We report the results of a microearthquake experiment conducted in 1987 in the active transform portion of the Kane Fracture Zone. The Kane is a slow slipping (25 mm/yr), large-offset (150 km) transform delineated by a pronounced transform valley. The experiment site lies in the eastern half of the transform, 40 km west of the eastern ridge-transform intersection, in a region of marked transform-parallel topography. The network consisted of 12 ocean bottom hydrophones and seismometers and extended for 25 km along the transform and 10 km in width, spanning the transform valley and a narrow median ridge to the north. Hypocentral parameters were determined for 86 earthquakes. Epicenters within the network define a narrow transform-parallel trend along the steep southern wall of the transform valley. Maximum focal depths increase from 6 to 9 km from east to west across the network. Significant activity was also detected outside the transform tectonized zone. To the southeast this activity may be associated with the inside corner of the ridge transform intersection, while to the north about 20 events occurred in 7-m.y.-old crust in a region of ridge-parallel bathymetry. Six focal mechanisms were obtained from P wave first motions for events within the trnsform valley.

The best constrained solutions, for four earthquakes within the network, show normal faulting on fault planes subprallel to the trend of the transform. All the mechanisms indicate a tension axis perpendicular to the trend of the transform. These results together with a significant historical record of large earthquakes near the experiment site lead us to conclude that the principal transform displacement zone was inactive during our experiment and that the activity we recorded is the result of extension in the adjacent lithosphere. The observed focal mechanisms and the the inference that the axis of least compressive stress is approximately perpendicular to the transform provide direct evidence that the transform fault is mechanically weak relative to the surrounding lithosphere. Potential sources of extension across the transform include thermal stress in the young oceanic lithosphere, topographic loading, a small component of plate divergence normal to the transform, and northward motion of the asthenosphere relative to the surface plate. ¿ American Geophysical Union 1990