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  • 1
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    Test sites in Europe for the evaluation of ground motion amplification: site response of the Gubbio basin (Central Italy) using weak motions recorded by linear seismic arrays (2007)
    Details
    Publication Date: 2020-10-26
    Description: The plain of Gubbio is located in a northwest-southeast oriented, 4-km wide, 20-km long intermountain basin in the northern Apennines, central Italy. The moderate-magnitude earthquakes of the 1997 Umbria-Marche seismic sequence, occurred 40 km southeast of Gubbio, generated displacements as large as 6 cm within the basin. The large amplitude phase, not observed outside of the basin, was followed by low-frequency wave trains lasting up to 1 minute. In order to investigate the mechanism of possible local amplification effects, different kind of geophysical and geological investigation of the basin started within the framework of the Italian DPC-INGV projects. In particular, the GFZ and the INGV deployed two linear seismic arrays. The first one was composed of ten seismological stations with 1-s receivers. It operated from June until December 2005. The array was oriented north-south, approximately: all the stations but two were installed on the sedimentary deposits. The remaining two stations (the northernmost and the southernmost) were installed on rock outcrops at the edges of the basin. The second array, composed by 10 stations with 5-s receivers, was deployed along the main axis of the basin, and is recording since November 2005. For 45 days, the two arrays worked simultaneously. A selected dataset of 250 earthquakes has been analyzed. H/V spectral ratio results show that systematic low-frequency (0.3-0.4 Hz) amplification affects the stations in the middle of the basin. The resonance frequency peaks are consistent with the thickness and the average S-wave velocity of soft sediments derived from microtremor measurements in the basin. The conventional spectral ratio results show a more complex broad-band (0.3-10 Hz) amplification. The analysis of selected records by means of a sonogram approach highlights the arrival of strong late phases increasing the signal duration at the stations located in the middle of the basin.
    Description: Unpublished
    Description: Geneva, Switzerland
    Description: open
    Keywords: weak motion analysis ; linear arrays ; polarization ; response spectra ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Poster session
    Format: 3885731 bytes
    Format: application/pdf
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  • 2
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    Crustal attenuation characteristics in northwestern Turkey in the range from 1 to 10 Hz (2007)
    Seismological Society of America
    Details
    Publication Date: 2017-04-04
    Description: We have analyzed the aftershocks (ML 4.5) following the 1999 Izmit earthquake (Mw 7.4) to infer the frequency-dependent attenuation characteristics of both P and S waves, in the frequency range from 1 to 10 Hz and in the distance range from 10 to 140 km. A linear-predictive model is assumed to describe the spectral amplitudes in terms of attenuation and source contributions. The results show that both P and S waves undergo a strong attenuation along ray paths shorter than 40 km, while the secondary arrivals significantly contribute to the spectral amplitudes over the distance range from 40 to 60 km, as also confirmed by the computation of synthetic seismograms. For longer ray paths, the decrease in attenuation suggests an increase in the propagation efficiency with depth. Finally, the spectral attenuation curves are flattened, or sloped upward at low frequencies in the range from 100 to 140 km, due to the contemporary arrivals of direct waves and postcritical reflections from the Moho. In terms of geometrical spreading and anelastic attenuation, the attenuation in the range from 10 to 40 km is well described by a spreading coefficient n 1 for both P and S waves, and the quality factors can be approximated by QS( f ) 17f 0.80 for 1 f 10 Hz and QP( f ) 56f 0.25 for 2.5 f 10 Hz. For ray paths in the range from 60 to 80 km, the attenuation weakens but the interaction between seismic waves and propagation medium is more complex. The multilapse time window analysis (MLTWA) is applied to quantify the amount of scattering loss and intrinsic absorption for S waves. The seismic albedo B0 decreases from 0.5 at 1 Hz to 0.3 at 10 Hz, while the total quality factor QT increases from about 56 to 408. The multiple lapse time-window analysis (MLTWA) results provide only an average estimate of the attenuation properties in the range from 10 to 80 km. In fact, by neglecting the variation of attenuation with depth, the MLTWA results underestimate attenuation for distances less than 40 km, and do not capture the significant features caused by the integrated energy of the secondary arrivals observed in the range from 40 to 60 km.
