11. Factors affecting extent of damage
Look at the map below which shows the intensity of the magnitude 6.9 earthquake which struck Lombok, Indonesia on 5 Aug 2018.
Can you see how intensity of earthquake decreases away from the epicentre?
How would the distance from the epicentre affects the extent of damage from earthquake?
Watch the video below and reflect on the following:
When did the earthquake occur?
Where are the areas affected?
What was the magnitude of the earthquake and how does this affect the extent of damage in Mexico?
How does the geology of Mexico city affect the extent of damage?
Why did the people have evacuation drills before the earthquake? *1985 earthquake
What are the responses immediately after the earthquake? (short-term responses)
Aftershocks are expected - will there be greater destruction?
Do take note of the following when you evaluate the factors which affect the extent of damage as shown by the map above.
1. Magnitude of the earthquake - What is the magnitude of the earthquake? Why does earthquake of higher magnitude results in greater damage and deaths?
Magnitude of an earthquake
The amount of energy released is described as the magnitude of an earthquake
The Richter Scale is used to measure the magnitude of an earthquake. For each increasing magnitude on the Richter scale, the impact of the earthquake becomes 10 times greater in magnitude than the previous one.
The strongest earthquake ever recorded is the earthquake in Valdivia, Chile in 1960, which measured 9.5 on the Richter Scale
The higher the magnitude, the greater the damage as it will lead to collapse of buildings and structures which will cause more people to be trapped, suffering from injuries or even loss of lives. An earthquake of magnitude 3 to 4 will cause hanging objects to swing and will cause minor damages such as cracks on the wall. An earthquake of magnitude 5 to 6 can be damaging to poorly constructed buildings. Earthquakes of magnitude 6 to 7 will cause many structures to collapse and cracks to appear on the ground. Earthquakes of magnitude 7 to 8 will cause many buildings to collapse and severe damages. Earthquakes of magnitude 8 to 9 will cause widespread destruction and trigger landslides.
However, earthquakes with greater magnitudes may not always cause more extensive damage and destruction. For example, the 9.0 magnitude earthquake in Tohoku, Japan in 2011 has a death toll of 28 000 people while the magnitude 7.0 earthquake in Haiti in 2010 had a death toll of more than 300 000 people
Apart from its magnitude, the extent of damage caused by an earthquake may vary based on other factors such as population density, geology, time of occurrence, level of preparedness etc.
2. Proximity to epicentre - Which city is nearest to the epicentre? Why do areas closer to the epicentre experience greater damage and deaths?
The epicenter is on the earth’s surface directly above the focus where seismic waves originate.
The damage caused by an earthquake is more severe when an area is closer to the epicenter of the earthquake as the intensity will be greatest/vibration strongest. More buildings and structures will collapse causing more damage and also more casualties as more people will be trapped or killed.
During the earthquake in Christchurch, New Zealand in 2011, the epicenter was in town a few kilometres away from the city centre. The city suffered more damage than areas further away from the city
3. Depth of focus - What is the depth of the focus? Is it shallow or deep? Why does a shallow-focus earthquake results in greater damage and deaths?
The focus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement.When the focus of the earthquake is shallower, which is nearer to the earth surface, the seismic waves reach the earth surface faster and with greater energy. More buildings and structures will collapse causing more damage and also more casualties as more people will be trapped or killed.
4. Population Density - Which city has a higher population density (no. of people living on a unit area)? Why do cities with high population density experience greater damage and deaths?
· Earthquakes in sparsely populated areas are likely to affect fewer people than in densely populated areas as there will be more high-rise buildings and structures in a densely populated area.
For example, an earthquake in a city can cause more casualties and damage than an earthquake in the countryside. Solomon Islands experience frequent earthquakes of magnitude 5 but there are lesser damage as population density is lower.
From the earlier videos:
5. Geology - Mexico city is built on soft volcanic soil and clay. Why would the geology of the area affects the extent of damage and deaths? What is liquefaction?
· In places where the sediments are loose and unconsolidated, the seismic waves are amplified and this results in greater damage when earthquakes occur
· Structures built on saturated and unconsolidated sediments can be affected by liquefaction (when the ground becomes unstable and saturated soil flow like a liquid
· In Christchurch, many houses and buildings has to be abandoned because of liquefaction after the earthquake in 2011
6. Time of occurence - The earthquake occured at 1.15pm (local time). How would this affect the extent of damage and deaths?
· The time of day during which an earthquake occurs will affect people’s chances of survival in an earthquake
· If the earthquake occurs when most people are sleeping, there is a higher chance that these people are trapped in their houses and more deaths may occur
· For example, more than 2400 people died when an earthquake occurred a couple of hours after midnight in the Sun Moon Lake Region in Taiwan in 1999
7. Level of preparedness - Just hours before the earthquake, many people went through an evacuation drill as it is the anniversary of a major earthquake which struck Mexico on 19 Sept 1985. How does higher level of preparedness reduce the extent of damage and deaths?
