User Submitted Questions

What is a hotspot and how do they affect volcanoes?

A hotspot is an isolated region of the earth that produces molten silicate rock, called lava. At temperatures in excess of 1000°C (1800°F), lava can periodically erupt from the ground. Before it erupts onto the earth's surface, this material is called magma. Magma contains many types of other chemicals, including large amounts of gases like carbon dioxide. Many of these gases are toxic.

Is there a correlation between the earthquake's magnitude and its depth?

The simple answer is that the largest earthquakes occur at shallower depths in the earth's crust, but smaller earthquakes can and do occur at all depths down to about 700 km (400 mi).

Earthquakes occur in the earth's crust, the topmost layer of the earth, which is typically 7 to 30 km (4 to 18 mi) thick. The crust is the coldest and most brittle part of the earth, and has many fault systems on which earthquakes occur. These earthquakes are caused by the buildup of tectonic stress, and result in frictional sliding on the faults.

Is the seismic gap theory valid and reliable?

The seismic gap theory says that, if there have been large earthquakes on an active fault's neighboring faults in the past, will that unbroken piece of fault be the most likely location for the next major earthquake? A considerable amount of research has tried to answer this question, and at the present time the answer seems to be "no." One reason might be that the unbroken piece of fault is just stronger than the surrounding faults, and it takes much more tectonic stress to break it.

Is there any way to predict where the next big earthquake is likely to occur?

Right now, an accurate prediction of the location of the next major earthquake is not possible. However, regions of high probability for the next large earthquake can be identified and mapped. In fact, the Personal Earthquake Forecast tool (under the Tools tab) here on this web site can display the probability that a major earthquake will occur within 50 miles of any location you choose.

What is the relationship between faults, earthquakes, and plate boundaries?

Think of the Earth as an onion, composed of layers made of rocks of various temperatures, getting hotter as you go deeper. The outer layer, the crust, is pretty rigid and floats along on top of the mantle, which can flow (slowly). The mantle can flow because radioactive elements (uranium and thorium) left over from the formation of the earth provide the heat. The top layer, which we live on, is 7-35 km thick, out of a total of 6368 km, so the skin is 0.2% of the radius, really very thin.

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