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Seismicity

Seismicity

Haiti - earthquake

Haiti – earthquake

Specification

a-level-seismicity

aqa-plate-tectonics

The causes and main characteristics of earthquakes: focus and epicentre; seismic waves and earthquake measurement.
Tsunamis – characteristics and causes.
Two case studies of recent (ideally within the last 30 years) seismic events should be undertaken from contrasting areas of the world. In each case, the following should be examined:
• the nature of the seismic hazard;
• the impact of the event;
management of the hazard and responses to the event.

What you need to know:

Causes and characteristics of earthquakes

Earthquakes are caused in two ways:

• Volcanic activity:
– Either small earth tremors caused by rising magma under a volcano (these can be used to predict volcanic eruption) or
– The resultant energy release from an explosive volcanic eruption (e.g. There were 10,000+ tremors associated with the build up to the Mt St Helens eruption in 1980 followed by an earthquake of magnitude 5.1 just before the main blast).

• Tectonic activity:

Much of the crust is moving, albeit very slowly. Where rocks are moving in different directions, there are faults. The largest faults are those associated with plate boundaries (see earlier). The rock movement is hampered by friction and so stresses build up in the rocks. When this stored energy is released shockwaves radiate out from the source. These are earthquake (or seismic) waves.

Focus and Epicentre

• The focus is the point where the energy is released, deep in the earth’s crust. The most damaging earthquakes are shallow focus quakes (0 – 70km).

• The epicentre is the point on the earth’s surface immediately above the focus. This is the point at which there is most seismic energy.

Focus and epicentre

Focus and epicentre

 

Seismic Waves

image

There are several types of seismic waves, but not all of them cause earthquakes.

• Body waves travel inside the earth. They cause little damage but are very useful to geologists studying the internal structure of the earth.

• Surface waves radiate out from the epicentre. The most destructive, Rayleigh waves, roll along the ground like a waves crossing the surface of the sea. They move the ground up and down and from side to side.

image

 

Earthquake measurement

There is confusion over this, mainly caused by the media. The Richter scale is often quoted, but rarely actually used. The world standard is the moment magnitude scale, MMS and is a measurement of an earthquake in terms of energy released. It is a logarithmic scale and so an increase in magnitude of 1 unit, means that the amount of energy has released has increased by 30.

MMS

MMS

 

Tsunamis

Tsunami

Tsunami

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, usually an ocean. They occur frequently in Japan; approximately 195 events have been recorded. Owing to the immense volumes of water and the high energy involved, tsunamis can devastate coastal regions.

Large tsunamis are generated by crustal movements deep in the rocks under the oceans. The two most recent major tsunamis (Indian Ocean 2004 and Japan 2011) have been formed at destructive plate boundaries. Here, one tectonic plate is subducted below the other. The plates often get stuck and stresses build up until there is a sudden release of energy. (See http://www.angelapplications.co.uk/teachersfirst/webplate3.png )

Japan

Japan

The upward waves radiate out from the epicentre. They are of relatively low amplitude, long wavelength and great speed. Out in the ocean they are relatively harmless, but as they approach shallow coastal waters the velocity is reduced, wavelength decreases and the waves get much higher and steeper. These high steep waves flood over low lying coastal areas causing immense damage.

Case Studies

The specification demands 2 case studies. For each one:

• Nature of the hazard
This should include a clear location with description of the earthquake itself and its cause. It should also include the magnitude of the earthquake, the area affected and any side effects (e.g. liquefaction).

• The impact of the hazard
This can be divided into:
– Environmental impacts
– Social impacts (deaths, property destroyed etc)
– Economic impacts (costs, loss of earnings etc)

• The management of the hazard

What did the authorities do to mitigate the effect of the hazard (e.g. ‘Earthquake-proof’ buildings in Tokyo, erection tsunami flood walls, warning systems etc)

• The responses to the hazard

What did the authorities and individuals do following the initial management phase? (E.g evacuation of people from around the Fukoshima nuclear plant in japan in 2011).
MEDC Earthquake Case Study – Japanese Earthquake of March 11th 2011

Japan 2011

Japan 2011

 

Plate boundaries

Plate boundaries

Japan is located at the meeting point of 3 tectonic plates, The Eurasian, Pacific and Philippines. The boundary is to the East of the 4 main Japanese islands, Hokkaido, Honshu, Shikoku and Kyushu. It is a convergent DESTRUCTIVE boundary, with faults running off the boundary. In effect, Japan owes its existence to this boundary and the Islands are volcanic in origin. Japan gets 30% of the world’s earthquakes every year, and there is 90mm of movement of the Pacific Plate under the Eurasian.

