Japan Earthquake 2011 Essay
An earthquake is a shaking or tremor of the ground, as well as an occurrence of seismic waves that result from an abrupt discharge of energy from the Earth's crust known as the hypocenter (Haggett 3068). The earthquakes differ in frequency, type, and size. At the Earth's surface, earthquakes are experienced through shaking and occasionally through displacement of the ground. Similarly, when the epicentre of a large quake is positioned offshore, the seabed may be displaced either vertically or horizontally, thus causing a tsunami. Earthquakes can also lead to landslides and sometimes volcanic activity. Earthquakes may be either natural or caused by humans’ activities that yield seismic waves (Haggett 3068). Quakes are instigated by ruptures of geological faults, as well as other events, such as volcanic activity, mine blasts, landslides, and tests-related to nuclear power. An earthquake's point of original rupture is referred to as a focus or hypocenter, while the direct point at the ground level just above the hypocenter is known as an epicentre.
Earthquakes are normally measured using seismometers on a moment magnitude scale. Earthquakes that record larger than magnitude 5 on the scale are usually reported in the entire globe. The most common earthquakes, which are usually smaller than magnitude 5 as reported by national seismological observatories around the world, are mostly measured on the local magnitude scale known as the Richter scale (Lee et al. 29). These two scales are numerically similar in their range of validity. The tremors with magnitude 3 or lower are weak and almost unnoticeable, while earthquakes with magnitude 7 and above potentially result in devastating damages over larger geographical areas, depending on their depth. The biggest earthquakes in momentous times have been of magnitude marginally over 9. The largest earthquake experienced above magnitude 9.0 was in Japan in 2011. It is considered the most destructive and horrible earthquake in the history of Japane. The intensity of a quake is measured on the improved Mercalli scale, and the shallower an earthquake is the more devastation and damage to structures it causes (Simpson & Rechards 268).
Causes of Earthquakes
The earth's external layer is normally fragmented into pieces known as tectonic plates whose thickness is approximately 100 km. These plates are ever in a constant move towards, past or away from each other. For example, the tectonic plate holding Australia and India moves northwards at the rate of 7cm a year, triggering an intra-continental collision with the Eurasian tectonic plate in the Himalayas (Karan 9). This is what makes the Himalayas Mountains so high. Since continents are part of these tectonic plates, they likewise move. In this case, earthquakes occur when the earth’s surface and rocks crack and move, due to pressures that arise from the plate movements (Karan 9).
Most quakes take place on the frontiers between plates, when one plate is forced under another plate. The following happens in off-island chains, such as Japan, the Solomon Islands and Indonesia, or when the plates are forced past one another as it happens in California and New Zealand. Some regions usually experience more earthquakes than others. It is worth noting that about 80% of all recorded quakes do occur at the margin of the Pacific Plate and involve Papua New Guinea, New Zealand, the Solomon Islands, Japan, Vanuatu, Canada, South America, and the USA.
Shallow-focus and Deep-focus Earthquakes
Usually, earthquakes can take place to the depths of 700k m in the regions where plates collide, while quakes are shallower in areas where the tectonic plates slide past each other as experienced in California or New Zealand. Equally, shallow earthquakes take place in the areas where plates pull away from each other along or under sea ridges, making the oceans grow bigger, such as the plate margin between the Antarctica and Australia (Boer & Sanders, 2005).
It is should be stressed that the majority of tectonic quakes develop next to the ring of fire at a depth not more than 10 kilometres. Earthquakes that take place at a depth not exceeding 70 km are categorized as 'shallow-focus' quakes, whereas those whose focal point is in the depth between 70 and 300 km are referred to as' intermediate-depth' or 'mid-focus' earthquakes. Deep-focus earthquakes are those that occur at depth between 300 and 700 kilometres or more. They are less destructive as compared to the shallow focus earthquakes (Karan 10).
