15WCEE_628_Craifaleanu
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The document assesses the relevance of parameters for characterizing ground motion frequency content, specifically in the context of Vrancea subcrustal earthquakes. It analyzes over 300 ground motion records, revealing stable correlations among various parameters and highlighting the influence of local site conditions versus the focal mechanism on ground motion characteristics. The findings indicate that low variability is influenced by local factors, while high variability is linked to the characteristics of different seismic events.
15WCEE_628_Craifaleanu
- 1. AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES Iolanda-Gabriela CRAIFALEANU Technical University of Civil Engineering Bucharest, Romania & National R&D Institute “URBAN-INCERC”, INCERC Bucharest Branch i.craifaleanu@gmail.com, iolanda.craifaleanu@utcb.ro
- 2. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES PECULIARITIES OF VRANCEA SEISMICITY Radiation directivity Difficulties in significantly identifying the depth differentiated between of the base rock for a the 4 analyzed large part of the area earthquakes (Sandi et al., affected by Vrancea 2004; Sandi&Borcia, 2011) Sandi&Borcia, earthquakes Strong Vrancea 04.03. 30.08. 30.05. 31.05. events 1977 1986 1990 1990 Seismic events: January 1st, 1900 – December 31st, 2008. Data according to ROMPLUS Catalogue (INFP, 2009) NE-SW NE-SW N-S NW-SE Radiation directivity Simplified classification: 2 basic types of sites, according to the event- to-event variability of the frequency content (Sandi et al., 2004): variable frequency content determinant influence of the focal mechanism & radiation / long distance attenuation stable frequency content determinant influence of local soil conditions
- 3. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES METHOD Database of 300+ ground motions Ground motion database: 313 records 122 recorded during 101 Vrancea 4 strong earthquakes Earthquakes 85 87 (Mw>6) generated by Total 70 61 the Vrancea Horizontal 37 seismogenic zone Vertical 31 26 since 1977 3 2 1 Comparative analysis March 4, 1977 Aug. 30, 1986 May 30, 1990 May 31,1990 of 11 analytical estimators of the frequency content March 4, Aug. 30, May 30, May 31, 1977 1986 1990 1990 Results correlated with information provided by Mw=7.4 Mw=7.1 Mw=6.9 Mw=6.4 4 spectral bandwidth h=94 km h=131 km h=91 km h=87 km measures
- 4. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES ANALYSED PARAMETERS: PERIOD-TYPE QUANTITIES… T1(PSD) - period for the highest PSD TgSA - predominant period based on amplitude peak acceleration spectrum Tcen - central period, based on Vanmarcke TgSV - predominant period based on central frequency, velocity spectrum Tmean - mean period, based on the mean frequency, ω , of the power spectrum TgSEI - predominant period based on Tms - mean square period (Rathje, 1998) input energy spectrum Tms = ∑ Ci2 1 ∑ Ci2 f Tmean* - modified mean period and mean* i i i for 0.25Hz ≤fi ≤20Hz Tcen* - modified central period (Ruiz- cen* (Ruiz- Garcia & Miranda, 2005) formulas similar to Tmean and where Ci are the Fourier amplitudes of the Tcen, but with modified definitions of spectral moments, accelerogram and fi are the discrete FFT based on the squared values of the velocity spectra for frequencies elastic 5%-damped SDOFs 5%- T4.3 - characteristic period, empirical relationship suggested by Heidebrecht in 1987: PGV … & BANDWIDTH MEASURES T4.3 = 4.3 PGA shape factor, q (Vanmarcke, 1976) and used by Fajfar & Fischinger in 1990 ε parameter (Cartwright & Longuet-Higgins, 1956) Longuet- TC - characteristic period, alternate ξ parameter (Boore, 2003) definition proposed by Lungu et al. in 1997 modified shape factor, q*, (Ruiz-Garcia & (Ruiz- Miranda, 2005)
