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Earthquakes are generated when a fault on the edges of the plates occurs. That is, part of the edges of the plate breaks. The breaking causes shaking on the plates that are felt on the surface. This shaking is what we call earthquakes. When part of the plate breaks during the collision, shifting of the ocean floor happens. During the shifting, energy is released. This energy pushes the ocean water above. When this ocean water reaches the shores, we call them tsunami. During subduction, as plates reach the mantle, it will eventually be melted as magma. When these magmas find a weak spot in the crust, it forms a volcano. This volcano erupts when the crust cannot withstand the pressure exerted by the magma. Earthquakes, tsunami and eruption of volcanoes are natural disasters brought by the activity of the subduction zone. These natural disasters may cause the loss of lives, damage to properties, displacement to other areas, and livelihood.
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The collision of oceanic and continental crust as well as the collision of two oceanic crust results in the formation of trenches and volcanic arcs. This will also result in the generation of earthquakes, tsunamis and volcanic eruptions. Earthquakes are generated when a fault on the edges of the plates occurs. That is, part of the edges of the plate breaks. The breaking causes shaking on the plates that are felt on the surface. This shaking is what we call earthquakes. When part of the plate breaks during the collision, shifting of the ocean floor happens. During the shifting, energy is released. This energy pushes the ocean water above. When this ocean water reaches the shores, we call them tsunami. During subduction, as plates reach the mantle, it will eventually be melted as magma. When these magmas find a weak spot in the crust, it forms a volcano. This volcano erupts when the crust cannot withstand the pressure exerted by the magma. Earthquake Hazards There are so many things that can happen during or after an earthquake. There are surface rupture and physical damage to buildings and other infrastructures, liquefaction, fire, landslide, and tsunami. Surface rupture and physical damage is the most obvious hazard of an earthquake the ground to break and buildings to collapse. Urban areas would experience more Earthquakes with higher energy create stronger ground motion, which can cause of this damage due to the presence of more infrastructures. Liquefaction occurs in areas where the soil becomes saturated with water. During an earthquake, the movement of the ground may loosen the soil and allow more water to seep in between the particles. This decreases the ability of the soil to support structures that are resting upon it. When it can no longer support a building, instead of being toppled over, the building starts to sink. Liquefaction mostly occur in reclaimed lands, which were once a part of a body of water. Fires can break out during or after an earthquake due to damaged or broken utility lines, substations, and power plants. It can also occur when ground rupture breaks gas tanks or pipes that lead to gas leaks. Tsunami or a harbor wave is an earthquake hazard that is generated when earthquakes occur on the seafloor. Tsunami displaces large volume of water from the sea to the land, causing damages in the cities and communities near the shore (figure 4-2).Earthquake Hazards There are so many things that can happen during or after an earthquake. There are surface rupture and physical damage to buildings and other infrastructures, liquefaction, fire, landslide, and tsunami. Surface rupture and physical damage is the most obvious hazard of an earthquake the ground to break and buildings to collapse. Urban areas would experience more Earthquakes with higher energy create stronger ground motion, which can cause of this damage due to the presence of more infrastructures. Liquefaction occurs in areas where the soil becomes saturated with water. During an earthquake, the movement of the ground may loosen the soil and allow more water to seep in between the particles. This decreases the ability of the soil to support structures that are resting upon it. When it can no longer support a building, instead of being toppled over, the building starts to sink. Liquefaction mostly occur in reclaimed lands, which were once a part of a body of water. Fires can break out during or after an earthquake due to damaged or broken utility lines, substations, and power plants. It can also occur when ground rupture breaks gas tanks or pipes that lead to gas leaks. Tsunami or a harbor wave is an earthquake hazard that is generated when earthquakes occur on the seafloor. Tsunami displaces large volume of water from the sea to the land, causing damages in the cities and communities near the shore.Volcanic Eruptions Earthquakes are sometimes used in predicting volcanic eruptions. An earthquake alerts the authorities to observe a nearby volcano. When a volcano shows signs of eruption, evacuation of the nearby villages should be immediately implemented Active volcanoes are the ones that are usually closely monitored by volcanologists These are commonly located along plate boundaries specifically along the Pacific Ring of Fire. The Philippines is one of the countries that have a lot of volcanoes. The Pacific Ring of Fire is a region in the Pacific where most active volcanoes are located. The dots in the figure represent the active volcanoes in the world. Active volcanoes are those that have a recorded volcanic eruption in their history. There are two types of volcanic eruptions depending on the magma composition: the explosive type and the Hawaiian or nonexplosive type. The types of eruptions depend on the viscosity and amount of dissolved gases in a magma. Explosive eruptions have magma that is highly viscous and contains large amounts of dissolved gases. On the other hand, the Hawaiian type or nonexplosive eruptions have magma that has low viscosity and low amount of dissolved gases. Viscosity determines the ability of magma to flow. The lower the viscosity, the easier it is for the magma to flow. This viscosity of the magma is affected by silica content and temperature. Low-temperature magma with high silica