To estimate the size of future earthquakes generated from active faults, it is important to define the extent of faulting from existing fault traces. This paper proposes new criteria for identification of segments for active strike-slip fault systems based on geometric surface rupture heterogeneity.
Geometric and structural characteristics are often used for fault segmenta t i on, in cases that historical and/or paleoseismological data are not sufficient to reveal coseismic behavior of faults.
We found an interdependent relation between the pattern of surface ruptures and the d i r ection of their propagation based on an investigation of recent earthquake fault ruptures. If a fault is associated with a simple baranching at one end in a plane view, it is rather simple to deduce the direction of future ruptures from its branching feature. If a fault brances at two ends, we may define a fault segment which raptures bilateralty and moves independanly at future earthuakes. If branchings of two faults face each other, we may expect a segment boundary between these branchings as a change in the direction of fault ruptures propagation take place between them.
Regarding dip-slip distribution along a strike-slip faul t segment, the upthrown sides is, in general, located in the area on the fault block in the relative strike-slip motion on a faulted block. For example, along an E-W trending right-lateral strike-slip fault, upthrown side is located toward the east end on the northern block and toward the west end on the southern block. Thus, a fault segment may be identified based on the pattern of dip-slip distribution.
We tested these criteria successfully on sever a rl recent surface fault ruptures and active faults, and applied them for segmentation of the active faults system of the Median Tectonic Line in Shikoku, Southwest Japan.