Hi I'm Don Garcia and I'm going to explain this technique called alzapua. This is a very unique and particular technique in flamenco guitar. It consists of a thumb movement and it's three different moves that your thumb is going to make.
First, your thumb is going to come down on the target string, which is usually the lowest string you're going to play, and usually a bass string, so that's the first move.Then the thumb is going to go and play at least two strings below that, and then it's going to come back up and play those strings again, in an upward motion.
To begin the alzapua technique, it's a good idea to do it in a triplet rhythm, so three notes per beat. So one-two-three, one-two-three, one-two-three. Notice this is a wrist movement also. Your wrist is helping your thumb and I repeat, your wrist not your arm, just like we talked about in the pulgar videos.
You want to have your index always, either touching or very close to the first string, this way we get this kind of movement. We want this, not this. So we go down on one string, down two strings and up, so that's alzapua. Have fun with that.