The Whittier Narrows, California Earthquake of October 1, 1987—Note on Peak Accelerations during the 1 and 4 October Earthquakes

1988 ◽  
Vol 4 (1) ◽  
pp. 101-113 ◽  
Author(s):  
M. D. Trifunac
Keyword(s):  
Wave Propagation ◽  
Los Angeles ◽  
Ground Motion ◽  
Strong Ground Motion ◽  
Strong Dependence ◽  
Three Dimensional ◽  
Physical Processes ◽  
Los Angeles Basin ◽  
Dense Arrays ◽  
Strong Ground

Attenuation patterns of the recorded peak accelerations during two moderate earthquakes (ML = 5.9 and 5.3) in Los Angeles, California are described. It is shown that the recording of earthquake motions by dense arrays of accelerographs can yield a detailed and deterministic picture of the physical processes which are involved in shaping the observed variations of strong ground motion. For the two earthquakes the observed changes of peak amplitudes with respect to the azimuth and distance are slowly and continuously changing functions showing strong dependence of amplitudes on the radiation patterns of the two earthquakes and on the effects of wave propagation through irregular three-dimensional geology of the Los Angeles basin.

Empirical Attenuation Equations for Vertical Ground Motion in Turkey

2004 ◽  
Vol 20 (3) ◽  
pp. 853-882 ◽  
Author(s):  
Erol Kalkan ◽  
Polat Gülkan
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Strong Dependence ◽  
Strong Motion ◽  
Vertical Acceleration ◽  
Data Set ◽  
Attenuation Relationships ◽  
Geological Conditions ◽  
Ground Motion Records ◽  
Strong Ground

In the aftermath of two destructive urban earthquakes in 1999 in Turkey, empirical models of strong motion attenuation relationships that have been previously developed for North American and European earthquakes have been utilized in a number of national seismic hazard studies. However, comparison of empirical evidence and estimates present significant differences. For that reason, a data set created from a suite of 100 vertical strong ground motion records from 47 national earthquakes that occurred between 1976 and 2002 has been used to develop attenuation relationships for strong ground motion in Turkey. A consistent set of empirical attenuation relationships was derived for predicting vertical peak and pseudo-absolute vertical acceleration spectral ordinates in terms of magnitude, source-to-site distance, and local geological conditions. The study manifests the strong dependence of vertical to horizontal (V/H) acceleration ratio on spectral periods and relatively weaker dependence on site geology, magnitude, and distance. The V/H ratio is found to be particularly significant at the higher frequency end of the spectrum, reaching values as high as 0.9 at short distances on soil sites. The largest long-period spectral ratios are observed to occur on rock sites where they can reach values in excess of 0.5. These results raise misgivings concerning the practice of assigning the V/H ratio a standard value of two-thirds. Hence, nonconservatism of this value at short periods and its conservatism at long periods underline the need for its revision, at least for practice in Turkey.

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