Theoretical Seismology
Spring Semester, 2005
Computational Problem In Reflectivity
For this exercise, I would like the class to work on the reflectivity problem together. Specifically, I would like you to execute the reflectivity code to generate synthetic seismograms for a variety of earth problems. This code should be linked via a pathway set up in your chsrc file.
crfl is a general code written originally by G. Muller and modified by many of us over the years. It is the most general code that I am aware of, but not necessarily the fastest. Its generality comes from the ability to vary many parameters such as depth of source, type of source (with a moment tensor formulation), introduction of Q, etc. It also allows flat vs. spherical earth coordinates depending upon the application. The file has an excellent Readme discussion, but you should copy and read it carefully. Also read the sections of the papers and tutorials that I handed out. Because of some confusion with the input, I have included some the definitions on the attached part for example 2.
To assist on what the range of slownesses (angles of incidence) for a given velocity model and to identify the types of waves you should use, I suggest that you use MacR1D, which allows you to vary the time window, distance, and slowness ranges, and to plot out the arrival branches using ray theory.
Attached are examples of the output, plotted on Z-plot, for the first two test cases to be run.
For the class assignment everyone should do problems 1 and 2, then each individual can do their version of problem 3.
1. For the simplest example, run the half-space model (this is essentially the case for Lamb’s problem) and a point source on the surface:
= 1.8 km/s
= 0.9 km/s
= 2 g/cm3
a) First make sure the model runs with the example shown.
b) Then execute different slowness and frequency windows to learn how the program operates. For example run the model with a slowness window only to include body waves, then body and surface waves. Run the program with short and long time-domain windows to simulate aliasing in the time domain. Then filter the latter data to exclude the surface waves.
c) Run Zplot or other seismic plotting package with and without gain ranging on a couple of examples.
d) Be sure and identify the wave types.
2. For the more complex model, shown on the attachment.
a) Run and verify the model.
b) Identify the main branches. To do this you should run Zplot with and without gain ranging.
3. For the last problem, run a model of your own choice which could be useful to your research or general understanding.
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