Peak Ground Acceleration Range Research Articles

Probabilistic evaluation of seismic soil liquefaction potential based on SPT data

The performance-based liquefaction potential analysis was carried out in the present study to estimate the liquefaction return period for Bangalore, India, through a probabilistic approach. In this approach, the entire range of peak ground acceleration (PGA) and earthquake magnitudes was used in the evaluation of liquefaction return period. The seismic hazard analysis for the study area was done using probabilistic approach to evaluate the peak horizontal acceleration at bed rock level. Based on the results of the multichannel analysis of surface wave, it was found that the study area belonged to site class D. The PGA values for the study area were evaluated for site class D by considering the local site effects. The soil resistance for the study area was characterized using the standard penetration test (SPT) values obtained from 450 boreholes. These SPT data along with the PGA values obtained from the probabilistic seismic hazard analysis were used to evaluate the liquefaction return period for the study area. The contour plot showing the spatial variation of factor of safety against liquefaction and the corrected SPT values required for preventing liquefaction for a return period of 475 years at depths of 3 and 6 m are presented in this paper. The entire process of liquefaction potential evaluation, starting from collection of earthquake data, identifying the seismic sources, evaluation of seismic hazard and the assessment of liquefaction return period were carried out, and the entire analysis was done based on the probabilistic approach.

Probabilistic Seismic Hazard Model for Vanuatu

Abstract This study develops a preliminary probabilistic seismic hazard model for Vanuatu. The area of investigation, formerly referred to as the New Hebrides, lies in the center of a chain of partly vulcanologically active islands that mark the present-day boundary between the Australia-India plate and the microplate of the North Fiji basin. The seismicity of the Vanuatu arc is dominated by an east-dipping subduction zone, which shows striking structural anomalies in the central part between 14° and 18° S. Our historical catalog contains 7519 events within the Vanuatu region for the period from 1964 to 2003, drawn from the global teleseismic catalogs by the United States Geological Survey/National Earthquake Information Center (USGS/NEIC, see Data and Resources section) and Engdahl et al. (1998). As a measure of seismic hazard, we use horizontal peak ground acceleration (PGA) and horizontal spectral ground acceleration (SGA) at a period of 1 sec. The hazard estimates are based on a logic-tree approach to account for the epistemic uncertainties associated with our analysis. Our results suggest that the entire island arc experiences a high and uniform seismic hazard. Typical values for PGAs range from 0.65 g to 0.77 g with a 10% probability of exceedence in 50 yr. For Port Vila, the capital and largest city in Vanuatu, we additionally present a PGA hazard curve and a uniform hazard spectrum over the period range 0.1–2 sec.

Effects of bearing damage upon seismic behaviors of a multi-span girder bridge

The effect of possible bearing damage during seismic excitations is investigated through examining the dynamic behavior of a multi-span simply supported bridge. Proper analytical models are developed, which can simulate the realistic seismic behavior of the bridge before and after the bearing damage. The damaged bearings are modeled as sliding elements with the appropriate friction between the superstructure and the top of the pier. Various values of the friction coefficients are examined to verify the effect of damaged bearings under the wide range of peak ground accelerations. It is found that the global seismic behaviors of the bridge are significantly influenced by the occurrence of bearing damage. It should be noticed that the most possible location of unseating failure of superstructures differs from that in the bridge model without consideration of the bearing damage. It can be concluded that bearing damage may play the major role in the unseating failure of a bridge system. The damage of bearings should be included to achieve more rational seismic safety evaluation.

Consistency of Ground-Motion Estimates Made using System Identification

This article isolates the systematic effects of the soil profile on earthquake ground motions recorded at vertical seismic arrays. An empirical Green's function is calculated for a soil interval between two sensors in a vertical array. The estimation technique used here falls into the category of site-response estimates but differs from the standard spectral ratio methods in that an extended Weiner filter (ARMA model) becomes the impulse-response function from one point to another in the soil profile. This method allows quantification of the accuracy of predicted ground motions at a given site with normalized mean square prediction errors generally under 10%, indicating effective and consistent estimates. The models are shown to reproduce site ground motions for inputs that differ over a wide range of peak ground acceleration (PGA), hypocentral locations, and over numerous occurrences. We demonstrate consistency of site ground-motion estimates at four sites that have undergone multiple strong shakings: Chiba, Japan; Garner Valley, California; Lotung, Taiwan; and Port Island, Japan. Consistency of site response over a wide range of shaking levels indicates an “effective” range of linear soil behavior for PGA up to 0.33 g at Chiba, 0.1 g at GVDA, and 0.21 g at Lotung. At Port Island, consistency was evident below 16 m at a surficial PGA of 0.54 g , but the surface layer liquefied. Results are presented as predicted time series and in the frequency domain with calculated variance. Results from Garner Valley and Chiba indicate that the location and magnitude of significant impedance contrasts within the soil profile control response. This article concentrates on levels of shaking that do not excite the soils into phase transitions. Our results indicate that strong nonlinear behavior (liquefaction) controls site response, but more minor and localized softening of the soil may not alter the site response enough to deter prediction within 10%.

The site response of two rock and soil station pairs to strong and weak ground motion

Abstract The site response to strong and weak ground motion depends largely on the subsurface conditions at the soil site for the two rock-soil station pairs studied. The first station pair consists of a soft-soil site (Treasure Island) and a sandstone and shale site (Yerba Buena Island). These stations recorded strong ground shaking from the Loma Prieta mainshock and weak ground motion from four aftershocks. The range of peak ground acceleration is from approximately 0.00006 to 0.07 g at the rock site. Compared to the rock site, the strong ground motion at the soft-soil site is amplified by a factor of about 3 over a frequency range from 0.5 to 2.0 Hz. The amplification is much higher for weak motion and suggests a dependence on signal amplitude. For example, near 1 Hz, the site response shows an increasing amplification as magnitude (and the peak velocity at the rock site) decreases. For events of local magnitude 7.0, 4.3, 4.1, 3.5, and 3.3, the maximum soil-site amplifications are 4, 12, 17, 19, and 25, respectively. A second station pair consisting of a stiff-soil site (Gilroy #2) and a sandstone site (Gilroy #1) was also studied with contrasting results. These two stations recorded strong ground shaking from the 1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta mainshocks. Weak ground motion was recorded at these stations after the Loma Prieta mainshock. The range of peak ground acceleration is from 0.006 to 0.43 g at the rock site. Unlike the results for the soft-soil study above, the estimated stiff-soil site responses are not significantly different for strong and weak motion from 0.5 to 2.0 Hz. Near 0.7 Hz, the stiff-soil site responses range from 2.5 to 4.5 for strong ground shaking from three mainshocks and from 1.5 to 4.0 for weak ground shaking from thirteen aftershocks.