The 2016 Kumamoto Earthquakes were in fact a series of earthquakes that occurred in Mashiki, Kumamoto Prefecture, Japan, caused by two tectonic plates slipping against each other. The slipping of these two tectonic plates occurred along an active inland fault. The events that took place occurred in a relatively shallow depth, causing the destruction of bedrock. A 7.3 magnitude mainshock occurred on the day of 16 April 2016, which was close to the epicenter of a magnitude of 6.5 foreshock, occurring 28 hours later. There were many strong characteristics that were recorded during these events, including, migrating seismicity, earthquake surface rupture, as well as major foreshock-mainshock earthquake sequences. The fault rupture that occurred, originated from the northern segment of the Hinagu fault. This earthquake resulted in intense shaking in the eastern area of the Kumamoto Prefecture, and major earthquake resulted in Mashiki Town near the epicenter. An earthquake measuring 7.3 on the Richter scale occurred on the fault of Futawaga, which caused significantly greater damage in the larger areas situated near the fault. These areas include Mashiki Town, Nishihara Village, and Minami Aso Village. The mainshock of this event also resulted in the prominent crustal deformation, which was clearly visible in ground surfac es through the ruptures that were formed. Deformation up to 2 metres was also reported in several places. The events taken place on the 14th and 16th of April were of shallow depths, and their focal depths were 11 and 12 kilometres. These events were mainly originated from different active faults, although the government of Japan claimed these events to be a foreshock and mainshock. The Kumamoto earthquakes on 14 and 16 April 2016 are similar to the Great Hanshin earthquake. These earthquakes had a magnitude 6.2 foreshock and magnitude 7.0 mainshock and occurred along the Futagawa- Hinagu fault zone southeast of the Kumamoto city, as well as by a nearly 2-metre dextral offset along its 30- to 50-km-long fault rupture. The field surveys had confirmed that the site of the surface rupture similarly matched the location of the Futagawa fault. The Futagawa fault has not ruptured in about thousands of years. Before the Kumamoto earthquakes occurred, the Futagawa- Hinagu fault zone was considered a entrant fault for an inland earthquake occurring in the future, which could measure no greater than a 7.0 magnitude earthquake. The two Kumamoto earthquakes proved the scientist’s predications right.
The Futagawa- Hinagu fault zone caused the earthquake events. It belongs to the Western extension of the Median Tectonic Line, extending from the central Honshu to Shikoku and the Kyushu island. The Median Tectonic Line runs about parallel to the Nankai Trough for more than 650 kilometers. The active fault is located on the West part of the Japan islands, and is considered to be an extremely important geological figure.
The kinematics of the Median Tectonic Line is affected upon the plate motion between the Philippine sea and Plate and the Eurasian plate. When the Philippine sea plate moves in a north-west direction beneath the Eurasian plate along the Nankai trough, a fraction of this plate motion that moves parallel to the subduction trench, translates to into the Eurasian plate, accumulating along the right lateral Median Tectonic Fault. This makes the Nankai Trough and the Median Tectonic Line a classic example of the slip partitioning system at the convergent plate boundary. The Median Tectonic Line produced many large earthquakes in the past 1,500 years. The Kumamoto earthquake sequence’s relationship with the active faults in Kyushu, is an example of a fault-rupture interaction, as well as its role in seismic hazard activity. The geological studies in japan enabled individuals to narrow down the potential hazard area before the earthquakes hit. There are around 2,000 active faults around Japan, around 100 of them are designated by the government as key active faults. The Futagawa and Hinagu faults, along which the recent quakes occurred, are among the 100 most active and dangerous faults in the country. Moreover, the Izu-Ogasawara Island Arc have collided with Honshu arcs, intruding to the northern direction. These consistent movements on the subduction zones, are predominantly the main causes of large earthquakes and tsunamis. And many active faults are distributed in the island arcs. The Okinawa Trough which locates north of Ryukyu Arc has been expanding to south direction. The Beppu-Shimabara rift zone in the Middle Kyushu is part of this Okinawa Trough zone. Therefore, tensional stress of north to south direction is dominant in the Kumamoto area. The epicentres of the Kumamoto earthquakes and aftershocks are distributed in a South-West and North-East direction, located along the Southern edge of the Beppu-Shimbara rift zone. Surface faults located along the Futagawa fault with right lateral displacement of maximum 2 metres were investigated. According to the USGS, the earthquake occurred several hundred kilometres north-west of the Ryukyu Trench, where the Phillipine sea plate begins its subduction beneath the Japanese and Eurasian Plate. The shallow depth of the earthquake therefore indicate that it occurred on a crustal fault.
Japan is located on ‘the ring of fire’, which is the belt of earthquakes, indicating and distinguishing between the Pacific Ocean margins, and the Atlantic Ocean margins. The great seismologist K. Wadati discovered in the 1920s that earthquaks beneath northern Japan form an inclined zone which extends from various points in the Japan Sea and the Japanese Trench. The cause of the active tectonic events was not well found out until the 1960s, when the plate tectonic theory was formed. The tectonic activity of north-west Japan are in the form of the manifestation of two subplates. Subduction occurs along the Japanese trench about 9 centimeters per year. This is concurrent to the convergence that is occurring near the eastern edge of the sea of Japan. The main focus of study is the active tectonics near Kyushu Island. Most of the bedrock that is present in the Japanese Islands was created as a result of subduction along the eastern margin of Asia.
The geologic history regarding the basement terranes of Kyushu is well understood as the long-term westward subduction of the Pacific ocean seafloor occurred. There is low convergence with left-lateral strike-slip movement along the Median Tectonic line, which caused the Ryoke belt to become contrasted directly against the Sanbagawa-Chichibu-Shimanto accretionary terranes. Westward subduction of the Philippine plate generated the Ryukyu trench and arc.