content are highly viscous, high-temperature magma with low silica content has low viscosity. Therefore, in explosive eruptions, the magma could not easily get out of the vent. This impedes the remaining magma below, causing an increase of pressure. Once the pressure is released. an explosive eruption occurs. Volcanic Hazards Explosive volcanic eruptions release pyroclastic flows and materials that are considered to pose the greatest threat. The pyroclastic flows often render people in a shock state since they become overwhelmed with what they are seeing Too much pyroclastic material (eg., tephra), may bury people and severely damage the agricultural land and livestock. Damaged agricultural land could lead to famine. After an eruption, pyroclastic materials that have settled along the slope of the volcano get mixed with rainwater. This would start a mudflow or lahar moving at high speed, destroying everything along its path. Poisonous gases are also released by volcanoes. These gases can be lethal to people, animals, and plants. Just like earthquakes, violent volcanic eruptions may also happen underwater, which can trigger a tsunami. What is an earthquake? Would you be surprised to learn that several million earthquakes happen every year? Seriously. Most are so small in magnitude or size that we cannot even feel them. In fact, only 20 earthquakes are efficiently reported each year in the United States Geological Survey. Wow! That is a huge difference! The Earth has four major layers. Inner core, outer core, mantle, and crust. Think of the crust and top of the mantle like the skin of the earth. This skin is made up of different pieces of rock called tectonic plates. There are about 15 major slabs that join together, kind of like a puzzle. The edges around the tectonic plates are called plate boundaries. These massive pieces of rock slide back and forth under the Earth's surface, bumping up against each other and creating a lot of tension. This tension and movement create faults, which are basically huge cracks in the rock. When the faults get stuck, they build up pressure. And when they get unstuck, you guessed it, an earthquake. So basically, an earthquake is caused by the shifting and sliding of tectonic plates on the Earth's upper mantle and crust. There are three ways that tectonic plates shift or slide. They are subduction, lateral sliding, and spreading. Subduction happens when plates crash into each other. This can cause one plate to slide under another and be destroyed. Or the edges of the plate may rise up and form mountains. Lateral sliding means that the plates slide alongside each other, which can create lots of friction. And like you might have guessed, spreading happens when plates move apart from each other. When they do, melted rock between the plates rises and cools, forming new crust. Here's an interesting fact. Nearly 90% of all earthquakes begin in the Pacific Ocean, in an area called the Ring of Fire. It's called the Ring of Fire because along with earthquakes, it's filled with many active volcanoes. More than 450! Earthquakes can be powerful enough to change the surface of the earth and can do a lot of damage. And sometimes earthquakes can even cause other natural disasters, like avalanches, landslides, and tsunamis. Pretty wild, right? The epicenter is the location of an earthquake on the Earth's surface. The closer you are to the epicenter, the more of the earthquake you will feel. Earthquakes lose intensity as they travel away from the epicenter. Scientists measure the intensity of an earthquake using a special device called a seismograph. Seismometers detect and measure the vibrations given off by an earthquake. Magnitude is the number given to record the size of an earthquake. For example, a magnitude 5.5 is considered moderate. Above 8.0 is considered a major earthquake and we see one every year or two. Earthquakes measured at 2.5 or less are usually not felt, but can be recorded. And believe it or not, there are millions that happen each year. You can make a model of a seismograph at home, and we are going to show you how. It's activity time! You can print off directions for this one on our website at learnbright.org. You'll need a cardboard box, string, a plastic cup, a marker, small heavy objects, a long strip of paper, and a friend because this is an activity for at least two people. Now comes the fun part. One friend shakes the box, alternating between hard and soft and slow and fast, while the other friend is pulling the strip of paper through the bottom. Watch the marker as it records the movement. This is exactly what a seismograph does during an earthquake. So, in a way, we have not only created our own seismograph, but our own earthquake as well. Now, we can analyze the data just like scientists. Can you tell how hard the box was shaking based on the line? Can you tell when it was barely shaking at all? You are on your way to becoming a seismologist. A seismologist is a person that studies earthquakes. It's pretty cool to watch the process, but it's even more exciting to do it yourself. You can head on over to our website to get detailed instructions for this activity. Just download the lesson plan and as always have fun! Hope you had fun learning with us! Visit us at learnbright.org for thousands of Hope you had fun learning with us! Visit us at learnbright.org for thousands of free resources and turnkey solutions for teachers and homeschoolers.Japan Where Is It? Japan is made up of a group of islands in the Pacific Ocean. It is just off the east coast of Asia. Japan has four main islands and thousands of smaller islands. The entire country is smaller than the state of California. Tokyo (TOH-kee-yoh) is the capital city of Japan. It is on the largest island, called Honshu (HON-shoo). Tokyo has many tall skyscrapers. More than thirty-two million people live there. People. More than 127 million people live in Japan. The country's main language is Japanese. More people live in cities and towns than in the country. City life in Japan is very busy. Most cities have little space, and people are crowded together. Most people in Japan eat rice. Japan grows much of the rice it uses. The Japanese also catch many fish and sell them across the world. Land. Most of Japan is covered with mountains. The