Slip compensation at fault damage zones along earthquake surface ruptures

Surface ruptures associated with earthquake faulting commonly comprise a number of segments, and the discontinuities form tip and linking damage zones, which are deformed regions consisting of secondary features. Stress transferring or releasing, when seismic waves pass through the discontinuities, could produce different slip features depending on rupture propagation or termination. Thus, slip patterns at fault damage zones can be one of the key factors to understand fault kinematics, fault evolution and, hence, earthquake hazard. In some previous studies (e.g. Peacock and Sanderson, 1991; Kim and Sanderson, 2005), slip distribution along faults to understand the connectivity or maturity of segmented faults system have commonly been analyzed based on only the main slip components (dip-slip or strike-slip). Secondary slip components, however, are sometimes dominant at fault damage zones, such as linkage and tip zones. In this study, therefore, we examine slip changes between both main and secondary slip components along unilaterally propagated coseismic strike-slip ruptures. Horizontal and vertical components of slip and the slip compensation patterns at tip and linking damage zones are various from slip deficit (decrease in both slip components) through slip compensation (increase of vertical slip with horizontal slip decrease) to slip neutral. Front and back tip zones, which are classified depending on main propagation direction of earthquake ruptures, show different slip patterns; slip compensation is observed at the frontal tip whilst slip deficit occurs at the back tip zone. Average values of the two slip components and their compensative patterns at linking damage zones are closely related with the ratio of length to width (L/W) of linkage geometry; the horizontal slip is proportional to the ratio of L/W, whilst the vertical slip shows little dependence on the value L/W. When the L/W is greater than ~2, average values of two slip components are almost similar to those of the main traces. In contrast, when the L/W < 2, the vertical slip is either increased or decreased as the horizontal slip is decreased, depending on the maturity of the linking zone. Thus, we argue that slip patterns at linking damage zones may be controlled by the LW-ratio of linking damage zones and hence structural maturities of the segmented fault systems. In conclusion, slip patterns at fault damage zones along earthquake surface ruptures are various depending on the maturity of linkage zones and/or the rupture propagation direction. Therefore, the consideration of slip compensation as well as damage structures along surface ruptures must be very useful to understand fault evolution and, hence, to assess seismic hazards around active fault systems.