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Defocusing of teleseismic P‐waves by the Tonga‐Kermadec Slab
Author(s) -
Suetsugu Daisuke
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1998gl005307
Subject(s) - slab , amplitude , seismology , geology , seismometer , anomaly (physics) , coda , broadband , geodesy , geophysics , optics , physics , condensed matter physics
We analyze P‐wave amplitude reduction for Tonga earthquakes observed at the SKIPPY broadband seismograph network in Australia. The negative amplitude anomaly diminishes with a focal depth, suggesting that the anomaly is due to defocusing caused by the fast Tonga slab. The SKIPPY network covers the distance range where the effect of the Tonga slab is most pronounced. We calculate theoretical amplitudes using simplified slab models based on previous delay time tomography, and show that the theoretical amplitude anomaly reproduces the observations reasonably well. A 100‐km thick slab provides a better fit to the data than a 50‐km thick slab. A thin slab penetrating deep into the lower mantle is inconsistent with the pattern of amplitude variation with distance.