Open AccessBias in seismic estimates of crustal properties
Author(s) -
Bostock M. G.,
Kumar M. Ravi
Publication year - 2010
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2010.04623.x
Subject(s) - geology , estimator , crust , seismology , least squares function approximation , geodesy , seismic velocity , grid , seismic array , waveform , matching (statistics) , geophysics , statistics , mathematics , physics , quantum mechanics , voltage
SUMMARY It has come to our attention that the least‐squares estimator we proposed in a recent paper to recover bulk crustal P velocity, V P , and P velocity/ S velocity ratio, R , of the crust from traveltimes of scattered teleseismic phases, is inconsistent. That is, in the presence of errors, estimates of R will be biased downwards and estimates of V P will be biased upwards from their true values. In this note we supply bias corrections for both quantities that depend upon an estimate of the variance in a ratio of traveltime sums, and demonstrate their validity through comparison with estimates based on a two‐parameter grid search. Application to station HYB yields R = 1.756 ± 0.005, V P = 6.2 ± 0.1 km s −1 , after correction of a systematic traveltime picking error that had affected our previous results. In addition, we provide an alternative waveform‐stacking approach that involves a 2‐D grid search over R and V P followed by a 1‐D line search over crustal thickness H . An estimate of the direct P s conversion time is required, and results from station HYB are consistent with those produced using traveltimes alone.