A Study Of Seismic Amplification In The Yuhuangguan Delta Area

In order to study the characteristics of surface seismic amplification, theYuhuangguan delta area was selected as the site for a seismic amplificationobservation experiment Field work carried out at the site include observation ofearthquakes, geological investigation and geophysical exploration.On the recordings of the seismic observation, earthquake events were firstlyidentified interactively. The parameters of the earthquakes, including arrival times ofthe P and S wave arrivals and the duration length of the events, were then read. In thefollowing data processing, VLF filtering, earthquake data resampling from the rawdata, quality controlling, were performed. S-wave parts of50earthquakes withhighsignal to noise ratio were selected for the study of seismic amplification at theexperiment site., The S-wave data was first tapered to reduce Gipps effect, thenFourier transform was performed to obtain the amplitude spectra of the data in thefrequency domain. Smoothing filtering was applied to the spectra to eliminate noisyfluctuations. Then spectral ratios of the corresponding components at eachobservation site to the reference site of R01were calculated for all50earthquakes.Finally, statistics and comprehensive analysis of the spectral ratios lead us to thefollowing understanding of the amplification pattern of the experiment site:(1) Recordings from a site close to the epicenter of an earthquake usually havehigh signal to noise ratio, which would result in good precision for spectrum ratiocalculation, and in turn results in accurate estimation of seismic amplification of thesite.(2) Quality controlling is a critical process for the identification of earthquakeevents from the raw data (3) Low signal-to-noise ratio seismic data would seriously interfere with theresult of the spectral ratios. Therefore improvement of signal to noise ratio for thedata and disposal of low signal to noise ratio data is important.(4) Effects is very minor for abnormal data on the amplification pattern of theexperiment site, characterized by statistics of peak frequencies and amplificationfactors.(5) Although no very large amplification was recorded at the experiment,significant amplification was observed at the frequencies ranging from5-10Hz.Among the amplification sites, S06is particularly outstanding, with an averageamplification factor of about4in50earthquake, at the frequency of7Hz.(6) The result of SH wave forward modeling at S06is in very good agreementwith the observations, which suggests that the methodology used in this paper iseffective.