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  • 1
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    Multimodal function optimization with a niching genetic algorithm: a seismological example (1999)
    In:  Bull. Seism. Soc. Am., New York, Conseil de l'Europe, vol. 89, no. 4, pp. 978-988, pp. L10606, (ISSN: 1340-4202)
    Details
    Publication Date: 1999
    Keywords: Seismology ; Data analysis / ~ processing ; BSSA
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    The frequency dependence and locations of short period microseisms generated in the Southern Ocean and west Pacific (2015)
    Wiley
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    Publication Date: 2015-08-07
    Description: The origin of the microseismic wavefield is associated with deep ocean and coastal regions where, under certain conditions, ocean waves can excite seismic waves that propagate as surface and body waves. Given that the characteristics of seismic signals generally vary with frequency, here we explore the frequency and azimuth dependent properties of microseisms recorded at a medium aperture (25 km) array in Australia. We examine the frequency dependent properties of the wavefield, and its temporal variation, over two decades (1991–2012), with a focus on relatively high-frequency microseisms (0.325–0.725 Hz) recorded at the Warramunga Array (WRA), which has good slowness resolution capabilities in this frequency range. The analysis is carried out using the Incoherently Averaged Signal (IAS) Capon beamforming, which gives robust estimates of slowness and backazimuth, and is able to resolve multiple wave arrivals within a single time window. For surface waves, we find that fundamental mode Rayleigh waves (R g ) dominate for lower frequencies (〈0.55 Hz) while higher frequencies (〉0.55 Hz) show a transition to higher mode surface waves (L g ). For body waves, source locations are identified in deep ocean regions for lower frequencies and in shallow waters for higher frequencies. We further examine the association between surface wave arrivals and a WAVEWATCH III ocean wave hindcast. Correlations with the ocean wave hindcast show that secondary microseisms in the lower frequency band are generated mainly by ocean swell, while higher frequency bands are generated by the wind sea, i.e. local wind conditions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Along-dip variation of teleseismic short-period radiation from the 11 March 2011 Tohoku earthquake (Mw 9.0) (2011)
    Wiley
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    Publication Date: 2011-11-16
    Description: Locations of coherent short-period seismic wave radiation from the 11 March 2011 Tohoku earthquake (Mw 9.0) are imaged by back-projecting teleseismic P waves recorded across North America for a series of narrow, overlapping passbands centered at 8s, 4s, 2s, 1s, and 0.5s. Initially the energy release for all five passbands migrates slowly down-dip, however over time the two longer-period passbands show coherent energy release systematically shifted up-dip of the shorter-period source regions. Back-projection images of P waves from ten (point-source-like) aftershocks do not show a frequency-dependent trend, implying that the frequency dependence observed for the main shock is not an artifact created by 3D earth structure, depth phase interference, or some other deficiency. We conclude that the unstable sliding properties along the megathrust are segmented, with faster moment rate variations in the down-dip region and relatively smooth sliding further up-dip.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    The 2009 Samoa-Tonga great earthquake triggered doublet (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-08-21
    Description: Great earthquakes (having seismic magnitudes of at least 8) usually involve abrupt sliding of rock masses at a boundary between tectonic plates. Such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks, as is commonly observed in the trench-slope region seaward of a great subduction zone thrust event. The earthquake sequence addressed here involves a rare instance in which a great trench-slope intraplate earthquake triggered extensive interplate faulting, reversing the typical pattern and broadly expanding the seismic and tsunami hazard. On 29 September 2009, within two minutes of the initiation of a normal faulting event with moment magnitude 8.1 in the outer trench-slope at the northern end of the Tonga subduction zone, two major interplate underthrusting subevents (both with moment magnitude 7.8), with total moment equal to a second great earthquake of moment magnitude 8.0, ruptured the nearby subduction zone megathrust. The collective faulting produced tsunami waves with localized regions of about 12 metres run-up that claimed 192 lives in Samoa, American Samoa and Tonga. Overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries, with the triggered thrust faulting only being revealed by detailed seismic wave analyses. Extensive interplate and intraplate aftershock activity was activated over a large region of the northern Tonga subduction zone.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lay, Thorne -- Ammon, Charles J -- Kanamori, Hiroo -- Rivera, Luis -- Koper, Keith D -- Hutko, Alexander R -- England -- Nature. 2010 Aug 19;466(7309):964-8. doi: 10.1038/nature09214.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA. tlay@ucsc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20725038" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    Energy release of the 2013 M(w) 8.3 Sea of Okhotsk earthquake and deep slab stress heterogeneity (2013)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2013-09-21
