Ok this is how I think tremorsense should work:
When activated with a click you will be able to see through all earth blocks, in a 20 block radius. connected to the place you are standing. All none bendable blocks (air included) will look like void blocks (execept the ones vible to you normally. If an entity in standing on earth them they will also be shown, and there will be glowstone there feet, which can be seen through any block including none bendable. This is because let's say you are in your house that has stone floors, you activate this ability and see there is a burgaler in your house because you are touching the floor and so is he, glowstone will be shown up at the place they are stepping, that can be seen through the wall.
I hope this gives an idea or solves the problem. This gives earth a cool move that actually is useful.