The tectonic earthquakes can occur anywhere in the earth as long as there is an adequate deposit of elastic strain energy to facilitate fracture propagation along a fault plane. The edges of the faults slide past each other seismically and smoothly only if there are no asperities along the surface of the fault that may increase the frictional resistance (Boer & Sanders 15). Normally, most fault surfaces have asperities that consequently lead to stick-slip behaviour. Once the fault locks, a persistent motion between the plates results in increased stress, and consequently, the large volumes of stored strain energy around the fault surface are released. The following process continues until the stress reaches a level sufficient to break through the asperity, hence discharging the build-up energy. This energy is discharged in a form of seismic waves, radiated elastic strain, heating of the fault line as a result of friction, and breaking of rocks, leading to an earthquake.
Earthquake Fault Types
There are three major types of faults that may cause earthquake: (1) strike-slip, (2) reverse (thrust), and (3) normal. Normal and reverse faults entail a dip-slip, in which the displacement along the fault line is in the dip or vertical direction (Haggett3069) Normal faults normally occur when there are divergent borders in regions where the crust is being extended. Reverse faults take place in the spheres where the crust is being shortened, like in a convergent boundary Haggett 3069). On the other hand, strike-slip faults are steep displacements when the two margins of a fault slide horizontally past each other as experienced in the transform boundaries. Most earthquakes are caused by a combination movement on faults dip-slip and strike-slip directions (Haggett 3069)
These are earthquakes that do not take place on the plate margins. For example, all the earthquakes taking place at the mainland of Australia and Tasmania are intra-plate earthquakes. The studies by seismologists on the intra-plate earthquakes in different continents reveal that most of them are as a result of thrust faulting generated when rocks are squeezed or compressed. It appears that a constant movement of the tectonic plates forces the rocks to move away from their margins leading to compression (Boer & Sanders 17). Notably, the intra-plate tremors are not common if to compare with those that occur on plate margins. However, the major earthquakes with magnitudes of 7.0 and above happen occasionally.
These earthquakes that are away from plate boundaries occur within the continental lithosphere, where the deformation as a result of compression is spread out to a much wider area outside the plate boundary. The examples are: the San Andreas’ fault, where most earthquakes are caused by irregularities in the fault trace, and the Northridge’s earthquake, which was linked to the movement on a blind thrust within the zone. In addition, the oblique convergent plate frontier is found between the Eurasian and Arabian plates, and the north-western part of the mountains of Zagros is another example. The deformation linked to the compression of rocks leads to thrust movements that are perpendicular to the boundary. Therefore, all tectonic plates have internal stress fields, and the stresses may be abundant enough to lead to failure along present fault planes, and subsequently result in the intra-plate earthquakes (Boer & Sanders 14).
Molten rocks commonly referred to as magma is normally stored in reservoirs under the volcanoes. During a volcanic activity, the magma moves upwards and may fracture the rock it squeezes through, resulting in earthquakes. It is recorded that the magnitudes of such earthquakes are not much greater than 5.0. Occasionally, the magma accumulates in a bigger reservoir before a volcanic discharge, and as it builds up, it moves around causing a breakup of rocks and bursts of continuous vibration known as a volcanic tremor. As a result of these precursors, the seismographs become very instrumental in monitoring active volcanoes to issue a warning of an impending eruption (Lee et al. 29). This means that earthquakes that occur in the volcanic regions are caused by either tectonic faults or movements of magma in volcanoes. In a number of occasions, such earthquakes serve as early warnings of a volcanic eruption to follow as it happened during the Mount St. Helen’s eruption of 1980.
Foreshocks and Aftershocks
Foreshocks are minor quakes that occur in the same area just before the occurrence of a larger earthquake. They are triggered by minor breaking of rocks under pressure prior to the main fracturing that takes place during the largest earthquake of the series known as the mainshock (Simpson & Richards 2). Foreshocks can be experienced earlier up to a year before the occurrence of the mainshock. For instance, the foreshocks were experienced before the occurrence of three large earthquakes with magnitudes between 6.3 and 6.7 recorded in Tennant Creek in January, in 1988. It is worth stressing that not all earthquakes experience foreshocks. Instead, a series of similar sized quakes referred to as earthquake swarm may occur over a long period without being followed by a considerably larger mainshock. Therefore, the use of foreshocks to predict earthquakes may be misleading in some occasions.
