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Application of the Multichannel Wiener Filter to Regional Event Detection Using NORSAR Seismic-Array Data (2011)

Wang, J. ; Schweitzer, J. ; Tilmann, F. ; White, R. S. ; Soosalu, H.

Seismological Society of America (SSA)

In: Bulletin of the Seismological Society of America (BSSA) 101: 2887-2896.

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Publication Date: 2011-12-01

Description: Seismic arrays for detection of small earthquakes benefit from array processing aimed at reducing noise levels. We present a frequency-dependent multichannel Wiener filtering (MCWF) technique, which employs an adaptive least-squares method to remove coherent noise in seismic array data. The noise records on a number of reference channels are used to predict the noise on a primary channel, which can then be subtracted from the observed data. A sequence of aftershocks caused by the Mw 6.1 21 February 2008 mainshock in Spitsbergen was recorded by the ARCES array in northern Norway. This aftershock sequence was filtered using the multichannel Wiener filters in both triggered and continuous modes. The Spitsbergen (SPITS) array, at a much closer distance to the source region, provides reliable reference information on the true number of detectable aftershocks. The conventional delay-and-sum beamforming combined with a band-pass filter could detect only 513 aftershocks with 181 false alarms, using a series of constraints comprised of signal-to-noise ratio, back azimuth, and slowness; the multichannel Wiener filtered results found 577 aftershocks with 165 false alarms using the same constraints. A complete automatic multichannel Wiener procedure is developed for event detection on continuous data. An appropriate signal-to-noise ratio threshold for aftershock detection of 2.7 is suggested. Compared to the beamforming method, the MCWF also reduces false alarms when detecting the same number of aftershocks.

Print ISSN: 0037-1106

Electronic ISSN: 1943-3573

Topics: Geosciences , Physics

Published by Seismological Society of America (SSA)

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Improvements to Seismic Monitoring of the European Arctic Using Three-Component Array Processing at SPITS (2011)

Gibbons, S. J. ; Schweitzer, J. ; Ringdal, F. ; Kværna, T. ; Mykkeltveit, S. ; Paulsen, B.

Seismological Society of America (SSA)

In: Bulletin of the Seismological Society of America (BSSA) 101: 2737-2754.

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Publication Date: 2011-12-01

Description: The detectability of low magnitude seismic events in the European Arctic is determined primarily by the small-aperture International Monitoring System arrays ARCES and SPITS. In August 2004, the SPITS array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 Hz. Most important, however, for the detection and location of small-magnitude seismic events was the deployment of three-component instruments at six of the nine sites. Detection and correct classification of secondary phases are of paramount importance for events observed by only a small number of stations at regional distances; and, in the absence of the strong Lg phases typically observed for continental propagation paths, multiple three-component stations were deemed necessary to exploit the higher S-phase amplitudes anticipated on the horizontal sensors. We demonstrate improved signal-to-noise ratios (SNRs) for S phases on horizontal beams for several events close to Novaya Zemlya. Horizontal component f-k analysis improves direction estimates and phase classification for low-SNR signals. We demonstrate secondary phases that are misidentified by vertical-only f-k analysis but which are correctly classified by three-component array processing. A significant problem with array processing at SPITS is the overlap in slowness space of regional P and S phases. Phase identification is improved greatly by comparing the coherence between vertical traces with the coherence between horizontal traces. Considerations in the routine array processing of SPITS data are reviewed, including the need for elevation corrections in slowness estimation and the need to take into account azimuth-dependent variation of apparent velocity estimates for regional phases.

Print ISSN: 0037-1106

Electronic ISSN: 1943-3573

Topics: Geosciences , Physics

Published by Seismological Society of America (SSA)

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GERESS - A new array for on-line monitoring the regional seismicity in Central Europe (1992)

J. Schweitzer ; M. L. Jost ; N. Gestermann ; [et al.]

Conseil de l'Europe

In: Bull., Open-File Rept., Local and National Seismic Networks: On Line Date Processing with Microcomputer Facilities, Luxembourg, Conseil de l'Europe, vol. 5, no. 16, pp. 1-10, (ISBN 1-86239-165-3, vi + 330 pp.)

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Publication Date: 1992

Keywords: Seismology ; Seismic arrays ; Review article ; Project report/description ; Seismicity

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BIBLIOGRAPHY SEISMOLOGY

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Measurement of the $^{12}\mathrm{C}(^{12}\mathrm{C},p)^{23}\mathrm{Na}$ cross section near the Gamow energy (2018)

J. Zickefoose, A. Di Leva, F. Strieder, L. Gialanella, G. Imbriani, N. De Cesare, C. Rolfs, J. Schweitzer, T. Spillane, O. Straniero, and F. Terrasi

American Physical Society (APS)

In: Physical Review C

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Publication Date: 2018-06-27

Description: Author(s): J. Zickefoose, A. Di Leva, F. Strieder, L. Gialanella, G. Imbriani, N. De Cesare, C. Rolfs, J. Schweitzer, T. Spillane, O. Straniero, and F. Terrasi The fusion reaction C 12 ( C 12 , p ) Na 23 has been studied from E = 2.00 to 4.00 MeV by particle spectroscopy. The data reveal broad resonances above E = 3.00 MeV and are compatible with previously reported resonance structure around E = 2.1 MeV. The data were limited at low energies by low count rates as well a... [Phys. Rev. C 97, 065806] Published Tue Jun 26, 2018

Keywords: Nuclear Astrophysics

Print ISSN: 0556-2813

Electronic ISSN: 1089-490X

Topics: Physics

Published by American Physical Society (APS)

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The 11 October 2010 Novaya Zemlya Earthquake: Implications for Velocity Models and Regional Event Location (2016)

Gibbons, S. J., Antonovskaya, G., Asming, V., Konechnaya, Y. V., Kremenetskaya, E., Kvaerna, T., Schweitzer, J., Vaganova, N. V.

Seismological Society of America (SSA)

In: Bulletin of the Seismological Society of America (BSSA)

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Publication Date: 2016-07-26

Description: Characterizing the seismicity of Novaya Zemlya and the surrounding Arctic seas requires accurate event-location estimates. Low-magnitude events in this region are currently observed only by a small number of stations in the European Arctic, with a large azimuthal gap, making the accuracy of regional velocity models all the more important. Regional travel-time calibration is difficult given the scarcity of sufficiently well-constrained events. On 11 October 2010, a magnitude 4.5 event occurred close to the northern tip of Novaya Zemlya. This event is significant in that it is the first event in this region to have been recorded both on the relatively recent regional networks and arrays, and also teleseismically with good azimuthal coverage. We examine how well we can constrain the location and origin time using only teleseismic phases. Using only first teleseismic P arrivals, we constrain the epicenter to approximately 76.25° N and 64.75° E but with no depth resolution. Clear depth phases, notably on stations in the southern United States, indicate a depth between 9 and 15 km. This independent hypocenter and origin time estimate allow evaluation of regional phase travel-time prediction using different models. The predicted Sn travel time appears to cause the greatest variability in regional location estimates. The 3D Regional Seismic Travel Times models provide excellent Pn travel-time estimates for Barents Sea paths but may slightly overestimate Sn travel times from this source region. A modified regional 1D velocity model is defined, which best predicts Pn and Sn observations at multiple stations up to 15°. The significance of the regional travel-time models for estimating location is demonstrated for a low-magnitude event on or close to the northern island of Novaya Zemlya in March 2014, recorded with a satisfactory signal-to-noise ratio at only four stations.

Print ISSN: 0037-1106

Electronic ISSN: 1943-3573

Topics: Geosciences , Physics

Published by Seismological Society of America (SSA)

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