Simultaneous Rupture along Two Conjugate Planes of the Wharton Basin Earthquake

Analysis of broadband teleseismic data shows that the 18 June 2000 Wharton Basin earthquake, a moment magnitude 7.8 intraplate event in the region of diffuse deformation separating the Indian and Australian plates, consisted of two subevents that simultaneously ruptured two near-conjugate planes. This mode of rupture accommodates shortening by a mechanism different from that previously known elsewhere in the region. The larger subevent occurred on a fossil fracture zone, with a relatively high stress drop of about 20 megapascals, showing that large stresses can accumulate in regions of distributed deformation.