Seismic Activity and Volcanic Eruption Mechanisms
Earthquake Mechanics and Measurement
Earthquakes: Ground vibrations are caused by the sudden release of energy accumulated in rocks that are undergoing stress. The place where they originate is called the seismic focus; from this focus, the vibrations are transmitted in all directions.
Measurement: Earthquakes are measured using seismographs. The magnitude of an earthquake is the amount of energy released, measured by the Richter scale, in which each degree equals approximately 31 times the energy released.
Seismic Risk and Perception
The ability to perceive or predict an earthquake depends on the seismic risk of each zone, as there is currently no reliable system to know the occurrence in advance. Risk factors include:
- a) The location or area within a plate boundary.
- b) Local geological characteristics, such as materials and the presence of active faults and their length.
- c) The seismic history of the area.
Prevention Strategies
- a) Seismic risk mapping, allowing for the adjustment of preventive rules to each set of circumstances.
- b) Establishing standards for earthquake-resistant construction.
Tsunami Formation and Impact
A tsunami designates a set of huge waves caused by the sudden rise in volume of a large body of water at the bottom of the sea.
How a Tsunami Originates
- The oceanic lithosphere is introduced into the ground; one end of the upper plate is locked and dragged down.
- The sudden release of this tension generates an earthquake; the seabed rises suddenly, and as a result, an enormous volume of water is displaced.
- The waves generated by the displacement of water spread in all directions.
- Friction with the bottom slows the wave, and a crowding effect occurs.
- The tsunami wave can penetrate several kilometers inland.
Volcanic Eruptions and Monitoring
Factors of Volcanic Danger
An eruption becomes dangerous due to various types of activity:
- a) Effusive activity: Low viscosity lava leaves the crater and flows out smoothly.
- b) Explosive activity: Lava is very viscous and obstructs ducts, causing pressure to accumulate and result in large explosions.
- c) The emission of noxious fumes.
- d) The formation of clouds and hot pyroclastic flows.
- e) Explosions.
- f) Lahars or mudflows.
- g) Lava flows.
Watching a Volcano
Signs that herald an eruption include:
- a) Small local earthquakes.
- b) Changes in the inclination of the terrain.
- c) Temperature rise of water in wells.
- d) Increasing emission of gases.
Human Influence on Flooding
Floods are often exacerbated by human activity, including:
- a) Occupation of flood plains.
- b) Deforestation.
- c) Ground cover with impermeable materials.
- d) Infrastructure works that interfere with the natural channel.