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The authors wish to thank Franjo Šumanovac for the very constructive remarks. In the attached fil... more The authors wish to thank Franjo Šumanovac for the very constructive remarks. In the attached file are listed the answers (in italic) to the reviewer's comments/suggestions.
Journal of Earthquake Engineering, Jun 13, 2023
Soil Dynamics and Earthquake Engineering, Feb 1, 2019
The objective of this study is to estimate and compare the site amplification factors (AFs) using... more The objective of this study is to estimate and compare the site amplification factors (AFs) using two different one dimensional (1-D) equivalent-linear (EQL) site response analysis approaches: the time series (TS) approach and the random vibration theory (RVT) based method. For this purpose, random soil profiles combined with different soil types, EQL soil properties, and unit weights are tested at several input ground motion levels. Analysis results showed that the AFs estimated by the TS-approach are systematically higher than the AFs estimated by the RVTbased method in the short period range (T < 0.5 s), especially when the bedrock peak ground acceleration is higher than 0.2 g. The relative difference between the AFs estimated in both methods is most prominent in granular soils: differences reach up to 35-40% compared to 10-15% for clays. On the other hand, the AFs calculated in this study are in good agreement with the empirical AF models utilized in recent ground motion models, indicating that the RVT-based AF models may be preferred in the future to cover a larger range of scenarios than the empirical datasets.
Natural Hazards, Jul 13, 2020
Seismic bedrock depth represents one of the crucial steps in site response analysis as the input ... more Seismic bedrock depth represents one of the crucial steps in site response analysis as the input seismic ground motion is propagated from the bedrock level through soil profile column to estimate surface ground motion. In the last two decades, several studies estimated bedrock depth using microtremor horizontal-to-vertical-spectral ratio fundamental (resonance) frequency and known (mostly boreholes) bedrock depth in different regions through power-law regression. In this study, seismic bedrock (H 800-depth of the bedrock formation identified by shear wave velocity V S ≥ 800 m/s) is estimated using H/V forward modelling routine in which shear wave velocity profile from geophysical measurements was used as an initial soil model. Based on geological, geophysical and microtremor data, empirical relationships between average shear wave velocity in top 30 m, resonance frequency and bedrock depth are derived. Given evaluation of sedimentary thicknesses showed to be within the range of published studies for similar geological and site characteristics if the errors between different methods, approaches and site parameters are considered. The main limitation to validate proposed relationships is the lack of realistic deep borehole data like in similar studies. Further work is required that should include deep data from borehole drilling, seismic refraction and reflection or vertical electrical sounding. The intention is that presented regressions between resonance frequency, bedrock depth and V S30 would be implemented into nonlinear site amplification model and further development towards Ground Motion Prediction Equations for Croatia.
Geophysical Journal International, Mar 30, 2011
Broad-band seismograms of teleseismic events recorded at the Croatian Seismological Network were ... more Broad-band seismograms of teleseismic events recorded at the Croatian Seismological Network were used to compute radial receiver functions (RFs) for eight locations in the External Dinarides. Waveform modelling was performed by a multistep matching of the theoretical RFs computed for horizontally layered 1-D isotropic models with the averaged observed RFs. Constraints from existing deep seismic sounding profiles, traveltime curves of regional crustal seismic phases and intuitive inferences gained from interactive forward modelling were used to construct initial 1-D models of the Earth. A non-linear inversion was performed in two stepsa grid search followed by the Monte Carlo search for the model parameters. Concurrently, RFs from different azimuths were stacked to obtain trade-off estimates of crustal thickness versus V p /V s ratios. The Moho depths were found in the range from around 40 km for Northern Adriatic stations to over 55 km for stations in the central part of the External Dinarides. Comparing our results with recent maps of the Moho topography inferred from seismic and gravimetric data, we find that for some stations the agreement between our results and the existing Moho maps is very good. For the others, we find the Mohorovičić discontinuity to be considerably deeper, indicating some of the thickest crust in Europe. Although it is plausible that such a deep Moho could be a consequence of a complex tectonic setting of the region (e.g. overlapping of two large tectonic units-the Adriatic microplate and the Dinarides), this result will have to be verified in the future studies using various other geophysical techniques.
