when someone has extreeemely large thighs (guy or girl) may be a very muscly guy and may involve OVERHANG. these thighs are so powerful that when running is done by the individual, the ground may rmble like thunder hence 'thunder' and some times sparks may be produced like lightining.
A - "wooow what the hell is that???"
B - "EARTHQUAKE!!!!!!!"
A - "oh wait no its only Jimmy and Singo, jesus look at those thunder thighs!!!!!"