ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    Along-strike rupture directivity of earthquakes of the 2009 L'Aquila, central Italy, seismic sequence (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-29
    Description: We perform a systematic investigation of along-strike rupture directivity of 70 earthquakes (3.0 ≤ M w ≤ 6.1) of the 2009 L'Aquila seismic sequence by analysing azimuthal variations of broad-band seismograms recorded in the distance range 60 km 〈 R 〈 230 km. We use reference spectra of events with little directivity (similar to the empirical Green's function method) to deconvolve propagation-site effects and focus on source properties. A directivity index (0 ≤ I DIR ≤ 1) calculated for each earthquake quantifies the spectral separation above the corner frequency of the target event at opposite along-strike directions. A large number (73 per cent) of events including the M w 6.1 main shock show high (〉0.7) I DIR values indicating predominantly unilateral rupture propagation. The preferred rupture propagation direction is generally to the southeast with no dependence on the earthquake magnitude or occurrence time. Events on two main faults (L'Aquila and Campotosto) show somewhat different behaviour. Almost all earthquakes on the L'Aquila fault have strong unilateral directivity to the southeast, whereas earthquakes on the Campotosto fault show more diverse behaviour. However, there is a predominance of unilateral ruptures (14 out of 22) also on the Campotosto fault, and the few (five) earthquakes with ruptures to the northwest are limited to the most northwestern segment of the fault. The spectral results are consistent with time-domain analysis when the latter samples adequately the frequency band above corner frequency. The preferred rupture direction may be produced at least in part by a velocity contrast across the fault. The results provide important input for estimates of seismic motion and physics of earthquake ruptures.
    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).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    Stress drop and source scaling of the 2009 April L'Aquila earthquakes (2012)
    Oxford University Press
    Details
    Publication Date: 2012-12-19
    Description: The empirical Green's function (EGF) technique is applied in the frequency domain to 962 broad-band seismograms (3.3 ≤ M W ≤ 6.1) to determine stress drop and source scaling of the 2009 April L’Aquila earthquakes. The station distance varies in the range 100–250 km from the source. Ground motions of several L’Aquila earthquakes are characterized by large azimuthal variations due to source directivity, even at low magnitudes. Thus, the individual-station stress-drop estimates are significantly biased when source directivity is not taken into account properly. To reduce the bias, we use single-station spectral ratios with pairs of earthquakes showing a similar degree of source directivity. The superiority of constant versus varying stress-drop models is assessed through minimization of misfit in a least-mean-square sense. For this analysis, seismograms of 26 earthquakes occurring within 10 km from the hypocentres of the three strongest shocks are used. We find that a source model where stress drop increases with the earthquake size has the minimum misfit: as compared to the best constant stress-drop model the improvement in the fit is of the order of 40 per cent. We also estimate the stress-drop scaling on a larger data set of 64 earthquakes, all of them having an independent estimate of seismic moment and consistent focal mechanism. An earthquake which shows no directivity is chosen as EGF event. This analysis confirms the former trend and yields individual-event stress drops very close to 10 MPa at magnitudes M W  〉 4.5 that decrease to 1 MPa, on the average, at the smallest magnitudes. A varying stress-drop scaling of L’Aquila earthquakes is consistent with results from other studies using EGF techniques but contrasts with results of authors that used inversion techniques to separate source from site and propagation effects. We find that there is a systematic difference for small events between the results of the two methods, with lower and less scattered values of stress drop resulting from the EGF approach.
    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).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    Isotopic carbon discrimination and leaf nitrogen content of Erica arborea L. along a CO2 concentration gradient in a CO2 spring in Italy (1995)
    Oxford University Press
    Details
    Publication Date: 1995-05-01
    Print ISSN: 0829-318X
    Electronic ISSN: 1758-4469
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Along-strike rupture directivity of earthquakes of the 2009 L'Aquila, central Italy, seismic sequence (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-27
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    On the reliability of long period response spectral ordinates from digital accelerograms (2008)
    WILEY
    Details
    Publication Date: 2020-03-11
    Description: Using records from co-located broad-band and digital strong motion instruments, it is first shown that the displacement waveforms obtained by double integration of the accelerogram need not be free of unrealistic baseline drift to yield reliable spectral ordinates up to at least 10 s. Secondly, to provide objective criteria for selecting reliable digital strong motion records for ground motion predictions at long periods, a set of synthetic accelerograms contaminated by random long period noise has been used and the difference between the original accelerograms and the spurious ones in terms of response spectra has been quantified, by introducing a noise index that can be easily calculated based on the velocity waveform of the record. The results of this study suggest that high-pass filtering the digital acceleration record from a cut-off period selected to suppress baseline drifts on the displacement waveform appears to be in most cases too conservative and unduly depletes reliable information on long period spectral ordinates
    Description: Italian seismological project S5 (Definizione dell'input sismico sulla base degli spostamenti attesi) of the 2006-07 DPC-INGV research programs
    Description: Published
    Description: 697-710
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: partially_open
    Keywords: displacement response spectra ; long period noise ; digital accelerograms ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OA)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...