An aftershock is in the same place of the main shock but always of a smaller magnitude. Ī foreshock is an earthquake that happens before a larger earthquake, called the mainshock.Īn aftershock is an earthquake that happens after a previous earthquake, the mainshock. Most earthquake clusters consist of small tremors which cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern. Most earthquakes form part of a sequence, related to each other in terms of location and time. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other.Įarthquake clusters Reverse faults occur in areas where the crust is being shortened. Normal faults occur mainly in areas where the crust is being extended. There are three main types of geological fault that may cause an earthquake: normal, reverse (thrust) and strike-slip. In Luoyang in 133 AD, it detected an earthquake 400 to 500 km (250 to 310 mi) away These are called collapse earthquakes.Įarthquake fault types Model of ancient seismometer with pendulum sensitive to ground tremors. In areas of intense mining activity, often the roofs of underground mines collapse and minor tremors take place. In other words, the cause is not known in detail. These are described as caused by very deep shifts in ancient rock formations. An example is the largest earthquake in the history of the United States: the 1811–1812 New Madrid earthquakes. Often the causes are not known, except in the most general terms. However, these earthquakes are confined to areas around active volcanoes. The San Andreas fault in San Francisco, and Rift valley fault in Africa are faults like this.Įarthquakes caused by volcanic eruptions can be quite devastating. This releases the stored energy as shock waves. This continues until the stress rises and breaks, suddenly allowing sliding over the locked portion of the fault. When they stick, motion between the plates leads to increasing stress. The boundaries between moving plates form the largest fault surfaces on Earth. The main cause is when tectonic plates ride one over the other, causing orogeny (mountain building), and severe earthquakes. Tectonically active places are places where earthquakes or volcanic eruptions are regularly repeated.Ĭauses of an earthquake Įarthquakes are caused by tectonic movements in the Earth's crust. Most earthquakes happen along the Pacific Ring of Fire but the biggest ones mostly happen in other places. The tectonic plates push on each other and make great amounts of tension.Įarthquakes sometimes hit cities and kill hundreds or thousands of people. These belts are along the edges of tectonic plates. It includes the seismic activities from Sumatra, to the Himalayas, to south Europe and north Africa, to the Atlantic Ocean. This part is the biggest seismic belt: it has the most active earthquakes and the most volcanoes. The first is the Pacific belt, which circles the Pacific Ocean. Zones Major earthquakes from 1900 to 2017Įarthquake zones are concentrated in some parts of the world. Tsunamis can also cause a lot of destruction. An earthquake under the ocean can create a huge wave called a tsunami. But we know where earthquakes are likely to occur in the future, such as near fault lines. No one can tell when an earthquake will happen. The largest earthquake ever measured had a magnitude of 9.5. And damage of size 5 (or more) in a wide area. A 2 on this scale is a tremor that is not easily recorded. The Richter scale was invented by Charles Francis Richter in 1935. The strength or magnitude of an earthquake can be measured using the Richter scale. A seismometer detects the tremors of the earth and plots the tremors on a seismograph. The effect of an earthquake can be measured with a seismometer. Seismology studies the cause, recurrence, type and magnitude of earthquakes. The sudden release of stress in the tectonic plates sends waves of energy that travel through the Earth. Many earthquakes can occur in a small area in a short period of time. People who study earthquakes are called seismologists. The epicenter is the point at ground level directly above the hypocenter. The first point of an earthquake's rupture is called its hypocenter or focus. Earthquakes occur when tectonic plates suddenly break free, so they start moving quickly. When they get stuck, tension builds up in them. Different tectonic plates are slowly moving. Strong earthquakes damage buildings.ĭisturbances in the Earth cause earthquakes. San Francisco, California earthquake, sometime in 1906Īn earthquake is when Earth's tectonic plates shake and move Earth's surface.
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