On the other hand, aftershocks are smaller earthquakes that occur after the main quake in the area. They usually result when the main shock area is readjusting to the fault movement or as a result of constant movement along a similar fault line (Simpson & Richards 1). The biggest aftershocks measure a minimum of half magnitude less than the mainshock, and the sequence of aftershocks may last for months or years after the main shock. Similarly, not all earthquakes have aftershocks (Simpson & Rechards 252). For instance, the Newcastle’s earthquake of 1989 that measured magnitude 5.6 only had one aftershock, which measured magnitude 2.1.
Measuring and Locating Earthquakes
Earthquakes are measured using such a device as seismometers. Earthquakes are detected up to longer distances, owing to the fact that seismic waves have the ability to move through the interior parts of the Earth. The total magnitude of an earthquake is usually recorded by the numerical values on the Moment magnitude scale. Then the magnitude is recorded using the improved Mercalli intensity scale (intensity II–XII) (Simpson & Rechards 268). Every quake produces diverse types of seismic waves, which spread with different velocities to the wider areas. These waves include: Longitudinal P-waves also known as the shock- or pressure waves, Transverse S-waves and Surface waves also known as the Rayleigh and Love waves (Boer 249).
The spreading velocity of the seismic waves ranges from approximately 3 kilometres per second (km/s) up to 13 km/s, subject to the elasticity and density of the moving medium. In the interior of the earth, the P waves move quicker than the S waves by a ratio approximately 1.7: 1. The variances in a travel time from the epicentre to the observation site are a measure of distance. They can be adopted to determine the sources of quakes and image structures within the Earth. P-waves travel at speed of about 6 to 7 km/s in solid rock with the velocity increasing in a deep mantle to approximately 13 km/s (Boer 10). Conversely, the velocity of S-waves is between 2–3 km/s in light sediments, 4–5 km/s in the Earth's crust, and up to 7 kilometres per second inside the deep mantle. In this case, the first waves to be detected at the observatory are those that travel via the Earth's mantle (Boer 248).
The earthquakes are also categorized by the place where they take place. For instance, the earth is separated into 754 Flinn-Engdahl zones (F-E). These zones are established under geographical and political boundaries, as well as the seismic activities reported in those regions. More active zones are further divided into smaller F-E regions. The standard recording and reporting of earthquakes comprise magnitude, date and time of occurrence, the geographic coordinates of their epicentre, geographical region, depth of the epicentre, location uncertainty, distances to population centres, a number of parameters that are incorporated in the United States Geological Servey (USGS) earthquake reports, such as the number of observations and stations reporting, as well as the unique event ID (Simpson & Rechards 268).
Earthquakes in Japan
History of Earthquake in Japan
The islands of Japan were formed as a result of numerous large oceanic movements that occurred in a span of millions of years. Their formation began in the mid-Silurian period to the Pleistocene period, due to the subduction of the Philippine Sea Plate under the continental Amurian Plate and Okinawa Plate to the south, as well as the subduction of the Pacific Plate beneath the Okhotsk Plate to the north (Simpson & Richards 65). Before the subduction, Japan had been attached to the Eurasian continent on the eastern coast (Simpson & Richards 65). As the subducting plates were deeper than the Eurasian Plate, the subducting plates pulled Japan eastward, thus creating the Sea of Japan, approximately 15 million years ago. Presently, the Japanese archipelago is regarded as a mature island arc, and it is the consequence of numerous generations of subducting plates (Karan 9; Haggett 3066). It is approximated that in the last 450 million years, 15,000 km of the oceanic floor have so far passed beneath the Japanese area, most of which have been fully subducted.
Furthermore, Japan is positioned in a volcanic sector on the Pacific Ring of Fire, making the recurrent low intensity tremors and sporadic volcanic activities being felt throughout the islands (Karan 11; Kitahara, 2003). Similarly, devastating and destructive earthquakes that often result in tsunamis occur in Japan several times in a century majorly because the Japanese archipelago is situated in a collision zone where numerous continental and oceanic plates converge. This results into frequent earthquakes and the existence of many hot springs and volcanoes across Japan. If earthquakes take place beneath or close to the ocean, the seismic waves may trigger tidal waves (tsunami) that are more destructive as experienced in 2011 (Johnson 1). These continental and oceanic plates (lithospheric plates) include: (1) the Eurasian/Chinese Plate, (2) the Philippine Plate, (3) the North American Plate, and (4) the Pacific Plate. The constant movements of these plates free a lot of energy that are released from time to time in a form of earthquakes and tsunamis of fluctuating magnitudes and effects (Haggett 3068).
