Exercises: Geological hazards

Distinguish between internal and external geologic hazards, and give two examples of each type.

Look at the diagram of an earthquake, which shows the hypocenter, epicenter, seismic waves and a seismograph recording. Using the diagram, explain the difference between the magnitude and intensity of an earthquake, and state which scale or instrument is used to measure each one.

What is a geological hazard map? Explain its purpose and give an example of how it can be used when planning the growth of a city.

Two earthquakes of the same magnitude hit two different regions: in one there is barely any damage, while in the other thousands of casualties are reported. Explain what factors, besides magnitude, determine the effects of an earthquake: hazard, vulnerability, and exposure.

Describe three seismic risk prevention measures that can be applied in building construction in high-risk areas.

During a volcanic eruption, lava flows, ash, gases and pyroclastic flows are emitted, and lahars can form. Choose three of these products and explain the type of damage each one can cause.

Compare the data from these two real seismic events:

• Earthquake A (Lorca, Spain, 2011): Magnitude $M_w = 5.1$; hypocenter depth = $1\ \text{km}$; epicentral distance to urban center = $2.5\ \text{km}$; maximum intensity = VII-VIII (EMS); 9 deaths and hundreds of damaged buildings.

• Earthquake B (Sea of Okhotsk, 2013): Magnitude $M_w = 8.3$; hypocenter depth = $609\ \text{km}$; distance to nearest inhabited area = $350\ \text{km}$; maximum surface intensity = V (MMI); 0 deaths and no property damage.

1. a) Based on the seismic risk equation ($\text{Risk} = \text{Hazard} \times \text{Exposure} \times \text{Vulnerability}$), analyze what specific factors caused the Lorca earthquake to be devastating despite its moderate magnitude.
2. b) Explain the conceptual difference between the "magnitude" and the "intensity" of an earthquake using data from both earthquakes to illustrate your answer.
3. c) Design two preventive measures (one structural and one related to land-use planning or education) to mitigate seismic risk in cities with characteristics similar to Lorca.

Unit challenge. Is your community prepared for the hazards of Earth's dynamics? Become a civil protection consultant and produce a technical seismic assessment report.

Follow these steps:

1. Data collection: Access the earthquake viewer of the Instituto Geográfico Nacional (IGN) and retrieve data for $5$ recent earthquakes occurring in the Iberian Peninsula with a magnitude $M \ge 2.0$. Record in a table: location, depth (in $\text{km}$), date, and magnitude (for example, $M = 3.4$).

2. Geodynamic analysis: Locate the epicenters relative to the boundary between the Eurasian and African plates. Justify in a paragraph how geosphere dynamics (mantle convection currents and lithospheric rigidity) generate the observed tectonic stresses.

3. Reasoned proposal: Based on the risk factors (hazard, exposure, and vulnerability), evaluate the seismic risk of one of the analyzed areas and develop a set of three viable preventive and self-protection measures to implement at home or at school.

Assessment criteria:

• Thoroughness in obtaining and tabulating real data from the IGN.

• Proper conceptual integration among recorded seismicity, plate tectonics, and Earth's internal dynamics.

• Suitability and realism of the proposed measures regarding the analyzed geological hazard.