﻿ Modeling the Specific Seismic Risk Considering the Weight of Determining Variables

Open Access Library Journal
Vol.02 No.04(2015), Article ID:68326,14 pages
10.4236/oalib.1101157

Modeling the Specific Seismic Risk Considering the Weight of Determining Variables

Liber Galbán Rodriguez, Elio Quiala Ortiz

Department of Hydraulic Engineering, Faculty of Construction, Universidad de Oriente, Santiago de Cuba, Cuba

Received 3 April 2015; accepted 19 April 2015; published 24 April 2015

ABSTRACT

The seismic risk determination for any country is a vital tool in the process of physical planning, construction and reduction of disasters caused by earthquakes. In recent years, there have been several studies on the subject, however, different methodologies could be improved from the design of a set of basic criteria, which using the advantages of Geographic Information Systems (GIS), could help to establish greater clarity in the seismic risk determining. To meet this goal, in this study, the authors propose a new allocation methodology based on levels of importance of variables that influence the specific seismic risk assessment and propose a new formula for mathematical determination through modeling with GIS.

Keywords:

Earthquakes, Methodology, Model, Risk, Variables

Subject Areas: Computer Engineering, Environmental Sciences, Geology, Geomorphology, Hydrology, Natural Geography

1. Introduction

An earthquake or seism is a geological phenomenon product to a sudden release of energy in a point of the earth’s crust, and this motion causes shock waves, also known as seismic waves, propagating from the point of origin and traveling through the Earth. Earthquakes are manifested in the formation and decay of rocks and soils, in the variation of their physical and stratified conditions, in the formation and variation of the relief of the land surface, in the construction of the crust and the internal structure of the Earth. To study them is extremely important for engineering processes, due to its influence on the stability of the ground, respectively, in existing works, planned, under construction, etc., (Cities, buildings, bridges, dams, roads, tunnels, airports , mines, quarries, etc.). The possible occurrence of earthquakes is a threat whose impact can lead to serious injury or geological risks.

Geological risks are events or circumstances that occur in the geological environment and can cause damage or harm to communities or infrastructure that are occupying a territory vulnerable areas [1] . According to Galbán et al. (2012) [2] , seismic risks are a type of geological risk because the event which takes place in the geological vulnerable enhancer of damage is the earthquake. The determination of the seismic risk leads to follow three key steps: 1) the hazard assessment, 2) vulnerability and, 3) the evolution of risk. Changes in one or more of these parameters influence the risk in itself. To consider these elements is necessary to use or design a methodology to provide as much detail as possible to determine the behavior of risk in a given geographic area.

In the analysis of the seismic risk assessment at the international level were detected several methodologies in this regard, although the methodology mostly employed are the HAZUS promoted by The United States Geological Survey (USGS) and Federal Emergency Agency (FEMA), and the one used by Japanese Geological Survey [3] .

Most of these methodologies modeled seismic risk from the occurrence or not of the different processes or factors that lead to hazards, vulnerability and seismic risk, however, with regard to the consideration of the effect or weight of the variables in their determination are not uniform, especially when it comes to damage to specific elements located on the ground (buildings and infrastructure, people, etc.), which is why it is necessary to address this gap and establish a new formulation for determining the seismic risk. To accomplish this task it is necessary to establish a new formula for mathematical determination of specific seismic risk through modeling with GIS. The novelty in this process comes in the allocation of a methodology based on levels of importance of variables that influence the specific seismic risk assessment which takes into account the behavior of elements involved in the manifestation of the phenomenon, as well as others related to the physical vulnerability discussed in the geographic spaces.

By other hand, the methodologies used so far internationally to determine the models do use the multiplication of hazard and vulnerability variables to find the risk. This point of view do not consider that factors multiplied only complicate the situation of the risk evaluation, giving them the possibility to be expressed in how many times or for which factor should be multiplied to obtain a final result, when in real life it is only a sum of pondered facts, which is why it is needed to solve these matters from a different perspective.

2. Definition of the Specific Seismic Risk Model

The Geographic Information Systems (GIS) are a valuable tool to tackle works that require multivariate modeling due to the large volume of information they can process, its ability to generate types, and therefore the possibility of overlapping maps coming to get a map that covers the features of all of them. These elements make them ideal tools for modeling the specific seismic risk.

