Why does earthquakes come

Technical Announcements. 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? The earthquake and aftershocks occurred along a well-known fault in California — the San Andreas Fault shown in Figure 3. This shows the positions and depths of the earthquake and aftershocks, i.

The San Andreas Fault is the largest and possibly most active of many faults in California. As well as the Loma Prieta earthquake, movement along the fault has caused other large earthquakes, including a major San Francisco earthquake in This resulted in the almost total destruction of the city by fire, following the rupture of gas mains; rupturing of the water mains made it impossible to put out the fires. The land to the west of the fault moved as much as 6 m north relative to the other side during this earthquake.

Now we know a bit more about what causes earthquakes, we can return to the first earthquake we considered Kobe, to look at it in terms of movement along a fault. The epicentre was about 30 km to the southwest of the city of Kobe Figure 6. The rocks moved up to 1. Aftershocks occurred on this fault, and to the northeast, over about 50 km. The only previously recorded significant earthquake along this fault was in , and that was much smaller than the earthquake.

The fault was thought to be moving only very slowly, enough to cause a large earthquake every thousand years or so. Unfortunately for Kobe, turned out to be the year in a thousand. Making the decision to study can be a big step, which is why you'll want a trusted University. Take a look at all Open University courses. If you are new to University-level study, we offer two introductory routes to our qualifications.

You could either choose to start with an Access module , or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information. Not ready for formal University study? Then browse over free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. Request an Open University prospectus The causes of earthquakes and the different types of tectonic boundaries and faults on which they usually occur.

Where do earthquakes occur? Discovering Geology — Earthquakes. You may also be interested in:. Earthquakes Earthquakes are among the most deadly natural hazards. How are earthquakes detected? How do earthquakes affect people? What causes earthquakes? Was this page helpful? Yes No.

Close Button. PDF version. Why do earthquakes happen? Where do earthquakes happen? References 1 Where Earthquakes Occur U. Seismicity of the Earth Website , U. Geological Survey Historical maps of seismic activity for the entire Earth, with higher-resolution maps of more seismically active areas.

Recent Earthquake Teachable Moments Website , Incorporated Research Institutions for Seismology IRIS Regularly updated website with downloadable slides and other teaching and learning materials for recent major earthquakes around the world.

Earthquake Factsheets Factsheet , Incorporated Research Institutions for Seismology IRIS A series of factsheets on different earthquake-related topics, such as the frequency of earthquakes, how they are located and detected, and how they can be used to study the Earth's interior.