- 5. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES CORRELATION STUDIES y=a— x+b, horizontal components y=a x+b, Tms T1(PSD) Tmean Tcen TgSA TgSV TgSEI TC Tmean* Tcen* T4.3 q q* ε ξ Good and remarkably Tms 1 0.531 0.763 0.570 0.441 0.285 0.417 0.831 0.330 0.235 0.759 0.515 0.574 0.445 0.551 stable correlations between: T1(PSD) 0.531 1 0.384 0.261 0.227 0.189 0.358 0.468 0.242 0.182 0.378 0.324 0.375 0.161 0.201 Tmean 0.763 Tms (Rathje et al., 1998) and Tcen 0.570 0.384 0.261 1 0.921 0.921 0.543 0.127 0.204 0.512 0.111 1 0.443 0.071 0.126 0.341 0.048 0.066 0.559 0.272 0.267 0.481 0.588 0.023 0.410 0.098 0.149 0.420 0.491 TC (Lungu et al., 1997) TgSA 0.441 0.227 0.543 0.443 1 0.030 0.064 0.276 0.023 0.007 0.307 0.196 0.108 0.356 0.435 Tmean (=1/mean freq. of TgSV 0.285 TgSEI 0.417 0.189 0.127 0.071 0.030 1 0.417 0.366 0.627 0.574 0.266 0.253 0.565 0.127 0.133 power spectrum) 0.358 0.204 0.126 0.064 0.417 1 0.426 0.403 0.338 0.318 0.258 0.474 0.111 0.127 TC 0.831 0.468 0.512 0.341 0.276 0.366 0.426 1 0.401 0.290 0.715 0.442 0.673 0.274 0.371 T4.3 (Heidebrecht, 1987) Tmean* 0.330 0.242 0.111 0.048 0.023 0.627 0.403 0.401 1 0.975 0.356 0.229 0.769 0.053 0.072 Tcen* 0.235 0.182 0.066 0.023 0.007 0.574 0.338 0.290 0.975 1 0.276 0.160 0.626 0.028 0.040 By using the y=a— x T4.3 0.759 0.378 0.559 0.410 0.307 0.266 0.318 0.715 0.356 0.276 1 0.379 0.519 0.310 0.372 dependency, both R2 and a > 0.5 good 0.1…0.5 intermediate < 0.1 weak correlation coefficients show remarkably low event-to-event variability All records, 30.08. 30.05. 31.05. y=a— xx incl. y=a— 1986 1990 1990 04.03.1977 Simple Simple R2 0.8122 0.8143 0.2084 0.7954 empirical empirical Tms-TC a 0.8006 0.7954 0.8083 0.8017 relationships relationships R2 0.7238 0.7723 0.6978 0.7619 between between Tms-Tmean a 1.5409 1.5304 1.4562 1.5328 the TT-type the -type R2 0.7146 0.6745 0.6137 0.7216 parameters parameters Tms -T4.3 a 1.2008 1.1049 1.1705 1.1508
- 6. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES SPATIAL & TEMPORAL VARIABILITY OF T-TYPE PARAMS T1(PSD) - period for the highest PSD amplitude peak 30.08.1986 30.08.1986 30.05.1990 30.05.1990 31.05.1990 31.05.1990 Stations in the NE & SE : relatively small variability of T1(PSD) values with the event suggests prevalent influence of local site conditions on freq. content Other stations : large T1(PSD) values (& narrowband motions) for one (two) events & much smaller values for the other event(s) suggests prevalent influence of focal mechanism & radiation for these stations Same observations for Tms
- 7. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES SPATIAL & TEMPORAL VARIABILITY OF T-TYPE PARAMS T1(PSD) - period for the highest PSD amplitude peak BUCHAREST BUCHAREST 30.08.1986 30.08.1986 30.05.1990 30.05.1990 31.05.1990 31.05.1990 Large values of T1(PSD) for the 1986 earthquake (& narrowband motions), for one or both horizontal components of all Bucharest records Opposite situation for the 1990 earthquakes (exception: 31.05.1990, MTR1 station) Probable explanation the different characteristics (directivity of radiation / attenuation) of the analyzed earthquakes
- 8. PPT available at: Iolanda-Gabriela CRAIFALEANU AN ASSESSMENT OF THE RELEVANCE OF PARAMETERS USED FOR GROUND MOTION FREQUENCY CONTENT CHARACTERIZATION WITH APPLICATION TO VRANCEA SUBCRUSTAL EARTHQUAKES CONCLUSIONS Good and remarkably stable correlations found between the mean square period, Tms (Rathje et al., 1998) and the characteristic period, TC (Lungu et al., 1997) the mean period of the power spectrum, Tmean the characteristic period based on peak ground motion values, T4.3 (Heidebrecht, 1987) simple empirical relationships between the above parameters Interevent (event-to-event) variability of T-type parameters and factors influencing the frequency content of the ground motion: low variability suggests prevalent influence of local site conditions high variability suggests prevalent influence of ground motion of focal mechanism & radiation, given the differences between the characteristics of the analyzed earthquakes The work reported in this paper was partly sponsored by the Romanian National Authority for Scientific Research, ANCS.