Using GIS seismic risk assessment is carried out through the acquisition or development of a set of maps or models of hazard, vulnerability and specific seismic risk, which are governed by the following mathematical formulation:

where:

1) R1 or Liquefaction Model = underwater level (0.30) + Geological Susceptibility (0.30) + Seismic Acceleration (0.40).

2) R2 or Earthquakes Landslide Model = Vegetation (0.05) + underwater level (0.05) + Geological Susceptibility (0.25) + Topographic slope (0.25) + Faults (0.10) + Seismic Acceleration (0.30).

3) R3 or Specific vulnerability model = structural seismic vulnerability of buildings per community (0.30) + structural seismic vulnerability of the Roads (0.10) + Population at risk (0.30) + Seismic Acceleration (0.30).

In the formulation are introduced values which should be multiplied by the variables that influence the hazard identification, vulnerability and seismic risk; they obey to the weight of these variables in the occurrence or not of different primary and secondary events.

To represent the interaction of the different variables was used the sums of each to obtain the different basic models. The final specific risk model obtained from this algorithm is reclassified by importance ranges, assigning to each basic model final weight. Each classification is made based on expert judgment, in this case with the support of other documented experiences and qualitative analysis of the distribution of the values of the variables in space.

For a better understanding and correspondence between levels and generating information through maps and graphics or mathematical models, it is suggested to standardize the values from the proposition made by Galbán et al. (2012) [2] , so that the hazards, vulnerability and risks are classified on a scale from zero to one (0 - 1) following levels represented in Table 1.

The proposal aims to integrate on a numerical scale that standardized assessments of hazard, vulnerability and risk, ensuring that all estimates are based probabilistically by its more affordable comparison; action that is performed by applying mathematical standardization and interpolation methods. The choice the method depends on the evaluators and can be done automatically with the help of GIS.

3. Evaluations of the Use of Variables

The underwater level is the underground water that exists on the planet and its depth varies depending on the geological and climatic circumstances. Its presence constitutes an extremely destructive agent when seismic waves are impacting soils and rocks, causing the phenomenon known as liquefaction. Its influence on the seismic risk is expressed in Table 2.

Seismic acceleration is the main characteristic of a seismic wave; its determination allows knowing its value at every point of the geography. The values used in the research for the consideration of seismic acceleration were taken form Galbán et al. (2012) [5] , and are expressed in Table 3.

The vegetation development and its type is an important element in the succession of landslides in a given area. The vegetation and its root system is a factor that can decrease the speed of the slides, and even prevent them in slope areas. For the consideration of this item assumes the proposition made by Galbán et al. (2012) [5] and are expressed in Table 4.

3.1. Submodel Geological Susceptibility

Lithological variety according to their physical and mechanical properties, express certain geological levels of susceptibility to the occurrence of different geological processes and phenomena. This influences susceptibility

Table 1. Classification and standardization of values for hazards, vulnerability and risks [4] .

Table 2. Categorization of the influence by depths of groundwater level. Adapted from Japan Working Group, 1993.

Table 3. Values considered for seismic acceleration [5] .

Table 4. Considerations for the influence of vegetation and hazard levels [5] .

rocks ability not only to allow passage of the seismic waves, but also to increase the translation speed of them. Considering the above is proposed to employ the susceptibility for determining geologic model serving as indicated in Table 5.

3.2. Topographic Slope Sub Model

The topographic slope value is an element that affects the performance of the force of gravity on the phenomenon of sliding slope areas, because the greater the slope will have greater performance out of gravity in conjunction with other factors that also act in landslides. For the consideration of this item assumes the proposition made by Galbán et al. (2012) [5] and are expressed in Table 6.

3.3. Faults Sub Model

For hazard assessment and risk estimation is consider that the main effects related to active faults in the occurrence of a strong earthquake are given mainly in the fact that these are weak areas in the surface were increases of seismic intensity is experimented. Are also areas where differential movements can occur because faults constitute limits of different dynamic blocks and serve as a waveguide from the seismic focus or hypocenter. Based on these criteria is considered the following (Table 7).

