Earthquake Risk, Prediction, and Prevention

Catastrophes that originate from natural phenomena are called natural disasters, distinguishing them from technological disasters caused by human activities or failures.

Understanding Risk

Risk is determined by several factors:

• Hazard: The threat level or magnitude of a potentially catastrophic event and its frequency.
• Exposure: The volume of population and property that may be affected.
• Vulnerability: The susceptibility of a community to be damaged.

(Danger does not equal risk). Risk = Hazard x Exposure x Vulnerability

Prediction and Prevention

• Prediction: Based on statistical data that indicates whether a particular phenomenon frequently occurs in a zone.
• Prevention: Proposes the adoption of necessary measures for an event to have minimal effects on the population or property.

Earthquake Basics

Terms related to earthquakes:

• Earthquake: Vibrations produced by the sudden release of energy accumulated in rocks subjected to stress.
• Focus or Hypocenter: The seismic place where the earthquake originates.
• Seismic Waves: Vibrations that originate from the seismic focus.
• Epicenter: The land surface point closest to the seismic source.

How an Earthquake Occurs

1. Rock is subjected to stress.
2. Tension builds, and the material deforms.
3. The material fractures, releasing energy.
4. The energy propagates as seismic waves.

Earthquake Distribution and Plate Tectonics

World Map Explanation:

• Limit of Plate
• Important Earthquakes
• © Major earthquakes of the century

The map shows that earthquakes are not randomly distributed. This concentration in certain locations is not coincidental but obeys a cause. Earthquakes occur when large masses of rock fracture along existing active faults. Therefore, places with high seismicity are those with the greatest fractures that coincide with the boundaries between lithospheric plates.

Lithosphere Creation and Destruction

Different types of plate boundaries are associated with seismic activity:

• Mid-Ocean Ridges: Where new terrestrial lithosphere originates. Plates diverge, and the gaps are filled by hot material from inside. Many earthquakes of moderate magnitude occur here.
• Subduction Zones: Places where lithosphere is destroyed. Plates converge, with one sliding beneath the other. These are areas of the highest seismicity, causing earthquakes of significant magnitude.
• Transform Faults: Places where lithosphere is neither created nor destroyed, but a lateral displacement of one plate over another occurs. These originate large earthquakes.

Can Earthquakes Be Predicted?

To create a seismic hazard map, several factors must be considered:

• Location or Area at the Plate Limit: The Iberian Peninsula is near a boundary between the Eurasian and African plates, which are converging at a speed of approximately 4mm/year.
• Local Geological Characteristics: Such as existing materials and especially the presence and length of faults. On the peninsula, there are no faults of great length, which means earthquakes of magnitude greater than 7 are unlikely.
• Seismic History of the Area: Knowing what happened in the past is essential for predicting future events.

Earthquake Prevention Measures

• Develop seismic hazard maps, allowing for the adjustment of preventive rules to specific circumstances. For example, setting restrictions for construction near active faults.
• Set standards for earthquake-resistant construction. For example, limiting building height, using proper construction techniques, utilizing steel structures, etc.