Earthquakes

FOCUS

CA- California K-12 Academic Content StandardsSubject : ScienceGrade : Grades Nine Through TwelveArea : Earth SciencesSub-Strand : Dynamic Earth ProcessesConcept 3: Plate tectonics operating over geologic time has changed the patterns of land, sea, and mountains on Earth’s surface. As the basis for understanding this concept:a: Students know features of the ocean floor (magnetic patterns, age, and sea-floor topography) provide evidence of plate tectonics.b: Students know the principal structures that form at the three different kinds of plate boundaries.c: Students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including plate tectonic processes.d: Students know why and how earthquakes occur and the scales used to measure their intensity and magnitude.

1. Compare and contrast plate boundaries: convergent, divergent, and transform

2. Learn about the causes and effects of earthquakes and where they occur

Seismologist- scientist who studies seismic waves

*Convection Currents move tectonic plates.

*Convection Currents in the Earth are caused by the Earth’s hot inner core heating the magma within the mantle.

The movement of tectonic plates is related to the distribution of heat by convection currents in the mantle.

*A Fault is a fracture, or break, in Earth’s Lithosphere.

Along parts of the fault, the rocks on either side may slide along slowly and constantly.

Along other parts of the fault, the rocks may

stick, or lock together.

The rocks bend as stress is put on them.

*Stress: Force exerted when an object presses on, pulls on, or pushes against another object.

*As stress increases, the rocks break free. A sudden release of stress in the Lithosphere causes an earthquake

*An Earthquake is the shaking of the ground caused by a sudden movement of large blocks of rock along a fault.

*Most faults are located along tectonic plate boundaries, therefore, most earthquakes occur at those points.

The rocks that move are much smaller than the tectonic plate.

Tectonic Plates can be thousands of kilometers long.

During even a powerful earthquake the rocks may only move a few meters past each other along a distance of several hundred kilometers.

*The strength of an earthquake depends in part on: *How much stress builds up (potential

energy) before the rocks move. *The distance the rocks move along

the fault.

80% of all earthquakes occur in a belt around the edges of the Pacific Ocean.

In the U.S. the best-known Fault in this belt is the San Andreas Fault in CA.

The Fault forms part of the boundary between the North American Plate and the Pacific Plate.

The San Andreas, unlike many other Faults, can be seen on the surface of the ground.

Earthquakes also occur along Faults within plates.

All Earthquakes occur in the Lithosphere where the rocks are cold, hard and brittle.

Below the Lithosphere is the hot malleable, and in spots, molten.

A few Earthquakes occur far below the normal depth of the Lithosphere because the plates being Subducted are still cold and rigid enough to break.

All Earthquakes occur in the Lithosphere where the rocks are cold, hard and brittle

Below the Lithosphere is the hot malleable, and in spots, molten.

A

A

A

AQ

Can you identify which of the plates are only made of oceanic crust?

Use usgs.gov to find earthquakes in real-time to map the tectonic plates.

Write three questions from this section, look in the book or on the Internet for the answers. Pg 543-551