Dear P-Wave and S-Wave,
I hope you both are
enjoying your trips traveling beneath earth's crust while occasionally giving seismologists a chance to observe you at the ground surface. In this letter
I would kindly request you to answer some of my questions.
I will be honest. I am
not a seismologist. I am just a PhD student who happens to be working on your
biography. Even though you are quite famous among many seismologists and I see
a lot of academicians referring to you in research papers in a manner which
suggests a good deal of intimacy between you and them, your origins during an
earthquake still elude me. Quite frankly, I am tired of being in this state of
perpetual ignorance.
I have tried searching
for your origins and travel plans in journals and books. I have come to understand
the basics: the relationship between your speed and earth's properties; the motion-pattern followed by the neighboring medium particles upon your arrival;
your appearance through the Helmholtz Decomposition method when applied to the
governing equations of motion. But what perplexes me is that how to extract you
from a seismic record in a fool-proof way!
Some people like
Castellani and Bofi have suggested a plane-wave model to (1) trace the time spent by
you at a particular location and (2) compute the amplitudes generated in the
medium particles. But these knowledgeable people, who I in no manner wish to
offend, have failed to provide justification for the underlying assumptions of
the model and have left me with a lot of unanswered questions, for e.g. (1) what
is the nature of the source that is generating you (2) why should this method
be so heavily relied upon when it can offer no scope for attenuation of
particle amplitudes with increasing epicentral distances (3) how can the
assumed angle of incidence proposed for you be trusted.
Some people have even
suggested that you do not like to travel alone at large epicentral distances,
and charitably, give your cousins, Rayleigh Wave and Love Wave, a chance to
become famous. These astute people, in a similar fashion, have proposed
models to extract you and your cousins from a seismogram without addressing my
above doubts.
I have now turned my
attention to works of some other seismologists and academicians like Lamb,
Knopoff, Burridge, Sato, Kanamori, Kawasaki, Aki, Richards, etc. who have used
the Green's reciprocal theorem in modeling the expected motion resulting from a
discontinuity (they give it a fancy name : dislocation) in the displacement
field across the fault plane. Unfortunately, their work is substantially more mathematical
than previously briefly discussed methods. And sadly, due to my past experience, I have
lost some faith as to whether this pursuit will lead me to what I am looking
for.
Hence this letter.
I would be much
grateful if you could spare some time from your busy travel schedule and answer
this: what criteria do you use to prepare your travel itinerary under different
faulting conditions? I wish I could directly ask you the details of your future
travel plans but we all know it’s something you don’t share with anyone. In
your view, things will get very mundane for us humans if it were known. On that
note, allow me to clarify that I do not hold any negative opinion of you. Some
humans are quite afraid of the prospect of your arrival. I think it’s simply because
they are not adequately prepared to receive you. And it is because of this
reason that I wish to learn more about you so as to help my fellow human beings
to become less secluded and more ready to welcome you.
Yours humbly,
Varun
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