We present a methodology for conducting a site-specific probabilistic analysis of fault displacement hazard. Two approaches are outlined. The first relates the occurrence of fault displacement at or near the ground surface to the occurrence of earthquakes in the same manner as is done in a standard probabilistic seismic hazard analysis (PSHA) for ground shaking. The methodology for this approach is taken directly from PSHA methodology with the ground-motion attenuation function replaced by a fault displacement attenuation function. In the second approach, the rate of displacement events and the distribution for fault displacement are derived directly from the characteristics of the faults or geologic features at the site of interest. The methodology for probabilistic fault displacement hazard analysis (PFDHA) was developed for a normal faulting environment and the probability distributions we present may have general application in similar tectonic regions. In addition, the general methodology is applicable to any region and we indicate the type of data needed to apply the methodology elsewhere.

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Locations, rates of occurrence, and composite focal mechanisms of microearthquakes in the Marlborough region are used to examine the tectonics of the region. Earthquakes in the upper crust reflect regional compression along ,an axis trending NW to WNW; their strike-slip and thrust mechanisms can be related to the regional geofogy. Seismicity deeper than about 20 km trends obliquely to the structural grain and appears to be intimately related to an underlying Benioff zone. Earthquakes in the 20-35 km depth range indicate a stress distribution markedly different from that in the upper crust and a predominance of normal faulting, suggesting either depthvarying stresses within continental crust or intraplate deformation within subducted oceanic lithosphere, depending on where the plate interface lies.

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