EARTHQUAKES AND PLATE TECTONICS CHAPTER 6 SECTION 1
ELASTIC REBOUND THEORY Rocks on each side of a fault are moving. Fault is locked, rocks stop moving. Rocks on each side of a fault are stressed. Rocks fracture and separate at weakest point. Rocks return to original shape.
Elastic Rebound Theory
AFTERSHOCKS Original earthquake releases energy in the form of vibrations called seismic waves. These vibrations may increase stress in other rocks along the fault. The increased stress on these rocks may cause them to fracture and spring back. The series of smaller tremors are called aftershocks.
FOCUS Area along a fault where the slippage first occurs Focus is beneath the earth’s surface The epicenter is directly above The depth of the focus varies
FOCUS DEPTH - 1975-95
FOCUS DEPTH OF EARTHQUAKES IN WASHINGTON 1977-1996
A point on the earth’s surface directly above the focus EPICENTER A point on the earth’s surface directly above the focus
MAJOR EARTHQUAKE ZONES Pacific Ring of Fire Mid-ocean ridges Eurasian-Melanesian Mountain Belt
MAJOR EARTHQUAKES AREAS
PUGET SOUND FAULT ZONES
Magnitude
STRUCTURAL DAMAGE Kobe Earthquake
LIQUEFACTION Kobe
RECORDING EARTHQUAKES CHAPTER 6, SECTION 2
TYPES OF SEISMIC WAVES P waves S waves L waves
P WAVES Fastest wave First recorded on seismograph Travel through solid and liquid Cause rock particles to move together and apart along the direction of the waves.
S WAVES Second wave to reach seismograph Travels through solids only Cause rock particles to move at right angles to the direction the wave is traveling
L WAVES Slowest moving of the three waves Also called surface or long waves Last to be recorded by the seismograph Travel over the earth’s surface similar to ocean waves Cause the greatest damage
SEISMOGRAPH A device used to measure seismic waves
LOCATING THE EPICENTER
EARTHQUAKE SCALES RICHTER MERCALLI
RICHTER SCALE Scale that ranges from 1-10 Each whole number increases the magnitude of the energy 31.7 times Largest recorded magnitude - 9.5 Above 7 - Major earthquake Between 6 and 7 - Moderate earthquake Between 2.5 and 6 - Minor earthquake Less than 2.5 - Microearthquake
MERCALLI SCALE Measures the intensity of the damaged caused by the earthquake Scale of I - XII (1-12)
I. Not felt except by a very few
II. Felt by a very few persons on the upper floors of buildings
III. Felt indoors
IV. Hanging objects swing
V. Felt outdoors
VI. Felt by all, many scared and run outdoors
VII. Difficult to stand
VIII. Damage slight in specially designed structures
IX. Damage considerable in specially designed structures
X. Ground cracked, rail bent
XI. Bridges destroyed, broad fissures in ground
XII. Damage total
Pacific Northwest Earthquake Information REQUEST FOR EARTHQUAKE INFORMATION
BEFORE - Be prepared DURING - Stay calm AFTER - Stay cautious EARTHQUAKE SAFETY BEFORE - Be prepared DURING - Stay calm AFTER - Stay cautious
ASSIGNMENT WORKSHEET 6.3 Page 111, #1-5