Defining fault avoidance zones and associated geotechnical properties using MASW: a case study on the Springfield Fault, New Zealand

Abstract

a b s t r a c tThe Springfield thrust fault at Dalethorpe, west Canterbury, New Zealand, provides a test case to explore the correlation between shear wave velocities at a range of scales, and direct field observations of distributed deformation and outcrop properties. The Springfield fault ruptures to the surface through hard Torlesse greywacke, overlain on a flight of late Quaternary glacio-fluvial terraces by~5 m of gravel. Fault slip has displaced all but the lowest terraces, revealing the geometry and location of faulting. We used multi-channel analysis of surface waves and meter-scale cross-hole measurements to map shear wave velocities below the lowest, apparently undisplaced, terrace. We correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory. Both field and laboratory results indicate that the shear wave velocity of Torlesse greywacke declines sharply with increasing fracture density. Field surveys further indicate that relatively unweathered, high velocity greywacke is being exhumed in a bivergent wedge between two oppositefacing thrusts. The fracturing and low shear wave velocities are focused in a wide, low-velocity damage zone that has developed in the hanging wall of the main thrust, and a smaller but similar feature in the hanging wall of the backthrust. This is consistent with the geomorphology of the site. Our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain. This type of analysis has utility for land use planning on, or close to, active faults, especially where they are obscured by fluvial deposits.

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation

“…The multichannel analysis of surface waves (MASW) method has been used to generate extensive data in a variety of natural and synthetic materials (e.g. Greenwood et al ., ; Duffy et al ., ). MASW employs a linear array of geophones and an impulsive source, or harmonic oscillator, to generate and measure Rayleigh waves.…”

Shear‐wave velocity structure from MASW and SPAC methods: The case of Adra town, SE Spain

“…As a consequence of the convergence between the African and Eurasian Plates, a great displacement of crustal and sub-crustal (Internal Betic) zones took place ending with the collision of the Internal and External Betic zones during the early Miocene (Sanz de Galdeano et al 1995;Alcalá et al 2013). In the study area, the active tectonics controls the basement uplift rate and the faulting style, the combination of the active tectonics and sea-level changes control the V s is a key parameter in dealing with mechanical properties of subsurface materials (e.g., Olona et al 2010;Duffy et al 2014;Lorenzo, Hicks and Vera 2014;Yilmaz 2015), ground amplification, and liquefaction potential phenomena in earthquake events (e.g., Chang et al 2011;Tarque et al 2013;Vella, Galea and D'Amico 2013). V s models have been applied to seismic hazard assessment since ground amplification, which may cause most earthquake-related damages, often changes with shallow ground stiffness (Park, 2013).…”

“…Within this framework, the shallow shear‐wave velocity was considered a good quantitative indicator for geological material stiffness, useful for soil microzonation of urban areas for earthquake disaster mitigation (Martínez‐Pagán et al ). is a key parameter in dealing with mechanical properties of subsurface materials (e.g., Olona et al ; Duffy et al ; Lorenzo, Hicks and Vera ; Yilmaz ), ground amplification, and liquefaction potential phenomena in earthquake events (e.g., Chang et al ; Tarque et al ; Vella, Galea and D’Amico ). models have been applied to seismic hazard assessment since ground amplification, which may cause most earthquake‐related damages, often changes with shallow ground stiffness (Park, ).…”

Shear-wave velocity map for Pohang Basin, South Korea, based on the P-wave seismogram method

“…In addition, abrupt changes in V S profiles can be used to identify faults (e.g. Catchings et al, 2017Catchings et al, , 2020Duffy et al, 2014;Ivanov et al, 2006;Lee et al, 2010;Martı´nez-Paga´n et al, 2018). The V S profiles have traditionally been measured through invasive active-source borehole-based field tests such as suspension PS (s-PS) logging, downhole, and crosshole tests.…”