There was a magnitude 7.2 earthquake on the 9th of March, 2 days before the 8.9-9.0 magnitude earthquake of the 11th.

There were also huge numbers of large sized aftershocks, as big as magnitude 6.

The reason why the Tōhoku Earthquake happened was due to the build up in strain energy as the Pacific plate subducted under the Eurasian plate. This strain energy eventually overcame the frictional force holding the plates in place, and was released as earthquake waves.

The tsunami is a secondary consequence of this initial movement. The Eurasian plate was down warped (dragged down) as the Pacific plate descended. When the strain energy was released this section of the Eurasian plate “popped” or bounced back upwards. This displaced the water above in the Pacific Ocean causing a Tsunami wave to ripple radially outwards. This was known as a megathrust earthquake.

The aftershocks occurred as the strain energy was passed along the fault, causing further quakes.

Plate boundaries

Plate boundaries

Magnitude

Magnitude 2011

Magnitude 2011

The earthquake was the biggest ever recorded to have stuck Japan, at approximately 9.0. The epicentre approximately 70 kilometres east of the Oshika Peninsula of Tōhoku and the hypocentre or FOCUS at an underwater depth of approximately 32 km (20 miles).

 

Frequency   

There were 7 foreshocks, including a magnitude 7.2 earthquake on the 9th of March, 2 days before the 8.9-9.0 magnitude earthquake of the 11th. There were also 1235 aftershocks, many at 7 of above and over eight hundred aftershocks of magnitude 4.5  MW or greater . The earthquake also followed Omori’s law, where the number & size of earthquake aftershocks declines with time from the largest event. In addition, 30% of the world’s earthquakes occur close to Japan, so Earthquakes are common, but earthquakes of this size are rare.

http://http://www.japantimes.co.jp/news/2013/06/04/national/quake-frequency-remains-high-in-tokyo-area-following-2011-megaquake/#.VBbFrIdwaAg

Vulnerability

Vulnerability due to proximity to the coast.

Vulnerability due to proximity to the coast.

Japan is highly vulnerable to Earthquakes, they occur here naturally and in high numbers. The coastline is also vulnerable, as the vast majority of people live on the coast of Japan. This is due to Japan’s physical geography, having a very mountainous spine to the country and only a narrow coastal strip. This exposes high numbers of people to the hazards of tsunami.

The upper 10m of the soil in this zone was also very vulnerable, as the waves amplified in this soil and caused liquefaction.

In this instance it was the Eastern seaboard of Japan and the Island of Honshu that were vulnerable. The Fukushima nuclear power plant also faced directly the epicentre of the Earthquake.

 

Nuclear power plant

Nuclear power plant

Capacity to cope (prediction, preparation, prevention)

earthquake japan 153973-004-E5881ECA

As a result of the high frequency of Earthquakes in this area Japan has developed a high capacity to cope with both Earthquakes and tsunami.

40% of Japan’s coastline has sea walls of up to 10m high to withstand incoming tsunami waves for example.

Japan has a hazards agency, the Japanese Meteorological Agency, which is set up for the prediction of earthquakes and tsunami. It detected the Earthquake and issued televised warnings just after the very rapid P-waves that arrived but before the more damaging S waves. This gave people a chance to get outside of buildings to safety. It also predicted the tsunami from this event just 3 minutes after the major earthquake, giving people 20 minutes to get to safety. The JMA broke this news on live television, and messages went out on Japan’s mobile network.

Buildings in Japan are also designed to cope with Earthquakes, and Japan’s high level of development means that buildings are made to be life safe and can actually move with earthquake waves and reduce damage.

earthquake japan 148663-004-5F78AB88Institutional capacity    

Japan had its emergency crews and the army on site very quickly after the event. They have readily trained teams of people to go in and assist with events like this

Buildings are earthquake proof and people in Japan are trained YEARLY on the 1st of September in how to survive earthquakes, this is a result of the Tokyo (great Kanto) Earthquake of 1923.

Japan has a huge GDP; it was $34,000 in 2011, which allows it huge leeway ion terms of planning for Earthquakes and tsunami. 40% of Japan’s coastline has sea walls of up to 10m high to withstand incoming tsunami waves for example.

To monitor earthquakes, the Japanese Meteorological Agency operates network of about 200 seismographs and 600 seismic intensity meters. It also collects data from over 3,600 seismic intensity meters managed by local governments and the National Research Institute for Earth Science and Disaster Prevention (NIED). This information is put into the Earthquake Phenomena Observation System (EPOS) at the headquarters in Tokyo When an earthquake occurs JMA immediately issues to the public, information on its hypocenter, magnitude and observed seismic intensity. This information also plays a vital role as a trigger for the initiation of rescue and relief operations related to earthquake disasters.

