Constraining recent fault offsets with statistical and geometrical methods: Example from the Jasneuf Fault (Western Alps, France)

Abstract

We propose two new approaches regarding recent fault offset measurements by studying the seismogenic potential of the Jasneuf Fault.The NE trending right-lateral strike-slip Jasneuf Fault is the southwestern extension of the Belledonne fault system in the Vercors Massif. This fault, which is located in an intraplate domain, does not show strongly associated seismicity but displays morphological anomalies that are related to recent faulting (right-lateral offset of Late Cenozoic cliffs, recent talwegs, and post Günz scarps).The two methods that we use to quantify fault slip are as follows. 1 - Recursive measurements of stream offsets are conducted. This analysis reveals that a stream network can display characteristic distances between streams that can be mistakenly interpreted as long-term cumulative fault offsets. A comparison of the apparent stream offset values and stream spacing values is necessary to identify the true offsets. 2 - We propose a new method that enables us to determine the fault offset and kinematics by using recursive measurements of topographic apparent offsets to counter the lack of morphologic features that are used to determine piercing points or lines. This method enables us to define each possible slip vector for numerous artificial piercing points along a fault. The slip vector that is shared by these piercing points is the true slip vector.By applying these methodologies, we determine that the Jasneuf Fault has accumulated slip since the Messinian, which corresponds to an average slip rate of 0.13±0.03mmyear−1. The extension of the fault is poorly constrained. Nevertheless, if we do not consider the potential aseismic (creep slip) component of the faulting, we calculate that this fault could generate Mw 5.7 earthquakes every ~500years according to Wells and Coppersmith's scaling laws and by assuming that the faulting is limited to the sedimentary cover and the Vercors Plateau.