Including site effects in seismic risk modeling

Overview

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What are site effects?

Site effects are the group of local characteristics that modify seismic strong motion.

They are called site effects due to their extremely local nature.

For example, within a city, these effects may change from one block to the next.

What are site effects?

Typical seismic site effects are related to: Soil deposits dynamic response

Topography

Soil liquefaction

Most important Site Effects

Soil dynamic response

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Michoacn earthquake (Mexico), 1985

Michoacn earthquake (Mexico), 1985

Near hypocentral area

Mexico City

400 Km

Energy attenuation process

Michoacn earthquake (Mexico), 1985

Bedrock Soft soil

Tauramena earthquake (Colombia), 1995

How to assess site effects?

Measuring them. By installing acceleration sensors and waiting for earthquakes to occur By measuring, trough geophysical methods, dynamic characteristics of soil deposits

Modeling them. This, of course, requires detailed knowledge and expert criteria

Site effects modeling

As mentioned, requires specific knowledge and criteria

May be assessed by means of several methods

Its a difficult problem. Soil dynamic response is highly non-linear, therefore it may be assessed only by means of specialized numerical methods

Site effects modeling

Given the mentioned characteristics, CAPRA does not model site effects

However, given their importance in seismic risk assessment, they can be included in risk analysis using CAPRA

Site effects modeling in CAPRA Response spectra transfer functions

Site effects modeling in CAPRA Response spectra transfer functions

Assessing site effects

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Measuring seismic response to strong motion Bogot accelerograph network

FUNCIN DE TRANSFERENCIA COMPONENTE EO

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Measuring seismic response to strong motion Bogot accelerograph network

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Measuring seismic response to strong motion Bogot accelerograph network

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Measuring seismic response trough geophysical methods Measuring ambient vibration at surface

Measuring seismic response trough geophysical methods Measuring ambient vibration at surface

Measuring seismic response trough geophysical methods Measuring ambient vibration at surface

Measuring seismic response trough geophysical methods Measuring ambient vibration at surface

Fundamental vibration period of soil deposits obtained for Bogot, by means of ambient vibration records

Modeling soil dynamic response

Linear models Non-linear models

1-dimension 2-dimensions 3-dimensions

How is it usually done?

1D non-linear soil response

Modos Principales de Vibracin

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Soil column vibration modes

1D non-linear soil response

Surface

Bedrock

Shear stress and strain

1D non-linear soil response Shear stress and strain

1D non-linear soil response Shear stress and strain

0.0001 0.001 0.01 0.1 1 (%)

Gs

Site effects example: Bogot

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Bogot site effects

Seismic hazard map including site effects 475 years return period Structural period T = 0 sec Low rise buildings

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Bogot site effects

Seismic hazard map including site effects 475 years return period Structural period T = 0.3 sec 3-4 stories buildings

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Bogot site effects

Seismic hazard map including site effects 475 years return period Structural period T = 1.0 sec 8-12 stories buildings

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Bogot site effects

Seismic hazard map including site effects 475 years return period Structural period T = 2.0 sec High rise buildings 20 stories

CAPRA tool for including site effects

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Site Effects format

Assess site effects by means of response spectra transfer functions

Allows geographical distribution of transfer functions

Allows non-linear soil response representation

Its a binary file. It cant be constructed by hand

Site Effects application