MEVE 015: Unit 06 - Risks and Vulnerability Assessment for Geological Hazards

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UNIT 6: RISKS AND VULNERABILITY ASSESSMENT FOR GEOLOGICAL HAZARDS

6.0 Introduction

Geological hazards are natural events resulting from geological processes such as earthquakes, landslides, and volcanic eruptions. These events can lead to immense loss of life, infrastructure damage, and socio-economic disruption. In disaster risk reduction frameworks, assessing geological hazard risk and vulnerability is vital to formulating proactive mitigation strategies. This unit provides insights into types of geological hazards, their consequences, and methods of assessing associated risks and vulnerabilities.

6.1 Objectives

After studying this unit, you will be able to:

  • Understand the nature and types of geological hazards.
  • Assess the associated risks and vulnerabilities.
  • Analyze qualitative methods of risk estimation.
  • Apply prevention and control strategies for minimizing impacts.
  • Link hazard risk with socio-economic vulnerabilities.
  • Understand assessment techniques specific to earthquakes and landslides.

6.2 Hazards

Hazards are events or phenomena that pose a potential threat to human life, property, or the environment. Hazards can be classified into natural (like earthquakes and floods) and anthropogenic (such as industrial accidents). Geological hazards are a subset of natural hazards originating from Earth’s internal processes.

6.3 Geological Hazards

Geological hazards include phenomena such as:

  • Earthquakes
  • Volcanic eruptions
  • Landslides
  • Sinkholes
  • Tsunamis (indirectly from seismic activity)

6.3.1 Effects of Geological Hazards

  • Loss of Life and Property: Instant deaths, injuries, and displacement.
  • Infrastructure Damage: Destruction of roads, buildings, power lines.
  • Economic Disruption: Suspension of business, agriculture, and services.
  • Environmental Changes: Altered river courses, destroyed vegetation.
  • Secondary Hazards: Fires, chemical spills, dam failures.

6.3.2 Assessment of Geological Hazards

Assessment includes:

  • Mapping hazard-prone areas
  • Monitoring seismic or ground movement activity
  • Analyzing geological history and landform features
  • Using remote sensing and GIS technologies

6.4 Risk and Vulnerability

  • Risk: The probability of harmful consequences resulting from interactions between hazards and vulnerable conditions.
  • Vulnerability: Degree to which a system or population is likely to experience harm due to exposure to hazards.

6.5 Risk Assessment

Risk assessment is the process of:

  • Identifying hazards
  • Analyzing potential consequences
  • Estimating the likelihood of occurrence
  • Formulating mitigation strategies

6.5.1 Risk Management

Risk management includes:

  • Avoidance: Land-use planning and hazard zoning.
  • Reduction: Earthquake-resistant construction, afforestation.
  • Transfer: Insurance mechanisms.
  • Preparedness: Early warning systems and drills.

6.6 Vulnerability Assessment

Vulnerability assessment includes:

  • Socio-economic factors: Poverty, literacy, access to resources.
  • Physical factors: Building materials, infrastructure condition.
  • Environmental factors: Deforestation, slope stability.
  • Institutional factors: Governance, emergency response.

6.7 Linking Hazard Risk with Vulnerability Assessment

Effective risk reduction requires integrating hazard analysis with vulnerability profiles. For example, a moderate earthquake may have devastating effects in a densely populated urban slum due to poor construction standards, while a rural area with better preparedness may suffer less.

6.8 Likelihood and Consequences

Assessing risk involves two core components:

  • Likelihood (probability) of a hazard occurring.
  • Consequences (impact) of the hazard if it occurs.

6.8.1 Acceptance Criteria for Any Risk

Risk acceptability is context-dependent. For example:

  • High-consequence, low-probability risks may be tolerated (e.g., nuclear events).
  • Low-consequence, high-probability risks may be managed through resilience strategies.

6.9 Qualitative Risk Estimation

In absence of sufficient data for quantitative methods, qualitative techniques are employed.

6.9.1 Qualitative Measure of Likelihood

Uses descriptors such as:

  • Rare
  • Unlikely
  • Possible
  • Likely
  • Almost certain

6.9.2 Qualitative Measure of Consequences

Assessed as:

  • Insignificant
  • Minor
  • Moderate
  • Major
  • Catastrophic

6.9.3 Qualitative Measure of Inferences

A risk matrix is developed to match the likelihood with consequences, enabling prioritization.

6.10 Categories of Consequences

6.10.1 Direct and Indirect Losses

  • Direct: Physical injury, deaths, property loss.
  • Indirect: Economic losses, long-term displacement, trauma.

6.10.2 Tangible and Intangible Losses

  • Tangible: Measurable (e.g., cost of destroyed buildings).
  • Intangible: Emotional loss, cultural heritage, ecosystem value.

6.11 Prevention and Control of Geological Hazards

  • Zonation and land use planning
  • Public awareness campaigns
  • Structural mitigation (e.g., retaining walls, earthquake-resistant design)
  • Environmental management (e.g., reforestation)
  • Early warning systems and drills

6.12 Risk and Vulnerability Assessment for Various Geological Hazards

6.12.1 Earthquake

  • Risk Factors: Tectonic settings, population density, building practices.
  • Assessment Tools: Seismic hazard maps, microzonation studies.
  • Mitigation: Seismic codes, retrofitting, public education.

6.12.2 Landslides

  • Risk Factors: Slope instability, deforestation, rainfall, earthquakes.
  • Assessment Tools: Slope maps, remote sensing, soil analysis.
  • Mitigation: Drainage control, slope reinforcement, vegetation cover.

6.13 Let Us Sum Up

This unit highlighted the importance of understanding and assessing geological hazards through both hazard mapping and vulnerability analysis. It covered a range of risks and consequences, introducing tools such as qualitative risk matrices and the linkage between likelihood and impact. Through case-specific assessments, such as for earthquakes and landslides, the unit emphasized the role of proactive risk reduction in minimizing geological hazard impacts.

6.14 Keywords

  • Hazard – A potential event or phenomenon that may cause harm to people, property, or the environment.
  • Risk – The probability of harmful consequences resulting from the interaction between hazards and vulnerability.
  • Vulnerability – The degree to which a system, community, or individual is susceptible to harm due to exposure to hazards.
  • Risk Assessment – A systematic process of identifying, analyzing, and evaluating the likelihood and impact of hazards.
  • Qualitative Risk – A non-numerical method of estimating risk using descriptive categories for likelihood and consequences.
  • Seismic Zonation – The division of a region into zones based on the severity of expected earthquake shaking.
  • Slope Stability – The resistance of inclined soil or rock surfaces to failure or landsliding.
  • Geological Hazard – A natural hazard caused by geological processes such as earthquakes, landslides, or volcanic eruptions.
  • Intangible Loss – Non-measurable losses such as emotional trauma, cultural damage, or ecosystem degradation.
  • Mitigation – Measures taken to reduce the severity or likelihood of hazard impacts on human life and infrastructure.

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