Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms

Nooshiri, Nima; Saul, Joachim; Heimann, Sebastian; Tilmann, Frederik; Dahm, Torsten

doi:10.1093/gji/ggw405

Cited by 14 publications

(13 citation statements)

References 42 publications

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“…The exploitation of readings from multiple events to account for, or to eliminate, bias in travel time estimates is a cornerstone of many advanced seismic event location algorithms (e.g. Douglas, 1967;Richards-Dinger and Shearer, 2000;Nooshiri et al, 2017). The solutions obtained using Bayesloc indicate that failure to account for Resolving Northern Alaska Earthquake Sequences Using the Transportable Array and Probabilistic Location Methods (final version on https://doi.org/10.1785/0220200142) Steven J. Gibbons ;Natalia A.…”

Section: Discussion and Future Perspectivesmentioning

confidence: 99%

Resolving Northern Alaska Earthquake Sequences Using the Transportable Array and Probabilistic Location Methods

Gibbons¹,

Ruppert²,

Karasözen³

et al. 2022

Preprint

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Between 2014 and 2017, almost 200 new seismic stations were installed in Alaska and northwestern Canada as part of the EarthScope USArray Transportable Array (TA). These stations currently provide an unprecedented capability for the detection and location of seismic events in regions with otherwise relatively sparse station coverage. Two interesting earthquake sequences in 2018/2019 in the north eastern Brooks Range were exceptionally well recorded due to this deployment. First is the aftershock sequence of the MW 6.4 and MW 6.0 Kaktovik earthquakes of 12 August 2018, the largest earthquakes recorded to-date in the region. The second is the Niviak swarm, southwest of the Kaktovik sequence. Since July 2018, over 4000 earthquakes between magnitudes 1 and 4.3 have been recorded across a region exceeding 5000 square kilometers. We explore how the Bayesloc probabilistic multiple seismic event location algorithm can better resolve features of these two sequences, exploiting the large numbers of readings that the improved station coverage provides from events down to magnitudes below 2. The Bayesloc calculations consistently move events in the Kaktovik sequence a few kilometers to the northeast, providing an almost linear ESE-striking southern limit to the aftershock zone. Analysis of the Bayesloc joint probability distribution of corrections to travel time predictions indicate that anomalously fast wave propagation to the southwest is likely the most significant contribution to the seismic event mislocation. The joint relocations are more consistent with InSAR-inferred coseismic displacement than the network location estimates. The Bayesloc relocation of the Niviak events confirms that the earthquakes are distributed between many distinct clusters of seismicity which have clearer spatial separation following the relocation. The probabilistic relocations motivate both double-difference studies to better resolve clustered seismicity at the smallest spatial scales and systematic multiple event relocation studies to calculate structure and travel time corrections over larger scales.

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Section: Discussion and Future Perspectivesmentioning

confidence: 99%

Resolving Northern Alaska Earthquake Sequences Using the Transportable Array and Probabilistic Location Methods

Gibbons¹,

Ruppert²,

Karasözen³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…However, this bias is not accounted for in generic location procedures at seismological observatories and the true location uncertainty for a given event is part of a truly joint probability depending also upon the constraints which apply to other nearby seismic events. If routine seismic bulletins are to achieve the same accuracy as that possible using contextual methods (e.g Myers et al 2011;Nooshiri et al 2017) then we need to find ways of applying and presenting the necessary corrections and associated uncertainties.…”

Section: Discussionmentioning

confidence: 99%

“…These outliers are clearly identifiable from the Bayesloc residuals but are quite typical of residuals from the single-event solutions. As with the SSST locations of subduction zone seismicity presented by Nooshiri et al (2017), Bayesloc is providing a probability distribution for traveltime corrections which compensates for inadequacies in the predicted 1-D velocity model. Fig.…”

Section: Overview Of Seismic Bulletins Of Ridge Seismicitymentioning

confidence: 99%

“…Five decades since Douglas (1967) demonstrated how deviations from predicted traveltimes could be compensated for by consideration of several events simultaneously, we have various alternatives for large-scale multiple event location. Nooshiri et al (2017) provide an extension of the shrinking-box source specific station term (SSST) method (Richards-Dinger & Shearer 2000;Lin & Shearer 2005) which provides a reduction in traveltime residuals (both regional and teleseismic) for multiple events in a complex tectonic environment using station correction terms. The Bayesloc program (Myers et al 2007(Myers et al , 2009) employs a Bayesian hierarchical method to solve for the joint probability of hypocenters and origin times, traveltime corrections and pick uncertainties, and phase labels.…”

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confidence: 99%

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Locating seismicity on the Arctic plate boundary using multiple-event techniques and empirical signal processing

