ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉Earthquake insurance has become a topic of major importance in mainland China ever since the Mw 7.9 Wenchuan earthquake in 2008. Site‐condition amplification is one of the essential factors that influences the prediction of strong ground motion and the assessment of damages of buildings and structures. The site effects should hence be included in calculating earthquake damage and determining the insurance rate for insurance companies. In particular, large‐scale site classification is required for the implementation of earthquake insurance. This study first used a slope method for site classification in China through the VS30 values from the topographic slope data and the correlation between VS30 and the topographic slope. A novel site classification method, called the slope–geological method, was then proposed in this study to improve the slope method by combining geological characteristics, including geological age, the depositional environment, and soil properties. Four hundred and fifty three pieces of borehole data in Northern Plain and Sichuan of China were used to verify the effectiveness and difference of the slope method and the slope–geological method proposed in this study. Site‐condition classification maps of China were drawn using the slope method and slope–geological method, respectively.〈/span〉

Description: Based on the parallel computing cluster platform of the ABAQUS software, a large-scale 2D finite-element refined nonlinear modeling approach was used to study seismic site effects in the Fuzhou basin, such as peak ground acceleration (PGA), spectral acceleration, duration, and acceleration transfer functions. A 1D equivalent linear wave propagation analysis was conducted also, with Proshake for supplementation and calibration. The simulation results demonstrated the following. (1) PGA amplification factors exhibited spatial variation characteristics that varied both laterally and with depth and exhibited a nonmonotonic decreasing characteristic with soil depth. From the 2D results, a greater motion amplification and focusing effect for some shallow soil layers was observed where there was significant fluctuation of the underlying bedrock interface. The moderate- and long-period ground-motion components were obviously amplified, but were was less pronounced in the 1D result. (2) For low-, moderate-, and high-level earthquakes, the surface PGA amplification factors were 1.4–2.5, 1.3–2.0, and 1.1–2.0, respectively, and the predominant periods of the basin were 0.35–0.65 s, 0.40–0.75 s, and 0.50–1.05 s, respectively. (3) Ground-motion durations were prolonged to different degrees, which were closely related to the characteristics of seismic bedrock motions. (4) The sensitive frequency band of the seismic site response was from 0.5 to 2 Hz. (5) Ground-motion amplification in the downtown section of the city of Fuzhou was generally larger. To a certain extent, the 2D results reflect the influences of the surface topography relief, the fluctuation of the underlying bedrock interface, and lateral heterogeneity of soils on seismic-wave propagation.

Description: Displacement time histories from double-integrated accelerograms typically cannot be used to recover near-field terms because of noise in the acceleration traces. To minimize this problem, empirical mode decomposition (EMD) is used to derive a baseline correction scheme. The scheme is tested against several models composed of a single frequency or two frequencies and offsets in acceleration. It is verified against real displacement time history using Global Positioning Systems (GPS) measurement. For single- and double-frequency-content models, obvious discontinuities are found at drift times for lower intrinsic mode function (IMF) components. A drift model, however, can be clearly found from summing higher IMFs and the residuals of simple frequency-content waveform models. On the other hand, results show that the lesser frequency-content signal has the greater decomposed result. Therefore, a suitable corner frequency for low-pass filtering is first implemented to reduce frequency content. In this case, the trend in the given drift model is easily found by summing higher IMFs for a complex frequency content model (model 3 of this study). A suitable corner frequency for low-pass filtering is attained using a grid-search method. A new semiautomatic EMD-derived baseline correction scheme is tested. The corrected coseismic deformation value (CDV, denoted hereafter as from preevent displacement to the final offset during strong motion), peak ground displacement, and displacement time history from this method have good agreement with 1-Hz continuous GPS measurement for the 2011 Tohoku earthquake.

Description: The time-averaged shear-wave velocity of up to 30 m ( V S 30 ), a vital parameter in building codes, is widely used in site classification and plays an important role in the analysis of site effects. Recently, the log–linear correlation ( Boore, 2004 ) has become more prevalent to estimate V S 30 of velocity profiles that do not extend to 30 m. In this study, we make a full analysis on the linear correlation with three publicly available data sets of shear-wave velocity profiles. A conditional independence property is derived from the partial correlation analysis of the data sets. Using this property, a new V S 30 estimation model is proposed. Comparison of models based on the setup of training and testing data sets suggests that the new model achieves improved performance on the V S 30 estimation. The impact of errors of estimation models on the prediction of ground-motion parameters is also evaluated, and the overall error of the predicted parameter by the new model is the least, especially at long periods.

