What physical boundary separates the united states from mexico along much of its border?

Maybe a horizontal because its a pattern

Answerdistinguish between the mercalli scale and the richter scale;

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.