Seismicity and aseismic slip along the Eltanin Fracture Zone

Table Al is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue N.W., Washington, DC 20009. Document B83-006; $2.50. Payment must accompany order. The seismic history of the Eltanin Fracture Zone on the Pacific-Antarctic Ridge for the years 1920-1981 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction (less than 10%) of the amount of slip predicted by kinematic models of plate motion. We propose that the remainder of the plate motion along the transform faults making up the Eltanin system occurs as aseismic creep. This property singles out the Eltanin among transform systems, where previous studies have found good agreement between seismic slip and predicted rates of motion. The absence of record of any gigantic earthquakes and the geometry of the fault area reduce the likelihood of the Eltanin rupturing along its entire length. We interpret the Eltanin Fracture Zone in the light of an "asperity" model, involving small, well-separated asperities. Its segmented nature and creeplike behavior may be due to the presence of excess magma and, possibly, local upwelling, which could also be involved in the mechanism of generation of the Louisville Ridge.