The June 9 Bolivia and March 9 Fiji deep earthquakes of 1994: I. Source processes

Abstract

We examined the source characteristics of the 1994 deep earthquakes of Bolivia (June 9) and Fiji (March 9) over a period range of 1–1000 s using moment tensor and body wave analyses. Moment tensor inversions from 100–1000 s reveal that these two earthquakes were essentially point sources at very long period with insignificant isotropic and non‐double couple components with scalar moments Mo = 2.56 × 1021 Nm for the Bolivia and Mo = 0.26 × 1021 Nm for the Fiji earthquakes. Body wave analysis for the Bolivia event reveals a 45 s duration, a nearly linear E‐NE 1 km/s rupture on the subhorizontal focal mechanism plane giving a stress drop Δσ = 114 MPa. For the Fiji earthquake we find a change in focal mechanism and a linear 3 km/s rupture plunging shallowly to the north on the steep dipping nodal plane with a duration of at least 20 s and Δσ = 14 MPa. Both ruptures propagated parallel their null (σ2) axis and suggests that their width is controlled by the thickness of the seismogenic volume in deep slabs.