THE EFFECTIVE DURATION OF EARTHQUAKE STRONG MOTION

The duration of strong ground shaking during earthquakes can play an important role in the response of foundation materials and structures, particularly when strength or stiffness degradation is encountered. A thorough seismic hazard assessment should therefore include an estimation of the expected duration of strong motion, which first requires criteria to define the part of an accelerogram considered to represent the duration of strong ground motion. Some 30 different definitions of strong motion duration are reviewed and classified into generic groups. Problems that arise with the use of these definitions for duration are highlighted. A new definition of duration is presented using a previously unexplored option which identifies the part of the record where the main energy is contained and constrains this strong shaking phase by absolute criteria. This new definition is shown to give consistently meaningful durations for strong earthquake accelerograms from an engineering viewpoint. The correlations between the new definition of duration and magnitude, soil conditions and distance are explored as a first step towards the development of predictive equations.     

Natural flood management: small-scale progress and larger-scale challenges

ABSTRACT

Management of fluvial flood risk in the UK is undergoing a paradigm shift, with a change in emphasis from solely working with structural defences to considering catchment-based measures which attenuate flood runoff. Natural Flood Management (NFM) is promoted as a method that can reduce flood risk through the alteration, restoration or use of landscape features. Here we highlight the potential to manage runoff locally in the rural landscape using NFM by targeting flow pathways and utilising floodplains and riparian zones. Using two case study examples from the UK, we show that by accumulating dispersed small-scale storage in small catchment areas (<10 km²) can assist in attenuating flood runoff. However, there is currently a lack of evidence of measure effectiveness at larger catchment scales and for managing extreme flood events. Nevertheless, there is a strong evidence base to suggest many of these measures deliver a range of different ecosystem services if installed in the correct location in the landscape.     

NOTE ON THE INCLUSION OF SITE CLASSIFICATION INFORMATION IN EQUATIONS TO ESTIMATE STRONG GROUND MOTIONS

Two main regression methods have been proposed for using site category information within ground motion prediction equations, these are: (a) joint estimation of the site category coefficients and the magnitude and distance coefficients; or (b) estimation of site category coefficients by using the residuals from the equation derived without considering soil conditions. Method (a) requires each record be assigned a site category whereas for method (b), because it relies on residuals, site information can be missing for some records. This short note finds that if the mean of the transformed distances within each site category is the same then the two methods give the same site coefficients. If, however, these means are significantly different then method (b) can yield incorrect site coefficients.     

ATTENUATION RELATIONSHIP FOR LOW MAGNITUDE EARTHQUAKES USING STANDARD SEISMOMETRIC RECORDS

Northwestern Italian weak-motion data were used to study attenuation characteristics of horizontal peak ground acceleration (PGA) and horizontal peak ground velocity (PGV) from earthquakes of local magnitudes (M _l ) up to 5.1. Data have been provided by the RSNI (Regional seismic network of Northwestern Italy) and RSLG (Regional seismic network of Lunigiana-Garfagnana) waveform database. The database consists of more than 14000 horizontal components recorded in the period 1999-2002 by both broadband and enlarged band seismometers. The accuracy of the procedure used to extract PGA values from the velocity recordings was verified comparing observed and derived PGA values at station STV2, which was equipped with both a temporary K2 Kinemctrtcs accelerometer and Guralp CMG40 broadband sensor. The attenuation of both peak ground acceleration and peak ground velocity was found to be logarithmically distributed with a strong attenuation for low distances (less than 50 km) and low M _l values (<3.0). The resulting equations are:

Log(PGA)=?3.19+0.87M?0.042M ²?1.92 Log(R)+0.249S,

Log(PGA)=?4.23+0.76M?0.018M²?1.56 Log(R)+0.230S,

where PGA is expressed in g, PGV is expressed in m/s, M is local magnitude, R is the hypocentral distance in kilometers and S is a dummy variable assuming values of 0 and 1 for rock and soil respectively. For increasing distance and magnitude, both PGA and PGV values show a linear distribution. The validity range of the obtained attenuation relationships is 0–200 km for distances and M _l up to 4.5. Sensitivity studies performed by analysis of residuals, showed that predicted PGA and PGV values are stable with respect to reasonable variations of the model and distances providing the data. Comparisons with attenuation relationships proposed for Italian region, derived from strong motion records, are also presented.     