<p>Seismological data from almost 100 broadband stations (70 < &#916... more <p>Seismological data from almost 100 broadband stations (70 < &#916; < 420 km) from Croatia, Slovenia, Hungary, Italy, Austria, Bosnia and Hercegovina, Montenegro, and Slovakia have been used in the rupture analysis of the Petrinja (Croatia) M<sub>W</sub>6.4 earthquake, that occurred on the 29th of December 2020. Several foreshocks and aftershocks have been used as empirical Green&#8217;s function (EGF) to isolate source effects from propagation and local soil effects. First, P-wave mainshock seismograms are deconvolved from the EGF seismograms in the frequency domain to obtain the corner frequency (<em>f<sub>c</sub></em>). Assuming Brune&#8217;s source model, the spectral analysis results in a large stress drop of 25 MPa. Second, using time-domain deconvolution of the Love wave time windows, apparent source time functions (ASTFs) have been computed and indicate an average source duration of 5 seconds. No significant directivity effects can be seen in both the <em>f<sub>c</sub></em> values and source durations, whose weak variability suggests a bilateral rupture. Lastly, physical rupture parameters, such as rupture velocity, rupture dimensions, slip model and rise time, have been extracted from the ASTFs by two different techniques: (1) the Bayesian inversion method (Causse et al. 2017) and (2) the backprojection of the ASTFs on the isochrones (Kir&#225;ly&#8208;Proag et al. 2019). Both techniques indicate a slow rupture velocity (about 50% of the shear-wave velocity) and a rather short rupture length for an M<sub>W</sub>6.4 event (about 8 km), consistent with the obtained large seismological stress drop. Such features may be explained by the relatively complex and segmented fault system, typical of immature fault contexts.</p> <p>&#160;</p> <p>References:</p> <p>Causse, M., Cultrera, G., Moreau, L., Herrero, A., Schiappapietra, E. and Courboulex, F., 2017. Bayesian rupture imaging in a complex medium: The 29 May 2012 Emilia, Northern Italy, earthquake.&#160;<em>Geophysical Research Letters</em>,&#160;<em>44</em>(15), pp.7783-7792.</p> <p>Kir&#225;ly&#8208;Proag, E., Satriano, C., Bernard, P. and Wiemer, S., 2019. Rupture process of the M w 3.3 earthquake in the St. Gallen 2013 geothermal reservoir, Switzerland.&#160;<em>Geophysical Research Letters</em>,&#160;<em>46</em>(14), pp.7990-7999.</p>
Swiss Journal of Geosciences, Jan 4, 2019
We present the results of local earthquake tomography (LET) analysis to investigate the crust and... more We present the results of local earthquake tomography (LET) analysis to investigate the crust and uppermost mantle structure in the northern Dinarides and southwestern Pannonian basin. Datasets of P-wave travel times are inverted to recover a three-dimensional P-wave velocity model of the survey area. Two data subsets were used in this study: (1) data recorded on 15 temporary seismic stations, which were deployed in Croatia in the framework of ALPASS-DIPS project, and (2) travel time datasets from the Croatian Seismological Survey and ORFEUS databases. The data enabled to achieve a resolution of less than a hundred kilometres in horizontal directions and a few kilometres in vertical direction in the area with good ray coverage, as is documented by the resolution tests. Velocity variations are computed on a grid using the three-dimensional nonlinear tomographic inversion method. Our study provides the first crustal three-dimensional seismic model of the studied area, and it is correlated with previous results in the survey area allowing us to infer the main crustal structures with high confidence. The velocity model reveals crustal thickening beneath the Dinarides and significant crustal thinning beneath the Pannonian basin. The Moho surface was determined on the basis of the highest velocity gradients in the vertical cross-sections. We find relatively high velocities below the northern Dinarides at shallow depths (\ 10 km), and low velocities caused by deep local depressions in the Pannonian basin. A very pronounced high-velocity body is present in the transitional part between the Dinarides and the Pannonian basin at a depth range of 5-15 km. The strong velocity increase at depth of about 20 km indicates that the Dinaridic crust could be interpreted as two-layered, while the Pannonian crust is probably one-layered.
Studia Geophysica Et Geodaetica, Oct 1, 2022
Kartografija i Geoinformacije, Dec 28, 2012
Inženjerstvo okoliša, Jul 10, 2020
Mohorovičić said in Introduction of his lecture in 1909: "another strong earthquake is needed to ... more Mohorovičić said in Introduction of his lecture in 1909: "another strong earthquake is needed to remind people that the building techniques should be further developed and improved…". Oliver Wendell Holmes (1809-1894) said once: "The young man knows the rules, but the old man knows the exceptions". This should remined us that going Back to the Future after strong earthquake, we must go Back to the Past, and look after Mohorovičić's 15 rules how to build earthquake-resistant buildings. He tells us how to build, and unfortunately, we were left unprepared again and didn't listen wisdom words of an "old man".
Dat je pregled sudjelovanja djelatnika Geofizickog zavoda u Zagrebu u srednjoskolskoj nastavi fiz... more Dat je pregled sudjelovanja djelatnika Geofizickog zavoda u Zagrebu u srednjoskolskoj nastavi fizike, matematike, geofizike te astronomije. U novije vrijeme djelatnici Geofizickog zavoda intenzivno rade na popularizaciji svih grana geofizike među ucenicima srednjih skola i gimnazija.
