Earth’s Dynamic Crust and Interior: small scale crustal changes  Movements of the crust is based on the concept of original horizontality. This concept assumes that sedimentary rocks and some extrusive igneous rocks, form in horizontal layers parallel to the Earth’s surface.  Rock layers that no longer show their original horizontality are called deformed layers. Some are folded, tilted and faulted.  Folded rock layers are bent or curved.  Faulted rock layers are offset. (A fault is a crack in a mass of rock along which there has been displacement or movement.)  Rocks can also be uplifted, meaning the land has been raised.

Folding, Faulting, and Tilting

Earthquakes and Igneous Activity, Including Volcanoes An earthquake is a natural rapid shaking of the lithosphere caused by the release of energy stored in rocks. Most earthquakes are caused by the movement along faults. During an earthquake the potential energy stored in rocks is given off as seismic waves. The location within the Earth, in which the earthquake originates is called the focus. The location on Earth’s surface directly above the focus is called the epicenter. Earthquakes are recorded using a seismograph and they produce a recording of “wiggles” called a seismogram

Earthquake Waves There are three different types of seismic waves: 1) P-waves: primary waves, cause particles they travel through to vibrate in the direction the waves are moving. 2) S-waves: secondary waves, cause particles they travel through vibrate at right angles to the direction the waves are moving. 3) Surface waves: produced when a p- wave or s-wave comes to Earth’s surface. These waves cause much of the surface shaking and damage of an earthquake.

Properties of Earthquake Waves In any one material, P-waves travel the fastest. The velocity of the seismic waves is dependent upon the material they travel through. Generally, the more dense a material, the faster the velocity will be. Waves will become bent if they travel through different material with different densities. P-waves pass through solids, liquids and gases. S-waves will only pass through solids.

Location of an Epicenter Epicenters are located by using the velocity differences between the P-waves and S-waves. Since P-waves move faster than S-waves, the farther an observer is from an epicenter, the larger the time interval between the arrival of the P and S waves. To find the position of the epicenter, at least three seismograph stations must be used. For each of the three locations, the epicenter distance is then used as a radius and circles are drawn on a map. The place where all three circles intersect is the epicenter of the earthquake.

Finding the Origin Time of Earthquakes In the ESRT (earth science reference tables), use the Earthquake P- wave and S-wave Travel Time on page 11. Examples: 1)If the S-wave first arrived at a station at 10 hr: 12 min: 30 sec, and the seismograph is 5500 km away from the epicenter, when did the earthquake occur? 9 hr: 56 min: 30 sec 2)What is the time interval between the P and S wave if the epicenter is 3000 km away? 4 min: 20 sec

Magnitude of the Earthquake Scientists often use an earthquake magnitude scale to measure the strength of the quake. Magnitude scales use the height of the “wiggles” produced on the seismogram. The lowest value of magnitude is less than 1 and the highest value is about 9.5

Tsunamis If there are strong earthquakes on the ocean floor they can produce a seismic sea wave called a Tsunami (Japanese word for “wave in the harbor”) The disruption creating the earthquake can be caused by the faulting, a volcanic eruption or a rapid landslide.

Igneous Activity and Volcanoes When magma reaches the surface it is called lava. If the lava forms a significant mound with a slope of at least a few degrees, the mass is called a volcano. A volcano is composed of extrusive igneous rocks. A volcanic eruption is the giving off of gases, lava, and/or lava rock onto the Earth’s surface and into the atmosphere through the opening of a vent of a volcano. Major areas of uplift, sinking, earthquakes, and volcanic eruptions are often found together. The “Ring of Fire” (region surrounding the Pacific Ocean) is where the majority of these related events occur

Ring Of Fire