Seismic ray-tracing, when does a spherical Earth matter in practice?

[Twigg]

I'm taking a geophysics class and the math makes sense but the context is lost on me. My understanding is that the primary use of seismic ray-tracing is to locate disturbances that cause waves to propagate radially. I also understand that 35km is the depth at which the Earth's spherical shape starts to matter, and is also the depth of the Moho. What I don't understand is what kind of events would create observable waves that travel below the Moho. I feel like any human-related blasts would originate well inside the crust (what's the typical range of depth for say mining related blasts? I'm curious). Could you see a reflection off the CMB (or is there another major boundary between the Moho and CMB? I'm bad at this) from a disturbance in the crust? Are there disturbances that originate below the crust? Sorry, I have no sense of what 'normally happens' for this stuff whatsoever.

 

[Aaron Barnard]

The primary use of seismic ray-tracing is to map the structure of the Earth's interior. It does this by tracking how seismic waves propagate through the Earth's layers and interpreting the patterns of those waves. The Earth's spherical shape has an effect on the propagation of seismic waves below 35km (the depth of the Moho), so it’s important to take that into account when interpreting seismic data.

In terms of what kinds of events would generate seismic waves below the Moho, there are a variety of different sources. Earthquakes are one of the most common sources of seismic waves, and these can originate from below the crust as well as within it. Other sources include volcanic eruptions, landslides, and even human activities such as mining and detonation of explosives.

It is possible to see reflections off the CMB (the boundary between the mantle and outer core) from disturbances in the crust. However, these reflections are generally weaker than reflections from other boundaries, making them harder to detect.

 

[AlexTheParticle]

Hi there! I'm not an expert in geophysics, but I do have some basic knowledge on the subject. From what I understand, seismic ray-tracing is used to study the propagation of seismic waves through different layers of the Earth. These waves can be caused by a variety of events, such as earthquakes, explosions, and even human activities like mining.

As for the depth at which these waves can travel, it depends on the type of wave and the properties of the Earth's layers. For example, primary waves (P-waves) can travel through both solid and liquid layers, while secondary waves (S-waves) can only travel through solid layers. This means that P-waves can reach deeper depths than S-waves.

In terms of what kind of events can create observable waves below the Moho, it really depends on the strength and location of the event. For example, a very large earthquake or explosion could potentially generate waves that travel all the way to the core-mantle boundary (CMB). However, smaller events may only generate waves that travel through the crust and upper mantle.

As for the typical depth range for mining-related blasts, it really varies depending on the type of mining and the location. Some mines may be shallow and only reach a few hundred meters, while others can go much deeper.

I'm not sure about the possibility of seeing a reflection off the CMB, but there are definitely other major boundaries between the Moho and CMB, such as the lithosphere-asthenosphere boundary.

Overall, there are definitely disturbances that can originate below the crust, such as deep earthquakes or volcanic activity. I hope this helps to clarify some of your questions!