· The amount of preparation taken by the authorities and citizens makes a significant difference to the impact of an earthquake
· These preparations include having evacuation plans, trained rescue workers and a range of action plans
· The damage caused by an earthquake is more manageable when people are better prepared for it
· Japan holds nationwide drill on 1st September, as part of Disaster Prevention Day. The exercise is carried out annually on the anniversary of the 1923 Great Kanto Earthquake, in which more than 100,000 people were killed.
http://www.bbc.com/news/world-latin-america-41327593
http://www.bbc.co.uk/news/world-latin-america-41337467
Find out more about the earthquake:
http://www.straitstimes.com/world/americas/mexico-city-shaken-by-strong-quake
http://www.channelnewsasia.com/news/world/at-least-100-killed-as-powerful-quake-rocks-mexico-9232234
Read the following article on why Mexico is prone to earthquake
http://edition.cnn.com/2017/09/20/opinions/what-made-mexico-shake-vidale/index.html
You can read more about the 19 Sept 1985 Earthquake here:
https://en.wikipedia.org/wiki/1985_Mexico_City_earthquake
Investigate the factors influencing the impact of an earthquake by doing a data interpretation activity through the interactive map of the 2011 Japanese earthquake on the website:
http://www.nytimes.com/packages/flash/newsgraphics/2011/0311-japan-earthquake-map/index.html
By clicking on each icon, interpret from the proportional circles and construct explanations on how magnitude and distance from epicenter has an impact on the extent of damage in an area affected by an earthquake.
Factors affecting the extent of damage from an earthquake
Magnitude of Earthquake
The higher the magnitude of the earthquake on the Richter scale the greater the intensity of the earthquake and thus the greater the damage. Earthquakes of higher magnitude will results in stronger vibration which can lead to the collapse of building and structures, causing more damage to properties and more casualties. e.g. earthquake of magnitude 8 struck Shensi, China on Jan. 23, 1556 leading to about 830,000 deaths. Earthquake of magnitude 7.5 which struck Tangshan, China on July 27, 1976 has an official casualty figure of 255,000 deaths but estimated death toll was as high as 655,000.
Download the app and see the different magnitudes of earthquake on buildings.
Android -click here to download simearthquake
iphone -https://itunes.apple.com/us/app/sim-earthquake/id725274179?mt=8
Video @https://youtu.be/i_bQ2TKwBRM
Simulate an earthquake - look at how the geology, prevention measures and magnitude can affect the extent of damage:
https://www.cosmeo.com/braingames/makeaquake/?title=Make%20a%20Quak
Type of soil
Recall your experience at the Science Centre. What type of soil leads to greater intensity of earthquake?
Watch this video on liquefaction - the influence of soil type when earthquake struck Christchurch, New Zealand in 2011: http://www.youtube.com/watch?v=j-hyOwsl_NY
Kobe earthquake
http://www.coolgeography.co.uk/GCSE/AQA/Restless%20Earth/Earthquakes/Kobe.htm
Haiti earthquake
http://www.coolgeography.co.uk/GCSE/AQA/Restless%20Earth/Earthquakes/Haiti.htm
You can click on the kml file below to see the major earthquakes of the world on google earth http://escweb.wr.usgs.gov/earthquakes/kml/feeds/WWeqANSS.kml
Observe the number of earthquakes that had taken place in the last 24 hours: http://earthquake.usgs.gov/earthquakes/map/
Read the updates on Earthquakes from my blog -http://olevelgeog.blogspot.sg/search/label/Earthquake
Other than magnitude and geology of a place, level of preparedness, time of occurrence and population density also affect the extent of damage. Do you know why?
Other than the above factors, is economic development of a place another factor? Is extent of damage lower in DCs than LDCs?
More economically developed countries (DC's) tend to survive earthquakes better than less developed countries (LDC's).
There are three main reasons for this.
1. DC's are likely to have buildings designed to withstand earthquakes. They have the money and systems to make sure that buildings are carefully designed to withstand shaking, and can afford to add safety features to older buildings that may be at risk. They may have huge rubber pads built into the foundations (seismic isolators) or very deep foundations to hold them firmly in place. In 1995 the Kobe earthquake hit in Japan. Measuring 7.2 on the Richter scale it had the potential to cause massive damage to vulnerable buildings, but because many buildings were designed to withstand earthquakes, only 5000 people were killed. LDC's often can't afford to build new structures to the same standards as DC's, they have a greater chance of poor quality construction, and they lack the money to upgrade older buildings. In contrast to the Kobe earthquake that killed 5000, an earthquake of a slightly smaller intensity hit Turkey in 1999. It killed 17,000 people.
2. DC's have disaster plans, government departments responsible for managing and coordinating emergency responses, and for educating the public about natural hazards. In Japan, all school children practice earthquake drill in the same way that we practice fire drill. Emergency services actually practice through simulations, so they know exactly what they should do if disaster strikes. Most LDC's don't have enough money to develop emergency plans, buy the response equipment and training needed, and conduct very expensive training exercises involving thousands of people.
3. DC's are self reliant. They can afford to allocate funds to 'just in case' measures. They keep emergency stocks of medicines, tents, blankets, food, water, and communications equipment. It's kept ready for use and constantly updated. Many LDC's struggle to provide these facilities for normal use let alone keep a spare set of everything in case of disasters. The speed with which these resources reach an area is critical to reducing deaths. DC's have the resources close at hand and can be sending them out within hours. By contrast, LDC's often have to ask for help, and mobilising international aid can take days. A homeless person in San Francisco who gets shelter, food and medical aid within 12 hours has a much better chance of survival than a Turkish farmer who will be waiting for days or even weeks before aid reaches him.
http://www.geography-site.co.uk/pages/physical/earth/earthquake_impact.html