The written records documenting strong earthquakes can be traced back to at least 1.6 million years. Previously, Japanese naturalists were less concerned with the determination of the cause of earthquakes. They were only concerned with the effects of the extraordinary occurrences. Thus, the mythical explanations on the causes of quakes were given (Clancey).
In December 31, 1703, Japan experienced a strong earthquake, which when measured had a reconstructed intensity of 8 using the Mercalli-scale (Simpson &Rechards 268). In Edo, (the modern Tokyo), most of the wood buildings collapsed, and the earthquake together with its aftermath effects, such as floods and fires, killed an estimated number of 150.000 people (Drake 2003). Out of these, more than 6.500 victims were killed by the resultant flood wave, which caused devastation in the Sagami Gulf and on the peninsula of Boso. Another historic earthquake that hit Tokyo, Japan, took place on the 11-th of November, 1855, killing between 16.000 to 20.000 people. This event and the aftermath are retold by hundreds of woodcuts. On the 28-th of October, 1891, another earthquake of magnitude 8 hit the agricultural region of Nobi. As a result, modern buildings as well as traditional houses were fiercely damaged and collapsed, leaving thousands of people without their homes ,and 7,000 people were killed (Drake 2003). The impact of this earthquake was later studied by English geologists between 1849 - 1913. In 1880, the Seismologists Society of Japan, which was to study seismology, was founded (Drake 2003).
Fusakichi Omori who became the director of the Seismological Institute of Japan (1868-1923) studied the occurrence of quakes around Tokyo. In 1922, the scholar observed that in as much as Tokyo was seismically quiet, the mountains regions around Tokyo in a distance of about 60 kilometres experienced light earthquakes. He noted that the seismic activities in those areas were to diminish gradually, but increase in Tokyo Bay to perhaps cause a strong earthquake. One year later, on the 1-st of September, 1923, just as predicted by Omori, the Yokohama and Tokyo cities experienced a great earthquake that was named as the Great Kanto- earthquake (Clancey 296). More than 99.000 people lost their lives because of the collapsed fires and a 10 to 12 meters high tsunami, while more than 40,000 victims were never found.
June 28, 1948, at 17:14 local time, the city of Fukui experienced another earthquake that left a lot of destruction, and more than 5,131 people were dead. Most of the victims who died were trapped under the debris and in the fire instigated by the earthquake. In January, 1995, the industrial city of Kobe was similarly hit by an earthquake with magnitude 7.2. This was the strongest quake in Japan since 1923, where more than 6,000 people died and more than 300, 000 lost their homes (Lee et al.3).
Historical Earthquakes in Japan
Many parts of Japan have been hit by numerous devastating earthquakes and tidal waves because Japan is situated on the collision zones of the continental tectonics that trigger more quakes. However, there are three outstanding and more devastating earthquakes that have been experienced in Japan in less than a century. The Great Kanto earthquake is one of the dreaded occurrences. It is considered the worst earthquake in Japanese history. It hit the Kanto Plain near Tokyo in 1923. As a result, over 100,000 people were dead and thousand others were left unaccounted. Most of the deaths were caused by the collapsed buildings, raging floods as a result of the tsunami, and fires that arose because of the earthquake (Clancey 296).
The second dreaded earthquake occurred in January, 1995 A quake destroyed the city of Kobe and its entire surroundings. This earthquake was later named the Great Hanshin Earthquake or the Southern Hyogo Earthquake 6,000 people were, 415,000 were injured, and approximately 100,000 homes were completely destroyed (Özerdem and Jacoby 29).
