Analysis of information sources in references of the Wikipedia article "Tsar Bomba" in English language version.
Despite being exploded in the atmosphere, it generated substantial seismic signals. According to a bulletin of the U.S. Geological Survey it had seismic magnitude mb = 5.0 to 5.25 . ... from fireball radius scaling laws, one would expect the fireball to reach down and engulf the ground ... In fact, the shock wave reaches the ground ... and bounces upward, striking the bottom of the fireball, preventing actual contact with the ground.