Description: The M w  7.0 Kumamoto, Japan, earthquake occurred on 15 April 2016 at 16:25 UTC. Using ground accelerations recorded by 104 near-field stations, we investigate spatial variability of observed ground motions, apparent period dependence, and azimuthal variation, as well as rupture directivity effects on various intensity measures. We develop a simplified ground-motion model that includes both geometric and anelastic attenuation terms. Comparisons of observed and predicted ground motions suggest that predictions from the Next Generation Attenuation-West2 models provide good fits for the overall observation. Analysis of spatial distribution of the residuals shows that observed peak ground velocity (PGV) and long-period spectral accelerations (SAs) in the 150°–180° azimuth range along the rupture backward direction (southwest of the fault) can be as low as 0.3–0.8 times the average observation of this event. Long-period ground motions on the northeast side of the fault in the forward direction are much higher than average, with PGV and long-period SAs ranging from 1.2 to 1.5 times the average. There is clear period dependence of the strong ground motion variation. The biases due to directivity generally decrease with decreasing period for all azimuth ranges. On the distance dependence of directivity effects, our study shows that directivity effects can be considered practically nonsignificant for stations close to the hypocenter. We also perform a log–linear regression of the residuals, using a new directivity predictor. Our results show that for the 2016 M w  7.0 Kumamoto earthquake, rupture directivity produces significant amplifications in the rupture forward direction, whereas deamplification effects are observed in the rupture backward region. Directivity effects are particularly relevant for PGV and long-period SA (i.e., SA at periods ≥2.0 s). Such effects do not have systematic influence on peak ground acceleration and short-period ground motions (i.e., SA at periods 〈2.0 s). Electronic Supplement: Figures of variation of regression residuals with R rup for observed peak ground acceleration (PGA), peak ground velocity (PGV), and spectral accelerations (SAs) and of regression residuals versus V S 30 .

Description: Earthquake ground-motion prediction models usually define site conditions based on the time-averaged shear-wave velocity in the upper 30 m ( V S 30 ). Proxy-based estimations of V S 30 are commonly used, if velocity measurements are not available. We compile a soil-profile database for the Beijing plain area (China), using data from research documents and technical reports. The database contains 479 soil profiles, 463 of which have depths greater than 30 m. We develop regional relationships for the Beijing plain area for extrapolating the time-averaged shear-wave velocity to a given depth less than 30 m to V S 30 , and then compare the performance of available models. We find that the second-order polynomial model ( Boore et al. , 2011 ), based on data from Japan, provides an overprediction, whereas the linear model ( Boore, 2004 ) calibrated on data from California underestimates V S 30 . We develop relationships for estimating V S 30 based on proxies such as ground slope gradients from radar-derived digital elevation models (DEMs) and surface geology at different scales. We find that local V S 30 data in the Beijing plain are generally lower than existing 30 arcsec gradient-based global models. Regression results show a modest correlation between V S 30 and topographic ground slope for several DEM resolutions (3, 15, 30, and 60 arcsec). Geology-based proxies are more effective than ground slope for V S 30 estimation in the analyzed area. We propose a bilinear model based on geologic ages and depositional environments for estimating V S 30 , which shows a statistically significant trend for application in the Beijing plain area. Online Material: Figures showing topographic ground slopes and correlations of V S 30 with topographic slope from digital elevation model (DEM) data and a table summarizing data from the 463 boreholes.

Description: Seismic instruments record horizontal ground motion into two orthogonal components, and the orientations of the components are dependent on the installed sensors. Ground-motion measures directly derived from the two components vary with the installation orientation, which will influence the result of the seismic design of structures and the variance of ground-motion prediction equations. Various orientation-independent measures have been proposed recently. We provide a thorough analysis of these measures and propose a new fast approach to compute most of them. The approach is based on the projected envelope algorithm that generates the omni-spectrum of horizontal ground motion, and its computation speed is faster than previous methods for this purpose. Visualizing the omni-spectrum helps to identify the maximum demand orientation and to capture effects of directionality. Moreover, most previous orientation-independent measures can be represented concisely in the functional form of the omni-spectrum.