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

Thread starter Twigg
Start date Apr 11, 2021
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Earth Matter Seismic Spherical

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Seismic ray-tracing is primarily used to identify disturbances that cause wave propagation, particularly in the context of geophysics. The Moho, located at a depth of approximately 35 km, marks a significant boundary where the Earth's spherical shape begins to influence seismic waves. The discussion raises questions about the types of events that can generate observable seismic waves below the Moho, noting that human-related blasts, such as those from mining, typically occur within the crust. The typical depth for mining-related blasts is often much shallower than the Moho. Additionally, there is curiosity about whether reflections can occur off the core-mantle boundary (CMB) and if there are other significant boundaries between the Moho and the CMB. The conversation highlights a lack of understanding regarding normal seismic activity and disturbances that may originate below the crust.

Apr 11, 2021

Twigg

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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.

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