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

Thread starter Twigg
Start date Apr 11, 2021
Tags

Earth Matter Seismic Spherical

AI Thread Summary

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

Science Advisor

Gold Member

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.

Thread 'Landslide, tsunami, seiche in Tracy Arm fjord, Alaska - 10 August 2025'

On August 10, 2025, there was a massive landslide on the eastern side of Tracy Arm fjord. Although some sources mention 1000 ft tsunami, that height represents the run-up on the sides of the fjord. Technically it was a seiche. Early View of Tracy Arm Landslide Features Tsunami-causing slide was largest in decade, earthquake center finds https://www.gi.alaska.edu/news/tsunami-causing-slide-was-largest-decade-earthquake-center-finds...

View full post »

Thread 'Could an external cosmic body have influenced Earth’s geology?'

Hello, I’m currently writing a series of essays on Pangaea, continental drift, and Earth’s geological cycles. While working on my research, I’ve come across some inconsistencies in the existing theories — for example, why the main pressure seems to have been concentrated in the northern polar regions. So I’m curious: is there any data or evidence suggesting that an external cosmic body (an asteroid, comet, or another massive object) could have influenced Earth’s geology in the distant...

View full post »

Thread 'Thwaites glacier instability'

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JF008118 A recent paper on the attempts to estimate when and how massive the Thwaites breakup may be.

View full post »