The third and most recent earthquake was on 11-th of March, 2011. It is the strongest earthquake in history that has ever hit Japan. This earthquake generated a colossal tsunami along the Pacific Coast of north-eastern Japan (Karan 11). It was named as the Great East Japan Earthquake. Approximately 20,000 people were dead, and a nuclear accident at the Fukushima Power Plant Prefecture took place (Johnson 1). At the Fukushima Daiichi Nuclear Plant, radiation particles were realised, due to the earthquake. As a result, thousand residents were evacuated from the area around the plant to avoid further deaths and radiation effects. According to the seismologists, the earthquake's devastating level of destruction was as a result of the relatively shallow depth of the earthquake but not its magnitude (Lee et al. 29). Equally, the epicentre of the quake was almost directly under the city. It should be mentioned that in the city, there were traditionally constructed timber-framed houses and heavy tiled roofs that crumbled easily and burned promptly in the fire caused by broken gas and fuel pipes.
According to the British Geological Survey located in Edinburgh, the Japan earthquake only measured 9.0 on the Richter scale. Its destruction was as a result of its shallow depth of only 30 km deep and being virtually directly beneath the city. This magnitude intertwined with the shallowness sent massive seismic waves to the earth surface that intensely shook and shattered buildings, roads and mains, and triggered as high as 40 meter tsunami waves that resulted in massive destructions and human deaths in the regions along Pacific coast of eastern Japan, particularly Iwate, Miyagi, and Fukushima Prefectures (Dokyumento 2003). The aftermaths of the quake were only the debris of shattered wooded buildings, crashed cars, cut roads and ships, pushed from the sea by the powerful Tsunami (Figure 1), as well as people’s deaths. Usually, the earthquakes occurring in Japan are deeper and in most cases have less effect at the surface unlike the 2011 occurrence. This is why most of the death occurring when an earthquake hits any part of Japan as a result of the secondary effects, such as fire and floods, but not the being buried in the debris when a particular area sinks or when eruption occurs.
This earthquake seriously affected transportation and tourism in Eastern Japan for several weeks. Roads were either cut off or barricaded by the debris; there were no power and water, and the whole infrastructure was totally destroyed. Key connection points, such as the major airports, train substations and lines, as well as the expressways were reopened after two months of the disaster (Johnson 1). Furthermore, no humans were allowed into the areas because of the accident at the Fukushima Nuclear Power Station at to avoid effects of radiation. In this area, there were contaminated parts of the sea water, flora, and fauna. Towns, such as Sendai, Iwaki, Matsushima, as well as the Sanriku coast were the only areas that suffered significant damages from the earthquake. Nevertheless, most tourist attractions in these areas were reopened after a few weeks (Karan 16).
Figure 1: Aftermath of 2011 Japan Earthquake
Nuclear Accident in the Fukushima Plant
The accident at the Fukushima Daiichi Nuclear Plant resulted in a massive radioactive release and upsurge in radiation throughout Eastern Japan in some weeks after the disaster. Eventually, thousand residents were evacuated from the area around the plant to avoid further deaths and radiation health risks.
As a result of the earthquake and subsequent accident, most nuclear plants across Japan remain shut today, making the deficit caused by the lack of nuclear power, which is being covered with increased utilization of gas, coal, and oil power plants. Nonetheless, there is still no enough power, and certain levels of power saving are still required in some regions of Japan, especially during the winters and summers when power consumption increases because of the use of air conditioners and heaters respectively. It should be noted that the power saving attempts have had no effect on tourism.
Figure 2. Simplified map of Japan showing a selection of earthquakes with magnitude greater than 7 after Richter in the last 100 years.
Earthquake Measurement in Japan
The Japanese mostly use their "shindo" scale in order to measure earthquakes than the famous Richter scale. The word ‘shindo’ refers to the earthquake’s intensity at a particular place. That is what members of the public essentially feel at a given locality On the other hand, the Richter scale is used to measure the earthquakes magnitude. That is the amount of energy, which an earthquake discharges at the epicentre (Özerdem and Jacoby, 2006). The design of the shindo scale starts from shindo one, which is recorded when a slight earthquake occurs that can only be felt by individuals who are stationary, to shindo seven, which is for a severe earthquake. A record of between shindo two to four is for minor earthquakes that cause no damage. Objects begin falling or ruining at shindo five, and devastating damages are witnessed at shindo six and seven.
