As far as I know, in seismology, we usually assume the dislocation on the fault is unidirectional thus we only see a positive part on displacement record. However, I could see not a few traces with a large negative part. Dose it mean the dislocation reverse it direction? Thanks!
if I understood your question correctly polarity is primarily controlled by radiation pattern for the very first pulse (but later in the CODA after STF length it will depend on reflection or refraction of waves based on the medium) which essentially is the type of dislocation (e.g. thrust, normal,strike-slip). As far direction of rupture is concerned it only enhances energy in the direction of propagation.
Hope it helps
I'm a little confused about your answer. I mean I could see some displacement records have shape similar to velocity records rather than a typically half-period sine function without the negative part. By the way, the events that I try to study are deep earthquakes. I think the source time function should be simple, which will not be contaminated by the reflection or refraction.
Now, I see you point now. Since you say you are looking at deep earthquakes and this relationship between displacement and velocity record works for double couple or with zero volume change earthquakes there could be a non-double component , causing this disparity. Though I am not sure just a thought from top of my head.
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