Improved HVSR site classification method for free-field strong motion stations validated with Wenchuan aftershock recordings

Local site conditions play an important role in the effective application of strong motion recordings.In the China National Strong Motion Observation Network System（NSMONS）,some of the stations do not provide borehole information,and correspondingly,do not assign the site classes yet.In this paper,site classification methodologies for free-field strong motion stations are reviewed and the limitations and uncertainties of the horizontal-to-vertical spectral ratio（HVSR） methods are discussed.Then,a new method for site classification based on the entropy weight theory is proposed.The proposed method avoids the head or tail joggle phenomenon by providing the objective and subjective weights.The method was applied to aftershock recordings from the 2008 Wenchuan earthquake,and 54 free-field NSMONS stations were selected for site classification and the mean HVSRs were calculated.The results show that the improved HVSR method proposed in this paper has a higher success rate and could be adopted in NSMONS.

Preliminary site classification of free-field strong motion stations based on Wenchuan earthquake records

During the great Wenchuan earthquake, about 460 permanent free-field stations in National Strong Motion Observation Network System （NSMONS） of China captured the main shock acceleration records. These records can be applied to site effect analyses, and then the site classification of those permanent stations can be carried out firstly, which will served as the fundamental information for further research. In this paper, the site of near-fault stations is classified by horizontal-to-vertical spectral ratio （HVSR） method according to the site class description of Japan earthquake resistant design code and response spectral shapes （RSS） method following the site class description of the 1997 Uniform Building Code （UBC） provisions. Then based on the detailed borehole data of those free-field stations, the equivalent shear wave velocity and overburden thickness are calculated and the site classifications are given by Chinese code for seismic design of buildings. Furthermore, for the stations having successful microtremor test data, the site dominant periods are computed to verify the results of site classification. Finally, combined with all the above results, the recommended site classes of near-fault permanent free-field stations are given.

Geomorphological site classification for the Fujian province

Geomorphological classification of the Fujian province was done based on remote-sensing imaging, digital elevation maps, and slope gradient data acquired by ArcGIS 9.2. The engineering geological units in the Fujian province were divided into five types by the geomorphologic shape and genesis. The relationship among geomorphological type, engineering geological unit, and site category was determined using engineering geological data and site category data. Then, after making a preliminary site classification adjusted by drill hole data, the site was classified into four types： Ⅰ0, Ⅰ1, Ⅱ, and Ⅲaccording to site classification standards of equivalent shear-wave velocity and overburden thickness. The results showed that the site categories in the Fujian province mainly consist of type Ⅱ, which accounts for 85.26 % of the land area. The percentage of Io was the smallest, which accounts for only 2.44 % of the total area.

SITE CLASSIFICATION FOR PROTECTIVE FOREST AFFORESTATION ON THE COAST OF CHINA

Land for protective forest on the coast has special site conditions, and site classification is the scientific basis for seaboard afforestation. The site classification system on the coast zone and islands of China may be classified into five levels-site region (sub - region), district, class, group, and type. The land division for afforestation is carried out by the principle of enviornmental heterogeneity among regions, sub-region and district on large scale, according to the difference of air temperature, moisture and type of coast geomorphy. It may be classified into 7 regions, 12 sub-regions and 55 districts. The medium and small scaled division for site class, group and type, subdivided in a site district, are based on medium topography, topographic climate, micro - relief and soil conditions.

Site coefficients suitable to China site category

The basis for the NEHRP site coefficients is summarized in the paper. The comparison of site classification between China and US code provisions has been carried out. The relationship between two site classifications has been found by the analysis of wave velocity of site soil. Thus amplitude-dependent site amplification factors for China site classification has been gained by transformation from US amplification factors. Two amplification factors are specified： Fa for short periods and Fv for longer periods. On the contrast, there is only one long period factor and not a short period factor in the current China code provision.

STUDY ON THE SITE OF KOREAN PINE PLANTATION ON THE MAOER MOUNTAIN

The site classification and site quality evaluation were studied in Korean pine (Pinus koraiends) plantations on the Maoer Mountain. All the Korean pine plantation were classified into 3 site classes including 13. site types, based on the three key site factors of soil type, humus horizon depth and aspect, which affect the growth of Korean Pine tree. Multiple regression eqwtion related to site facors and dominant tree height was developed by using the Numeral Model I for site quality evaluation of Korean pine plantation. A table of site quality evalwtion was mede on the basis of the table of forest site type and the dominant tree height predicting equation of Korean pine plantation.

