How to identify the arrival of P,S and Surface waves?

[Alejandro]

Hi guys
I'been practicing some scripting on MATLAB for seismic signal analysis. I'm looking for a way to find the P and S wave arrival times, but without the need of looking at it visually. I mean, I could identify this wave visually, but I would like to implement a criteria for a script, for example, the one I'm using (not very accurate) the P wave arrival time will be picked when the seismic peak reach a value equals to 0.1*max(Vertical component of the seismogram), this is, when the amplitude value reach a value of 0.1 times the maximum amplitud of the vertical component seismogram.
I would like to use this arrival times to find the distance between source and detector.
My questions are:
i) In your experience, how do you identify the arrivals of the P, S and Surface waves?
ii) Which criteria do you use when picking seismic arrival times (P, S and Surface waves)? an amplitude threshold? a statistical approach?

thanks for your attention