Essential of Geology , 2 ed.

(8.1) Types of Faults

This animation shows the differences between the three types of faults and illustrates how they are formed. View 1 shows a normal fault, View 2 shows a reverse fault, and View 3 shows a strike-slip fault.

Created by: Stephen Marshak

(8.2) What a Geologist Sees: Offset Fence along San Andreas Fault

The photo shows a wooden fence built across the San Andreas Fault. During the 1906 San Francisco earthquake, slip on the fault broke and offset the fence; the displacement of the fence indicates that the fault is strike-slip, as we see no evidence of up or down motion. The amount the fence was offset indicates the displacement on the fault.

(8.3) Seismic Wave Motion

Seismologists distinguish between different types of seismic waves based on how they move, and whether they travel along the Earth's surface (surface waves) or pass through its interior (body waves). This animation shows two types of body wave motion: View 1 shows shear body waves (also called S-waves) and View 2 shows compressional body waves (P-waves).

Created by: Stephen Marshak

(8.4) How a Seismograph Works

Seismologists use two basic configurations of seismographs, one for measuring horizontal ground motion, like the one shown in this animation, and the other for measuring vertical ground motion. Both work on the principle of inertia as described by Newton's law, which states that an object at rest tends to remain at rest unless acted on by an outside force. Thus, during an earthquake, vibrations cause the frame of the seismograph to move. The pendulum apparatus remains fixed as the paper cylinder moves back and forth beneath it.

Created by: Stephen Marshak