Download Lesson 15 - Seismology Earths Interior

Chapter 17: Earth’s interior (Part I )
Ch 17: Earth’s interior
1) How is it done? Why care?
Ch 17: Earth’s interior
1) How is it done? Why care?
seismology
high-pressure/temperature
lab experiments
meteorite studies
computer modeling
studies of magma
gravity and magnetism studies
understand how: Earth formed
what causes volcanoes
plate tectonics
2) Probing Earth’s interior
 earthquake happens (slip on a fault)
 seismic waves travel away from earthquake
 they carry info about material they travel through
2) Probing Earth’s interior
 earthquake happens (slip on a fault)
 seismic waves travel away from earthquake
 they carry info about material they travel through
 earthquakes make P-waves & S-waves
 seismologists use them to:
 locate earthquakes
earlier lecture
 determine what deep Earth is made of
today
2) Probing Earth’s interior
 The nature of seismic waves
Seismic wave speeds:
 depend on material properties
 are faster in more rigid materials
 increase with increasing depth (from more pressure)
P waves:
 compressional waves: are fastest
 vibrate material back/forth in direction wave travels
S waves:
 shear waves: slower than P-waves
 vibrate material side-to-side in direction wave travels
2) Probing Earth’s interior
 The nature of seismic waves
 P waves always faster than S-waves
“primary”
“secondary”
 wave paths are “bent” when crossing from one
material into another
2) Probing Earth’s interior
 The nature of seismic waves
 wave paths are “bent” when crossing from one
material into another
reflections
refractions
q4 q3
q2 q2
2) Probing Earth’s interior
 The nature of seismic waves
 wave paths are “bent” when going deeper in Earth
 higher pressure = higher wave speed
3) Seismic waves & Earth’s Interior
 Compositional layers
crust
3-70 km thick
mantle down to 2900 km depth
core
2900-6370 km depth
 Mechanical layers
layer
lithosphere
stiff/strong,
asthenosphere soft/weak,
depth
0-100 km
100-660 km
4) Discovering Earth’s major boundaries
 crust
 mantle
 core
boundaries
between
layers
4) Discovering Earth’s major boundaries
 The Crust
Thickness: ~ 30 km (continents)
3-15 km (oceanic)
Composition:
similar to granodiorite (continents)
predominantly basalt (oceanic)
4) Discovering Earth’s major boundaries
 The “Moho”
Boundary between
the crust and mantle
Discovered in 1909 by
Andrija Mohorovicic
4) Discovering Earth’s major boundaries
 The Mantle
upper
mantle
Over 82% of Earth’s volume
lower
mantle
mantle
upper mantle 0 - 670 km
lower mantle 670-2900 km
D” region 2600-2900 km
400 & 670 km depth
“phase transitions”
Material suddenly compresses to
a more compact form
D”
4) Discovering Earth’s major boundaries
 The core-mantle boundary
Boundary between
the mantle and core
mantle
Discovered in 1914 by
Beno Gutenberg
…how?
core
Core-mantle
boundary
S-wave shadow zone
Core was discovered …from a “shadow zone”
P-wave shadow zone
4) Discovering Earth’s major boundaries
 The inner core
Boundary between
the outer liquid and
solid inner core
Discovered in 1936 by
Inge Lehman
…how?
mantle
core
Inner core
4) Discovering Earth’s major boundaries
 The inner core
She discovered reflections of seismic waves