Remote yield estimation of the underground nuclear explosions is possible by the inspection of different seismic phases. In order to estimate unknown yields, it is necessary to obtain relationships between seismic parameters and known yields of underground nuclear explosions. In this regard, the most important seismic parameters are the amplitude, body wave and surface wave magnitudes. Since the Pakistan nuclear explosion of May 28, 1998, was the first explosion in this country, there was not any relevant information. Therefore, to estimate the yield of the Pakistan explosion we need to find the necessary relationships. In Iran, only Iranian Long Period Array (ILPA) has recorded the Pakistan explosion. The methodology we used here is first to derive several relationships for Semipalatinsk Test Site (STS) east Kazakhstan, and then to employ these relationships for estimating the yield of Pakistan explosion. In this paper, different methods have been used to derive relationships between the recorded seismic parameters by the seismograms at ILPA and the known yields of STS. These methods include: the amplitude of P-wave with a period of one second, the body wave magnitude, mb, the surface wave (Rayleigh) magnitude in the time domain and in the frequency domain, Mf. The derived equations are as follows:
log(Y)=1.21 log(A)+ 2.80
mb = 1.05 log(Y)± 3.90
Mst=0.69 log (Y)+2.36
Msf= 0.80 log (Y) + 2.68
where, A is the amplitude of P-wave in micron and Y is the yield in kilotons TNT. Using above equations. the yield of Pakistan nuclear explosion has been estimated for five possible media which may affect the explosion test sites. These media were dry alluvium, water saturated alluvium, tuff, salt and granite. The yield average of this explosion is estimated to be 14 kt TNT with an error of± 20%.