The Gujarat quake started just 9.6km below ground. The point underground where rock begins to break up at weak seams or fault lines - triggering the shock waves - can be up to 720km deep but it is usually less than 72km.
The Gujurat region stands on a layer of hard sandstone rock resting on softer alluvial deposits.
As the quake struck the alluvial layer flexed upwards, forcing the surface sandstone to break up along a 70km fault line in the Rann of Kutch, before lifting upwards creating dramatic 7m wide cracks in the ground at the quake's epicentre, in a salt marsh about 40km north of Bhuj.
Powerful shock waves travelled much further through the Kutch region, transmitted through the alluvial layer.
Waves of energy travelled far beyond the 70km fault line, as far down as Gujarat's biggest city Ahmedebad 400km away, where nearly 100 buildings collapsed.