Chapter 10 - Earthquakes and Earth's Interior Flashcards
Seismology
Study of earthquakes
Seismometer
used to record shocks and vibrations from earthquakes
Inertial Seismometer
Relies on resistance of stationary mass to movement
Focus
point where earthquake starts to release elastic strain of surrounding rock
Epicenter
point on earth’s surface lying vertically above focus
Seismic Waves
vibrational waves that spread out in all directions initially from focus
Body waves
seismic waves that travel through earth’s interior
Primary (P) Wave
compressional - can pass through solids or fluids - rock vibrates back and forth in line of wave motion - fastest
Secondary (S) Wave
cannot pass through fluids - rock moves sideways perpendicular to direction of wave travel - slower that P waves
Surface Wave
pass around earth rather than through it - slower than either P waves or S waves - different wavelengths develop different velocities (dispersion)
Determining Epicenter
locate from arrival times of P waves and S waves at 3 or more seismometers
Richter Magnitude Scale
estimated by measuring amplitudes of seismic waves - divided into steps representing 30 times increase in energy
Earthquake Hazard
most large earthquakes occur along plate boundaries - seismic risk maps based on acceleration relative to gravity used to design roadways and public buildings
Earthquake Disasters
Based on number of people killed
Earthquake Damage
1) Ground motion - 2) displacement along faults - 3) fire - 4) landslides - 5) liquefaction - 6) tsunamis
Ground Motion
results from movement of seismic waves: especially surface waves
Displacement Along Faults
Features that cross or sit on faults can be broken
Fire
started by broken gas mains and electrical wires - water mains also broken
Landslides
earthquakes may trigger rapid mass wasting movements
Liquefaction
shaking can turn saturated sediment/regolith into liquid mass
Tsunamis (Seismic Sea Waves)
High velocities - low amplitude in deep water but dramatic increase in shallow water
Modified Mercalli Scale
Based on amount of vibration felt and building damage - depends on distance from epicenter as well as magnitude
World Distribution
plate boundaries most subject to frequent earthquakes
Circum-Pacific Belt
accounts for 80% of all earthquakes
Mediterranean Himalayan Belt
accounts for 15% of all earthquakes
Benioff Zone
depth of focus up to 700km
First Motion Studies
can determine movement direction if fault orientation is known
Elastic Rebound Theory
Energy stored in elastically deformed rock bodies - when fault slips rocks rebound to original shapes
Seismic Gaps
Strain is steadily increasing but no earthquakes for a long time
Earthquake Precursors
One case of odd animal behavior before earthquake
Foreshocks
smaller earthquakes preceding a large earthquake
Fluids in Faults
Will decrease friction that holds rock faces in place
Discontinuities (Boundaries)
detected from refraction and reflection of body waves
Moho
boundary between crust and mantle
Oceanic Crust
8 km thick - Basalt then Gabbro
Continental Crust
20-70 km thick - Granite then Diorite
Mantle
Comprised of peridotite (rock made up of olivine and pyroxene)
Core
P & S wave shadow zones indicate - outer core is liquid - composed of iron - inner core is solid
