5.1 The journey of signals from the ground to the computer 2/2

Apparently each step of the signals' journey can mathematically be reversed. We could just as easily calculate the initial ground movement from the signal on our PC. This is evidenced by the following mathematical chart analysing the movement of the ground, which was brought about by the P-wave of the Ascension earthquake of the 18th February 1996 (the seismograph of the quake will be further examined below).

Fig. 44: The way back from the PC-signal to its cause - the ground-movement

Here the voltage-signal stored in the PC amounts to 32 millivolts. To this amplitude the filter has reduced the signal from 34,04 mV at the input of the filter. Since that voltage is caused by 40-fold amplification (i.e. kv = 40), at the input of the amplifier you find a signal of 0,851 mV, which is leaving the damping-resistance R_D.

To that value the voltage is reduced from the original induction-voltage of Uo=1,8 mV by ohmic resistance of the coil of the seismograph. That means - with a generator-constant of S = 191,5 Vs/m - a velocity-amplitude of vo = 9,4 �m/s for the movement of the induction-coil.

For a period of 5s the deflection of the coil is 7,48 �m. At the center of movement the deflection is reduced by k _λ and so is just AoB=5,88m. Due to the angular frequency ω = 2π/T and the adjusted mechanical damping g of the pendulum you can calculate the ground-amplitude a_o with the help of the transfer-function H(w) from AoB. (Cf. the diagram for the transfer-function above.)