c ML Magnitude  (JCL 4/5/2005)
      	
	real ml

1       print *, 'Compute local magnitude, ML, given distance (km),',
     *    ' depth (km),',
     *    ' maximum peak-to-peak amplitude (microns) and period', 
     *    ' (seconds) of earthquake signal.'
        print *, 'What is the distance, depth, amplitude & period?'
        read(5, *) dist, depth, amp, t

c first find the magnification of a Wood-Anderson seismograph at this period.

	f = 1/t
	fzero = 1.25
	b = 0.8
	staticmag = 2080.
	wamagnif = staticmag * (f)**2 /
     *    sqrt((fzero**2 - f**2)**2 + 4*(b*fzero*f)**2)
	write(6, '(a, f5.1, a, f6.0)') 
     *    ' Wood-Anderson magnification at ', f, 'Hz = ', wamagnif

c computer the amplitude in mm that would have been measured on a W-A
	a = amp * wamagnif / 1000

c although depth was not used in the original formulation because the 
c earthquakes in California are shallow (for the most part), depth is 
c used here to allow for large depths in other areas, as is the 
c practice in Alaska.

	d = sqrt(dist**2 + depth**2)

c select the correct values for b1 and b2
c allow d to be as large at 1000 km, even though the original ML limit was 600 km.
	if (d .lt. 1) then
	  print *, 'Distance must be larger than 1 km.'
	  stop
	else if(d .lt. 200.) then
	  b1 = 0.15
	  b2 = 0.80
	else if(d .gt. 1000.) then
	  print *, 'Distance must be less than 1000 km.'
	  stop
	else
	  b1 = 3.38
	  b2 = 1.50
	endif

	ml = alog10(a/2.) -b1 + b2*alog10(d**2)

	write(6, '(a, f5.1)') ' ML = ', ml
	goto 1

      	stop
      	end