Gibbons

Harris

Dahl‐Jensen

et al. 2017

Geophysical Journal International

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The oceanic boundary separating the Eurasian and North American plates between 70 and 84 degrees North hosts large earthquakes which are well recorded teleseismically, and many more seismic events at far lower magnitudes that are well recorded only at regional distances. Existing seismic bulletins have considerable spread and bias resulting from limited station coverage and deficiencies in the velocity models applied. This is particularly acute for the lower magnitude events which may only be constrained by a small number of Pn and Sn arrivals. Over the past two decades there has been a significant improvement in the seismic network in the Arctic: a difficult region to instrument due to the harsh climate, a sparsity of accessible sites (particularly at significant distances from the sea), and the expense and difficult logistics of deploying and maintaining stations. New deployments and upgrades to stations on Greenland, Svalbard, Jan Mayen, Hopen, and Bjørnøya have resulted in a sparse but stable regional seismic network which results in events down to magnitudes below 3 generating high quality Pn and Sn signals on multiple stations. A catalog of several hundred events in the region since 1998 has been generated using many new phase readings on stations on both sides of the spreading ridge in addition 2 S. J. Gibbons et al. to teleseismic P phases. A Bayesian multiple event relocation has resulted in a significant reduction in the spread of hypocenter estimates for both large and small events. Whereas single event location algorithms minimize vectors of time residuals on an event-by-event basis, the Bayesloc program finds a joint probability distribution of origins, hypocenters, and corrections to travel time predictions for large numbers of events. The solutions obtained favour those event hypotheses resulting in time residuals which are most consistent over a given source region. The relocations have been performed with different 1-D velocity models applicable to the Arctic region and hypocenters obtained using Bayesloc have been shown to be relatively insensitive to the specified velocity structure in the crust and upper mantle, even for events only constrained by regional phases. The patterns of time residuals resulting from the multiple-event location procedure provide well-constrained time correction surfaces for single-event location estimates and are sufficiently stable to identify a number of picking errors and instrumental timing anomalies. This allows for subsequent quality control of the input data and further improvement in the location estimates. We use the relocated events to form narrowband empirical steering vectors for wavefronts arriving at the SPITS array on Svalbard for azimuth and apparent velocity estimation. We demonstrate that empirical matched field parameter estimation determined by source region is a viable supplement to planewave f-k analysis, mitigating bias and obviating the need for Slowness and Azimuth Station Corrections (SASCs). A database of reference events and phase arrivals ...

show abstract

Section: Discussionmentioning

confidence: 99%

Locating Seismicity on the Arctic Plate Boundary Using Multiple-Event Techniques and Empirical Signal Processing

Gibbons¹,

Harris²,

Dahl‐Jensen³

et al. 2017

Preprint

View full text Add to dashboard Cite

The oceanic boundary separating the Eurasian and North American plates between 70 and 84 degrees North hosts large earthquakes which are well recorded teleseismically, and many more seismic events at far lower magnitudes that are well recorded only at regional distances. Existing seismic bulletins have considerable spread and bias resulting from limited station coverage and deficiencies in the velocity models applied. This is particularly acute for the lower magnitude events which may only be constrained by a small number of Pn and Sn arrivals. Over the past two decades there has been a significant improvement in the seismic network in the Arctic: a difficult region to instrument due to the harsh climate, a sparsity of accessible sites (particularly at significant distances from the sea), and the expense and difficult logistics of deploying and maintaining stations. New deployments and upgrades to stations on Greenland, Svalbard, Jan Mayen, Hopen, and Bjørnøya have resulted in a sparse but stable regional seismic network which results in events down to magnitudes below 3 generating high quality Pn and Sn signals on multiple stations. A catalog of several hundred events in the region since 1998 has been generated using many new phase readings on stations on both sides of the spreading ridge in addition to teleseismic P phases. A Bayesian multiple event relocation has resulted in a significant reduction in the spread of hypocenter estimates for both large and small events. Whereas single event location algorithms minimize vectors of time residuals on an event-by-event basis, the Bayesloc program finds a joint probability distribution of origins, hypocenters, and corrections to travel time predictions for large numbers of events. The solutions obtained favour those event hypotheses resulting in time residuals which are most consistent over a given source region. The relocations have been performed with different 1-D velocity models applicable to the Arctic region and hypocenters obtained using Bayesloc have been shown to be relatively insensitive to the specified velocity structure in the crust and upper mantle, even for events only constrained by regional phases. The patterns of time residuals resulting from the multiple-event location procedure provide well-constrained time correction surfaces for single-event location estimates and are sufficiently stable to identify a number of picking errors and instrumental timing anomalies. This allows for subsequent quality control of the input data and further improvement in the location estimates. We use the relocated events to form narrowband empirical steering vectors for wavefronts arriving at the SPITS array on Svalbard for azimuth and apparent velocity estimation. We demonstrate that empirical matched field parameter estimation determined by source region is a viable supplement to planewave f-k analysis, mitigating bias and obviating the need for Slowness and Azimuth Station Corrections (SASCs). A database of reference events and phase arrivals is provided to facilitate further refinement of event locations and the construction of empirical signal detectors.

show abstract

Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms

Cited by 14 publications

References 42 publications

Resolving Northern Alaska Earthquake Sequences Using the Transportable Array and Probabilistic Location Methods

Resolving Northern Alaska Earthquake Sequences Using the Transportable Array and Probabilistic Location Methods

Locating seismicity on the Arctic plate boundary using multiple-event techniques and empirical signal processing

Locating Seismicity on the Arctic Plate Boundary Using Multiple-Event Techniques and Empirical Signal Processing

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