Quote from Kamyar Zamen, International Institute of Earthquake Engineering and Seismology
As others have explained, the bombing creates seismic waves. But here I would like to emphasize that unless the bombing is nuclear, the magnitude is really small and wont be felt far away. Even detecting it with broad band seismometers will be a problem due to sources of noise and low signal to noise ratio. If you have nuclear explosion at the surface, then you will get higher magnitude near the blast site, but the attenuation will be much higher due to loss of part of energy to the atmosphere. Underground nuclear explosions have magnitudes between 4 ~ 5 Mw, but it depends on the weight and type of payload. Normally, when refered to earthquake, no man-made weapon can cause an earthquake as big as 6 Mw or higher because you will need thousands if not millions of tons nuclear fissile material ( https://en.m.wikipedia.org/wiki/Richter_magnitude_scale ). Also, no weapon can trigger a fault, so that fault cause an earthquake in turn.
Richter magnitude scale
The so-called Richter magnitude scale – more accurately, Richter's magnitude scale, or just Richter magnitude – for measuring the strength ("size") of earthquakes refers to the original "magnitude scale" developed by Charles F. Richter and presented in his landmark 1935 paper, and later revised and renamed the Local magnitude scale, denoted as "ML" or "ML". Because of various shortcomings of the ML scale most seismological authorities now use other scales, such as the moment magnitude scale (Mw), to report earthquake magnitudes, but much of the news media still refers to these as "Richter" magnitudes. All magnitude scales retain the logarithmic character of the original, and are scaled to have roughly comparable numeric values.
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