It was said that Mount Aso, one of the most active volcanoes located in Japan, contributed to stop the powerful earthquake of Kumamoto before it diminished on its own. The 7.1 magnitude earthquake of Kumamoto opened surface ruptures on the ground, which was approximately 40 kilometers in length. Scientists had suggested that the extremely powerful earthquake was halted by a magma chamber under the volcanic cluster of Aso. Which located approximately 30 kilometers from the region of the earthquake. This provided scientists to look at two natural phenomenon (earthquakes and volcanoes), and how they linked together and interact with each other. A volcano is formed by the sudden release of energy that has been built up. This is generated by the shift of the plate tectonics. After the Kumamoto earthquake, scientists vistited and investigated in the epicenter of the earthquake, as well as regional areas. They had discovered fresh ruptures, which stretched into Mount Aso’s bowl-shaped depression at the summit of the volcano. The suddenly ended at the depths of 6 kilometers below the earth’s surface. Seismic activity was investigated deep into the caledra, where the ruptures had stopped. This indicated that there was a chamber which held magma. At this exact spot, energy waves that were created from the earthquake travelled towards the direction of Mount Aso, through the cold and brittle rock that was present at the scene. The sudden encounter of the heat of the magma present under the volcano, was able to disperse the existing energy in an upwards and outwards direction. This then was able to sap the strength of the earthquake’s flow, causing the rupture to stop. Many reports suggest that there are similar historical events that occurred, which resembled this event. The ruptures that were generated in the 1707 Houei-Tokai-Nankai earthquake originally extended in a north direction, although it diverted and terminated on the west direction of mount Fuji. Another instance occurred in 1903. An earthquake measuring 7.3 was also disturbed and terminated at the Hakone volcano in the Izu Peninsula.
Damaged caused, cost to the economy and the deaths that resulted from the disaster
The tremors that were present in these events, resulted in the city of Kumamoto without any water. The entirety of the village in Nishihara Village in Kumamoto Prefecture were evacuated, as they feared that a dam nearby would collapse. Kumamoto Airport was also closed due to this event, except for the emergency flights. As well as that, the service on the Kyushu Shinkansen was also suspended, as a train derailed due to the earthquake. Several buildings collapsed and set on fire due to the strength of the earthquake. In fact, the government estimated that the average estimated number of collapsed buildings was more than 1,000. These 1,000 buildings were seriously damaged, with another 90 being completely destroyed. A hospital in Kumamoto City, consisting of 500 beds was also evacuated, as the earthquake knocked off all of its foundations. A natural gas leak also occurred as a result, which made the Saibu Gas destination to turn off the gas in various areas of homes in and near the cities.
The intensity of the earthquake resulted in landslides across the mountains of Ky ushu. The Great Aso Bridge was also affected, as it collapsed into the Kurokawa river when the earthquake event was occurring. A large rockslide was also photographed. This photograph showed the rockslide blocking the entirety of a four-lane express-way close to the fallen Great Aso Bridge, which resulted in leaving a large scar that ran almost completely up the hill that suffered the rockslide. Another destination that was also heavily affected was the Aso Shrine. The Shrine’s romon (tower gate), and the haiden (worshipping hall), both completely collapsed. Kumamoto Castle, which is another important cultural property sustained damage to its roof and exterior buildings and walls because of the earthquakes and associated aftershocks. The castle’s ornaments were destroyed, and a number of kawara tiles also fell from the roof. Other historical buildings such as Janes’ Residence, the first western-style house built in Kumamoto (dating from 1871) were also totally destroyed. The former registered Cultural Asset was initially located in the grounds of Kumamoto Castle, but was later relocated near Suizen-ji J?ju-en.
The economic costs of the damage were estimated, and they ranged from $5.5 billion to $7.5 billion, with insured property losses estimated to be between $800 million to $1.2 billion, according to Risk Management Solutions or between $1.7 billion to $2.9 billion, according to Guy Carpenter. Through the first half of 2016, about $3.2 billion of claims for damage to residential dwellings were paid out by insurance companies, according to data from the General Insurance Association of Japan. Although, ‘Japan Times’ has stated that the economic result of the Kumamoto earthquakes was worth 3.8 trillion Yen. This cost is branching from residential property, as well as industrial and commercial buildings.
The Kumamoto earthquakes resulted in the loss of many individual’s lives. Over 200 individuals were killed due to the disaster, with over 40,000 living in temporary housing. Among the injuries that were present due to this natural disaster, 52 were reportedly in serious condition. In the town of Mashiki, 56 individuals were rescued from collapsed structures. There were many collapsed utility poles and cut power lines. It was also reported that 7 individuals went missing at the time of the earthquake, and approximately over 95,000 individuals were evacuated from certain areas of destruction. Shockingly, 71 individuals died from post-quake stress in Kumamoto, Japan. Chief Cabinet Secretary Yoshihide Suga mentioned that nearly 80 individuals were assumed trapped or buried due to the extensive damage caused to buildings, resulting in them collapsing. The main cause of death for individuals who experience the Kumamoto earthquakes was the collapsed structures and their debris which resulted in people being buried underneath them. The panic that struck individuals when they were experiencing the earthquake, also contributed to the disastrous effect that the event had on them. Dozens of people were fearing of being buried alive, and at least 1,000 were being treated for injuries. The series of earthquakes contained two strong ones. The second earthquake that hit in the same area resulted in diminishing the pre-existing emergency and rescue efforts, resulting in more damage of individuals and their surroundings. Several people reported that they were not able to stand up, and that things were being thrown around at them due to the intensity of the earthquake. A lot of people had also been affected mentally. One individual said that the people were very considerate during the earthquake, as they were helping each other out despite the circumstance that they were all in. On that Saturda y evening, many reports were coming related to people being trapped in buildings and landslides.
The small town of Mashiki is located a few miles east of the Kumamoto City. Although, Unfortunately, it is located right on the Futagawa fault, which was the cause of the Kumamoto earthquakes. Kumamoto had moderate damage, although the town of Mashiki was severely impacted. The site after the earthquake occurred was known to be like a war zone. A major part of the wooden homes was all in the ruins of the earthquake occurrence. In some areas of the town, all of the site of the buildings was destroyed and in other areas, approximately 20% of the buildings were destroyed, about 15% of the buildings were needed to be built from scratch, and more than 30% required extensive repair. The first earthquake (magnitude 6.5), was enough to alert the individuals of the Mashiki and Kumamoto area. So, when the 7.3 earthquake occurred following that, most of the buildings were not occupied by individuals. Much of the damaged that occurred was due to localised failures of the ground beneath several structures. The worst damaged that occurred was on flat land, right near where the ground started sloping upwards to become hills. The severe damage extends up into the hills for a few hundred metres and diminishes down beyond that. This concentration of damage is partially due to the way the earthquake waves are reflected and refracted at the interface within a few hundred yards in either direction.