Soft Soil Site Characterization on the Coast of Yantai and Its Effect on Ground Motion Parameters

According to the Chinese GB50011-2001 code and the recommended provisions of FEMANEHRP and EUROCODE 8, by using shear wave velocity and borehole data, the site classification is evaluated for a typical soft soil site on the Yantai seacoast. The site seismic ground motion effect is analyzed and the influence of the coastal soil on design ground motion parameters is discussed. The results show that the brief site classification can not represent the real conditions of a soft soil site; the soft soil on the coast has a remarkable impact on the magnitude and spectrum of ground motion acceleration. The magnification on peak acceleration is bigger, however, due to the nonlinear deformation of the soil. The magnification is reduced noulinearly with the increase of input ground motion; the spectrum is broadened and the characteristic period elongated on the soft soil site.

On the Disadvantages of the NEHRP Soil Classification

The study of the relationship of local ground conditions with the parameters of seismic vibrations carried out by the section of engineering seismology called seismic microzonation. In this branch of applied science radical changes have taken place at the end of the last century. The Commission on Seismic Safety of the National Institute of Building Sciences of the United States has developed new recommendations, which are significantly different from all that used in the world practice of anti-seismic construction. The main provisions of this NEHRP (National Earthquake Hazards Reduction Program) classification adopted in many national building codes, including Eurocode 8. At the same time, a number of papers appeared in subsequent years criticizing the use of the NEHRP soil classification. This article examines in detail and, most importantly, comprehensively the shortcomings of the NEHRP classification.

Seismic performance of high-rise buildings in selected regions in Saudi Arabia according to different seismic codes

The design code for each country is revised and updated based on an expected zone’s seismic intensities,geotechnical site classifications,structural systems,construction materials and methods of construction in order to provide more realistic considerations of seismic demand,seismic response,and seismic capacity.Based on the aforementioned provisions,structures designed according to different seismic codes may yield different performances for the same level of hazard.This study aims to investigate and compare the induced responses related to the earthquake-resistant design of reinforced concrete(RC)buildings according to the Saudi building code(SBC-301),American code(ASCE-7),uniform building code(UBC-97),and European code(EC-8).In order to account for the provision regarding the hazard specification and its effect on the induced seismic responses,four regions in the Kingdom of Saudi Arabia with different seismic levels are selected.The code provisions related to the specification of site classification and its effect on the induced design base shear are investigated as well.Significant differences are observed in the induced responses with the variation in seismic design codes for the considered seismic hazards and site classifications.

A Seismic Hazard Map Based on Geology and Shear-wave Velocity in Rawalpindi–Islamabad,Pakistan

The‘twin cities’district of Rawalpindi–Islamabad is among the most endangered seismic regions in Pakistan,with the seismic hazard assessed(0.32 g)to intensity IX MMI for a 475-year return period.A seismic hazard map for Rawalpindi–Islamabad is presented herein,based on 85 shear-wave velocity(VS)profiles obtained through geophysical H/V measurements and from the geological map of the region.Relationships between the average top thirty-meter shear-wave velocities(VS30)and surficial geological units have been determined.The peak ground acceleration(PGA)maps for 150,475 and 2475-year return periods were converted into a seismic intensity map.Intensity increments for different soils were used to compute PGA values for 150,475 and 2475-year return periods.Sites located on softer ground experienced a higher degree of damage from moderate earthquakes.Due to the presence of soft clay or liquefiable soil and lateral spreading,a few locations may be classified as hybrid sites class C and D.This map is a critical step in facilitating code-based site classification and seismic design throughout Rawalpindi–Islamabad.Although the seismic hazard map based on seismic intensities is no longer used in engineering geology,it is still important in seismological analysis and for civil protection purposes.

Simulation of scenario earthquake influenced field by using GIS

The method for estimating the site effect on groundmotion specified by Borcherdt (1994a, 1994b) is briefly introducedin the paper. This method and the detail geological data and site classification data in San Francisco bay area ofCalifornia, the United States. are applied to simulate the influenced field of scenario earthquake by GIS technology,and the software for simulating has been drawn up. The paper is a partial result of cooperative research project betweenChina Seismological Bureau and US Geological Survey.