Disaster Preparedness in Japan
Natural disasters, including those not related to earthquakes, may take place at any time and place in Japan. For example, typhoons hit Japan from mid-August to the end of September. On the contrary, volcanic activities and Earthquakes may occur all year round. They may take place both in the rural and densely populated areas, like the cities. In most cases, floods, storms, tsunamis, and volcanic activities may be experienced, as well. In most cases the typhoons and volcanic eruptions can be predicted to facilitate adequate disaster preventive measures, but earthquakes hit without prior warning. Thus, the devastating effects are normally experienced together with the earthquake related disasters (Simpson & Richards 65).
It is essential to stress that it is relatively impossible to achieve 100% protection or prevention from such disasters in Japan, owing to the frequency in which they occur. However, people can prepare themselves and minimize the expected danger for themselves and their family (Coburn & Spence 85). Japan authorities usually offer an information sheet to people with the intention to provide some safety guidelines that are supposed to be considered and followed in case an earthquake occurs. These guidelines and numerous safety measures make Japan one of the most prepared countries in the world for any natural disasters, including earthquakes. One of the programs to ensure full preparation is the plan to reinforce the entire older timber-framed housing. Other preparation measures set by the authorities include:
- Preparation of the homes. This includes: building homes according or superior to the standards that were set in 1981, securing the furniture to the wall through the use of special devices in order to stop them from toppling over in case of shakings, avoid placing any heavy items on top of shelves and cupboards, and making sure that everyone is aware of where and how to switch off the supply of gas to in the apartment (Coburn & Spence 156). Every individual should also be aware of the emergency exit doors in their building and ensure that they are not blocked in any way. People should stock up food and water supply enough to sustain the family for at least 3 days, and finally, always arrange for a ready escape bag composed of radio, spare batteries, flash lights, solid fuel for a cooker, toiletries, a set of underwear, candles, money, and ID documents. Furthermore, families should make their members, including children, to know the assembly point where they can meet immediately after an earthquake. Parents need to consult with the respective school officials for special guidelines in this area (Coburn & Spence 85).
- Evacuation: Evacuations from the danger sites must be undertaken, especially when fires are spreading or when buildings are at risk of being destroyed by landslides or swept away by raging typhoons and floods (Haggett 3068). In Japan, city police together with fire authorities usually issue evacuation advice. In case there must be an evacuation from the office or apartment building, people are advised to take a walking pre-survey to identify the designated areas of evacuation that are nearest to the home and office. Equally, people are advised to be acquainted with the location of the ward office as well as the telephone number of the Disaster Relief Headquarters responsible for the zone (Coburn & Spence 87). As a sign of preparedness, the Tokyo Metropolitan Government has ready maps identifying the evacuation points in case of any disaster, which can be accessed through the landlords or zone offices. These evacuation points usually supplied with food, fresh water, and medical supplies, which may be used by all irrespective of whether they were evacuated or not (Karan 24).
- During a quake. Normally, falling objects, toppling furniture, as a result of the quake, and panic present the highest dangers during an earthquake. While inside a building, people are advised not to use an elevator during or immediately after an earthquake to avoid any eventuality of power cut or breaking stay away from loose objects, which may easily fall or break, shelter themselves under a table or any other solid object, cover the head, avoid running outside, and remain as composed as possible, turn off gas supply and to open all doors and exit points immediately in order to access a clear escape route (Coburn & Spence 156). While outside the building in an open air, people are advised to guard themselves against falling objects and stay away from narrow passages, try to hide behind a rock or a concrete wall to protect against flying glass, walk in the middle of the road while observing the houses, and watching out for tumbling power lines and in a case of fire. People need to check the wind direction and then walk to the opposite direction. In case an earthquake occurs when driving a car, people are advised to stop on the left side of the road to create room for emergency vehicles, leave a car key in the car, and avoid locking the doors then walk to the adjacent evacuation point (Karan 24). Immediately after a strong earthquake, people must turn off all electric and gas devices. . In coastal regions, people need beware of likely tidal waves while those in mountainous regions must beware of potential landslides or even volcanic eruptions (Peter 3068).
