TY - JOUR A1 - Pilz, Marco A1 - Cotton, Fabrice A1 - Zaccarelli, Riccardo A1 - Bindi, Dino T1 - Capturing Regional Variations of Hard-Rock Attenuation in Europe JF - Bulletin of the Seismological Society of America N2 - A proper assessment of seismic reference site conditions has important applications as they represent the basis on which ground motions and amplifications are generally computed. Besides accounting for the average S-wave velocity over the uppermost 30 m (V-S30), the parameterization of high-frequency ground motions beyond source-corner frequency received significant attention. kappa, an empirical parameter introduced by Anderson and Hough (1984), is often used to represent the spectral decay of the acceleration spectrum at high frequencies. The lack of hard-rock records and the poor understanding of the physics of kappa introduced significant epistemic uncertainty in the final seismic hazard of recent projects. Thus, determining precise and accurate regional hard-rock kappa(0) values is critical. We propose an alternative procedure for capturing the reference kappa(0) on regional scales by linking thewell-known high-frequency attenuation parameter kappa and the properties of multiple-scattered coda waves. Using geological and geophysical data around more than 1300 stations for separating reference and soft soil sites and based on more than 10,000 crustal earthquake recordings, we observe that kappa(0) from multiple-scattered coda waves seems to be independent of the soil type but correlated with the hard-rock kappa(0), showing significant regional variations across Europe. The values range between 0.004 s for northern Europe and 0.020 s for the southern and southeastern parts. On the other hand, measuring kappa (and correspondingly kappa(0)) on the S-wave window (as classically proposed), the results are strongly affected by transmitted (reflected, refracted, and scattered) waves included in the analyzed window biasing the proper assessment of kappa(0). This effect is more pronounced for soft soil sites. In this way, kappa(coda)(0) can serve as a proxy for the regional hard-rock kappa(0) at the reference sites. Y1 - 2019 U6 - https://doi.org/10.1785/0120190023 SN - 0037-1106 SN - 1943-3573 VL - 109 IS - 4 SP - 1401 EP - 1418 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Pilz, Marco A1 - Cotton, Fabrice T1 - Does the One-Dimensional Assumption Hold for Site Response Analysis? BT - A Study of Seismic Site Responses and Implication for Ground Motion Assessment Using KiK-Net Strong-Motion Data JF - Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute N2 - The one-dimensional (1-D) approach is still the dominant method to incorporate site effects in engineering applications. To bridge the 1-D to multidimensional site response analysis, we develop quantitative criteria and a reproducible method to identify KiK-net sites with significant deviations from 1-D behavior. We found that 158 out of 354 show two-dimensional (2-D) and three-dimensional (3-D) effects, extending the resonance toward shorter periods at which 2-D or 3-D site effects exceed those of the classic 1-D configurations and imposing an additional amplification to that caused by the impedance contrast alone. Such 2-D and 3-D effects go along with a large within-station ground motion variability. Remarkably, these effects are found to be more pronounced for small impedance contrasts. While it is hardly possible to identify common features in ground motion behavior for stations with similar topography typologies, it is not over-conservative to apply a safety factor to account for 2-D and 3-D site effects in ground motion modeling. Y1 - 2019 U6 - https://doi.org/10.1193/050718EQS113M SN - 8755-2930 SN - 1944-8201 VL - 35 IS - 2 SP - 883 EP - 905 PB - Earthquake Engineering Research Institute CY - Oakland ER - TY - JOUR A1 - Zhu, Chuanbin A1 - Cotton, Fabrice A1 - Pilz, Marco T1 - Testing the Depths to 1.0 and 2.5 km/s Velocity Isosurfaces in a Velocity Model for Japan and Implications for Ground-Motion Modeling JF - Bulletin of the Seismological Society of America N2 - In the Next Generation Attenuation West2 (NGA-West2) project, a 3D subsurface structure model (Japan Seismic Hazard Information Station [J-SHIS]) was queried to establish depths to 1.0 and 2.5 km/s velocity isosurfaces for sites without depth measurement in Japan. In this article, we evaluate the depth parameters in the J-SHIS velocity model by comparing them with their corresponding site-specific depth measurements derived from selected KiK-net velocity profiles. The comparison indicates that the J-SHIS model underestimates site depths at shallow sites and overestimates depths at deep sites. Similar issues were also identified in the southern California basin model. Our results also show that these underestimations and over-estimations have a potentially significant impact on ground-motion prediction using NGA-West2 ground-motion models (GMMs). Site resonant period may be considered as an alternative to depth parameter in the site term of a GMM. Y1 - 2019 U6 - https://doi.org/10.1785/0120190016 SN - 0037-1106 SN - 1943-3573 VL - 109 IS - 6 SP - 2710 EP - 2721 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Zhu, Chuanbin A1 - Pilz, Marco A1 - Cotton, Fabrice T1 - Which is a better proxy, site period or depth to bedrock, in modelling linear site response in addition to the average shear-wave velocity? JF - Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering N2 - This study aims to identify the best-performing site characterization proxy alternative and complementary to the conventional 30 m average shear-wave velocity V-S30, as well as the optimal combination of proxies in characterizing linear site response. Investigated proxies include T-0 (site fundamental period obtained from earthquake horizontal-to-vertical spectral ratios), V-Sz (measured average shear-wave velocities to depth z, z = 5, 10, 20 and 30 m), Z(0.8) and Z(1.0) (measured site depths to layers having shear-wave velocity 0.8 and 1.0 km/s, respectively), as well as Z(x-infer) (inferred site depths from a regional velocity model, x = 0.8 and 1.0, 1.5 and 2.5 km/s). To evaluate the performance of a site proxy or a combination, a total of 1840 surface-borehole recordings is selected from KiK-net database. Site amplifications are derived using surface-to-borehole response-, Fourier- and cross-spectral ratio techniques and then are compared across approaches. Next, the efficacies of 7 single-proxies and 11 proxy-pairs are quantified based on the site-to-site standard deviation of amplification residuals of observation about prediction using the proxy or the pair. Our results show that T-0 is the best-performing single-proxy among T-0, Z(0.8), Z(1.0) and V-Sz. Meanwhile, T-0 is also the best-performing proxy among T-0, Z(0.8), Z(1.0) and Z(x-infer) complementary to V-S30 in accounting for the residual amplification after V-S30-correction. Besides, T-0 alone can capture most of the site effects and should be utilized as the primary site indicator. Though (T-0, V-S30) is the best-performing proxy pair among (V-S30, T-0), (V-S30, Z(0.8)), (V-S30, Z(1.0)), (V-S30, Z(x-infer)) and (T-0, V-Sz), it is only slightly better than (T-0, V-S20). Considering both efficacy and engineering utility, the combination of T-0 (primary) and V-S20 (secondary) is recommended. Further study is needed to test the performances of various proxies on sites in deep sedimentary basins. KW - Site effects KW - Amplification KW - Site proxy KW - Surface-to-borehole spectral ratios KW - KiK-net KW - Earthquake Y1 - 2019 U6 - https://doi.org/10.1007/s10518-019-00738-6 SN - 1570-761X SN - 1573-1456 VL - 18 IS - 3 SP - 797 EP - 820 PB - Springer CY - Dordrecht ER -