The method that you cited is quite used for the slope stability in case of earthquake. The relation between horizontal acceleration and magnitude is used to asses the stability of the soil (liquefaction e.g) by the evaluation of the number of cycles. Going back to the question, the magnitude used is ML (which is based on induced displacement in ground), so you have a ratio between acceleration and "displacement". This is "appropriate" to define the stability of wedges.
Enclosed a compilation for you to determin the horizozal coeffizient to calculate the slope stability. Methods: first according to standard second with FEM, see pdf. I dont know if in India exists a standard for that?
At risk of liquefaction of soil failure these methods. You must investigate the soil characteristics then. Is there a danger to soil liquefaction, one should improve the soil, or prevent that dynamic loads occur.
@Andrea Leanza, Thanks. I have used some standard relations of Bray (1998) and Hynes-Griffin and Franklin (1984). I am getting allowable displacement considering seismicity of my region.
@Michael Lersow, Thank you very much for that pdf. Interesting content. However, i am dealing with rockmass not soil but still thanks again. I got my answer.
it is not different between hard rock and loose rock. It is the same procedure.You can use everything which is describes in the pdf-file.
But the danger of liquifaction exists only at loose rock, of course. But, you have not described the material, to which you relate your question, sorry.
It also depends on the scale. If it is a regional scale, or between site-specific and regional I would recommend Arias Intensity or similar (http://www98.griffith.edu.au/dspace/bitstream/handle/10072/42218/73244_1.pdf?sequence=1).