The recorded average of the acceleration of gravity was recorded to be 0.93g, in the two horizontal directions. The most effected area in Mashiki could be possibly recorded as 9 or 10 based on the effects. The area surrounding this was surrounded by a larger area measuring approximately 10 kilometres east-west by 5 kilometres north-south, and would be rated an intensity of 8. The area of moderate to serious damage stretched from the Kumamoto Airport, to the edge of the urban area of Kumamoto. Soil conditions had a major effect due to the intensity of the shaking experienced by the earthquake. The image above shows the investigations of strong motion records. The strong motion record that was recorded over the severely damaged residential area of Mashiki was recorded to be 1.0g in an east-west direction. However, this is recorded using the acceleration of time history in a short duration. The amplitude measures more accurate results, recording 0.50g in less than 0.1 second. This peak acceleration would’ve brought minimal energy, which means it would not have been a major contributor to the damaged caused during the earthquake. Realistically, an area that experiences an intense earthquake like the Kumamoto earthquakes, it is highly likely that an area surrounding on within it will experience loss of powerlines and power. In the time of the Kumamoto mainshock, Kyushu electric reported loss of power to about 165,000 customers in the area of Kumamoto. From Saturday (the day of the mainshock) to Tuesday, a number of customers still reported that their power was not back on. Major substations were located in the safe zone during the earthquake and did not experience any damage. This meant that the power could still be restored easily, despite the earthquake in Kumamoto.
Loss of telecommunication was also present during the Kumamoto earthquakes, like there would be in most other similar disasters. This is because telecommunication usually overloads in any natural disaster, due to the heavy and sudden traffic volume. After the initial shocks of the Kumamoto earthquakes, the three major service providers of the area set up temporary Wi-Fi set-ups around the area that was affected, allowing free cell phone access to anyone that ad range. Restoration of water tanks is slightly more difficult. The heavily shaken area of Mashiki was visited immediately days following the earthquake. In this time, water was noticed to be leaking in streets to the heavily damaged area of Mashiki. Similar to water systems, gas systems is susceptible to damage in buried pipelines. Gas was shut off in the Kumamoto region after the initial earthquake. Gas service was expected to require more than a week for restoration in the heavily shaken Mashiki Valley as testing for leaks is a necessary precaution. The most common effect/damage that natural disasters such as the Kumamoto earthquakes have are related to transportation. Rail service to central Kyushu was closed for a prolonged period of time after the earthquake occurred. Kumamoto Airport northeast of the City closed, due in part to non-structural damage within the terminals. A few flights were resumed to the airport on Tuesday and Wednesday. The airport generally escaped significant structural damage. Restoration within the terminals focused on repairing isolated areas of ceiling damage and clean-up of fallen merchandise in f ood and shopping marts. Concrete shear walls in the buildings’ core suffered shear cracking, but far short of serious structural damage. The main north-south Kyushu Expressway was closed south of the town of Tamana due to damage at bridges and overpasses. Traffic detoured on two-lane peripheral highways, causing delays of hours. Only the fact that the mountainous and agricultural area of central Kyushu has only a moderate population density allowed traffic to move at all.
Extensive ground disturbances occurred during the Kumamoto earthquakes. This will affect future sustainability of ecosystem services. Numbers of earthquake-initiated landslides per unit area were higher in grasslands than forests, and mostly initiated on ridgelines and/or convex/planar hillslopes. Most landslides travelled short distances and did not originally become more into debris flow. Fissures along ridgelines might stimulate the water ingress and induce future landslides and debris flows that affect residents downstream. Native grasses are at risk because of habitat fragmentation caused by ground disturbances, extensive damage to rural roads, and abandonment of traditional pasture management practices. Sustainable management of affected areas needs to consider future risk of cascading hazards and long-term socioeconomic impacts.
The sports complex that is located in the town of Mashiki was used for shelter and protection in the widely damaged area. The sports complex was a relatively new structure, and only experienced minor cracking and damage. An investigation of the Kumamoto earthquake was also made four days after the 7.0 earthquake of the Kumamoto earthquakes. The airport is located west of the City of Kumamoto, and north of the town of Mashiki. The recorded Mashiki ground motion had peak accelerations of 1.18g in an East-West direction, 0.67g in a North-South direction and 0.89 in a vertical direction. These are extremely high records. The image on the left summarises the ground motions that were experienced near the epicentre of the Kumamoto earthquakes. After six days of the mainshock event of the Kumamoto earthquake, the domestic area of the airport was operating, although the international terminal (which is older) was still closed as the damage that was done to this area was extremely high. Although, parts of the newer terminal was also closed off as staff were still cleaning up the damage that resulted from the extreme tremors.
The Kumamoto earthquakes were so destructive, that they caused several landslides to occur in the areas that were affected. The area that was most affected by the landslides were terrains with significant slopes, containing a high concentration of aftershocks. The Kumamoto earthquake resulted in several landslides around the Minamiaso village, occurring in slopes steeper than 25 degrees. The largest landslide which was a result of the Kumamoto earthquakes occurred in the western caldera wall, which damaged national route 57 and the Hohi line of the Japan railway. Various sorts of earthen damaged also occurred, as well as natural slopes. Various roads experiences severe damage, causing it to be closed to prevent vehicles from damaging, and for individuals to be safe. A large landslide also occurred behind Okhirihata bridge. Surface ruptures also appeared in the mountain at south of the landslide. The distance between these two were approximately 200 metres. This reveals that the landslide was affected by the strong motion due to the earthquakes, instead of the fault rupturing. The Shimokomori pond is a relatively small irrigation pond which was also affected during the earthquake. A minor section of its north bank was breached in the earthquake and the water that was present flowed into a rice field. This pond is located on the extension of the Futagawa fault trace. Although, the relation of this to the earthquake is not entirely clear, as the surface ground rupture diminished before reaching the pond.
