Displacement and Geometrical Characteristics of Earthquake Surface Ruptures: Issues and Implications for Seismic-Hazard Analysis and the Process of Earthquake Rupture

Abstract

There now exist about three dozen historical earthquakes for which in- vestigators have constructed maps of earthquake rupture traces accompanied by de- scriptions of the coseismic slip observed along the fault strike. The maps and slip distributions are compiled here to place observational bounds on aspects of seismic- hazard analysis and fault mechanics. Analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults. The observations also give support to the ideas that there exists a process zone or volume of about 3-4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults, and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes. To this may be added the observation that the form of earthquake surface-slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike. Online Material: Maps of surface ruptures, digitized values and curve fits to surface-slip distributions, and notes and references for Tables 1 and 2.