The magnitude 7.9 Bonin Islands earthquake sequence in May 2015, which ruptured deep within the earth near the base of the upper mantle, did not include an aftershock that extended to record depths into the lower mantle, according to a study appearing in The Seismic Record.

When Hao Zhang of the University of Southern California and colleagues re-examined the aftershock sequence of the earthquake, they did not find evidence for a 751-kilometer-deep aftershock as reported by previous researchers. This aftershock has been called the deepest earthquake ever recorded.

Instead, their study found a distribution of aftershocks that is compatible with a 12-kilometer sliver of a mantle mineral called olivine that could shed light on how deep earthquakes can occur.