Impact 

The Tsunami and Earthquake both had devastating impacts, but the tsunami caused the most damage.

Tsunami impact

Tsunami impact

The tsunami waves that reached heights of up to 40 metres in Miyako and which, in the Sendai area of Honshu, travelled up to 10 km (6 mi) inland.

The island of Honshu was moved 2.4 m east and shifted the Earth on its axis by estimates of between 10 cm and 25 cm.

The most worrying impact was on Japan’s famed nuclear power industry. There were several nuclear incidents but the most notable was 3 nuclear meltdowns at the Fukushima power plant. This cause contamination of the sea and land, and force the evacuation of local residents. A brave team of nuclear power plant workers battled bravely to prevent the nuclear reactors overheating completely and exploding.

This resulted in a social impact; residents within a 20 km radius of the Plant were evacuated.

Evacuation

Evacuation

The official death toll report confirmed 15,854 deaths, 26,992 injured and 3,155 people missing across twenty prefectures.

In addition 130,000 buildings totally collapsed and another near 700,000 buildings partially damaged.

The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse.

Around 4.4 million households in north eastern Japan were left without electricity and 1.5 million without water.

The economic losses are thought to be huge, given Japan’s highly developed infrastructure and level of development there was a lot to be damaged. The World Bank estimated cost was US$235 billion, making it the most expensive natural disaster in world history.

Estimates of insured losses from the earthquake alone ranged from US$14.5 to $34.6 billion. The Bank of Japan offered 15 trillion Yen (US$183 billion) to the banking system to normalize market conditions.

All of Japan’s ports had to close at least temporarily during the disaster, and 10% of the fishing ports were damaged.

 

LEDC Earthquake Case StudyHaïti earthquake, January 12th at 4:53pm, 2010

Haiti 2010

Haiti 2010

Tectonic setting

Haïti sits between the Caribbean and North American plates, and is in a very tectonically active zone of our planet. The Windward Islands of the Caribbean are volcanic in origin and many active volcanoes still exist there. The inner islands, Haïti included, are known as the Leeward Islands and are less volcanically active but do suffer from Earthquakes. Haïti itself is on a strike slip fault that runs off a destructive plate margin to the north of the Island of Hispaniola, which Haïti shares with the Dominican Republic.

Haiti - plate boundaries

Haiti – plate boundaries

 

Haiti - plate boundaries

Haiti – plate boundaries

Magnitude

Magnitude and death

Magnitude and death

The magnitude of the earthquake was actually quite small, at only 7.0 on the Richter scale. In comparison, The Japanese tsunami of 2011 had bigger fore and aftershocks! This earthquake lasted 1 minute but because of Haïti’s circumstances caused incredible damage. The epicentre was 15 miles or 20km from the nation’s capital, port au Prince, and the hypocentre or focus was very shallow at only 13km deep. Seismic waves started at a fault line that was 10km in length.

Haiti - magnitude

Haiti – magnitude

Frequency

It is 200 years since the last major earthquake, so big earthquakes are actually reasonably rare. However, following the 1755 earthquake there was an even bigger event in 1770. This activity moved west in the 18th century, with Jamaica suffering at this time too, geologists are worried that this could be a new phase in seismic activity in this area with strain energy moving along the fault line.

Vulnerability

The vulnerable

The vulnerable

Haïti was incredibly vulnerable to this earthquake. The earthquake struck close to the nation’s capital of 2 million people and the geology of the area did not help. The capital has many areas built upon unstable soils and seismic waves amplified within the soil. This caused intense shaking and liquefaction, particularly in the Port area which suffered from lateral spreading and land falling into the sea.

In addition and underling all of this is the fact that Haïti is the poorest country in the western hemisphere with a highly vulnerable population:

  • 38% of the population are under 14
  • Infant Mortality is 60/1000
  • Life expectancy was just 60
  • GDP was only $1,300
  • 80% of the population lived below the poverty line and
  • 53% were literate

(All statistics for 2009)

Capacity to cope (prediction, preparation, prevention)

Famous Geologist Paul Mann wrote a report in 2008 that a major earthquake could happen here, and that the damage could be catastrophic. Unfortunately, Haïti does not have the resources to heed such warnings. The building quality was also proved to be very poor, and most loss of life was due to building collapse.

Also, because people were so poor they had few ‘reserves’ (money, food) to draw on and there is a very limited social safety net.

