Plate Tectonics

PLATE TECTONICS

Lithosphere consists of crust and upper portion of the mantle. There are two types of crust, the Continental crust and the Oceanic crust. Because of the difference in density, continental crust floats higher than the oceanic crust.

The lithosphere is said to be in constant but slow motion. These motion can range widely. The Artic Ridge has the slowest rate ( less than 2.5 cm/yr ), and the East Pacific Rise near Easter Island, in the South Pacific abot 3,400 km west of Chile, has the fastest rate ( more than 15 cm/yr ). This movement of the lithosphere is called Tectonics.

Locating earthquake epicenters will pinpoint which fault lines are active. Usually, the less active fault lines are active. Usually, the lest active fault line store great amount of potential energy that could cause major earthquake once released. Therefore, places near fault lines that remain inactive for a long period of time are due to experience a major earthquake.

In order to locate the epicenter of an earthquake, you need to determine the time interval between the arrival of the P (Primary) and S (Secondary) waves ( the S-P interval ) on the seismograms from at least three different stations. You have to measure the interval to the closest second and the use of a graph (distance-time graph) to convert the S-P interval to the epicentral distance.

Once you have the epicentral distances, you can draw circles to represent each distance on a map. The radius of each circle corresponds to the epicentral distance for each seismic recording station. Once you have drawn all three circles and located the point where all three intersect, you will successfully located (triangulated) the epicenter of the earthquake.

To compute the distance of the epicenter from each of the stations using this formula.

d= Td/8 seconds x 100 km

where d= distance

Td= Time difference in the arrival time of P-wave and S-wave (seconds)

This formula is suited because of 8 seconds is the interval between the times of arrival of the

P-wave and S-wave at a distance of 100 km.

If we have at least three recording stations that can tell how far away from them the earthquake occurred, the epicenter can be determined using the triangulation method. It uses distances information from three seismic stations to locate the earthquake epicenter. On a map, circles are drawn around each seismic station. The radius of the circles are scaled to the estimated distance from the station to the earthquake. The three circles will intersect at one point that locates the earthquake.

What is Plate Tectonics?

The Earth’s crust and upper mantle are broken into sections called plates.

Plates move around on top of the mantle like rafts.

The lithosphere is the solid, outer part of Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure.

The crust is made of a variety of solid rocks like sedimentary (-formed from pre-existing rocks or pieces of once living organisms.), metamorphic (-rocks that have become changed by intense heat or pressure while forming.),

and igneous(-formed by the cooling and hardening of magma or molten lava.). It has an average density of 2.8g/cm3 and its thickness ranges from 5 to 50 km. The crust is thickest in a part where a relatively young mountain is present and thinnest along the ocean floor.

TWO TYPES OF CRUST

1.      Continental Crust

2.      Oceanic Crust

Continental Crust – thicker but less dense. It floats higher than oceanic crust.

Oceanic Crust – denser and thinner.