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.
This process of reconstructing ancient A new report issued by the American Red Cross and the U. Geological Survey documents the Chilean response and recovery efforts following the Feb.
According to the U. Geological Survey USGS , was the deadliest year for earthquakes since the Renaissance Age, making it the second most fatal in recorded history, with more than , deaths reported from the magnitude 9. This database contains information on faults and associated folds in the United States that demonstrate geological evidence of coseismic surface deformation in large earthquakes during the Quaternary the past 1.
Skip to main content. Search Search. Natural Hazards. Apply Filter. What is the difference between aftershocks and swarms? Scientists can determine the time, location and intensity of an earthquake from the information recorded by a seismometer. This record also provides information about the rocks the seismic waves traveled through. A seismometer records seismic waves as a series of zig-zags. Scientists have measured quakes on Earth's Moon, and see evidence for seismic activity on Mars, Venus and several moons of Jupiter, too!
On Earth, we know that different materials vibrate in different ways. By studying the vibrations from marsquakes, scientists hope to figure out what materials are found on the inside of Mars.
An artist's illustration of the Mars InSight lander operating on the surface of Mars. InSight is collecting tons of information about what Mars is like under the surface.
When an earthquake occurs, different types of energy waves are generated. These are compressional waves that push and pull as they move through rock and fluids. These waves move only through rock. They move up and down or side to side, perpendicular to the direction in which the wave is moving.
Surface waves follow P and S waves. They travel along the surface of the earth and thus cause the most damage.
Surface waves can be characterized as Love waves, which are faster and move the ground from side to side, and Rayleigh waves, which roll like waves on the surface of oceans and lakes. Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded.
So how do they measure an earthquake? They use the seismogram recordings made on the seismographs at the surface of the earth to determine how large the earthquake was figure 5.
The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip. The size of the earthquake is called its magnitude. There is one magnitude for each earthquake. Scientists also talk about the intensity of shaking from an earthquake, and this varies depending on where you are during the earthquake. Seismograms come in handy for locating earthquakes too, and being able to see the P wave and the S wave is important.
P waves are also faster than S waves, and this fact is what allows us to tell where an earthquake was. Light travels faster than sound, so during a thunderstorm you will first see the lightning and then you will hear the thunder. If you are close to the lightning, the thunder will boom right after the lightning, but if you are far away from the lightning, you can count several seconds before you hear the thunder.
The further you are from the storm, the longer it will take between the lightning and the thunder. P waves are like the lightning, and S waves are like the thunder. The P waves travel faster and shake the ground where you are first. Then the S waves follow and shake the ground also. If you are close to the earthquake, the P and S wave will come one right after the other, but if you are far away, there will be more time between the two.
P Waves alternately compress and stretch the crustal material parallel to the direction they are propagating.
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