Q1. Gradient versus sharp velocity changes. What is the best way to get closest to the reality?

: This question has been staying in my mind ever since, but especially more these days. This problem is important considering their different consequences in ground-shaking prediction. I would be happy to learn your ideas. 

Q2. What is the best approach for a passive seismologist to get closer to the world of active source seismology?

: Am I the only one feeling like a barrier/wall in between? If not, why? If yes, why!?

I have been gaining experience in answering the previous questions written in Jul 23, 2023, especially on Q3 (better joint inverting surface waves and body waves) and Q4 (assumptions too off from real earth). 

New questions, or a problem that I want to understand more, would be:

1. How can we build a seismic velocity model (Vp, Vs, and density) that explains high- and low-frequency measurements?

2. How can we build a model that is good enough to integrate well with local earthquake predictions (travel time, ground shaking hazard)?

3. What assumptions on inversion (i.e., prior constraints) are acceptable/helpful/harmful?

As always, let me know your interesting ideas!

I am interested in imaging the interior earth from very shallow to deep. Below are some questions I have in mind these days (Jul 23, 2023)

1. How much can we neglect the shallow structure (e.g., sediment, crust)?

2. What are the unexpected consequences of the shallow layers of the earth (e.g., seafloor sediment, water, sedimentary basins)?

3. How can we better joint invert surface wave measurements (phase velocity, group velocity, H/V, etc) and the scattered body waves (S and P receiver functions)?

4. Are there some assumptions that are too strong or off from the real Earth? 

5. Are we using sufficient/reliable information from the waveforms?

I enjoy discussions and learning new things! Let me know your interesting ideas!