What Does A Reflected Wave Tell Us About Earth’S Interior?
Ch.17, pg.440: #1-4, 6, 7, 12 Describe how seismic reflection and seismic refraction demonstrate the existence of Earth’s layers. When seismic waves hit a layer of rock with a differing density, they may reflect or bend as they pass the barrier. By observing these patterns of reflection and refraction, the presence and depth of Earth’s strata may be determined.2.
- Draw a cross-section of the entire planet, indicating the major inner divisions and providing the name, thickness, and likely composition of each.
- Figure 17.7 appears on page 423.
- What evidence suggests that the majority of the Earth’s core is formed of iron? Estimates of the core’s density, the abundance and composition of iron meteorites, and the existence of a magnetic field on Earth all indicate that iron is the predominant element.
Describe the distinctions between continental and oceanic crusts. The oceanic crust is 7 kilometers in thickness, denser, and formed of basalt-like rock. Continental crust is thicker (30-50 km), less dense, and consists of granite-like rock coated with sedimentary rock than oceanic crust.
Discuss seismic-wave shadow zones and what they reveal about the interior of the Earth. For P-waves, the Earth has a shadow zone extending from 103 to 142 degrees from the earthquake’s epicenter. This shadow zone is the result of P waves being refracted (bent) when they meet the core barrier. It is known that S-waves cannot pass through liquid.
There is an S-wave shadow zone beyond 103 degrees from the epicenter where S-waves do not propagate. Describe the magnetic field of the Earth. Where is it produced? It is an area of magnetic force that encircles the Earth. Its invisible magnetic force lines encircle the planet and deflect magnetized things, such as compass needles.
At the magnetic poles, where magnetic lines of force appear to exit and enter Earth vertically, the Earth’s magnetic field is greatest. It is presumably formed in the outer core’s liquid metal. What distinguishes the lithosphere from the asthenosphere? Consisting of the crust and mantle, the lithosphere is generally solid and brittle.
The asthenosphere is comprised of ductile-appearing mantle rocks located close under the lithosphere. It is likely that the asthenosphere reflects a minute fraction of partial melting. Last update 2/24/2005 Jackson created the website. Hiram Jackson, the Geology webmanager, may be reached at [email protected]
What do earthquake waves reveal about the interior of the earth?
Seismic waves indicate that the interior of the Earth is composed of a series of concentric shells, including a thin outer crust, a mantle, a liquid outer core, and a solid inner core. P waves, or primary waves, move the quickest and hence reach at seismic stations first. The S waves, or secondary waves, follow the P waves.
Seismic Waves and Determining the Earth’s Structure: A Comparison and Connections Even if the technology to go through all of the Earth’s strata does not exist, scientists may still learn a great lot about Earth’s structure via seismic waves. Seismic waves are vibrations in the ground that convey energy and occur during seismic events such as earthquakes, volcanic eruptions, and even explosions caused by humans.
- There are two distinct types of seismic waves: primary and secondary.
- Primary waves, sometimes called P waves or pressure waves, are longitudinal compression waves that resemble the action of a slinky (SF Fig.7.1 A).
- S waves, or secondary waves, are slower than P waves.
- The motion of secondary waves is equivalent to violently shaking a rope perpendicular to the direction of wave flow (SF Fig.7.1 B).
SF Figure 7.1 C depicts the motion of primary or P waves (on top) and secondary or S waves (on bottom). Seismometers (Figure 7.2) are used by scientists to measure seismic waves. Seismometers monitor the ground’s vibrations in comparison to a stationary device.
Seismometer data, often known as a seismogram, depicts velocity on the y axis and time on the x axis (Fig.7.3). Observe in SF Fig.7.3 that the P wave arrives first due to its higher velocity. SF Table 7.1 demonstrates that P waves have a greater velocity than S waves while going through various types of minerals.
The velocity of seismic waves relies on the qualities of the material through which they travel. For instance, the greater the density of a substance, the quicker a seismic wave travels (SF Table 7.1). P waves are able to move through liquids, solids, and gases, but S waves can only pass through solids.
| Mineral | P wave velocity (m/s) | S wave velocity (m/s) | Density (g/cm 3 ) |
|---|---|---|---|
| Soil | 300-700 | 100-300 | 1.7-2.4 |
| Dry sand | 400-1200 | 100-500 | 1.5-1.7 |
| Limestone | 3500-6000 | 2000-3300 | 2.4-2.7 |
| Granite | 4500-6000 | 2500-3300 | 2.5-2.7 |
| Basalt | 5000-6000 | 2800-3400 | 2.7-3.1 |
Because of SF Figure 7.4 depicts the propagation of waves through the Earth. Note that P waves go through all layers of the ground, however S waves cannot travel through the solid core, resulting in a S wave shadow on the opposite side of the earthquake: Compare-Contrast-Connect: Seismic Waves and Determining the Structure of the Earth
Which waves are found within the earth’s interior?
Internal waves within the earth Earthquakes create two types of waves that go through solid rock: With P or compressional waves, the rock vibrates in the propagation direction. The earthquake’s P waves move the fastest and are the first to arrive. Rock oscillates perpendicular to the propagation direction of S or shear waves.
In rock, S waves move at approximately 60% the speed of P waves and always arrive after P waves. For instance, sound waves are P waves with a sufficiently high frequency to be audible. Wiggling or shaking a rope that is secured at one or both ends is an illustration of a S wave. Both P and S waves radiate from the epicenter of an earthquake within the ground.
Seismographs frequently record the waves as independent arrivals at great distances from the earthquake. The direct P wave reaches sooner because its path is via denser, faster-moving rocks located deeper inside the ground. The PP (one bounce) and PPP (two bounces) waves move more slowly than the straight P as a result of passing through shallower, slower-moving rocks.
- The S waves arrive following the P waves.
- Surface waves, such as the L wave, are the slowest (and last to arrive on seismograms).
- L waves are called after the Cambridge mathematician who initially characterized them, A.E.H. Love.
- Generally, the surface waves are the biggest recorded during an earthquake.
As they move away from the epicenter of an earthquake, body waves in the earth’s interior lose amplitude fast due to their dispersion inside the earth’s volume. However, surface waves propagate more slowly and exclusively on the earth’s surface. The surface confines the energy of surface waves to a smaller volume, hence the wave amplitude required to transport this energy is greater than that of body waves.
Why does an earthquake cause the ground to shake? – While the edges of faults are locked together and the remainder of the block is moving, the energy that would ordinarily force the blocks to glide past one another is saved. All of the stored energy is released when the force of the sliding blocks eventually overcomes the friction of the jagged edges of the fault and it detaches.