HKDSE Geography/M1/Factors Affecting the Power of Tectonic Hazards

Numerous factors affect the power of tectonic hazards.

Nature of Hazards

Earthquakes

• The depth of the focus is the distance from the focus to the earth's surface. Earthquakes can be shallow (0-70 km), intermediate (70-300 km) or deep (>300 km). The shallower the earthquake,

the more serious it is.

• The distance from the epicentre is also important. Areas closer to the centre receive more damage from earthquakes.
• Magnitude measures the amount of energy released by an earthquake. Each earthquake is assigned a number on the Richter Scale, usually ranging from 1 to 9.
• Intensity measures the damage done by an earthquake. Each earthquake is assigned a grade on the Modified Mercalli Scale, from I to XII.

Volcanic Eruptions

• The power of a volcano can be classified as 'explosive' or 'gentle'. Explosive eruptions cause much more damage than gentle ones.
• Acidity of magma: Non-viscous lava can spread further away from viscous lava and cause greater destruction.

Tsunamis

• A tsunami's power depends on the strength of its source. The stronger the submarine eruption/landslide/earthquake, the more serious the tsunami.
• Tsunami intensity is measured by run-up height, or the maximum wave height. The greater the run-up height, the longer the waves will last when they rush inland, and the larger the area affected.
• It also depends on the distance of an area from the source of a tsunami. (NOT the proximity from the sea! See CE09Q13.)

The longer the time it takes to travel from the source of the tsunami to an area, the less an area is hit. Interpreting tsunami time travel maps occasionally pops up in the examination.

Note, in the above map, that it does not take only 11 hours for the tsunami to travel to the eastern coast of South Africa, but slightly more than 11 hours. (A similar case is CE09Q15 - don't be tricked.)

Common Attributes

• Frequency: The more frequently an hazard occurs, the more damage it does. A dormant volcano does less damage than an active one. An area near a conservative or destructive plate boundary has more earthquakes than an intraplate area.
• Duration: The longer the duration of a hazard, the more damage it brings. The Indian Ocean Tsunami was triggered by a huge earthquake in Sumatra, lasting ten minutes.
• Areal extent: The larger the size of the area impacted, the more damage it brings. A submarine earthquake has large areal extent as it affects lots of countries that surround the ocean.
• Speed of onset: If a hazard appears faster, people will have less time to prepare and evacuate, increasing damage.

Other Natural Factors

• Relief: Low-lying areas, coastal plains and narrow water inlets are more vulnerable to tsunamis. Steep slopes create faster lava flow and mudflow after volcanic eruptions and landslides after earthquakes.
• Weather: Extreme weather conditions like cold spells and heat waves can raise the death toll, since shelter and shade are insufficient.
• Geology/Lithology: the type of rock or ground near the earthquake has an effect on it's impact. For example coastal or wetland areas with saturated sand or earth will lead to the seismic waves being slowed down thus making them far more destructive. On the other hand a granite-based area will not have this effect and will see less destruction

Human Factors

• Population density: Areas of higher population density have greater casualties and economic loss.
• Building strength: Brick or wooden buildings cannot withstand heavy shaking or fires.
• Preparedness: Citizens who are poorly informed and prepared about hazards will panic if a hazard occurs. Strong traditional values and low education level also lower the level of preparedness.
• Monitoring and warning systems in place:
• Government efficiency: A government hindered by corruption and excess bureaucracy cannot rescue effectively.
• Technology: Countries with higher technology can better rescue humans after earthquakes.
• Land use planning: Good land use planning can avoid creating more damage. For example, protecting hospitals will allow more victims to be treated. Moving nuclear power plants away from destructive plate boundaries will prevent them from failing.