How do earthquakes created

Employees in the News. Emergency Management. Survey Manual. An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

The primary boundary between these two plates is the San Andreas Fault. The San Andreas Fault is more than miles long and extends to depths of at least 10 miles. The Pacific Plate grinds northwestward past the North American Plate at a rate of about two inches per year. Parts of the San Andreas Fault system adapt to this movement by constant "creep" resulting in many tiny shocks and a few moderate earth tremors.

In other areas where creep is NOT constant, strain can build up for hundreds of years, producing great earthquakes when it finally releases. The mission of the USGS in natural hazards is to develop and apply hazard science to help protect the safety, security, and economic well-being of the Nation.

The costs and consequences of natural hazards can be enormous, and each year more people and infrastructure are at risk. The USGS conducts hazard research and works closely with stakeholders Earthquakes are one of the most costly natural hazards faced by the Nation, posing a significant risk to 75 million Americans in 39 States. The risks that earthquakes pose to society, including death, injury, and economic loss, can be greatly reduced by 1 better planning, construction, and mitigation practices before earthquakes happen, and The severity of an earthquake can be expressed in terms of both intensity and magnitude.

However, the two terms are quite different, and they are often confused. Intensity is based on the observed effects of ground shaking on people, buildings, and natural features. It varies from place to place within the disturbed region depending on the In the early s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes.

We now know that, directly or indirectly, plate tectonics Where were the land areas and oceans of the North American Continent one million years ago, compared to our present geography?

Was North America always about the same size and shape as it is today? To answer these questions, we must construct maps of the lands and sea that existed during the past ages.

Earth's crust is fractured into tectonic plates that have been moving very slowly over the Earth's surface for millions of years. Credit: USGS. When the stresses get too large, it leads to cracks called faults. When tectonic plates move, it also causes movements at the faults. This photograph shows the San Andreas Fault, a mile-long fault in California.

Credit: Public Domain. The location where an earthquake begins is called the epicenter. However, the vibrations from an earthquake can still be felt and detected hundreds, or even thousands of miles away from the epicenter. The concept of a seismometer is simple: a weight tends to stay still as the earth moves and the relative motion can be drawn on a reel of paper as a zig-zag line. The bigger the vibration, the bigger the zig-zag.

Modern systems use electronics to give more accurate results but the principle is the same. The scale is logarithmic, meaning that an earthquake of magnitude 6 is ten times stronger than one of magnitude 5. A magnitude 7 quake is 10 times stronger than a magnitude 6, and times stronger than a magnitude 5. This measures how strong the ground is how much energy is needed to break it , how much actual displacement occurs, and the amount of rock that is displaced.

To give a sense of what different magnitudes feel like for people experiencing them, anything above a magnitude of 5. As scientists continue to study its inner workings, we may be able to better predict the severity of earthquakes before they happen.

This can help us understand the relative movement of the plates and the type of deformation. In a normal fault, the block above the fault moves down relative to the block below the fault.

In a reverse fault, the block above the fault moves up relative to the block below the fault. In a strike-slip fault, the movement of blocks along a fault is horizontal. 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. Faults are classified using the angle of the fault with respect to the surface known as the dip and the direction of slip along the fault.

Faults that move along the direction of the dip plane are called dip-slip faults while strike-slip faults 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. Boundaries between tectonic plates are made up from a system of faults. Discovering Geology introduces a range of geoscience topics to school-age students and learners of all ages.

The Earth beneath our feet is constantly shifting and moving, and violently with catastrophic and immediate results. Find out more about earth hazards. Earthquakes are among the most deadly natural hazards. They strike without warning and many earthquake zones coincide with areas of high population density. Seismometers are used to record the seismic waves produced by earthquakes. Relative arrival times of these waves is used to determine earthquake location.

The extent of damage an earthquake causes depends not only on the magnitude of the earthquake, but also on local geology and on building techniques. What causes earthquakes?

Discovering Geology — Earthquakes. The structure of the Earth Seismic waves from large earthquakes pass throughout the Earth. The crust This brittle, outermost layer varies in thickness from about 25 to 70 km under continents and from about 5 to 10 km under the oceans. The mantle Below the crust lies the dense mantle, extending to a depth of km.

Plate tectonic map of the world showing direction of movement. Divergent boundary Plates can move apart at a boundary. A divergent, or constructive, plate boundary, where new material is produced at the surface. The Mid-Atlantic Ridge is a good example of a constructive plate boundary. You can see normal faulting at the surface where the Mid-Atlantic Ridge crosses Iceland.