Abstract
Surface slip distributions for an active normal fault in central Italy have been measured using terrestrial laser scanning (TLS), in order to assess the impact of changes in fault orientation and kinematics when modelling subsurface slip distributions that control seismic moment release. The southeastern segment of the surface trace of the Campo Felice active normal fault near the city of L'Aquila was mapped and surveyed using techniques from structural geology and using TLS to define the vertical and horizontal offsets of geomorphic slopes since the last glacial maximum (15±3ka). The fault geometry and kinematics measured from 43 sites and throw/heave measurements from geomorphic offsets seen on 250 scarp profiles were analysed using a modification of the Kostrov equations to calculate the magnitudes and directions of horizontal principal strain-rates. The map trace of the studied fault is linear, except where a prominent bend has formed to link across a former left-stepping relay-zone. The dip of the fault and slip direction are constant across the bend. Throw-rates since 15±3ka decrease linearly from the fault centre to the tip, except in the location of the prominent bend where higher throw rates are recorded. Vertical coseismic offsets for two palaeo earthquake ruptures seen as fresh strips of rock at the base of the bedrock scarp also increase within the prominent bend. The principal strain-rate, calculated by combining strike, dip, slip-direction and post 15±3ka throw rate, decreases linearly from the fault centre towards the tip; the strain-rate does not increase across the prominent fault bend. The above shows that changes in fault strike, whilst having no effect on the principal horizontal strain-rate, can produce local maxima in throw-rates during single earthquakes that persist over the timescale of multiple earthquakes (15±3ka). Detailed geomorphological and structural characterisation of active faults is therefore a critical requirement in order to properly define fault activity for the purpose of accurate seismic hazard assessment. We discuss the implications of modelling subsurface slip distributions for earthquake ruptures through inversion of GPS, InSAR and strong motion data using planar fault approximations, referring to recent examples on the nearby Paganica fault that ruptured in the Mw 6.3 2009L'Aquila Earthquake.
Highlights
This paper examines the possible effects of bends and relay zones measured at the surface on subsurface slip distributions
The subsurface slip distribution is important for two reasons: (1) it defines the ruptured area and amount of slip, which alongside the stiffness of the deforming material define the seismic moment, or energy release in an earthquake (Kostrov, 1974; Wells and Coppersmith, 1994); (2) it is used to model how stress is transferred onto fault surfaces that were not ruptured in that particular earthquake, but could represent the sites of future earthquake rupture (e.g. Walters et al, 2009)
Our main finding is that an anomaly in the orientation of the Campo Felice fault plane has produced a local maximum in fault throw since 15 ± 3 ka and throw rate over this time period, even though the strain-rate represented by the faulting shows a simple, almost linear decrease towards the fault tip
Summary
M. Wilkinson et al / Geomorphology 237 (2015) 130–141 ruptures to individual earthquakes can follow these discontinuities, wrapping around small-scale bends in the fault trace and crossing relay zones (Roberts, 1996a, 1996b; Wesnousky, 2006). Wilkinson et al / Geomorphology 237 (2015) 130–141 ruptures to individual earthquakes can follow these discontinuities, wrapping around small-scale bends in the fault trace and crossing relay zones (Roberts, 1996a, 1996b; Wesnousky, 2006) This implies that at depth the fault may be continuous across such small-scale surface discontinuities. The surface slip distribution can be examined by geomorphologists, in contrast, the subsurface slip distribution can only be inferred through inversion of seismological and geodetic data, and only for that particular earthquake (Fig. 1). In this paper we show that the subsurface slip-distribution is beyond the direct observation of geomorphologists, geomorphic observations of the surface slip distribution can provide fundamental constraints on these earthquake processes
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