Six bridges and a tunnel was investigated to be found damaged due to the result of the Kumamoto earthquakes. The Okhirihata dam bridge is located near the north-eastern dam of Okhirihata. The bridge was found compressed in its axial direction. Although, the damage that the earthquakes had on this structure was not significant. The Kuwazuru Bridge is a 160 metre long cable stayed bridge. The deck of the bridge was originally pinned against the beam of the X-shaped tower. The deck was detached from the tower and had been moved sideways to the north direction. So, the entire deck moved apart from the south-eastern incline column of the tower. After the earthquake, the deck was found bent downward, and the other end was found lifted upwards. Surface ruptures were found, and showed right-lateral offset. They were diagonal to the south-eastern side of the bridge. This therefore revealed that the intensity of the ground shaking, as well as the surface ruptures contributed to the damaged upon the bridge. The Oginosaka bridge is 128 metres long, and is curved slightly to the west direction. There was displacement that was measured in the transverse direction from the bridge. It measured to be approximately 30 cm in the north side of the bridge. Surface ruptures could also be seen towards the bridge, which means that the damage that was caused to the bridge might’ve been because of the fault that ruptured. The Tawarayama tunnel has a length of 2,057 metres. Diagonal cracks were present on both of the concrete sides, and there were large amounts of concrete that came off the joint of the lining.
Scientists discovered a surface rupture concentration zone (RCZ), which formed three ruptures bands with several surface ruptures and landslides which extended from west to the centre location of the Aso Volcano region. The magmatic volcanic vents that formed during are situated along the north margin of the RCZ. There is a strong relationship between the volcanic vents and fault structures in the central cones of Aso volcano. The Futagawa faults extend about 64 km in length from the Uto Peninsula to Aso caldera. These are separated into three categories: Futagawa, Uto, and the northern coast of the Uto Peninsula. The Futagawa fault and related faults included in the Futagawa segment, which were oriented NE–SW on the western flank of Aso caldera. This affected the edifice of the central cones of Aso volcano. In the western region of Aso caldera, earthquake surface ruptures, hereafter referred to as surface ruptures, appeared on the Kitamukiyama ridge. Movement along these faults created numerous ground fractures observed in Minamiaso village at the western side of the central cones of Aso volcano. In addition, many landslides occurred on the central cones of Aso volcano and its caldera walls.
There have been a variety of observed occurrences after the 2016 Kumamoto earthquakes. There have been various hydrological changes in the area in which the Kumamoto earthquakes took place. This includes various aspects like lakes drying up, as well as groundwater level dropping and rising (fluctuating). There were also water quality changes that were found before and after the earthquake. Sandy soils that were normally stable and supportive were able to mix with the water during the Kumamoto earthquakes, which creates a substance which is similar to quicksand. The result of this is liquification, which can come in many forms. The sideways movement of the large areas of the soil can move from 10 to 150 feet, which resulted in the damage of underground pipelines. Soil would usually support a building such as a structure. When the soil liquified in during the earthquakes, the buildings experienced loss of that support, which allowed the structures to settle down and tip slightly. The earthquakes that occurred were also able to modify the groundwater flow that is origina lly present. This is done when the earthquakes cause the contraction and expansion of the aquifer from which the spring is able to be flown. This change either permanent or temporary. Water was also collected upon a depression along the strik-slip fault like of the Kumamoto earthquakes.
Scientists were able to find immense changes in the ionosphere, 10 days before earthquakes occurred in areas like Japan. The changes that they had measured involved electromagnetic signals. This includes, the conductivity of the air, ionizing radiation levels, disturbances in magnetic field, low frequency waves, and many more other components. Scientists are not completely sure of what caused this as yet. Through the satellites that they used, they were able to hypothesise that, when pressure builds up at a fault line, it releases a measurable amount of radon gas. Seven deep groundwater samples were collected in the Futagawa-Hinagu fault zones, eleven days after the mainshock of the events. Helium and neon substances were measured by conventional mass measures. They showed that the Futagawa-Hinagu fault zones contained mantle helium contributions.
Predictions on the likely recurrence (happening again) of the tectonic process
The Meteorological Agency warns that an earthquake similar to the intensity of the Kumamoto earthquakes can occur anytime, anywhere near where it occurred originally. There are various aftershocks that took place since the occurrence last year. 4291 aftershock earthquakes have occurred since the big occurrence of the Kumamoto earthquakes. The earthquake research committee of Japan had estimated previously that the chances of an earthquake with the magnitude above 6.8 hitting in the next 30 years in Futagawa and Hinagu fault zones was 7-18 percent. Active faults move in cycles of 1,000 to several tens of thousands of years, however, it is impossible to accurately predict when fault-induced quakes will take place. There are many faults in South-east Asia, and have a higher fault-slip rate than the fault that moved during the Kumamoto earthquakes, and will generate an earthquake every few hundred years. Some of these have not ruptured in hundreds of years, which means it is likely that they will in the coming future. In Kumamoto, earthquakes measuring 6.3-6.5 occur every 50 to 100 years. These earthquakes had a similar result to the recent 2016 Kumamoto earthquakes, so this was not an unusual event. The Headquarters for Earthquake Research Promotion of the Government of Japan, were able to evaluate the seismic process over a long term. The evaluated the seismic potential in 2002, and again in 2013. A research group published that they studied over 97 active faults across the country of Japan. They found out that an active fault causes a major earthquake once every 1,000 years. According to this statistic, the probability of a major earthquake occurring is relatively low. This gave people a false sense of security, as the Kumamoto earthquakes occurred a few times on the same fault. The criticism that was released to the group of researches lead them to re-investigating. The group of members decided to use a probability ranking system, indicating the level of risk among the active faults. It labelled the faults with 3% or higher chance of having a big earthquake within 30 years as a particular pronumeral, and those with a less chance as another. Although, there are other active faults near the desig nated faults and movement along any of these can occur at any time. Researched then began publishing the probability according to the region. After determining the overall probability, they c ame to the conclusion that before the Kumamoto earthquake occurred, there was a 18-27% chance of a large earthquake in central Kyushu, and the areas neighboring Kumamoto.
The seismic activity around Japan is extremely high, meaning disasters related to tectonic plates (earthquakes) are extremely common. Long term forecasts are made in terms of the probability of future earthquakes in a particular area. If earthquakes of similar size recur more or less regularly, the time dependant probabilities are calculated from the average recurrence interval. Japan is located in the ‘Pacific Ring of Fire’. This is where tectonic activity is extremely high. This is the most active earthquake belt. The Ring of Fire consists of several tectonic plates — including the Pacific Plate beneath the Pacific Ocean and the Philippine Sea Plate — mash and collide. “The Earth’s surface is broken up into about a dozen or so major chunks that are all moving around. Where they all interact at their edges, interesting things happen,” The Kumamoto earthquake seems to have been caused by the Philippines Sea Plate diving underneath the Eurasia Plate, according to Paul Caruso, a geophysicist with the USGS. This tells us that the tectonic activity of Japan is extremely high, and earthquakes are more likely to occur, and recur there.
