# earthquake characteristics

## focus and epicenter

In an earthquake, the initial point where the rocks rupture in the crust is called the focus. The epicenter is the point on the land surface that is directly above the focus (Figure 1.2). In the vertical cross section of crust, there are two features labeled - the focus and the epicenter, which is directly above the focus. Click image to the left or use the URL below. URL:

## earthquake

An earthquake is sudden ground movement caused by the sudden release of energy stored in rocks. Earthquakes happen when so much stress builds up in the rocks that the rocks rupture. The energy is transmitted by seismic waves. Earthquakes can be so small they go completely unnoticed, or so large that it can take years for a region to recover.

## elastic rebound theory

The description of how earthquakes occur is called elastic rebound theory (Figure 1.1). Elastic rebound theory. Stresses build on both sides of a fault, causing the rocks to deform plastically (Time 2). When the stresses become too great, the rocks break and end up in a different location (Time 3). This releases the built up energy and creates an earthquake. Click image to the left or use the URL below. URL:

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

the earthquakes initial point where the rocks rupture in the crust.

``````a) breaking point

-->  b) focus

c) epicenter

d) focal point
``````

when an earthquake happens, we say that its ____ was located 100 miles northwest of san francisco.

``````a) breaking point

b) focus

-->  c) epicenter

d) focal point
``````

the theory that stress builds up in rocks until they can no longer bend so they break, causing an earthquake is

``````a) continental drift theory

b) plate tectonics theory

-->  c) elastic rebound theory

d) earthquake action theory
``````

shearing is the stress that causes an earthquake.

``````a) true

-->  b) false
``````

scientists call the energy from earthquakes

``````a) electromagnetic waves

b) earthquake waves

-->  d) seismic waves
``````

when stresses build on rocks they

``````-->  a) deform plastically then break.

b) just break.

c) immediately have an earthquake.

d) none of these
``````

deep focus earthquakes cause the most damage.

``````a) true

-->  b) false
``````

an earthquake can be so small it can go unnoticed.

``````-->  a) true

b) false
``````

most earthquakes happen in the top portion of the crust.

``````-->  a) true

b) false
``````

## diagram questions

No diagram questions associated with this lesson