The authors wish to thank Franjo Šumanovac for the very constructive remarks. In the attached fil... more The authors wish to thank Franjo Šumanovac for the very constructive remarks. In the attached file are listed the answers (in italic) to the reviewer's comments/suggestions.
Journal of Earthquake Engineering, Jun 13, 2023
Soil Dynamics and Earthquake Engineering, Feb 1, 2019
The objective of this study is to estimate and compare the site amplification factors (AFs) using... more The objective of this study is to estimate and compare the site amplification factors (AFs) using two different one dimensional (1-D) equivalent-linear (EQL) site response analysis approaches: the time series (TS) approach and the random vibration theory (RVT) based method. For this purpose, random soil profiles combined with different soil types, EQL soil properties, and unit weights are tested at several input ground motion levels. Analysis results showed that the AFs estimated by the TS-approach are systematically higher than the AFs estimated by the RVTbased method in the short period range (T < 0.5 s), especially when the bedrock peak ground acceleration is higher than 0.2 g. The relative difference between the AFs estimated in both methods is most prominent in granular soils: differences reach up to 35-40% compared to 10-15% for clays. On the other hand, the AFs calculated in this study are in good agreement with the empirical AF models utilized in recent ground motion models, indicating that the RVT-based AF models may be preferred in the future to cover a larger range of scenarios than the empirical datasets.
Natural Hazards, Jul 13, 2020
Seismic bedrock depth represents one of the crucial steps in site response analysis as the input ... more Seismic bedrock depth represents one of the crucial steps in site response analysis as the input seismic ground motion is propagated from the bedrock level through soil profile column to estimate surface ground motion. In the last two decades, several studies estimated bedrock depth using microtremor horizontal-to-vertical-spectral ratio fundamental (resonance) frequency and known (mostly boreholes) bedrock depth in different regions through power-law regression. In this study, seismic bedrock (H 800-depth of the bedrock formation identified by shear wave velocity V S ≥ 800 m/s) is estimated using H/V forward modelling routine in which shear wave velocity profile from geophysical measurements was used as an initial soil model. Based on geological, geophysical and microtremor data, empirical relationships between average shear wave velocity in top 30 m, resonance frequency and bedrock depth are derived. Given evaluation of sedimentary thicknesses showed to be within the range of published studies for similar geological and site characteristics if the errors between different methods, approaches and site parameters are considered. The main limitation to validate proposed relationships is the lack of realistic deep borehole data like in similar studies. Further work is required that should include deep data from borehole drilling, seismic refraction and reflection or vertical electrical sounding. The intention is that presented regressions between resonance frequency, bedrock depth and V S30 would be implemented into nonlinear site amplification model and further development towards Ground Motion Prediction Equations for Croatia.
Geophysical Journal International, Mar 30, 2011
Broad-band seismograms of teleseismic events recorded at the Croatian Seismological Network were ... more Broad-band seismograms of teleseismic events recorded at the Croatian Seismological Network were used to compute radial receiver functions (RFs) for eight locations in the External Dinarides. Waveform modelling was performed by a multistep matching of the theoretical RFs computed for horizontally layered 1-D isotropic models with the averaged observed RFs. Constraints from existing deep seismic sounding profiles, traveltime curves of regional crustal seismic phases and intuitive inferences gained from interactive forward modelling were used to construct initial 1-D models of the Earth. A non-linear inversion was performed in two stepsa grid search followed by the Monte Carlo search for the model parameters. Concurrently, RFs from different azimuths were stacked to obtain trade-off estimates of crustal thickness versus V p /V s ratios. The Moho depths were found in the range from around 40 km for Northern Adriatic stations to over 55 km for stations in the central part of the External Dinarides. Comparing our results with recent maps of the Moho topography inferred from seismic and gravimetric data, we find that for some stations the agreement between our results and the existing Moho maps is very good. For the others, we find the Mohorovičić discontinuity to be considerably deeper, indicating some of the thickest crust in Europe. Although it is plausible that such a deep Moho could be a consequence of a complex tectonic setting of the region (e.g. overlapping of two large tectonic units-the Adriatic microplate and the Dinarides), this result will have to be verified in the future studies using various other geophysical techniques.
