radial modes. An independent moment tensor inversion, using the standard GlobalCMT algorithm but after relaxing its zero-trace constraint, similarly yields an implosive isotropic component, albeit with a larger amplitude, while it fails to document one in the case of the 1994 Bolivian deep earthquake. An implosive component to the source is expected in the model of transformational faulting in which deep earthquake rupture nucleates and grows upon transformation of metastable olivine to ringwoodite in the cold subducting slab. This interpretation is supported by quantitative estimates (0.9–4 m) of the thickness of the transformed shear zone, which scale favorably, relative to earthquake fault length, with the upper end of the range of laboratory results reported for ices, germanates and silicates. The resulting extent of the transformation in the metastable wedge is consistent with the local geometry of the deep slab, as recently determined by rupture modeling and aftershock distribution. Our results are in contrast to those for the two runner-up largest deep earthquakes, the 1994 Bolivian and 1970 Colombian shocks, for which a similar isotropic component could not be detected. We attribute this difference to variability in the ratio of isotropic to deviatoric components, which combined with the smaller size of the 1970 and 1994 events, would make any putative implosive component fall below detection levels, especially in the case of the 1970 Colombian earthquake for which only analog narrow-band records were available.
AB - We study the spectral amplitudes of the first two Earth radial modes, 0S0 and 1S0, excited by the Sea of Okhotsk earthquake of 24 May 2013, the largest deep event ever recorded, in the search for an isotropic component to its source. In contrast to the case of the 1994 Bolivian earthquake, we detect an implosive component MI=-1.1×1027 dyn*cm, equivalent to 3% of the full scalar moment, but 14% of the lone deviatoric component exciting the Earth's radial modes. An independent moment tensor inversion, using the standard GlobalCMT algorithm but after relaxing its zero-trace constraint, similarly yields an implosive isotropic component, albeit with a larger amplitude, while it fails to document one in the case of the 1994 Bolivian deep earthquake. An implosive component to the source is expected in the model of transformational faulting in which deep earthquake rupture nucleates and grows upon transformation of metastable olivine to ringwoodite in the cold subducting slab. This interpretation is supported by quantitative estimates (0.9–4 m) of the thickness of the transformed shear zone, which scale favorably, relative to earthquake fault length, with the upper end of the range of laboratory results reported for ices, germanates and silicates. The resulting extent of the transformation in the metastable wedge is consistent with the local geometry of the deep slab, as recently determined by rupture modeling and aftershock distribution. Our results are in contrast to those for the two runner-up largest deep earthquakes, the 1994 Bolivian and 1970 Colombian shocks, for which a similar isotropic component could not be detected. We attribute this difference to variability in the ratio of isotropic to deviatoric components, which combined with the smaller size of the 1970 and 1994 events, would make any putative implosive component fall below detection levels, especially in the case of the 1970 Colombian earthquake for which only analog narrow-band records were available.
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U2 - 10.1016/j.pepi.2018.04.007
DO - 10.1016/j.pepi.2018.04.007
M3 - Article
AN - SCOPUS:85047869745
VL - 281
SP - 68
EP - 78
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
SN - 0031-9201
ER -