Dept. of Earth Sciences
University of Oxford
Oxford, UK
Email:
das@earth.ox.ac.uk
poster/oral: poster
| We present an example of dynamic stress triggering of a second earthquake with Mw 7.4 15 seconds after the initiation of the first earthquake with Mw 7.8, but on the conjugate fault plane. This is the first clear recent example known to us of this behavior, the 1927 Tango, Japan earthquake also being believed to have ruptured two perpendicular faults. The earthquake occurred on 18 June 2000 in the middle of the Wharton Basin of the Indian Ocean, far from all major plate boundaries. The first earthquake ruptured a 80 km long segment along an old fossil fracture zone, with about 8 m of average slip and a very large stress drop of 21 MPa. The second rupture on the near-conjugate fault was 50 km long, with an average slip of 3 m and stress drop of 8 MPa. The second fault was parallel to the ridge fabric which is perpendicular to the old fracture zone and was the plane of weakness emplaced at the time of formation of the oceanic crust. The rather large stress drop of the first earthquake may have been cause of the dynamic triggering of the second one. D. P. Robinson, C. Henry, S. Das and J. H. Woodhouse (2001), Simultaneous Rupture Along Two Conjugate Planes of the Wharton Basin Earthquake, Science, 292, 1145-1148. C. Deplus (2001), Perspectives: ``Indian ocean actively deforms", Science, 292, 1850-1851. |