<p>Seismological data from almost 100 broadband stations (70 < &#916... more <p>Seismological data from almost 100 broadband stations (70 < &#916; < 420 km) from Croatia, Slovenia, Hungary, Italy, Austria, Bosnia and Hercegovina, Montenegro, and Slovakia have been used in the rupture analysis of the Petrinja (Croatia) M<sub>W</sub>6.4 earthquake, that occurred on the 29th of December 2020. Several foreshocks and aftershocks have been used as empirical Green&#8217;s function (EGF) to isolate source effects from propagation and local soil effects. First, P-wave mainshock seismograms are deconvolved from the EGF seismograms in the frequency domain to obtain the corner frequency (<em>f<sub>c</sub></em>). Assuming Brune&#8217;s source model, the spectral analysis results in a large stress drop of 25 MPa. Second, using time-domain deconvolution of the Love wave time windows, apparent source time functions (ASTFs) have been computed and indicate an average source duration of 5 seconds. No significant directivity effects can be seen in both the <em>f<sub>c</sub></em> values and source durations, whose weak variability suggests a bilateral rupture. Lastly, physical rupture parameters, such as rupture velocity, rupture dimensions, slip model and rise time, have been extracted from the ASTFs by two different techniques: (1) the Bayesian inversion method (Causse et al. 2017) and (2) the backprojection of the ASTFs on the isochrones (Kir&#225;ly&#8208;Proag et al. 2019). Both techniques indicate a slow rupture velocity (about 50% of the shear-wave velocity) and a rather short rupture length for an M<sub>W</sub>6.4 event (about 8 km), consistent with the obtained large seismological stress drop. Such features may be explained by the relatively complex and segmented fault system, typical of immature fault contexts.</p> <p>&#160;</p> <p>References:</p> <p>Causse, M., Cultrera, G., Moreau, L., Herrero, A., Schiappapietra, E. and Courboulex, F., 2017. Bayesian rupture imaging in a complex medium: The 29 May 2012 Emilia, Northern Italy, earthquake.&#160;<em>Geophysical Research Letters</em>,&#160;<em>44</em>(15), pp.7783-7792.</p> <p>Kir&#225;ly&#8208;Proag, E., Satriano, C., Bernard, P. and Wiemer, S., 2019. Rupture process of the M w 3.3 earthquake in the St. Gallen 2013 geothermal reservoir, Switzerland.&#160;<em>Geophysical Research Letters</em>,&#160;<em>46</em>(14), pp.7990-7999.</p>
Swiss Journal of Geosciences, Jan 4, 2019
We present the results of local earthquake tomography (LET) analysis to investigate the crust and... more We present the results of local earthquake tomography (LET) analysis to investigate the crust and uppermost mantle structure in the northern Dinarides and southwestern Pannonian basin. Datasets of P-wave travel times are inverted to recover a three-dimensional P-wave velocity model of the survey area. Two data subsets were used in this study: (1) data recorded on 15 temporary seismic stations, which were deployed in Croatia in the framework of ALPASS-DIPS project, and (2) travel time datasets from the Croatian Seismological Survey and ORFEUS databases. The data enabled to achieve a resolution of less than a hundred kilometres in horizontal directions and a few kilometres in vertical direction in the area with good ray coverage, as is documented by the resolution tests. Velocity variations are computed on a grid using the three-dimensional nonlinear tomographic inversion method. Our study provides the first crustal three-dimensional seismic model of the studied area, and it is correlated with previous results in the survey area allowing us to infer the main crustal structures with high confidence. The velocity model reveals crustal thickening beneath the Dinarides and significant crustal thinning beneath the Pannonian basin. The Moho surface was determined on the basis of the highest velocity gradients in the vertical cross-sections. We find relatively high velocities below the northern Dinarides at shallow depths (\ 10 km), and low velocities caused by deep local depressions in the Pannonian basin. A very pronounced high-velocity body is present in the transitional part between the Dinarides and the Pannonian basin at a depth range of 5-15 km. The strong velocity increase at depth of about 20 km indicates that the Dinaridic crust could be interpreted as two-layered, while the Pannonian crust is probably one-layered.
Studia Geophysica Et Geodaetica, Oct 1, 2022
Kartografija i Geoinformacije, Dec 28, 2012
Inženjerstvo okoliša, Jul 10, 2020
Mohorovičić said in Introduction of his lecture in 1909: "another strong earthquake is needed to ... more Mohorovičić said in Introduction of his lecture in 1909: "another strong earthquake is needed to remind people that the building techniques should be further developed and improved…". Oliver Wendell Holmes (1809-1894) said once: "The young man knows the rules, but the old man knows the exceptions". This should remined us that going Back to the Future after strong earthquake, we must go Back to the Past, and look after Mohorovičić's 15 rules how to build earthquake-resistant buildings. He tells us how to build, and unfortunately, we were left unprepared again and didn't listen wisdom words of an "old man".
Dat je pregled sudjelovanja djelatnika Geofizickog zavoda u Zagrebu u srednjoskolskoj nastavi fiz... more Dat je pregled sudjelovanja djelatnika Geofizickog zavoda u Zagrebu u srednjoskolskoj nastavi fizike, matematike, geofizike te astronomije. U novije vrijeme djelatnici Geofizickog zavoda intenzivno rade na popularizaciji svih grana geofizike među ucenicima srednjih skola i gimnazija.