1. I. What is an earthquake? Earthquake defined Fractures and faults
An earthquake is a series of vibrations (shaking) at the earth’s surface produced by the sudden release of energy by movement along a fault.
Other mechanisms of earthquake generation…
Volcanic activity
Landslides
Meteorite impacts
Major explosions
Fractures and faults
Some terminology

2. I. What is an earthquake? Earthquake defined Fractures and faults
Faults are fractures within the earth (rocks and soils) along (across) which movement has occurred
Faults are 2 dimensional planes within the 3D earth
Faults appear as 1 dimensional lines at the earth’s 2D surface, on maps of the earth’s surface and on vertical cross-sections
[the fault is a plane, the surface is a plane where two plane intersect you get a line]
Fractures with no movement are called joints.

3. Three Types of Faults Strike-Slip Thrust Normal
Form depending on type of plate motion and complex reaction of earth’s lithospheric blocks
Strike-slip
Normal
Thrust
Normal
Slide source: Lisa Wald – USGS Pasadena

4. Near Kingman AZ; image from R.J. Varga
Faults: Normal faults offsetting layers in volcanic ash deposits 2D cross-section view of fault in road cut (plane of the faults intersect the plane of the vertical road cut, looks like a line)
Faults cutting layered volcanic rocks
Near Kingman AZ; image from R.J. Varga

5. (right-lateral strike-slip fault)
San Andreas Fault
(right-lateral strike-slip fault)
Wallace Creek,
Carrizo Plain, CA
2D map view of fault from above
(plane of vertical fault intersects plane of the surface of the earth = line
SERC and USGS

6. Faults: Strike-slip fault near Valley of Fire (Clark Co, NV)
East of Las Vegas: image from M.B. Miller

7. I. What is an earthquake? Earthquake defined Fractures and faults
Some terminology
Seismology – field of study of earthquakes
Seismic waves – vibration energy transmitted through earth materials (rocks and soils)
Earthquake focus (or hypocenter) – site within the earth where fault fails, source of seismic waves
Earthquake epicenter – position on the earth’s surface above the focus
Magnitude – calculated energy released at the earthquake focus
Intensity – experienced effects of seismic waves on people and materials (varies with location and materials, type of building, rocks vs. loose soils)

8. Earthquake Magnitude M5 M6 M7 Magnitude scale is logarithmic
Slide source: Lisa Wald – USGS Pasadena

9. Earthquake Intensity – Shake Maps