HOTSPOTS
 Areas of unusually high volcanic activity
 Unusually hot magma rises in the mantle & breaks
through the crust, forming a volcano
 The Hawaiian Islands were formed by a hot spot
 As the Pacific Plate moves northwest, the hot spot
stays in place, making a chain of volcanoes
EARTHQUAKES
 Earthquakes occur whenever there is movement of Earth’s Tectonic Plates.
 They occur along all types of plate boundaries and along faults within the plates
Structure of an Earthquake
 The FOCUS is the point underground where the earthquake
originated
 The EPICENTER is the point on the surface directly above the
focus.
Types of Seismic Waves
 P: “Primary” or “Push-Pull” waves, first to arrive (fastest waves), causes ground
compression and expansion
 S: “Secondary” or “Shear” waves, travel half the speed of P waves, moves
ground side-to-side and up-and-down
 SURFACE WAVES; Arrive last, travel the slowest, but cause the most ground
movement and damage
Locating the Epicenter of an Earthquake
 The device that detects seismic activity is called a SEISMIGRAPH
 The paper that records the seismic activity is a SEISMIGRAM
 In order to locate the Epicenter, you must have data from 3
seismic stations.
Measuring Earthquakes
 Earthquake intensity is measured using the RICHTER Scale
 Each number on the scale releases about 31 times*
more energy than the previous number
* So, an 8.0 earthquake releases 29,791 times more energy than a 5.0
Effects of an Earthquake

Collapsed buildings & bridges

FIRES (from broken gas lines)

LANDSLIDES & LIQUEFACTION

TSUNAMIS
Studying Earth’s Interior
 We know the structure of Earth’s interior from studying the P & S WAVES of earthquakes
 P-WAVES can travel through any material, but they bend when moving through liquid. This
bending creates “SHAWDOW ZONE”
 S-WAVES can only travel through solids, so they create a much larger “shadow zone” on the
other side of the Earth.