The map below indicated information on the likely predictions of a similar earthquake (to the Kumamoto earthquakes) occurring in various areas in Japan. It was released in 2018, and is an earthquake forecast map for Japan. The earthquake forecast map is created using information provided based upon the evaluation results of ocean trench earthquakes and fault type earthquakes (Kumamoto earthquakes). Many of the cities located in Japan are over coastal plains which are originally formed by sandy sediments and clay soil deposits. Th ground is extremely soft and is prone to the lateral motion that occurs during earthquakes.
Technology used to measure the impact on the local environment
Earthquakes are measured according to the Richter Scale. In the case of the Kumamoto earthquakes, the first earthquake that occurred measured to be a magnitude of 6.5, and the one following that was measured to be a magnitude of 7.3. Although, according to Japan’s earthquake intensity scale, different intensities are shown. The intensity scale offers the opportunity to communicate the intensity of the feeling, which means that immediate indication for possible consequences is far more efficient than the magnitude scale. Japan’s Meteorological Agency seismic activity scale is a seismic scale that is used by japan to measure earthquakes and seismic waves. It is measured in the units called ‘shindo’. Other scales such as the Richter scale describe the energy that is released during an earthquake, the Japanese Meteorological Agency (JMA) describes the degree of the shaking that is present on various points on the Earth’s surface. The intensity of the earthquake is not fully determined by its magnitude, since it various with the event’s depth, and distance from the event. The JMA currently operates a network of 180 seismographs and 627 seismic intensity meters. This provides a live earthquake report to the media and internet. Japan experiences approximately 400 earthquakes every day, but the majority of them are are shindo scale “0” or less and are able to be detected by using specialist resources. The JMA first came up with a ‘scale’ consisting of four stages, with the levels: ? (faint), ? (weak), ? (s trong), and ? (violent). In 1898 this scale was changed to a numerical system, assigning earthquakes levels 0–7. In 1908, the levels present on this scale were given descriptions, and earthquakes were assigned levels based on the effect it had on people. This scale was widely used during the Meiji period, and revised during the Sh?wa period. Following the Great Hanshin earthquake in 1995, the first time an earthquake had received the highest rating of 7 on the scale, levels 5 and 6 were divided in two, giving a total of 10 levels of earthquake: 0–4, lower/upper 5, lower/upper 6 and 7. The Shindo scale has been used in Japan from 1996 without change. The JMA scale has levels that run from 0-7. This means that the lower the number, the weaker the earthquake is. Live earthquake reports are calculated automatically from measurements of ground acceleration. The earthquake level is reported using the JMA based on the ground acceleration, measured automatically with seismic intensity meters. There is no simple and linear relationship between Shindo Number and peak ground acceleration as Shindo Number also depend on duration.
Earthquakes are recorded by a seismic network. There are seismic stations in the networks which measures the movement of the ground in the particular area. In an earthquake, the vibrations are measured by measuring the rock over another rock which releases energy and causes the ground to vibrate. The vibration that is caused pushing the piece of ground, which causes it to vibrate. The energy carries out from the earthquake into a seismic wave, and passes through the seismic station. Seismologists know how fast the seismic waves travel through the earth, and can therefore calculate the time corresponding to the occurrence of the earthquake, by comparing it to the shaking that was recorded. A seismograph is able to produce a graph-like representation of the seismic waves that were recorded. These convert this information to a seismogram, and can be used to determine how strong the earthquake is. The method that is taken place has to be straightforward and simple for seismologists.
Earthquake waves can vary from small to extremely large. Having the right tool to measure the range of the earthquake waves is important. A common method that is used to measure weaker ground vibrations is by the measurement of displacement or velocity of the ground during an earthquake. Ground acceleration is measured if an earthquake has more severe ground vibrations. Engineers use computer models of buildings to different representations of earthquake waves to determine the performance of the building. If needed, they are able to adjust their design and feel confident the building can withstand certain levels of earthquake motion.
The oldest scale to measure the intensity of earthquakes is the Mercalli Intensity scale. In this, earthquakes are describe as what the nearby residents feel. This is similar to the Japanese version of the intensity scale, which was used to measure the Kumamoto earthquake. This scale is more so based upon the visual damage of the earthquake, instead of relating to the literal energy released during it. Nowadays, the Richter scale is used to measure earthquakes for its accuracy and reliability. The magnitude of the earthquake is measured by the logarithm of the amplitude of waves recorded by seismographs. On the Richter scale, the magnitudes are expressed as either whole numbers or decimals.
The moment magnitude scale (MW) is one example of many seismic measuring devices. In comparison, the formulas of this scale, and the Richter scale are different. The values of them are although similar. The moment magnitude scale is now the most common method for measuring medium to large earthquakes. Although, this scale is not used regularly to measure smaller earthquakes that commonly occur. This scale is based upon the total movement released in an earthquake. Moment is the product of the distance a fault moved, as well as the force that was required to do this. This is provided by the modelling recordings of the earthquake, although at different stations.
The Shindo scale:
Magnitude-Shindo Number Effects on people Indoor situations Outdoor situations Residences Other buildings Lifelines Ground and slopes Peak ground acceleration
0 (0) / 0–0.4 Not felt by individuals as tremor is not present Indoor objects will not shake due to the lack of tremors Buildings will not receive damage as tremor is not present Less than 0.008 m/s² as there are extremely low tremors
1 (1) / 0.5–1.4 Felt by only some people indoors, as the tremor is low but can be felt slightly Objects may swing/rattle very slightly, as tremor causes minor vibrations The top sections of multi-story buildings may feel the earthquake, as slight tremor and vibrations are present. 0.008–0.025 m/s² as the tremors are low, and ground acceleration is extremely low.
2 (2) / 1.5–2.4 Felt by many to most people indoors, as tremor is slightly more prominent Hanging objects such as lamps swing slightly, as the tremors result in minor vibrations Homes and apartment buildings will shake, but will receive no damage, as vibrations are not strong enough to cause damage, although can be felt. No buildings receive damage, as the tremors and vibrations are not strong enough, although they can be felt. 0.025–0.08 m/s², as tremors result in slight increase of prominent acceleration.
