Study On Relationship Of Response Spectrum Attenuation Of Wenchuan Earthquake

With the development of seismology and strong motion observation,great progress has been made on research of ground motion attenuationrelationship. Before2008, such researches were mostly established withthe employment and conversion of western US data. After the WenchuanEarthquake in2008, the country received a large number of strong motionrecords which worked as the initial value for studies on how attenuationrelations of response spectrum were influenced by different types of sites.In this paper, with the systematical collection of the strong motionrecords in Wenchuan Earthquake, the author fitted with various kinds ofground motion parameters attenuation relationships and studied howcharacteristic parameters of response spectrum attenuation were affected bysite types.The primary researching works are as follows,a) An historical review of international studies on ground motionattenuation relationships from the perspective of attenuation model, fittingmethod, and researching theory. The definition of a workable model onattenuation relation fitting by trailing of different attenuation models.b) A briefing of strong motion records in Wenchuan Earthquake; aselective statistics on the strong motion records of158soil stations and16bedrock stations; a baseline correction of over500pieces of strong motionrecords; an acceleration response spectrum calculation of each record anddemarcated by employing least squares sectional fitting; an statisticalanalysis on the characteristic parameters of acceleration response spectrum.c) A brief study of the attenuation characteristics of seismic peakacceleration. By employing least squares regression to calculate theattenuation relationships of the four kinds which contains20items of peakground motion parameters in terms of earthquake peak acceleration, effectivepeak acceleration, peak velocity and effective velocity. Further studiesincluding: a detailed analysis of attenuation features; the impact sitecondition has on the attenuation of four kinds of ground motion parameters.On average, the four peak value of ground motion indicates that the vibrationincreases while the sites becoming softer.d) The attenuation characteristics of acceleration response spectrumgiven by calculating V/H acceleration response spectrum attenuationrelations; the comparative analysis on spectral shapes of different faultdistances and the attenuation relationship of acceleration response spectralvalues of different natural vibration periods, as well as V/H spectral ration.By fitting the attenuation relationships between response spectrum platform values and characteristic cycles, the author also made comparative analysison the characteristic parameters of acceleration response spectrumattenuation of different types of sites in different directions. Conclusionreached: spectral ratios>1happened when near-fault acceleration responsespectra cycles were at either0.01s~0.1s or3s~6s; with the increase offault distance, the V/H values first decrease and then increase, showingsignificant vertical effects at the fault distance of30km with V/H>2/3.e) How characteristic parameters of response spectrum attenuationwere influenced by site types. The author proposed a “platform siteattenuation value impact factor” to make quantitative research of site types’influence on platform value of response spectra; a “decay curve lowing rate”to make quantitative analysis on the decay rates of various decay curves.Calculation showed the average coefficient of site attenuation values forType Ⅰplatform in horizontal is0.5358, while the value became into1forType Ⅱ platform in horizontal and1.579for Type Ⅲ, which shared theminimum decay rate.f) The attenuation characteristics of dynamic coefficient spectrum.Provided attenuation relations on horizontal dynamic coefficient spectrum invarious vibration periods and spectral shapes of various fault distances. Byapplying fitting method calculating the platform values’ attenuationrelationship of different site types, and directions. Conclusions were drawnthat with the increase of fault distance, the platform value of dynamiccoefficient spectrum tends to increase first and then decrease, ranging from1.8to2.8; the value increased slightly in vertical while showed no obviousorder in horizontal with site softened.g) A compared and validated analysis showed that the attenuationrelationship author raised in this paper was similar to that of Huo Junrong innear field while similar to Campbell in medium-and far filed. The intensitydistribution chart based on the fitted attenuation values of response spectrumplatform value shared great similarity with the actual chart of WenchuanEarthquake, indicating a good mirror of ground motion attenuationcharacteristics.Based on limited data of Wenchuan Earthquake main shock, this paperonly severed as a preliminary analysis and summary of above mentionedtopics. Conclusions reached were for reference only.