Teleseismic investigation of the January 22, 1988 Tennant Creek, Australia, earthquakes

Abstract

The three January 22, 1988, earthquakes are the largest to occur within the Australian continent in 20 years and produced two colinear but discontinuous WNW trending scarps enclosing a shorter ENE trending scarp. Teleseismic long period P and SH and short period P waves are used to constrain the locations and source parameters for the three events. The third earthquake has a seismic moment (1019Nm) equal to that of the 1968 Meckering event and most likely ruptured the southern of the WNW trending faults. Relative relocations suggest that the two smaller earthquakes initiated north or NW of the third event. Centroid depths are less than 6 km, but most likely 3 to 4 km, and source durations are 4 to 6s so it is probable that each event broke the surface. All three earthquakes have predominantly thrust mechanisms and nodal planes that strike west to WNW, consistent with faults dipping southward at 30° to 40°. Only the first has a nodal plane that could support a north dip for the ENE trending fault, as proposed by other researchers on the basis of ground deformation and preliminary aftershock locations. However, source directivity evident in the short period P waves and relocations are interpreted better if this event, like the others, ruptured a SW dipping fault plane. The ENE trending scarp is interpreted to be a tear fault in the hanging wall that may have acted as a barrier to slip on a single continuous SW dipping fault, resulting in this unusual, at least for Australia, sequence of three large similar earthquakes.