3 (3) / 2.5–3.4 Felt by most to all people indoors, as tremors become very prominent. Objects inside rattle noticeably and can fall off tables, as tremors result in prominent vibrations causing motion indoors Electric wires swing slightly. People can feel it outdoors, as vibration are more present and are resulting in movement of objects. Houses may shake strongly. Less earthquake-resistant houses can receive slight damage, as tremors are capable of doing slight damage to buildings due o increase of vibration. Buildings may receive slight damage if not earthquake-resistant. None to very light damage to earthquake-resistant and normal buildings. No services are affected. 0.08–0.25 m/s² as tremors become even more prominent.
4 (4) / 3.5–4.4 Many people are frightened. Individuals try to escape from danger., as the vibrations become more intense Hanging objects swing considerably and dishes in a cupboard rattle. There are very loud noises present due to the movement of objects from the tremors and vibrations. Electric wires swing considerably. People outside can notice the tremor. Less earthquake-resistant homes can suffer slight damage. Most homes shake strongly and small cracks may appear. The entirety of apartment buildings will shake. The vibrations become more dangerous and individuals have to exit the buildings. Other buildings can receive slight damage. Earthquake-resistant structures will survive, most likely without damage. Electricity may go out shortly due to the disturbance of powerlines etc. No landslides or cracks occur as the earthquake is not strong enough to do so. 0.25–0.80 m/s², acceleration becoming very prominent.
5-lower (5) / 4.5–4.9 Most people try to escape from danger by running outside. Some people find it difficult to move, due to the higher intensity of the earthquake. Hanging objects swing violently. Most unstable items fall. Dishes in a cupboard and books fall and furniture moves. The vibrations are fully capable of damaging inside structures. People notice electric-light poles swing. Occasionally, windowpanes are broken and fall, unreinforced concrete-block walls collapse, and roads suffer damage. Less earthquake-resistant homes and apartments suffer damage to walls and pillars due to intense vibration intensities. Cracks are formed in walls of less earthquake-resistant buildings. Normal and earthquake-resistant structuresreceive slight damage. A safety device can cut off the gas service in some residences. Sometimes, water pipes are damaged and water service is interrupted. Electricity can be interrupted. Cracks may appear in soft ground, and rockfalls and small slope failures take place. 0.80–1.40 m/s²
5-upper (5?) / 5.0–5.4 Many people are considerably frightened and find it difficult to move, as the vibrations cause severe discomfort and possible damage. Most dishes in a cupboard and most books on a bookshelf fall. Occasionally, a TV set on a rack falls, heavy furniture such as a chest of drawers fall, sliding doors slip out of their groove and the deformation of door frames makes it impossible to open doors. Unreinforced concrete-block walls can collapse and tombstones overturn. Many automobiles stop because it becomes difficult to drive from the shaking. Poorly installed vending machines can fall. Less earthquake-resistant homes and apartments suffer heavy/significant damage to walls and pillars and can lean. Medium to large cracks are formed in walls. Crossbeams and pillars of less earthquake-resistant buildings and even highly earthquake-resistant buildings also have cracks. Gas pipes and water mains are damaged. (Gas service and/or water service are interrupted in some regions.) Cracks may appear in soft ground. Rockfalls and small slope failures would take place. 1.40–2.50 m/s²
6-lower (6?) / 5.5–5.9 Difficult to keep standing, as shaking of the ground is extreme prominent and individuals cannot balance with the motion. A lot of heavy and unfixed furniture moves and falls. It is impossible to open the door in many cases. All objects will shake violently. Strongly and severely felt outside. Light posts swing, and electric poles can fall down, causing fires. Less earthquake-resistant houses collapse and even walls and pillars of other homes are damaged. Apartment buildings can collapse by floors falling down onto each others. Less earthquake-resistant buildings easily receive heavy damage and may be destroyed. Even highly earthquake-resistant buildings have large cracks in walls and will be moderately damaged, at least. In some buildings, wall tiles and windowpanes are damaged and fall. Gas pipes and/or water mains will be damaged. Gas, water and electricity are interrupted. Small to medium cracks appear in the ground, and larger landslides take place. 2.50–3.15 m/s²
6-upper (6?) / 6.0–6.4 Impossible to keep standing and to move without crawling. Most heavy and unfixed furniture moves and becomes displaced. Trees can fall down due to violent shaking. Bridges and roads suffer moderate to severe damage. Less earthquake-resistant houses will collapse or be severely damaged. In some cases, highly earthquake-resistant residences are heavily damaged. Multi-story apartment buildings will fall down partially or completely. Many walls collapse, or at least are severely damaged. Some less earthquake-resistant buildings collapse. Even highly earthquake-resistant buildings suffer severe damage. Occasionally, gas and water mains are damaged. (Electrical service is interrupted. Occasionally, gas and water service are interrupted over a large area.) Cracks can appear in the ground, and landslides take place. 3.15–4.00 m/s²
7 (7) / 6.5 and up Thrown by the shaking and impossible to move at will. Most furniture moves to a large extent and some jumps up. In most buildings, wall tiles and windowpanes are damaged and fall. In some cases, reinforced concrete-block walls collapse. Most or all residences collapse or receive severe damage, no matter how earthquake-resistant they are. Most or all buildings (even earthquake-resistant ones) suffer severe damage. Electrical, gas and water service are interrupted. The ground is considerably distorted by large cracks and fissures, and slope failures and landslides take place, which can change topographic features. Greater than 4 m/s²
A study was shown that the Shindo scale is more suitable for smaller earthquakes.
The Richter scale is an earthquake scale which measures the magnitude of an earthquake. This scale was based on the seismogram measured by a particular seismometer at a distance of 100 kilometres from the earthquake.
