Ch 29 Geologic Time & Dating

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

1* The FOCUS is the point underground where the earthquake originated

2* The EPICENTER is the point on the surface directly above the focus.

Types of Seismic Waves

3* P: “Primary” or “Push-Pull” waves, first to arrive (fastest waves), causes ground compression and expansion

4* S: “Secondary” or “Shear” waves, travel half the speed of P waves, moves ground side-to-side and up-and-down

5* SURFACE WAVES; Arrive last, travel the slowest, but cause the most ground movement and damage Locating the Epicenter of an Earthquake

6* The device that detects seismic activity is called a SEISMIGRAPH

7* The paper that records the seismic activity is a SEISMIGRAM

8* In order to locate the Epicenter, you must have data from 3 seismic stations.

Measuring Earthquakes

9* Earthquake intensity is measured using the RICHTER Scale

10* 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.