Asking about the time- frequency graphs

Hi every one

I have some seismic data in time domain which is developed by BEM. The time step is 0.05, and the time is presented with unit second.

I prepare the frequency domain result by usuing the fft code :

y=load('filename.txt');

length(y)

Nsamps = length(y);

fs=20;

t = (1/fs)*(1:Nsamps);

y_fft = abs(fft(y));

f = fs*(0:Nsamps/2-1)/Nsamps;

y_fft = y_fft(1:Nsamps/2);

plot(f, y_fft)

xlim([0 10])

xlabel('Frequency (Hz)')

ylabel('Amplitude')

After that I have used the TFA by matlab code:

(Synchrosqueezing transform (SST))

aa= load ('Acceleration.txt');

Fs = 20;

wsst(aa,Fs,'bump','VoicesPerOctave',48)

I have a problem with time-frequency graph, the frequency range which is shown in this graph is not match with frequency graph that provided by fft.

Can you help me to solve this problem?

Thank you.