Geophysics: An observation of PKJKP: Inferences on inner core shear properties

Science

Volumn 308, Issue 5727, 2005, Pages 1453-1455

  Cao, Aimin ^a   Romanowicz, Barbara ^a   Takeuchi, Nozomu ^b  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b UNIVERSITY OF TOKYO   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EARTH (PLANET); GEOPHYSICS; SEISMOLOGY; SIGNAL TO NOISE RATIO; VELOCITY;

BROADBAND RECORDS; EARTH MODEL; SIGNAL-TO-NOISE PHASE; SOLIDITY;

SEISMIC PROSPECTING;

INNER CORE; S-WAVE;

ARTICLE; EARTHQUAKE; GERMANY; PREDICTION; PRIORITY JOURNAL; SHEAR RATE; SIGNAL NOISE RATIO; THEORY; VELOCITY; WAVEFORM;

EID: 20344376451     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1109134     Document Type: Article

References (17)

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8. The relocated catalog by Engdahl et al. is available for this time period; E. R. Engdahl, R. D. van der Hilst, R. P. Buland, Bull. Seismol. Soc. Am. 88, 722 (1998).
9. From 100 s before PKIKP and 200 s after PKJKP, the amplitude spectrum (fig. S1B) indicates that the amplitude decays significantly at periods longer than 0.06 Hz. Only in the frequency range 0.06 to 0.1 Hz is the amplitude relatively constant.
10. The GRF seismic array has a relatively small aperture, but there is still noticeable variation of differential travel times of PKIKP, which can be as large as 0.6 s across the array. This variation is presumed to be primarily related to crust and/or uppermost mantle heterogeneity just beneath the array. This heterogeneity should also influence PKJKP at a similar level, because the two ray paths are very close in this region (Fig. 1A). GRB2, which is at the center of this broad-band seismic array, is chosen as the reference station.
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13. Materials and methods are available as supporting material on Science Online.
14. The phase observed in Fig. 2, C and D, cannot be due to random noise. (i) The PWS stacking technique (11) is designed specifically to remove the influence of the background incoherent noise. (ii) If what we observed had been random noise, the energy extrema should have also distributed randomly in the observed vespagram.
15. B. Although the aperture of GRF seismic array is relatively small for this very sharp large event, it is sensitive to small perturbations in arrival times (as low as ∼0.3 s) using vespagrams. This is also the reason that the array-sided travel time correction is necessary.
16. A. Cao, B. Romanowicz, Earth Planet. Sci. Lett. 228, 243 (2004).
17. We thank the Gräfenberg Array operators for the long-term high-quality maintenance of their array. This work was supported by NSF grant EAR-0308750. This is Berkeley Seismological Laboratory contribution 05-08.