Geophysical hazards are natural events that originate from geological and geomorphological processes. These hazards include earthquakes, volcanic eruptions, tsunamis, and mass movements such as landslides. In this study note, we will explore the distribution, magnitude, frequency, and risk associated with geophysical hazards, along with the factors affecting their impacts.
Earthquakes are primarily associated with plate boundaries. The majority of earthquakes occur along the Pacific "Ring of Fire," which accounts for approximately 90% of all seismic activity. Earthquakes can be categorized based on the type of plate boundary they occur at:
Volcanoes are also predominantly found along plate boundaries but can also occur at hotspots due to magma plumes. Key areas include:
Magnitude refers to the size or energy release of a geophysical event. For example:
Frequency refers to how often a geophysical event occurs. There is often an inverse relationship between magnitude and frequency: high-magnitude events occur less frequently than low-magnitude events.
Example:
For instance, the 2010 Haiti earthquake had a magnitude of 7.0 Mw and caused significant damage due to its high magnitude and the country's vulnerability.
Risk is a function of hazard, vulnerability, and capacity to cope. The hazard risk equation is given by:
$$ \text{Risk} = \frac{\text{Hazard} \times \text{Vulnerability}}{\text{Capacity to Cope}} $$
Example:
The 2015 Nepal earthquake and the 2016 New Zealand earthquake had similar magnitudes but vastly different impacts due to differences in vulnerability and capacity to cope.
Higher magnitude events generally cause more damage, but frequency also plays a role. Frequent, smaller events can cause cumulative damage over time.
Urban areas often experience greater impacts due to higher population densities and infrastructure concentration.
Higher population density increases the potential for casualties and damage.
Poorly constructed buildings are more likely to collapse, causing higher casualties and economic losses.
Common Mistake:
A common misconception is that all buildings in earthquake-prone areas are earthquake-resistant. In reality, many buildings, especially in less developed countries, do not meet safety standards.
The time of day when a hazard occurs can significantly affect its impact. For example, an earthquake during the night can catch people off guard, leading to higher casualties.
Proximity to the hazard's epicenter or source can greatly influence the level of impact.
The type of underlying geology can amplify or dampen the effects of a geophysical event. Soft sediments can amplify seismic waves, while hard rock can dampen them.
More developed countries often have better infrastructure, emergency services, and preparedness plans, reducing the impact of geophysical hazards.
Tip:
In the exam, be prepared to discuss how these factors interlink and affect each other. For example, higher levels of development can lead to better building quality and lower population density in hazard-prone areas.
Understanding the distribution, magnitude, frequency, and risk associated with geophysical hazards, along with the factors affecting their impacts, is crucial for effective hazard management and mitigation. By studying these elements, we can better prepare for and respond to these natural events, reducing their devastating effects on human life and property.