3.4. Structural Seismic Vulnerability of Buildings per Community Sub Model

The structural seismic vulnerability of buildings is given by elements related to construction technical states of buildings in different areas, communities or cities that comprise the study area, taking into account the different constructive pathologies, speaking states (Table 8). Example: For states often adopt four levels or states of harm they might suffer these buildings and infrastructure [6] :

E1 = no damage;

E2 = slight damage, operating;

E3 = damage repairable, not operating;

E4 = severe damage or ruin, out of service.

Given these evaluations is then used the proposition of Galbán et al. (2012) [5] .

3.5. Structural Seismic Vulnerability of the Roads Submodel

The structural seismic vulnerability of roads is given by elements related to construction technical states of roads in different areas that comprise the study area, taking into account the different pathologies that are presented from the bedrock to the asphalt or concrete surface. Given these assessment evaluations is then used on a scale of 1 to 10 for vulnerability levels as proposed in Table 9.

3.6. Population at Risk Sub Model

The population sub-model is obtained from the database for each region edited by government statistics offices. In it should be introduced, according to the population of different communities and local considerations, the evaluation criteria. One of the criteria set forth in Table 10.

4. Result of the Application of the General Formulation and Discussion of Models

To determine the resulting specific seismic hazard model, the basic models are calculated as stated below:

Table 5. Classification of lithological or geological susceptibility influence, according to the general conditions [5] .

GS: geological susceptibility, RGS: Range of geological susceptibility for groups of rocks.

4.1. Liquefaction Model

Liquefaction of soils is a physical phenomenon characterized by the complete loss of shear strength. This is bas-

Table 6. Considerations for the influence of the slope and hazard levels [5] .

Table 7. Considerations for the influence of faults and hazard levels [5] .

Table 8. Classification of construction technical states for buildings and infrastructure [5] .

Note: CTE construction technical states.

Table 9. Classification and constructivos of technical states road const [5] .

ically the result of increased pore pressure caused by cyclic strain: a granular material such as soil sands are shaken and these are subjected to a rapid compaction also when is saturated, the result of this compaction gives a rapid lifting of the pore pressure or, since the cutting resistance, which is directly and simply related to the effective force.

For determination of liquefaction model (R1) is considering making queries to the system from the primary base values established in the basic sub-models discussed above, obtaining the final model. Their basic interpretations are made from what was proposed in Table 11.

4.2. Earthquakes Landslide Model

It is called slide to the mass of rock of low consolidation or compaction that has been moved or moves downhill slope shed or (artificial slope) under the effect of gravity, hydrodynamic pressure (saturation effect), seismic forces of various origins, etc. These agents may also act in landslides in combination. From the primary data of the final model is obtained by earthquakes landslides. Their results are interpreted as posed in Table 12.

4.3. Specific Vulnerability Model

To determine the specific vulnerability model (R3), it was considered make queries to the system from the primary core values, levels of specific damages are classified and interpreted as follows (Table 13).

4.4. Specific Seismic Risk Model

Finally the specific seismic risk model is obtained from the superposition of the previously obtained submodels. With the specific purpose of making an assessment as accurate as possible of the elements or variables that characterize the specific seismic risk, we suggest that the analysis for interpretation be made from what is stated in the Table 14.

5. Conclusions

A methodology for the determination of specific seismic risk through its modeling with the use of GIS, which has the novel feature weight consideration with the different variables in the process.

Sub models are some variables in concordance by level and values that can be obtained; the valuation of the

Table 10. Criteria for evaluation of the population at risk.

Table 11. Evaluation of risk levels for soil liquefaction.

Table 12. Evaluation of risk levels for soil liquefaction.

Table 13. Levels of specific vulnerability proposed.

Table 14. General elements to consider in the interpretation of the specific seismic risk model.

variables can be adjusted or improved with more detailed requirement.

Cite this paper

Liber Galbán Rodriguez,Elio Quiala Ortiz, (2015) Modeling the Specific Seismic Risk Considering the Weight of Determining Variables. Open Access Library Journal,02,1-14. doi: 10.4236/oalib.1101157

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