University of Oulu

S J Gibbons, T Kværna, T Tiira, E Kozlovskaya, A benchmark case study for seismic event relative location, Geophysical Journal International, Volume 223, Issue 2, November 2020, Pages 1313–1326,

A benchmark case study for seismic event relative location

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Author: Gibbons, S. J.1,2; Kværna, T.1; Tiira, T.3;
Organizations: 1NORSAR, P.O. Box 53, 2027 Kjeller, Norway
2NGI, Sognsveien 72, 0855 Oslo, Norway
3Institute of Seismology, Department of Geosciences and Geography, P.O. Box 68, FI-00014 University of Helsinki, Finland
4Oulu Mining School, Faculty of Technology, POB 3000, FIN-90014 University of Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 5.4 MB)
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Language: English
Published: Oxford University Press, 2020
Publish Date: 2021-01-21


‘Precision seismology’ encompasses a set of methods which use differential measurements of time-delays to estimate the relative locations of earthquakes and explosions. Delay-times estimated from signal correlations often allow far more accurate estimates of one event location relative to another than is possible using classical hypocentre determination techniques. Many different algorithms and software implementations have been developed and different assumptions and procedures can often result in significant variability between different relative event location estimates. We present a Ground Truth (GT) dataset of 55 military surface explosions in northern Finland in 2007 that all took place within 300 m of each other. The explosions were recorded with a high signal-to-noise ratio to distances of about 2°, and the exceptional waveform similarity between the signals from the different explosions allows for accurate correlation-based time-delay measurements. With exact coordinates for the explosions, we are able to assess the fidelity of relative location estimates made using any location algorithm or implementation. Applying double-difference calculations using two different 1-D velocity models for the region results in hypocentre-to-hypocentre distances which are too short and it is clear that the wavefield leaving the source region is more complicated than predicted by the models. Using the GT event coordinates, we are able to measure the slowness vectors associated with each outgoing ray from the source region. We demonstrate that, had such corrections been available, a significant improvement in the relative location estimates would have resulted. In practice we would of course need to solve for event hypocentres and slowness corrections simultaneously, and significant work will be needed to upgrade relative location algorithms to accommodate uncertainty in the form of the outgoing wavefield. We present this data set, together with GT coordinates, raw waveforms for all events on six regional stations, and tables of time-delay measurements, as a reference benchmark by which relative location algorithms and software can be evaluated.

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Series: Geophysical journal international
ISSN: 0956-540X
ISSN-E: 1365-246X
ISSN-L: 0956-540X
Volume: 223
Issue: 2
Pages: 1313 - 1326
DOI: 10.1093/gji/ggaa362
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
1171 Geosciences
Copyright information: © The Author 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.