At least 500,000 people in the slum of Cité de Soleil in Port-au-Prince live in abject poverty, these people were the worst affected

Haïti was already reliant on international aid for over 30% of national GDP even before the earthquake.

Preparation

Preparation

Institutional capacity

Haïti had a very poor institutional capacity to withstand this earthquake. First, major transport links were completely knocked out by the earthquake. The port was damaged by liquefaction and lateral spreading, and cranes and debris fell into the sea. The airport control tower and runway were damaged too, to compound matters.

A “pancaked” building

Pancaked building Haiti

Pancaked building Haiti

Politically, Haïti was in bad shape too. From 1957–86 people lived under the brutal dictatorship of Papa Doc and Baby Doc Duvalier. In 1987 Elections abandoned due to violence. By 1990 President Aristide was elected, but political chaos is the order of the day. By 2004 Military coup removes Aristide. United Nations Stabilisation Mission enters Haïti. Since 2004 the UN has attempted to help stabilise the country, sometimes described as a ‘failed state’.

Earthquakes Haiti%20pancaked%20building

Many institutions were destroyed, including; Three Médecins Sans Frontières hospitals, the landline telephone system, the Palace of the president, the Finance Ministry, the HQ of the UN Mission, the World Bank office in Haïti and the Main prison in Port-au-Prince. All of these undermined recovery efforts.

Immediate response

Individuals tried to recover their belongings, and scientists flocked to the area to gather vital research data. The actual aid effort was almost non-existent from within Haïti as its institutions had been destroyed or did not have the resources to cope. The foreign aid effort was slowed down by the lack of transport infrastructure and a lack of coordination.

Satellite Imagery was used in London to guide relief efforts on the ground in Haïti.

Many countries responded to appeals for aid, pledging funds and dispatching rescue and medical teams, engineers and support personnel.

There was much confusion over who was in charge, air traffic congestion, and problems with prioritisation of flights further complicated early relief work.

Port-au-Prince’s morgues were quickly overwhelmed with many tens of thousands of bodies having to be buried in mass graves.

As rescues tailed off, supplies, medical care and sanitation became priorities.

Delays in aid distribution led to angry appeals from aid workers and survivors, and looting and sporadic violence were observed.

Social, Economic & Environmental impact (include primary and secondary Hazards)

316,000 people died and more than a million people were made homeless, even in 2011 people remained in make shift temporary homes. Large parts of this impoverished nation where damage, most importantly the capital Port Au Prince, where shanty towns and even the presidential palace crumbled to dust. 3 million people in total were affected. Few of the Buildings in Haïti were built with earthquakes in mind, contributing to their collapse.

Social unrest and looting after the earthquake.

Social unrest and looting after the earthquake.

The government of Haïti also estimated that 250,000 residences and 30,000 commercial buildings had collapsed or were severely damaged. The port, other major roads and communications link were damaged beyond repair and needed replacing. The clothing industry, which accounts for two-thirds of Haïti’s exports, reported structural damage at manufacturing facilities. It is estimated that 1 in 5 jobs were lost as a result of the quake

Rubble from collapsed buildings blocked roads and rail links.

The port was destroyed

Sea levels in local areas changed, with some parts of the land sinking below the sea

The roads were littered with cracks and fault lines.

Long term responses (domestic, international, NGOs)

The EU gave $330 million and the World Bank waived the countries debt repayments for 5 years.

The Senegalese offered land in Senegal to any Haïtians who wanted it!

6 months after the quake, 98% of the rubble remained uncleared; some still blocking vital access roads.

The number of people in relief camps of tents and tarps since the quake was 1.6 million, and almost no transitional housing had been built. Most of the camps had no electricity, running water, or sewage disposal, and the tents were beginning to fall apart.

Between 23 major charities, $1.1 billion had been collected for Haïti for relief efforts, but only two percent of the money had been released

One year after the earthquake 1 million people remained displaced

The Dominican Republic which neighbours Haïti offered support and accepted some refugees.

Medicines San frontiers, a charity, tried to help casualties whilst the USA took charge of trying to coordinate Aid distribution.

 

Questions:

7. Describe the distribution of earthquakes and explain the pattern shown on the map. [7 marks]

earthquake photo
8. Describe the effects that a major earthquake can have on the population of an area.[8 marks]

9. A tsunami can result from tectonic activity. Explain how tsunamis are formed and how they can be so destructive. [8 marks]

10. Discuss the ways in which people and organisations respond to earthquakes and their effects. [10 marks]

11. With reference to two earthquakes you have studied from contrasting areas of the world, discuss the effectiveness of the methods used to lessen the impact of earthquakes on the Population. [10 marks]

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