- The role of the Embassy. The e Government of Japan is always ready and responsible for supporting foreigners immediately after a major quake. In most cases, telephone services are always severely overloaded during and after an earthquake. Thus, the Japanese Government often limits the phone use to priority users. Foreigners are, therefore, advised to adhere to the instructions given by the Japanese authorities at the evacuation area. Foreigners who are linked to the larger organizations, such as companies, church groups or schools should inform their respective organizations of their well-being and whereabouts. Beside the use of the Embassy’s priority phone lines, foreigners may use the NTT disaster message telephone service, particularly the 171connection.
Effects of Earthquakes
Earthquakes result into a number of devastating effects, which are discussed in the next subchapters:
Shaking and Ground Rupture
Shaking and ground rupture are the leading consequences that arise from earthquakes, which subsequently result in more or less severe destructions of buildings and other inelastic structures. The severity of the local impacts of quakes depends on a multifaceted combination of factors, such as the distance in terms of the magnitude of the earthquake, depth from the epicentre, and the local geomorphological and geological conditions, which may magnify or decrease wave propagation from one location to another. The ground-shaking is usually measured by ground acceleration. This means that particular geological characteristics, the geomorphological and geo-structural features of the earth, could promote high levels of quaking on the ground surface even if the intensity of the tremor were low. This outcome is referred to as site or local amplification. It is predominantly as a result of the shifting of the seismic motion from the hard rocky deep soils to soft shallow ones, or due to the effects of the focalization seismic/tectonic energy caused by the geometrical setting of the deposits.
A ground rupture, on the other hand, is an observable cracking and displacement of the earth surface usually along the fault lines either through normal, reverse or strike-slip faults, which may several meters deep or wide in the scenario of main earthquakes. A ground rupture effect is a key risk for big engineering structures, such as bridges, dams, and nuclear power stations. Thus, a careful mapping is required to avoid existing faults that can potentially break the earth surface where the structures are erected. Ground rapture is a common effect that is experienced in almost all the major earthquakes that have taken place in Japan. For example, it was observed during the earthquake of 1891. It had a magnitude 8 in the agricultural region of Nobi. As a result of the ground rapture, modern buildings as well as traditional houses were fiercely damaged and collapsed. It was also experienced during the 28-th of June, 1948. The earthquake hit Fukui region, thus leaving a lot of destruction and more than 5,131 people dead. Most of the victims who died were trapped under the debris and in the fire instigated by the earthquake. A similar situation was also seen in the industrial city of Kobe in 1923(Özerdem and Jacoby 29).
Landslides and Avalanches
A combination of earthquakes, severe typhoons, volcanic activity, tidal wave attack, and wildfires can result in slope instability, especially in the mountainous regions leading to landslides that sweep away all structures on the surface, including buildings (Haggett 3068). Such effects cause a lot of deaths especially when people are trapped under the debris. It is also a key geological hazard, and its danger may be felt as emergency rescue teams attempt the rescues.
Fires are common effects of earthquakes when the quake damages electrical power or breaks gas lines (Boer & Saunders 139). The effects may be worsened as water supply to such regions is also cut off by the earthquake, making it difficult to control the spread of the fire. For example, more reported death cases in the 1906 San Francisco earthquake were as a result of fire, not the earthquake itself (Boer & Saunders 139). Similarly, the fire caused a lot of deaths in the Fukui Japan during the 1948 earthquake and during the 1923 earthquake that hit the Kanto Plain, near Tokyo. Most of the deaths were caused by collapsed buildings, raging floods, and fires that arose as a result of the earthquake (Clancey 297).
Mass-wasting Events and Soil Liquefaction
Ground motion during earthquakes may generate landslides and other rapid mass-wasting events with the ability to cause loss of people’s lives and severe damage to buildings. A mass-wasting refers to a landslide by liquefaction, which occurs when water-soaked a sediment flow down a slope in a form of slurry, causing buildings that were constricted on solid sediment to sink (Haggett 3069). It imperative to note that rocks and soil can be permanently displaced during an earthquake. This can occur when fault blocks move vertically, forming a new escarpment along the fault plane or when horizontal ground movement occur and tear apart roads, pipelines, and any other engineering structures constructed across the fault zone.
