Characterisation of Surface Fault Rupture for Civil Engineering Design

Abstract

The general behaviour of surface rupturing faults can be predicted by empirical relationships among several physical parameters such as length, earthquake magnitude and average or maximum displacement. However the behaviour of a fault at a specific location along its length can be harder to forecast. If site-specific palaeoseismic data are available then, assuming characteristic fault behaviour, the displacement-per-event can be determined with some degree of confidence. What is poorly understood is the distribution of strain across the width of the fault damage zone; smaller, more distributed displacement on secondary fault strands are unlikely to be preserved in the palaeoseismic record. For an understanding of displacement distribution within the damage zone we need to examine historical earthquake surface ruptures. Unfortunately, due to a lack of detailed documentation of historical surface faulting events, there are few empirical data with which to characterize the distribution of strain during surface faulting events. Therefore, either we are required to perform expensive, invasive, site-specific fault investigations to characterize each fault crossing, or in the absence of detailed understanding of the characteristics of fault rupture, we generally have to adopt overly conservative and costly approaches to mitigation. A limited dataset of well-documented events provides the opportunity to study in detail the strain distribution within the damage zone, allowing the development of preliminary empirical models for surface rupture. This in addition to developing models of slip decay towards the ends of ruptures allows the development of better constrained mitigation measures including set-back distances