# Core Mantle Boundary Ray Reflection Geometry

I have a Raspberry Shake and Boom and have been noticing the arrival time variations on the PcP, ScP, PcS and ScS arrivals.

I presume this is mainly due to deviations of the core mantle boundary from “spherical” in the iasp91 model.

How could I extract the data from Obspy to map the variations? e.g. position (lat and lon, depth or radius, approach angle and departure angle). Using this data and the wave velocities at that depth, the true position of the reflection point on the CMB should be able to be calculated for mapping.

Thanks,

Al.

I’m not sure, I understand what you are asking exactly. Are you asking how to use obspy’s taup port to calculate phase timings based on custom 1D models for station/receiver combinations?

Phase timings are not a problem. I have my head around that.

I regularly see actual PcP and ScP phase arrivals which deviate from the predicted arrival time by up to a few seconds. I presume this is the result of the CMB not being perfectly spherical/elliptical.

For example, an arrival that is 1 second early c.w. the theoretical arrival time suggests the CMB is higher than the theoretical model at that point. i.e. the travel distance is less so the travel time is less.

What I want to know, is how to calculate where the reflection point on the CMB is, and what the approach and departure angles are at that point? The ray paths are plotted, so presumably that information must be calculated or used or in a form that can be manipulated to give the position of the reflection and the approach and departure angles.

If I have that information, I reckon I can calculate the true position and height of the CMB, and so produce a map of the “ridges and valleys” in the CMB.

I’ve seen similar 3D models of proposed “structures” in the core, which is a much more complex problem to solve.

Am I making myself clear?

Thanks,

Al.

As an example, here is a PcP arrival that is possibly 3s late, suggesting the CMB is lower than the iasp91 model at the point of reflection. I want to try to calculate the true reflection point position.

FYI I use the Specific Energy Plot in particular to identify the actual arrival time.

Ah, I understand. I believe the information you’re looking after should be there (I remember stuff going on about the pierce point information), but I have to admit that I didn’t use those things myself, so I can’t give you pointers really. Maybe somebody else can help?