SEISMIC VIBRATION MONITORING
Instrumentation for geognostic investigation
The survey methodologies based on passive seismic may be of "on time" type, where the instrument performs a constant recording of the signals coming from the sensor connected to it, or of "trigger" type. The seismic vibrations monitoring called "trigger", or threshold, is one of the methodologies the non-destructive testing (CND) surveys are made up of and it is widely used within structural monitoring and dynamic surveys on the structures. In the trigger acquisitions such "stand alone" seismographs are used; these are specifically designed for the continuous seismic monitoring, where even if they are constantly listening, they are ready to start recording as soon as an event exceeding the trigger threshold (time 0 , start of recording) set in the instrument at the programming time. The sensors used are usually the tri-axial low frequency 1, 2 Hz type.