Transcript The Milne horizontal seismograph (modified from Milne

Field Trip Information
• Depart 7:45 AM - Circle Drive, West side of
Bone Student Center
• Lone Star Quarry
– Limestone in real life, FOSSILS
• Buffalo Rock State Park
– Restrooms, Mining, coal, sandstone, Illinois River
• Mathessen State Park
– Restrooms,Geologic Structures, fossils, canyons
Return 5 PM
Field Trip Information
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Lunch and beverage (water is best)
Sturdy? Shoes
Old cloths (chance of getting muddy)
Hat might be nice
Camera
What do we know about the interior
of the earth?
• Direct observations
Outcrops a bit over a mile (2 km)
Deep mines to about 3 miles (5 km)
Deep borings to about 6 miles (9 km)
• Indirect Observations
Earthquakes
Meteorites
Most of our knowledge of Earth’s interior
comes from the study of earthquake waves
• Travel times of P (compressional) and S
(shear) waves through the Earth vary
depending on the properties of the materials
• Variations in the travel times correspond to
changes in the materials encountered
The Milne horizontal seismograph (modified from Milne, 1898a).
Light from L is reflected by M through the intersection of two crossed slits
onto photographic paper. The lower illustration is a top view of the
instrument with its outer case removed. T is a flexible wire holding up the
boom. The weight W is pivoted on the boom.
A record obtained with a Milne horizontal seismograph on April 5 1901. As may be seen,
the usefulness of Milne's instrument was diminished by its lack of damping.
Representative Materials
Material
Air
Dry Sand
Wet Sand
Water
Glacial Moraine
Limestone-Dolomite
Rock Salt
Basement
Vp (ms-1)
330
300-800
1500-2000
1450
1500-2700
3500-6500
4000-5500
4600-7000
Vs (ms-1)
---100-500
100-500
---930-1300
1800-3800
2000-3200
2500-4000
• Abrupt changes in seismic-wave velocities
that occur at particular depths helped
seismologists conclude that Earth must be
composed of distinct shells
• Layers are defined by composition
Layers are defined by composition
– Crust – the comparatively thin outer skin that
ranges from 3 km (2 miles) at the oceanic ridges
to 70 km (40 miles in some mountain belts)
– Mantle – a solid rocky (silica-rich) shell that
extends to a depth of about 2900 km (1800 miles)
– Core – an iron-rich sphere having a radius of
3486 km (2161 miles)
Figure 22.1
Meteorites
• Irons (two types of iron-nickel minerals) (Core)
• Stony Irons (Iron and calcium rich silicate
minerals) (Mantle)
• Stony (Crust)
– Condrite (silicate rich glass blobs)
– Carbonaceous Condrites (carbon compounds, simple
amino acids)
– Sherogitie (Chunks of Martian Crust)
• ALH 84001