Soil liquefaction, on the other hand, takes place when the process of shaking the water-saturated materials, like sand, momentarily loses their strength. It is worth noting that the state changes from solid to liquid. The weight of soil liquefaction may force rigid permanent structures, such as buildings, bridges and power lines to bend or slump into the liquefied deposits. It was once experienced during the 1964 Alaska earthquake.
These are seismic sea waves that arise when the seabed abruptly experiences upward or downward thrusts. The abrupt displacement of water cases into the seismic sea waves is also known as tsunamis. Tsunamis are massive and can be up to 90 meters (300 feet) high with a speed of up to 400 miles per hour; this is much higher and faster than greatest storms. Furthermore, tsunamis comprise wavelengths as long as 160 kilometres (100 miles), of which the water takes time to withdraw from the coast after the tsunami breaks. During the formation of tsunami, the sea water rises up to ten minutes until the long wavelength is achieved, thus leading to widespread coastal damage.
The long-wavelength and longer-period tidal waves produced by the sudden movement of large volumes of water are strong enough to sweep include permanent structures. In the open ocean, the distance existing between the wave crests may exceed 100 kilometres with wave periods varying from five minutes to one hour. Such long wavelengths tsunamis travel 600-800 kilometres per hour depending on the depth of water. Large waves produced by a submarine landslide or earthquake can swarm the adjacent coastal areas in minutes. Equally, the tidal waves can also travel for thousands of miles across the open ocean and cause massive destruction on shores far away from the epicentre of the quake hours after the earthquake (Haggett 3068), has occurred, for instance, as it was seen in India.
Floods usually occur when water volume within a water-body like a dam, river or lake surpasses the capacity of the formation, making a section of the water to overflow or sit outside the standard perimeter of the body. In most cases, floods are usually secondary impacts of earthquakes, particularly when dams are damaged. In 2011, tsunamis caused mass flooding and consequently massive destruction of houses, infrastructure, and loss of human life (Özerdem and Jacoby2).
Human Impacts and Structural Damage
Surface vibration and shaking triggered by the seismic waves often destroy physical structures, such as buildings and bridges. Based on the severity and intensity of the earthquake, gas mains may be broken, starting several fires. To avoid this, Foreshocks should be used as warnings since they precede the mainshocks (Simpson 252). A number of aftershocks may also be experienced after the main earthquake. They can be quite destructive, particularly to the structures already weakened or damaged by the main earthquake. Earthquakes also cause injuries and death because of falling objects, fires, suffocation by the debris, and drowning in the raging floods. It may also bring waterborne diseases, as a result of contamination of the water system after the pipes are damaged, or the effects of radiation as it were in Japan, in 2011, when the Fukushima Nuclear Power Plant was affected. Quakes also cause the lack of basic needs and may result into the higher insurance premiums (Johnson 10).
An earthquake is a shaking of the ground, as well as an occurrence of seismic waves that result from an abrupt discharge of energy from the crust of the earth, commonly known as the hypocenter.
The study discussed the general causes of earthquakes that include the plate tectonics, which occur when the earth surface and rocks crack and move due to pressures that arise from plate movements, shallow-focus and deep-focus earthquakes with a range to the depths of 700km, intra-plate earthquakes that do not take place on plate margins, volcanic earthquakes as a result of the magma that moves upwards under great pressure and temperature, fracturing the rock resulting in earthquakes (Dokyumento 2003). There are also foreshocks and aftershocks.
This study discussed earthquakes in Japan, starting with the history of earthquakes in the country. It was established that the frequency of earthquakes in Japan depends on the fact that Japan is situated in the volcanic sector on the Pacific Ring of Fire, making the recurrent low intensity tremors and sporadic volcanic activities being felt throughout the islands (Karan 11). Furthermore, four continental and oceanic plates that cause frequent collision converge in the zone beneath Japan, thus causing recurrent earthquakes. One of the historical quakes discussed is the 2011 earthquake that generated massive Tsunami in the Pacific coast of Eastern Japan. This caused massive destructions and deaths, as well as the accident at the Fukushima Nuclear Power Station (Johnson 1). The Measurement of earthquakes in Japan is done using the Japanese ‘shindo’ scale. The study also discussed the level of preparedness for natural disaster in Japan. The following level is considered the best in the world. Finally, effects of earthquakes in Japan were analysed.