"Tail-like" response from digital microphone
The tail is most likely the impulse response of a high pass filter. All acoustic system  are highpass by nature since air really can't transmit DC pressure. In addition many data acquisition systems have DC blocking filters and/or high passes build in to keep undesirable "rumble" signals that's below the range of hearing out of the recording.  

Could also be in the microphone itself. It looks like you are hitting really hard and the recording is clipped. It takes a bit of time for the microphone and the pre-amp to recover from a major overdrive.