    Description: Published
    Description: 200-214
    Description: JCR Journal
    Description: reserved
    Keywords: aftershocks ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    ML scale in Northwestern Turkey from 1999 Izmit aftershock: updates (2007)
    Seismological Society of America
    Details
    Publication Date: 2017-04-04
    Description: Abstract We present an update of the local magnitude scale previously calibrated for northwestern Turkey by Baumbach et al. (2003). The path coverage in the westernmost part of the analyzed area has been increased, as well as the number of amplitudes for distance greater than 110 km. Furthermore, a set of recordings from accelerometric stations operated by the Kandilli Observatory and Earthquake Research Institute (KOERI) has been merged with the recordings by the Sapanca-Bolu and German Task Force seismological networks. In all, 4047 recordings from 528 earthquakes recorded by 31 seismometers and 23 accelerometers are considered to calibrate the local magnitude scale over a hypocentral distance range from 10 to 190 km. By analyzing the unit covariance matrix and the resolution matrix, we show how the source-to-station geometries of the seismic and strong-motion networks affect the uncertainties of the computed station corrections, attenuation coefficients, and magnitudes. The assumptions made concerning the reference station correction, and the change in the amplification for the Wood–Anderson torsion seismograph from 2800 to 2080 (Uhrhammer and Collins, 1990) introduced an offset of about 0.34 in the magnitudes with respect to Baumbach et al. (2003), with the updated local magnitude scale ranges from 0.50 to 5.91. The distribution of the residuals with distance confirms that the extension of both the magnitude and distance ranges and the improved path coverage have preserved the high quality that characterized the data set analyzed by Baumbach et al. (2003).
    Description: Published
    Description: 331-338
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: partially_open
    Keywords: local magnitude ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Cumulative attenuation along source to receiver paths in northwestern Turkey (2007)
    Seismological Society of America
    Details
    Publication Date: 2017-04-04
    Description: The attenuation of shear waves propagating in the crust of northwestern Turkey has been investigated in the frequency range 1–10 Hz. A standard spectral inversion scheme is applied to a data set of 245 aftershocks (ML 4.5) of the 1999 Izmit earthquake. The obtained attenuation-with-distance curves have been described in terms of the t* cumulative attenuation parameter and its dependence on frequency and distance investigated. At 1 Hz, Q 1, evaluated by normalizing t* to the travel time, is generally larger than 0.025 for source-to-station distances smaller than 40 km, indicating the presence of a highly attenuating upper crust in the area. Over longer distances, Q 1 decreases, suggesting a decrease in the attenuation with depth. By contrast, the normalized t* computed for earthquakes recorded at stations having almost the same distance from the sources do not show a strong dependence on the backazimuth. These results suggest that the decrease of Q 1 with depth is more significant than its lateral variations. Regarding its frequency dependence, Q 1 almost linearly decreases with frequency. Finally, the near-surface-attenuation parameter k is evaluated at 12 stations and the results discussed in terms of site, event, and propagation contributions. The event contribution is not negligible and shows a significant positive correlation with magnitude. The site term is smaller than 0.020 sec for rock or topographic sites, while it assumes values of 0.036 sec and 0.042 sec for two stations installed over thick soft sedimentary layers.
    Description: Published
    Description: 188-199
    Description: JCR Journal
    Description: reserved
    Keywords: waves propagating ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Empirical site-specific response-spectra correction factors for the Gubbio basin (central Italy) (2008)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: Providing quantitative microzonation results that can be taken into account in urban land-use plans is a challenging task that requires collaborative efforts between the seismological and engineering communities. In this study, starting from the results obtained by extensive geophysical and seismological investigations, we propose and apply an approach to the Gubbio basin (Italy) that can be easily implemented for cases of moderate-to-low ground motion and that takes into account not only simple 1D, but also more complicated 3D effects. With this method, the sites inside the basin are classified by their fundamental resonance frequencies, estimated from the horizontal-to-vertical spectral ratio applied to noise recordings (HVNSR). The correspondence between estimates of the fundamental frequency from this method and those derived from earthquake recordings was verified at several calibration sites. The amplification factors used to correct the response spectra are computed by the ratio between the response spectra at sites within the basin and the response spectra at a hard-rock site using data from two seismic transects. Empirical amplification functions are then assigned to the fundamental frequencies after applying an interpolation technique. The suitability of the estimated site-specific correction factors for response spectra was verified by computing synthetic response spectra for stations within the basin, starting from the synthetic recording at a nearby rock station, and comparing them with observed ones.
    Description: In press
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: sedimentary basin ; response spectra ; site effects ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Site effects observed in alluvial basins: the case of Norcia (Central Italy) (2012)
    Springer
    Details
    Publication Date: 2017-04-04
    Description: In this work, we investigate the site amplification effects observed in the Norcia plain, Central Italy. Data from 30 selected local earthquakes (2 ≤ Ml ≤ 4.1) recorded by a temporary seismic network composed by 15 stations, are analyzed to determine the spa- tial variability of site effects. Both the Horizontal-to-Vertical spectral ratio and the Standard Spectral Ratio techniques are applied to estimate the site amplification effects. The results show that most of the sites in the valley are affected by strong amplifications (up to a factor of 20) in the frequency range 0.5–5 Hz. The value of the fundamental frequency of resonance is strictly dependent on the location within the basin and on the sediment thickness. Strong amplifications also affect the vertical components. The time-frequency analysis performed on a station located inside the basin shows the presence of a large spectral amplitudes after the S-wave phase, not observed on a station located on the bedrock, suggesting the pres- ence of locally generated wave trains. Then, in agreement with earlier observations for other alluvial basins in Central Italy, 2D–3D effects play an important role in determining the site amplification effects in Norcia.
    Description: Published
    Description: 1941-1959
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: site effects ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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