Key factors influencing the impacts of geophysical events

Geophysical events, such as earthquakes and volcanic eruptions, have varying impacts based on a range of interconnected factors. These elements determine the extent of damage, loss of life, and overall disruption caused by such events.

Determinants of geophysical event impacts

• Magnitude and frequency - The strength and regularity of an event play a critical role. Stronger earthquakes or frequent aftershocks tend to cause greater destruction. Earthquakes that occur close to the surface are potentially more damaging than earthquakes deep underground since overlying rocks will absorb more of the energy of the deep-focus earthquakes.
• Population density - Areas with high population concentrations, such as urban centres, often experience more severe impacts compared to sparsely populated rural regions.
• Building quality - Structures in wealthier nations are often designed to withstand earthquakes, reducing potential damage compared to less robust buildings in lower-income areas.
• Timing of the event - The time of day an event occurs can influence its impact. For instance, an earthquake during peak hours like rush hour may result in higher casualties than one at night.
• Proximity to the event - The impact can vary with distance. Volcanic effects often lessen further from the eruption site, while earthquake damage might intensify away from the epicentre due to wave propagation.
• Geological conditions - The type of ground material affects outcomes. Loose sediments can undergo liquefaction during shaking, behaving like a liquid and causing severe structural damage, whereas solid rock offers more stability.
• Secondary hazards - Additional dangers, such as lahars (mudflows) after volcanic eruptions, can lead to more fatalities than the initial event itself.
• Level of economic development - Higher-income countries typically have better preparedness, advanced emergency response systems, superior technology, and more effective healthcare, mitigating the impacts compared to less developed regions.

The role of magnitude and frequency in event severity

The power and occurrence rate of geophysical events are fundamental in determining their destructive potential.

Measuring earthquake strength

• Moment Magnitude Scale (M) - This is the preferred scientific measure for earthquake strength, replacing the older Richter scale. It quantifies the energy released during an event.
• Energy release dynamics - An increase of 1.0 on the M scale corresponds to approximately 30 times more energy released. A smaller increment of 0.2 on the scale doubles the energy output.
• Depth of focus - Earthquakes occurring near the surface tend to be more destructive as the energy is less absorbed by overlying rock layers, unlike deeper events where energy dissipation is greater.

Impact of frequency

• Aftershocks and cumulative damage - Repeated aftershocks following a main event can exacerbate destruction by weakening already compromised structures, leading to higher overall impact.

The significance of population density and building types

Human and structural factors significantly influence the consequences of geophysical events. The concentration of people and the resilience of infrastructure are pivotal in shaping outcomes.

Effects of population density

• Urban vs. rural impact - High-density urban areas face greater risks of casualties and property damage due to the sheer number of people and structures affected, compared to low-density rural zones where impacts are often less severe.
• Infrastructure strain - Dense populations can overwhelm emergency services and infrastructure during a disaster, complicating rescue and recovery efforts.

Importance of building types

• Construction standards - In high-income regions, buildings are frequently engineered to resist seismic activity, incorporating materials and designs that enhance stability.
• Vulnerability in lower-income areas - Conversely, in less economically developed regions, buildings may lack such reinforcements, making them more susceptible to collapse during geophysical events.

The WorldRiskIndex and its components for assessing hazard impacts

The WorldRiskIndex (WRI) is a tool used to evaluate the risk posed by natural hazards to different regions by combining exposure to hazards with societal vulnerability.

Components of the WorldRiskIndex

• Natural hazard sphere - Focuses on exposure, which measures the extent to which a region or population is at risk from natural hazards like earthquakes or volcanoes.
• Vulnerability – societal sphere - Assesses societal capacity to handle hazards through three key aspects:
  • Susceptibility - The likelihood of a community suffering harm due to a hazard.
  • Coping - The ability to reduce negative consequences through immediate actions and resources.
  • Adaptation - Long-term strategies and capacities for societal change to mitigate future risks.

WorldRiskIndex classification ranges

Examples of WorldRiskIndex for selected countries