Fourier amplitude spectra of strong motion acceleration: Extension to high and low frequencies

Abstract

SUMMARYIt is shown how the empirical equations for scaling the Fourier amplitude spectra in the frequency band from -0.1 to 25 Hz can be extended to describe the strong motion amplitudes in a much broader frequency range. At long periods, the proposed equations are in excellent agreement with (1) the seismoiogicai and fieid estimates of permanent ground displacement (near field) and (2) the independent estimates of seismic moment (far field). At high frequencies,f> 25 Hz, the spectral amplitudes can be described by exp (-rrkf), where k ranges from 0.02 (near source) to about 0.06 at an epicentral distance of about 200 km. It is also shown how amplification by local soil and geological site conditions can be defined to apply in the same broad frequency range.

On the Characterisation of the Phase Spectrum for Strong Motion Synthesis

“…Thus the proposed approach can be easily used together with the available empirical scaling relations (see [Trifunac, 1987[Trifunac, , 1994, Trifunac and Lee [1985]) for Fourier amplitude spectrum to generate realistic, site and event-specific accelerograms.…”

“…Since recorded accelerograms rarely conform to the design specifications, the required time histories need to be synthesised from appropriate Fourier amplitude and phase spectra. A considerable amount of research effort has been devoted in the past in studying and characterising the Fourier amplitude spectra of strong ground motion in terms of various parameters, such as magnitude, epicentral distance, focal depth, local geology, soil conditions (see, for example, [Trifunac, 1987[Trifunac, , 1994, Trifunac and Lee [1985]). Recently, a similar characterisation of the phase properties of earthquake accelerograms also has been reported [Thráinsson and Kiremidjian, 1998;Thráinsson, 2000].…”

Soils' seismic property research on the basis of investigation of their nonlinear properties

“…Nonlinear distortions of the wave shape, which take place in the bi-modular medium, occur in the spectrum "spreading" to the areas of low and high frequencies (Nikolaev, 1967;Vasilyev et al, 1969;Trifunac, 1994). The energy transition to the low-frequency area is connected with modulation, difference in character of soil movement up and down as a result of different modularity.…”

Selection of the appropriate methodology for the probabilistic seismic hazard analysis on the territory of the Republic of Serbia

“…The upper bound magnitude, M max , reflects the maximum expected magnitude for the specific source zone, while the lower bound magnitude M 0 represents the magnitude below which no significant damage will occur. The maximum expected magnitude for a source zone can be estimated through a detailed analysis of various seismotectonic features and statistical analysis of the available data on magnitude-fault length relationships [30].…”