The spatial scope of agglomeration economies in Brazil

This paper provides evidence about location and colocation patterns of manufacturing entrepreneurship and spatial scope of agglomeration economies in the context of a developing country. Using microgeographic data for all Brazilian manufacturing activities and distance-based measures, we find clear patterns of colocalization between entrants and existing establishments, and that these patterns occur mainly at short distances. For activities presenting colocalization between entrants and existing establishments, our results also indicate that a greater number of incumbent establishments in a given location positively affects the number of entrant establishments that decide to locate there, an effect that attenuates rapidly with distance (generally disappearing after 5 km). This pattern of attenuation is robust to both the inclusion of a comprehensive set of controls for observable and unobservable local characteristics and the use of instrumental variables to address remaining endogeneity concerns.     

ARTIFICIAL ACCELEROGRAMS REPRESENTATIVE OF THE DAMAGE DISTRIBUTION ON A LOW-RISE SHEAR WALL

This study attempts to reproduce in an artificial way, at a given magnitude-distance couple, the statistical characteristics of damage caused by real accelerograms. The structure adopted is a low-rise shear wall, modelled as a nonlinear, one degree of freedom system with a degrading frequency as a function of a non-cumulative damage variable. Strong-motion records, contained in a large database, are characterised in terms of seismological and seismic parameters. Artificial accelerograms are generated from response spectra representative of real accelerograms belonging to different magnitude-distance zones. Although the mean damage is consistent, the low dispersion of damage caused by the artificial accelerograms with respect to that caused by the real accelerograms is highlighted. In order to reproduce the damage dispersion in addition to the mean damage, a generation method of representative artificial accelerograms is proposed. This method introduces the standard deviation drawn from attenuation relationships into a dispersion pre-process with respect to the regressed spectrum at a given magnitude-distance point. The method turns out to be capable of reproducing the statistical features of damage produced by real strong-motion records.     

A THEORETICAL ATTENUATION MODEL FOR EARTHQUAKE-INDUCED GROUND MOTION

A theoretical attenuation model of earthquake-induced ground motion is presented and discussed. This model is related directly to physical quantities such as source and wave motion parameters. An attenuation formula for rms acceleration of ground motion is derived and verified using acceleration data from moderate-sized earthquakes recorded in Iceland from 1986 to 1997. The source parameters and the crustal attenuation are computed uniformly for the applied earthquake data. Furthermore, attenuation formulas for peak ground acceleration are put forward.     

A NON-PARAMETRIC APPROACH TO ATTENUATION RELATIONS

Abstract

A non-parametric multidimensional regression method is proposed for the prediction of seismic ground motion parameters. The main features which distinguish the method from standard regression procedures are: (1) The relationship between the input and output variables is not selected a priori by a prediction law, (2) an arbitrary number of input variables Can be taken into account, provided that an appropriate data base exists, and (3) the computational procedure is very simple. The results can be easily updated when new information becomes available. The method has been applied for the derivation of attenuation relations by using a combination of databases compiled by other researchers. In the majority of the cases discussed in this paper, the method was used for the prediction of horizontal peak ground acceleration as a function of magnitude and distance. In some cases, ground conditions were also taken into account. Some results on the attenuation relations of peak ground velocity and displacement, as well as Arias intensity, are also presented.     

中、美旅游网站对比分析及"虚拟距离衰减"预测模式

在解决旅游网站使用者满意度及其由此引发的旅游在线服务质量问题时,单维分析效果有限,本研究将评估推进到多维的新阶段。本文对中美旅游网站的类型、市场规模和经营模式进行对比分析,认为两地旅游网站的差异在于区域内部意识性、经营策略和发展阶段等方面。同时,发现两地旅游网站共同遵守“虚拟距离衰减”规律,并依此解释了旅游网站赢利与发展乏力的问题,提出了预测旅游网站发展模式的新方法—“虚拟距离衡量法”,这将为加强区域旅游在线管理提供参考。     

旅游口号设计框架构建及其偏离分析:基于衰减器作用视角

作为建立品牌认知、创建品牌资产和投射品牌形象的重要手段,旅游口号在"目的地竞争战"中发挥了重要作用。立足于"衰减器"作用机理,构建旅游口号设计规则框架。同时,根据旅游口号评价指标与设计规则的分歧倾向比例来定义偏离级次,实证分析不同地域尺度的旅游口号的偏离程度和偏离分布差异。研究结论显示：①衰减器的内部作用过程包括特征抽取和口号衰减两个阶段;②旅游口号的偏离情况具有地域尺度差异性。省域旅游口号的总偏离程度最高,景域旅游口号的偏离分布差异性最明显,而市域旅游口号和我国旅游口号的偏离分布一致。