Modern Methods of Estimating Local Effects of Earthquakes
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rn Methods of Estimating Local Effects of Earthquakes O. V. Pavlenko* Schmidt Institute of Physics of the Earth of Russian Academy of Sciences, Moscow, 123242 Russia *e-mail: [email protected] Received April 3, 2019; revised January 24, 2020; accepted January 27, 2020
Abstract—Local effects pertain to the main factors determining the ground motion parameters during earthquakes. The local effects associated with seismic ground response have always been paid much attention in the practice of engineering seismology since most urban regions in the world are situated in river valleys, on the soft young sedimentary deposits. The river valleys in the earthquake-prone areas host a number of large cities of the world such as Tokyo, Osaka, Kobe, Los Angeles, San Francisco, San Salvador, Caracas, Lima, Bogota, Kathmandu, Manila, Thessaloniki, Mexico City, etc. The abundance and significance of these effects stimulated numerous instrumental, theoretical, and numerical studies aimed at better understanding and quantifying these effects. To date, the methods have been developed in seismology for reliable assessment of these effects. In this paper, the methods of assessing the local effects of the earthquakes that were used at the early stages of seismology and their evolution up to the modern level are described. Keywords: local effects, ground motion parameters, seismic ground response DOI: 10.1134/S1069351320040060
INTRODUCTION Along with the effects of the source and the propagation path the local effects determine parameters of Earth surface shaking in earthquakes. Estimation of earthquake local effects is an important component in assessing seismic hazard. Probabilistic parameters of surface shaking are needed to calculate the response spectra, dynamic stresses and strains that might lead to destruction of buildings and to estimate the possibility of soil liquefaction. The spectrum of surface shaking in a point may be presented as a production of the source contribution E by the propagation path of seismic waves P and by the local conditions in the receiving point G:
Y ( M , R, f ) = E ( M , f ) P ( R, f ) G ( f ) ,
(1)
here M is the moment magnitude of the earthquake, R is the source-receiver distance, f is the frequency. It is a traditional approach used in seismic hazard assessment, when a model is required that could describe the surface shaking spectrum in a given point. Separation of the spectrum into the components “source,” “propagation path” and “local effects” allows to modify the model for different situations or to consider new information concerning particular aspects of the model (Boore, 2003). Effects of the source and the propagation path of seismic waves are usually presented as functions of magnitude and distance. These are regional characteristics that can be estimated via the available seismic records for a given region. Local effects manifest a
more pronounced spatial variability. They can alter noticeably in the limits of a small area, at bases of tens of meters. Local effects of earthquakes are soil res
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