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Lower bound estimate of average earthquake mislocation from variance of travel-time residuals

Davies, John Huw ORCID: 1992. Lower bound estimate of average earthquake mislocation from variance of travel-time residuals. Physics of the Earth and Planetary Interiors 75 (1-3) , pp. 89-101. 10.1016/0031-9201(92)90120-K

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We introduce a novel method by which one can estimate absolutely (i.e. independent of forward modelling assumptions, e.g. velocity model) a lower bound on the average contribution of incorrect hypocentral parameters (total mislocation, sum of contribution due to spatial mislocation and origin-time error) to the variance of travel-time residuals. The method involves estimating the variance of fans of rays with a common station, and also the variance of fans of rays with a common event. One estimates the variances for fans of different extent by evaluating the variance in grid cells of different size. The lower bound estimate of the contribution of total mislocation is derived from the difference between the two variances in the limit of small grid size. Applying this method to P-wave travel-time residuals from the Bulletins of the International Seismological Centre (ISC), we demonstrate that the mislocation signal is appreciable, of order 35% of the total signal. We also find that the ISC data have very little intrinsic, spatially uncorrelated noise. The observation that the variance decreases for all grid-sizes, including very small grid sizes, is suggestive of structural signal at all scale lengths. The method has also been investigated in simple synthetic models, in both one and three dimensions. The synthetic studies illustrate how the method can lead to underestimates of total mislocation when the total mislocation is spatially coherent at the smallest separations. They also reinforce the fact that relocation masks structural signal.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Subjects: Q Science > QE Geology
Publisher: Elsevier
ISSN: 0031-9201
Last Modified: 18 Oct 2022 12:38

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