Banjawarn is a remote pastoral station in Western Australia, out where the mulga scrub of the Goldfields gives way to the Great Victoria Desert, north of the mining town of Leonora. In 1993 it was bought by a front company for Aum Shinrikyo, the Japanese doom cult that two years later released sarin on the Tokyo subway. In the same year, on a night in late May, something shook the desert nearby hard enough to register on seismographs across the country. The coincidence has fed one of the most persistent theories of the 1990s: that the cult tested an atomic bomb in the outback.
What happened
The event came at about 11 p.m. on May 28, 1993. People scattered across a thinly populated region, among them prospectors camped in the bush, long-haul truck drivers on the Leonora to Laverton road and members of Aboriginal communities, later described a bright light or fireball crossing the sky, flashes, and a deep, drawn-out boom. Geoscience Australia recorded a seismic event of about magnitude 3.6 and at first logged it as a small earthquake. The local Kalgoorlie Miner ran a short item on the fireball, and the matter was forgotten.
The investigation
Aum’s interest in the area is well documented, mostly through a 1995 staff report of the United States Senate’s Permanent Subcommittee on Investigations, which drew on files from the Australian Federal Police. Senior cult figures, including its construction chief Kiyohide Hayakawa, flew into Perth in April 1993 and toured remote stations, running unexplained tests with a laptop and electrodes pushed into the ground. Hayakawa’s notes show an interest in Australian uranium. An offer to buy Banjawarn outright was refused, so the cult set up companies and bought the lease through one of them in June 1993, for about $400,000. In September the cult’s leader, Shoko Asahara, arrived with two dozen followers and a mountain of excess baggage, from generators and gas masks to chemicals; customs seized acids hidden in soap containers, and two members were fined. A small laboratory was later set up on the property, which the cult sold at a loss in July 1994. After the Tokyo attack in March 1995, police searched it and, by the ABC’s account, found traces of sarin in the remains of 24 sheep and in the surrounding soil, evidence the cult had tested nerve agent there.
The seismic event was pulled into this story by Harry Mason, a geologist and UFO enthusiast with an interest in exotic weapons. In 1995 he collected witness accounts, searched for a crater without finding one, and proposed that Aum had set off a nuclear device or an electromagnetic weapon. He took his case to the Senate investigators, who asked the Incorporated Research Institutions for Seismology to examine the records. A New York Times report in January 1997 brought the theory to a wide audience, and Bill Bryson later repeated it in a popular travel book.
The explanations
The seismologists did not find a bomb. The team, Christal Hennet and Gregory van der Vink of IRIS with Danny Harvey of the University of Colorado and Christopher Chyba of the University of Arizona, presented its analysis to the American Geophysical Union in May 1997. It ruled out a nuclear explosion. The waveforms were smoother than an explosion produces and more like those of a natural earthquake, and the team suggested an iron meteorite more than three meters across, striking the ground, as another possibility. Such an impact should have left a crater more than 90 meters wide, and none has been found. Australian authorities likewise concluded that the signal was the wrong type for a nuclear test and that the cause was most likely an earthquake or a meteorite.
The timeline is the weakest point of the bomb theory. The Senate report shows that Aum did not complete its purchase of Banjawarn until June, after the event, and did not bring people and equipment onto the property until September. Building a nuclear weapon would also have required enriched uranium or plutonium, and despite the cult’s approaches in Russia there is no evidence it ever obtained either. A Senate counsel later said investigators came to believe the cult’s members were out of the country on the night in question.
Where it stands
The cause of the 1993 event has never been pinned down beyond the choice between a modest earthquake, possibly coinciding with a bright meteor, and a meteorite impact whose crater nobody has located. The idea that Aum Shinrikyo detonated a nuclear device at Banjawarn is not supported by the seismic record, the chronology or the cult’s capabilities. What happened at the station afterward was real and sinister: it was a place where a group planning mass murder tested its poison on sheep.