    Description: Earth's deepest earthquakes occur in subducting oceanic lithosphere, where temperatures are lower than in ambient mantle. On 24 May 2013, a magnitude 8.3 earthquake ruptured a 180-kilometer-long fault within the subducting Pacific plate about 609 kilometers below the Sea of Okhotsk. Global seismic P wave recordings indicate a radiated seismic energy of ~1.5 x 10(17) joules. A rupture velocity of ~4.0 to 4.5 kilometers/second is determined by back-projection of short-period P waves, and the fault width is constrained to give static stress drop estimates (~12 to 15 megapascals) compatible with theoretical radiation efficiency for crack models. A nearby aftershock had a stress drop one to two orders of magnitude higher, indicating large stress heterogeneity in the deep slab, and plausibly within the rupture process of the great event.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ye, Lingling -- Lay, Thorne -- Kanamori, Hiroo -- Koper, Keith D -- New York, N.Y. -- Science. 2013 Sep 20;341(6152):1380-4. doi: 10.1126/science.1242032.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24052306" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    En echelon and orthogonal fault ruptures of the 11 April 2012 great intraplate earthquakes (2012)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2012-10-02
    Description: The Indo-Australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary--from an environment of continental collision to an island arc subduction zone. On 11 April 2012, one of the largest strike-slip earthquakes ever recorded (seismic moment magnitude M(w) 8.7) occurred about 100-200 kilometres southwest of the Sumatra subduction zone. Occurrence of great intraplate strike-slip faulting located seaward of a subduction zone is unusual. It results from northwest-southeast compression within the plate caused by the India-Eurasia continental collision to the northwest, together with northeast-southwest extension associated with slab pull stresses as the plate underthrusts Sumatra to the northeast. Here we use seismic wave analyses to reveal that the 11 April 2012 event had an extraordinarily complex four-fault rupture lasting about 160 seconds, and was followed approximately two hours later by a great (M(w) 8.2) aftershock. The mainshock rupture initially expanded bilaterally with large slip (20-30 metres) on a right-lateral strike-slip fault trending west-northwest to east-southeast (WNW-ESE), and then bilateral rupture was triggered on an orthogonal left-lateral strike-slip fault trending north-northeast to south-southwest (NNE-SSW) that crosses the first fault. This was followed by westward rupture on a second WNW-ESE strike-slip fault offset about 150 kilometres towards the southwest from the first fault. Finally, rupture was triggered on another en echelon WNW-ESE fault about 330 kilometres west of the epicentre crossing the Ninetyeast ridge. The great aftershock, with an epicentre located 185 kilometres to the SSW of the mainshock epicentre, ruptured bilaterally on a NNE-SSW fault. The complex faulting limits our resolution of the slip distribution. These great ruptures on a lattice of strike-slip faults that extend through the crust and a further 30-40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the Indian and Australian plates.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yue, Han -- Lay, Thorne -- Koper, Keith D -- England -- Nature. 2012 Oct 11;490(7419):245-9. doi: 10.1038/nature11492. Epub 2012 Sep 26.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23023129" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 7
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    Full wavefield decomposition of high frequency secondary microseisms reveals distinct arrival azimuths for Rayleigh and Love waves (2017)
    Wiley
    Details
    Publication Date: 2017-06-13