country has more than seventy volcanoes. The most famous one is Mount Fuji (FOO-jee). It has not erupted in many years. Earthquakes are also common. The land near the coast is the only flat land in Japan. Japan's biggest cities are on the coasts. The country has many rivers and lakes. History. Japan is thousands of years old. Ancient Japanese and Chinese people traded things and ideas. Some experts think that Japan learned to grow rice from China. Japanese writing even borrows from Chinese writing. In the past, Japan was an empire. It was ruled by emperors. Later, powerful military leaders called shoguns (SHOH-guns) took control away from the emperors. Samurai (SA-muh-rye) warriors also had power. The samurai were known as brave and skilled fighters. Celebrations. The Japanese New Year is an important holiday in Japan. It starts a week before the first day of January. People send cards for the New Year's holiday. They also clean their homes, and children often get gifts. Food. Rice is an important food in Japan. It is eaten at most meals. Noodles are also served with some meals. Another important food is fish. Japanese people sometimes eat raw fish called sushi (SOO-shee). Conclusion. Japan is a small island country, yet it has many people. It has tall mountains and volcanoes. It also has crowded cities with skyscrapers. Japan is a mix of many things-old and new, large and small.What is the relationship between faults and earthquakes? What happens to a fault when an earthquake occurs? Earthquakes occur on faults - strike-slip earthquakes occur on strike-slip faults, normal earthquakes occur on normal faults, and thrust earthquakes occur on reverse or thrust faults. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. The fault surface can be vertical, horizontal, or at some angle to the surface of the earth. The slip direction can also be at any angle. What is a fault and what are the different types? A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between. Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults. Faults which move along the direction of the dip plane are dip-slip faults and described as either normal or reverse (thrust), depending on their motion. Faults which move horizontally are known as strike-slip faults and are classified as either right-lateral or left-lateral. Faults which show both dip-slip and strike-slip motion are known as oblique-slip faults. The following definitions are adapted from The Earth by Press and Siever. normal fault - a dip-slip fault in which the block above the fault has moved downward relative to the block below. This type of faulting occurs in response to extension and is often observed in the Western United States Basin and Range Province and along oceanic ridge systems. Normal Fault Animation reverse (thrust) fault - a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block. This type of faulting is common in areas of compression, such as regions where one plate is being subducted under another as in Japan. When the dip angle is shallow, a reverse fault is often described as a thrust fault. Thrust Fault Animation Blind Thrust Fault Animation strike-slip fault - a fault on which the two blocks slide past one another. The San Andreas Fault is an example of a right lateral fault. Strike-slip Fault Animation A left-lateral strike-slip fault is one on which the displacement of the far block is to the left when viewed from either side. A right-lateral strike-slip fault is one on which the displacement of the far block is to the right when viewed from either side. Lesson 2: Plate Tectonics There are a few handfuls of major plates and dozens of smaller, or minor, plates. Six of the majors are named for the continents embedded within them, such as the North American, African, and Antarctic plates. Though smaller in size, the minors are no less important when it comes to shaping the Earth. The tiny Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of the United States. The plates make up Earth's outer shell, called the lithosphere. (This includes the crust and uppermost part of the mantle.) Churning currents in the molten rocks below propel them along like a jumble of conveyor belts in disrepair. Most geologic activity stems from the interplay where the plates meet or divide. The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other. They move at a rate of one to two inches (three to five centimeters) per year. Convergent BoundariesWhere plates serving landmasses collide, the crust crumples and buckles into mountain ranges. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya, the highest mountain system on Earth. As the mash-up continues, the mountains get higher. Mount Everest, the highest point on Earth, may be a tiny bit taller tomorrow than it is today. These convergent boundaries also occur where a plate of ocean dives, in a process called subduction, under a landmass. As the overlying plate lifts up, it also forms mountain ranges. In addition, the diving plate melts and is often spewed out in volcanic eruptions such as those that formed some of the mountains in the Andes of South America. At ocean-ocean convergences, one plate usually dives beneath the other, forming deep trenches like the Mariana Trench in the North Pacific Ocean, the deepest point on Earth. These types of collisions can also lead to underwater volcanoes that eventually build up into island arcs like Japan. Divergent Boundaries At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. Mountains and volcanoes rise along the seam. The process renews the ocean floor and widens the giant basins. A single mid-ocean ridge system connects the world's oceans, making the ridge the longest mountain range in the world. On land, giant troughs such as the Great Rift Valley in Africa form where plates are tugged apart. If the plates there continue to diverge, millions of years from now eastern Africa will split from the continent to form a new landmass. A mid-ocean ridge would then mark the boundary between the plates. Transform Boundaries The San Andreas Fault in California is an example of a transform boundary, where two plates grind past each other along what are called strike-slip faults. These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes, such as the 1906 one that devastated San Francisco.