Description Richter Magnitude number Damage caused Frequency of occurrence
Micro Less than 2.0 These are xtremely small earthquakes and individuals are not able to feel these. Approximately 8,000 each day
Very minor 2.0-2.9 Individuals are not able to feel these, but seismographs are able to detect them. About 1,000 per day
Minor 3.0-3.9 Individuals are able to feel the vibrations, but they almost never cause damage. About 49,000 each year
Light 4.0-4.9 Objects inside houses are disturbed, and are able to cause noise. Things are rarely damaged. About 6,200 each year
Moderate 5.0-5.9 Building structures that are not built well may be damaged. Light objects inside a house may be moved. About 800 per year
Strong 6.0-6.9 These earthquakes are moderately powerful. They are able to cause a lot of damage in a larger area. About 120 per year
Major 7.0-7.9 These earthquakes are able to damage objects seriously over larger areas. About 18 per year
Great 8.0-9.9 These earthquakes are able to cause a lot of damage. Heavy objects are thrown into the air, and visible shockwaves are visible. Highways have the capability of being destroyed, and buildings are collapsed. About 1 per 20 years
Meteoric 10.0+ There are no records of an earthquake that is relative to this size. The vibration is about the same as that of a 15 mi meteor. Unknown
Solutions to minimize the disastrous/negative effects of future events
There are various methods that can be taken into consideration to minimize the disastrous effect of earthquakes, or to take precaution of it earlier. Scientists have come up with various solutions. As earthquakes are a natural process and cannot be prevented by humans, individuals can only prevent DAMAGE that originates from it.
Constructing seismic hazard maps includes one of the prevention strategies of damage that is caused by earthquakes. Many regions have the availability of seismic expectancy maps, or hazard maps for planning purposes. The anticipated ground intensity is shown by a number called the peak velocity or peak acceleration. The most common solution to minimise the effect of earthquakes is to build buildings that can withstand the intensity of the ground shaking by an earthquake. Earthquake resistant buildings have several scientific components which help the buildings create less damage to the surroundings during the earthquake. In the recent years, the knowledge and understanding of earthquake resistant structures has increased drastically. Although this is true, it is certainly not a new topic that scientists have been discussing about. There are several ancient structures that are still standing today, despite the natural phenomenon that they have been through. The techniques that are used to build structures today are different, although the concepts and principles are fairly the same. Anti-seismic technology is considered to be very advanced in today’s engineering field.
Isolation systems or base isolation is a technique that was developed to minimise the damage of buildings during an earthquake. It has been used by not only Japan, but also India, N ew Zealand, Italy, and also the USA. A building that is base fixed moves with the earthquakes motion. This means that there is most likely to be less damage. On the other hand, a building that is not fixed base is more likely to experience damage, as it cannot sustain the movement and vibrations. When a building is built isolated from the ground, resting on pads known as base isolators, it will only move a little or not at all during an earthquake. The building isolators work similarly to car suspensions, allowing a car to travel over a rough ground, without the car being bumped side to side. Base isolation technology can make medium-rise stone or brick, or even reinforced concrete structures to withstand earthquakes, which protect them and the people within it from major damage or injury. It is not suitable for all types of structures and is designed for hard soil, not soft. Base isolators are one of the most powerful tools of earthquake engineering, and in some cases can improve structure’s seismic performance, as well as seismic sustainability. Although base isolators can significantly cause less damage to the environment and the building itself, is it NOT earthquake-proof. The base isolation system consists of isolation units, as well as with or without isolation components. Isolation units are the basic elements of the base isolation system which are incorporated to provide a decoupling effect to a particular structure. Isolation components are the connections that are present between isolation units and their parts. Base isolation can be used at a large or small scale. For example, it can sometimes be used only in a single room. These techniques that are present in the seismic base isolators reduce the seismic forces by altering the stiffness or damping within the structures. The most effective way to control movement with base isolators is to use members. These have hysteretic energy damping capability. Mechanical equipment have been developed for this reason, using the plastic deformation of steel and lead. There are various types of bearings that are used in base isolators. They vary depending on the material that they are made of, as well as several other properties that they have. The types that are used the most include Rubber bearings, High Damping Natural Rubber Bearings and Steel Laminated Rubber Bearings. Rubber bearings have steel laminated rubber. Elastomeric bearings are widely used as seismic isolators. Some Japanese engineers have taken the concept of base isolation, and turned it into something even more advanced. The system that they have come up with involves the structure levitating on air. Sensors on the building are quick to detect the vibration from an earthquake. The sensors communicate with the air compressing technology. Within half a second of being aware of the situation, forces air between the foundation. When an earthquake hits, the foundations are able to move without moving the structure that is situated above it. The cushions of air that are present, are able to lift the particular structure up 3 centimetres from the ground. This isolates the structure from the ground which is shaking during the earthquake, causing minimal to no damage to the structure, and the individuals within it, and its vicinities.
Active control systems is based upon providing a continuous energy from the outside. Ultimately, this means that the cost of implementing these systems is extremely high. The active control system has the capability to control the acceleration, displacement or velocity of the particular structure. Active control systems consist of electronic devices such as computers, actuators and starters. The design of active control systems is independent from the intensity of the ground movement. The system is able to alter its rigidity or the amount of motion that is present according to the intensity of the ground motion. There are three main application forms of active control systems. In the Active Mass Damper system, by forming actuator control force, the acceleration, displacement and velocity of the structure affected by lateral forces are controlled by computer systems. In the Active Variable Stiffness, there is no need for forming of actuator control force. Although, the resonance that results from coinciding of fundamental period of the system and ground motion period depends on choosing the appropriate rigidity for the system and making the corresponding design. They are developed for utilization in case of strong ground motion. Active Passive Composite Tuned Mass Dumper: The hybrid structural control systems, which were developed in the recent years, are based on joint utilization of both active and passive systems.
