Table of Contents
What happens to P-wave velocity at the core mantle boundary?
The P–wave velocity increases smoothly beneath 700 km through the lower mantle to ∼ 13.6 km/s at the core–mantle boundary. Just above this boundary there appears to be a layer in which the velocity flattens out or may even decrease slightly.
Do P waves travel faster in the mantle?
Sound waves are P-waves moving through the air. Because the earth’s mantle becomes more rigid and compressible as the depth below the asthenosphere increases, P-waves travel faster as they go deeper in the mantle. The density of the mantle also increases with depth below the asthenosphere.
Why P-wave velocity is maximum at lower mantle?
This is because fluids do not support shear stresses. Correspondingly, Vp drops precipitously. In the solid inner core, μ is nonzero hence there is a jump in velocity at the inner/outer core boundary. The combination of K, μ, and ρ in the inner core is such that Vp doesn’t exceed the lower mantle values.
What happens to P waves in the mantle?
Figure 19.2a: P-waves generally bend outward as they travel through the mantle due to the increased density of mantle rocks with depth. When P-waves strike the outer core, however, they bend downward when traveling through the outer core and bend again when they leave.
Why does P wave seismic velocity increase with depth in the mantle?
Seismic velocities tend to gradually increase with depth in the mantle due to the increasing pressure, and therefore density, with depth.
Why does a drop in velocity at the core mantle boundary cause a P wave shadow zone?
The P-wave shadow zone occurs because seismic velocities are much lower in the liquid outer core than in the overlying mantle, and the P-waves are refracted in a way that leaves a gap.
Where do P waves travel the fastest?
Generally, p-wave velocity increases with depth and increases with increasing rigidity of a material. Therefore p-waves travel fastest through the solid, iron inner core of Earth.
Where is P wave velocity maximum?
P-wave can travel in all mediums and their velocity varies according to the elasticity of the medium. The velocity of P-wave in Solid>Liquid>Gases. Its velocity is maximum in the lower mantle i.e. 13.5 km/s.
Why does a drop in velocity at the core mantle boundary cause a P-wave shadow zone?
How does the velocity of seismic waves change with increasing depth in the lower mantle?
Seismic velocities tend to gradually increase with depth in the mantle due to the increasing pressure, and therefore density, with depth. However, seismic waves recorded at distances corresponding to depths of around 100 km to 250 km arrive later than expected indicating a zone of low seismic wave velocity.
What is the velocity of P wave?
The p-wave velocity at the upper most mantle is 7.97 km/s, and the S-wave 4.55 km/s. The low velocity layer in the upper mantle occurs approximately at 140 km deep with a thickness of about 55–62 km.
Where do P waves travel the slowest?
The speed of p-waves is relatively slow through some looser solids, like scree (smaller rocks) and substances that are mostly solid, like soil. These can be as low as 300 m/s, which is slower than the generally referenced speed of sound (about 340 m/s at sea level).
What is the velocity of P waves?
Typical values for P wave velocity in earthquakes are in the range 5 to 8 km/s. The precise speed varies according to the region of the Earth’s interior, from less than 6 km/s in the Earth’s crust to 13.5 km/s in the lower mantle, and 11 km/s through the inner core.
Why does velocity increase as depth increases in the mantle?
How does the velocity of P waves change as they travel through the mantle outer core and inner core?
What is P wave and S wave velocity?
Velocities of P wave and S wave are 8.1 and 4.5 km/s respectively. Peridotite is the rock type found in mantle. From 50 to 250 km seismic wave velocity decreases, indicating a change in composition. Here P wave velocity decreases from 8.1 to 7.8 km/s and S wave velocity decreases from 4.6 km/s.
How do you find the velocity of a P wave?
The velocity of a P wave can be expressed as:
- Velocity P wave = ((B + 1.3G)/Density)1/2, where: B = the bulk modulus – the resistance to change in volume. G = the Shear modulus – the resistance to change in shape. Density = mass/volume.
- Velocity S wave = (G/Density)1/2
Does the velocity of P waves and S waves increase or decrease with increased depth in the lithosphere?
The velocity of P waves and S waves increases with increased depth in the lithosphere but.
What is the velocity of a P wave at the bottom?
With the p wave’s velocity plotted from a depth of 0 km to a depth of 6371 km it shows the p wave velocity reaching about 14 km/sec by the time it reaches the bottom of the mantle. Then of course it drops precipitously through the mantle/outer core boundary.
What is the average velocity of a P-wave?
The P-wave velocities in both layers are rather uniform, generally ranging from 6.0 to 6.3 km s −1 in the upper layer, 6.3 to 6.6 km s −1 in the middle layer, and 6.8 to 7.2 km s −1 in the lower layer. Upper mantle velocities beneath shields and platforms are typically in the range of 8.1–8.2 km s −1, rarely reaching 8.6 km s −1.
What is the velocity of the upper mantle?
Upper mantle velocities beneath shields and platforms are typically in the range of 8.1–8.2 km s −1, rarely reaching 8.6 km s −1. Seismic reflection studies show an increase in the number of reflections with depth, and generally weak, but laterally continuous, reflections at the Moho, the seismic discontinuity defining the base of the crust.
What is the normal p wave velocity in an earthquake?
In typical situations in the interior of the Earth, the density ρ usually varies much less than K or μ, so the velocity is mostly “controlled” by these two parameters. Typical values for P wave velocity in earthquakes are in the range 5 to 8 km/s.