Source rupture process of the Papua New Guinea earthquake of July 17, 1998 inferred from teleseismic body waves

Abstract

A large earthquake (Ms 7.1) occurred off northwest coast of Papua New Guinea (PNG), and a massive tsunami attacked villages to cause a devastating damage. In an attempt to ascertain the tsunami source, we investigate the source rupture process using teleseismic data at IRIS network as well as local data at Jayapura, Irian Jaya, station. The source parameters obtained are: (strike, dip, slip) = (301°, 86°, 91°); the seismic moment = 4.3 x 1019 Nm (Mw = 7.0); the duration of main rupture = 19 s; the centroid depth = 20 ± 5 km; the extent of rupture along the fault strike = 40 km; the average dislocation = 1.8 m; the stress drop = 7.3 MPa. The tsunami magnitude Mt determined from tide-gage data at long distance is 7.5, significantly larger than Ms, so that the PNG earthquake is characterized as a tsunami earthquake. Tsunami earthquakes might have been caused by slow rupture, submarine landslide, and high-angle dip-slip. Our teleseisimic analysis precludes the first two candidates and favors the third one as a source of the present earthquake, although it does not necessarily exclude the possibility of an aseismic landslide induced by the main shock or its aftershocks.