REACTIVATION OF AN OCEANIC FRACTURE BY THE MACQUARIE RIDGE EARTHQUAKE OF 1989

THEORETICAL calculations show 1 that the occurrence of an earthquake leads to regions of increased shear stress on both sides of the ruptured fault. If this stress increase is sufficiently large, or if neighbouring faults are close to their failure stress, the result may be triggering of earthquakes on pre-existing faults in the region. A search for this effect 2 produced only a few examples, all in continental areas, where clusters of aftershocks were located in the regions of increased stress. The linear dimensions of these clusters were generally less than 20 km, and less than one-half of the fault length that ruptured in the main shock. Here I report an example of this phenomenon in which the fault that is reactivated is a nearly 175-km-long segment of an oceanic fracture, and its length is comparable to that of the main shock, the 1989 Macquarie Ridge earthquake.