    Description: In the secondary microseism band (0.1-1.0 Hz) the theoretical excitation of Rayleigh waves ( R g / L R ), through oceanic wave-wave interaction, is well understood. For Love waves ( L Q ), the excitation mechanism in the secondary microseism band is less clear. We explore high frequency secondary microseism excitation between 0.35-1 Hz by analyzing a full year (2013) of records from a three-component seismic array in Pilbara (PSAR), Australia. Our recently developed three-component waveform decomposition algorithm (CLEAN-3C) fully decomposes the beam power in slowness space into multiple point sources. This method allows for a directionally dependent power estimation for all separable wave phases. In this contribution, we compare quantitatively microseismic energy recorded on vertical and transverse components. We find the mean power representation of Rayleigh and Love waves to have differing azimuthal distributions, which are likely a result of their respective generation mechanisms. Rayleigh waves show correlation with convex coastlines while Love waves correlate with seefloor sedimentary basins. The observations are compared to the WAVEWATCH III ocean model, implemented at the Institut Fran ç ais de Recherche pour l'Exploitation de la Mer (IFREMER), which describes the spatial and temporal characteristics of microseismic source excitation. We find Love wave energy to originate from ray paths coinciding with seafloor sedimentary basins where strong Rayleigh wave excitation is predicted by the ocean model. The total power of R g waves is found to dominate at 0.35-0.6 Hz and the Rayleigh/Love wave power ratio strongly varies with direction and frequency.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Detecting and characterizing coal mine related seismicity in the Western U.S. using subspace methods (2015)
    Oxford University Press
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    Publication Date: 2015-10-16
    Description: We present an approach for subspace detection of small seismic events that includes methods for estimating magnitudes and associating detections from multiple stations into unique events. The process is used to identify mining related seismicity from a surface coal mine and an underground coal mining district, both located in the Western U.S. Using a blasting log and a locally derived seismic catalogue as ground truth, we assess detector performance in terms of verified detections, false positives and failed detections. We are able to correctly identify over 95 per cent of the surface coal mine blasts and about 33 per cent of the events from the underground mining district, while keeping the number of potential false positives relatively low by requiring all detections to occur on two stations. We find that most of the potential false detections for the underground coal district are genuine events missed by the local seismic network, demonstrating the usefulness of regional subspace detectors in augmenting local catalogues. We note a trade-off in detection performance between stations at smaller source–receiver distances, which have increased signal-to-noise ratio, and stations at larger distances, which have greater waveform similarity. We also explore the increased detection capabilities of a single higher dimension subspace detector, compared to multiple lower dimension detectors, in identifying events that can be described as linear combinations of training events. We find, in our data set, that such an advantage can be significant, justifying the use of a subspace detection scheme over conventional correlation methods.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    Rapid Seismological Quantification of Source Parameters of the 25 April 2015 Nepal Earthquake (2015)
    Seismological Society of America (SSA)
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    Publication Date: 2015-10-29
    Description: The 25 April 2015 M w  7.9 Nepal earthquake is used to explore rapid seismological quantification methods to determine point-source parameters (seismic moment, focal mechanism, radiated energy, and source duration) and rupture directivity parameters (fault length and rupture velocity). Given real-time access to global seismic data, useful results can be obtained from W -phase, energy estimation, cut-and-paste, and backprojection analyses within 20–30 min of origin time or even faster if regional data were openly available (which is not the case at present for stations in China and India). This information can augment ground-shaking prediction procedures such as ShakeMap, which is currently provided by the U.S. Geological Survey National Earthquake Information Center. For such procedures to achieve their full potential, open access to calibrated high-quality ground-motion recordings at local, regional, and global stations is critical, and this should be embraced internationally.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 10
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    A Model of Ambient Seismic Noise Recorded by the Utah Regional Network of Strong-Motion Seismometers (2013)
    Seismological Society of America (SSA)
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    Publication Date: 2013-09-04
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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