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

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SUMMARY

The discussion centers on the significance of seismic ray-tracing in geophysics, particularly regarding the Earth's spherical shape and its implications for wave propagation. It is established that the Earth's spherical geometry becomes relevant at depths of approximately 35 km, coinciding with the Mohorovičić discontinuity (Moho). The conversation highlights the need for clarity on the types of seismic events that can generate waves below the Moho, such as potential reflections from the core-mantle boundary (CMB) and the depth range of human-induced seismic activities like mining blasts.

PREREQUISITES
  • Understanding of seismic ray-tracing principles
  • Familiarity with the Earth's structure, including the Moho and CMB
  • Knowledge of geophysical wave propagation
  • Basic concepts of human-induced seismicity, particularly mining activities
NEXT STEPS
  • Research the types of seismic waves generated by events below the Moho
  • Study the characteristics of reflections from the core-mantle boundary (CMB)
  • Explore the depth ranges and effects of mining-related seismic blasts
  • Investigate the implications of Earth's spherical shape on seismic modeling
USEFUL FOR

Geophysics students, seismic analysts, and professionals involved in earthquake research or mining operations will benefit from this discussion.

Twigg
Science Advisor
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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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