Passive control systems are able to operate without the use of external energy sources. Ultimately, this means that the implementation cost of the passive control system is less then that of an active control system. These systems are only able to control the displacement to a particular limit. Passive control systems are designed accordingly to the intensity of the earthquake, as well as the magnitude of it. The Passive Control Systems are composed of dampers, isolators, and various other devices that can easily be implemented into the system. Passive control systems are consisted of many other types of sub-systems. Irreversibly displacement systems are composed of rolls, which can enable the structure to move horizontally during an earthquake. Sliding systems are frequently used in applications as they are easy to construct and have a reasonably low cost. However, when these types of systems are used in structures, there is the possibility for the building to move from its original location after the earthquake as there is excess drifting present. For that reason, elements such as stoppers may be required. They consist of sufficient number of rolls that are placed perpendicular to each other or spherical steel balls between the steel plates. Plastic systems are also implemented, by benefiting from the plasticity of lead, that provides ideal energy absorption for seismic isolation and other vibrations. In these systems, usually there is a cylinder that contains lead and a piston that moves with difficulty inside that cylinder. The lead in the cylinder limits the motion of the piston, so that absorption of the energy is achieved. Lead extrusion dampers are generally used for controlling the major displacements. Elastic systems have two distinct direct behaviours, which are the rigidity of the structural element and the sum of the structural rigidity and isolator rigidity. Rubber or neoprene dampers are commonly used, and are able to be considered as the examples of such systems. The isolation of the structure from the movement and vibration of the ground is normally implemented by placing these dampers between the foundations and the columns. Viscous systems consist of a polymer liquid. This is placed between the two cross-sections. Displacement occurs during an earthquake. When this occurs, the deformation of the viscous absorbs the vibrations that are present during the earthquake. Viscous systems can be in the form of the common shock absorbers. They function by moving of a vertical steel plate containing viscous liquid that is suspended from the top storey floor between two open-top plates which are fixed on the floor of the lower storey. Kinematical systems are systems such as balls, rolls. These components have a distinct geometrical structure. These allow them to return to their original form. These characteristics enable the structure to move in a ‘concave elliptic nest’. These are egg-shaped concrete elements, placed between two rigid plates and columns with elliptic edges. Friction sliding systems are based upon the characteristics of friction. This system is used as both base isolation systems between the foundation, as well as the columns themselves. Friction sliding system is used in bearings. In the case of seismic loading, the dissipation of energy is obtained by the friction forces that occur while the system moves on the sliding friction components. Friction sliding systems can be used as friction devices that are placed in the intersection points of the steel braces in the building. Steel hysteretic systems are developed using the knowledge of the advantages of torsion and the bending characteristics that are present in steel. Steel torsional beams, honeycomb as well as nodal dampers combine the characteristics that are present in steel, are able to allow a massive amount of energy dissipation, bending and torsion. On the other hand, characteristics of lead and rubber allow displacement, and have an accurate quality that allow for energy absorption. Honeycomb dampers are made from several steel damper plates, and take the shape of a honeycomb, hence its name. These dampers are usually placed in places such as walls and columns. By using this method, they dissipate the vibration energy by forming a proportional motion.
A shock absorber is able to control the unwanted spring motion in vehicles and can be applied as a solution to minimise damage caused by earthquakes on structures. This is known as damping. To apply this to an earthquake situation, engineers generally implement these dampers on the columns and beams. Each damper is composed of a piston head that moves inside a cylinder filled with silicone oil. When an earthquake strikes, the horizontal movement of the building causes the piston in each damper to push against the oil, transforming the quake’s mechanical energy into heat. Damping can be in the form of many things. Another solution is to take away a large amount of mass near the top of the tall structure, while the steel cables support the mass and viscous liquid dampers are situated near the mass and the building. Seismic activity will cause it to sway, although the pendulum that is created will move the opposite direction, which will ultimately dissipate the energy.
Many new tall buildings use the technique of core-wall construction. This is implemented as a solution to improve seismic performance, although at a much lower economic impact (cost). A concrete core runs along the main part of the structure. The core-wall strategy is a good performing solution, although man have reported that it is still not perfect. This is because even when this method is implemented, deformation still occurs and slight damage is still present. A better solution of this would be to combine the base isolation and rocking-core. This will most definitely lower the damage and deformations caused by the tremors, in comparison of just using the core-wall construction method by itself. While the use of these technological facilities is extremely advanced, engineers have also been inspired by the animal kingdom. Underwater, mussels create sticky fibres known as threads, which come in the form of either rigid and hard, or flexible. These threads are able to be mimicked as a component that can absorb shock. When waves make contact with mussels, it stays on the spot as the fibres that they create absorb the shock and dissipate the energy. Researchers have in fact calculated the ratio of stiff fibres, to flexible fibres that are present. This ratio is 80:20. All engineers have to do now is develop construction materials that mimic the mussel and its ability to stay in place. Another interesting yet useful thread comes from spiders. Scientists believe that it’s the response of the natural material under heavy strain that makes it so unique. When researchers tugged and pulled on individual strands of spider silk, they found the threads were initially stiff, then stretchy, then stiff again. It’s this complex response that makes spider webs so resilient and spider thread a perfect material to mimic in the next generation of earthquake-resistant construction.
A small group of researchers have previously prevented a large portion of damage by using technology to detect earthquakes ahead of time. They used satellites to look at the ionosphere, which is filled with electrically charged particles. They found immense changes in the ionosphere, 10 days before earthquakes occurred in areas like Japan. The changes that they had measured involved electromagnetic signals. This includes, the conductivity of the air, ionizing radiation levels, disturbances in magnetic field, low frequency waves, and many more other components. Scientists are not completely sure of what caused this as yet. Through the satellites that they used, they were able to hypothesise that, when pressure builds up at a fault line, it releases a measurable amount of radon gas, trapped in air pockets. This is a radioactive gas and may be the reason why it disturbed the electromagnetic signals in the ionosphere. Their mission consists of spotting electromagnetic signals with two satellites a couple kilometres apart with one satellite. When the other satellite shows up, they will ‘triangulate’ the spot from where the signals are coming from. Although this is only a hypothesis, there have been various other occurrences where many lives have been saved due to the early detection of earthquakes. Currently, Japan has the most extensive and advanced early warning systems. The Earthquake Early warning system (EEW) is a warning that is issued when an earthquake is detected in Japan. These are normally issued by the Japan Meteorological Agency, as well as the guide on how to react and act upon the upcoming earthquake. There are two Early Earthquake Warning (EEW) systems. One is for the public, whilst the other one is for the National Meteorological and Hydrological Services. When a P-wave is detected from the seismometers installed all over Japan, the JMA analyses and predicts the approximation of the epicentre of the upcoming disaster. This allows the JMA to report individuals in affected and vulnerable areas through the use of TV or radio. This is only usually when a strong or destructive earthquake is detected. An Earthquake Early Warning alert is spread, in order to alert the public about the situation. This is only done when an earthquake of higher than 5 on the Japanese Seismic Scale is detected. This is equivalent to 3.5 on the Richter scale. The EEW was developed to warn individuals prior to the earthquake event, so that they can seek shelter, and so transport and various other facilities are stopped for safety of individuals.