Delimitation of domains with uniform stress in the subducted Nazca plate

Abstract

This work concentrates on the determination of detailed variations of stress in the descending Nazca plate and is based on the distribution of seismic activity and the orientation of P- and T-axes of fault plane solutions. International Seismological Centre (ISC) and Harvard Centroid Moment Tensor Solutions (HCMT) data were used. The method of Gephart and Forsyth [J. Geophys. Res. 89 (1984) 9305–9320] was applied to determine the state of stress. It is shown that the state of stress varies along the whole Wadati–Benioff zone, where 16 different domains with uniform state of stress were delimited. The state of stress tends to change more systematically with the depth of the Wadati–Benioff zone than laterally, and is connected with the morphology of the Wadati–Benioff zone. A decreased stability of the state of stress in the Wadati–Benioff zone was found in the depth range 50–300 km. The state of stress in the depth ranges 0–100 km and deeper than 500 km appears to be very stable. The physical interpretation of the observed phenomena is not the subject of this investigation.