Answer:
soil liquefaction is the answer you're looking for.
The three rivers are;
The Satluj Basin
The Ganga Basin
The Brahmaputra Basin
Tectonically stable means that this part of the continent has not moved for billions of years. The rock formation is important understanding the history of Earth since its unmoved and untouched state can provide ideas about how the Earth looked like as seen on the layers of the rock formation.
I believe you can measure a lightning strike in miles!