The mystery of the series of aftershocks that ranged more than 400 km away from the epicenter of the 1992 Landers earthquake in southern California may be solved, according to a report in the September 29 issue of Nature. Seismologists at the Carnegie Institution in Washington have an interesting interpretaion of data obtained by instruments in Long Valley. They suggest that bubbles of gas in the molten rock beneath the Earth's crust may be responsible. When an earthquake hits, pressure waves radiate from its epicenter. Though the pressure waves themselves go unnoticed, they can trigger aftershocks in volcanic areas at large distances.