The hand posture of a Buddha is also called mudra. The gesture depicted here is the gesture of touching the earth. The Buddha's right arm hangs above the knee and the palms of his hands point inwards. All fingers point down. The left hand lies on the lap with the palm of the hand open upwards. The seated Buddha touches the earth with his fingertips to call upon it as a witness to the truth of his words.
The sculpture was produced by hollow casting. This saves enormous weight and the article is much lighter!