Compressional reactivation of E–W inherited normal faults in the area of the 2010–2011 Canterbury earthquake sequence

Abstract

Earthquake ruptures of the 2010Á2011 Canterbury sequence exploit a varying mixture of optimally oriented newly formed faults and inherited discontinuities that are favourably oriented for reactivation within the prevailing tectonic stress field. Reinterpretation of subsurface data shows that the Torlesse basement is imprinted with an EÁW fault fabric inherited from Late CretaceousÁEocene rifting. The prevailing EÁW band of rupturing illuminated by seismicity lies at the southern boundary of a Late Cretaceous basin, terminating against the Banks Peninsula structural high. Analysis of a set of seismic lines in the Ashley River region (c. 30 km north of the Greendale fault) demonstrates compressional inversion of inherited high-angle EÁW normal faults and folding and detachment of the Neogene cover sequence, together with propagation of new faults through the Pliocene and Quaternary cover sequences. These structures provide an analogue to deformation in the epicentral region of the Greendale fault.

The geological setting of the Darfield and Christchurch earthquakes

“…Pre-existing faults strongly influence the spatial distributions and geometries of active faults throughout New Zealand (e.g., Barnes 1994;Nicol & Van Dissen 2002). In the Canterbury region, some east-striking Late Cretaceous faults were reactivated in the Neogene to Quaternary (e.g., Nicol 1993;Sibson et al 2011;Campbell et al 2012;Ghisetti & Sibson 2012;Jongens et al 2012). Studying the history of faulting in the Canterbury region may, therefore, improve our understanding of active faults and their future earthquakes.…”

The tectonic and structural setting of the 4 September 2010 Darfield (Canterbury) earthquake sequence, New Zealand

“…The association of these east-striking faults with reactivated and inverted Cretaceous normal faults in the basement is evident in seismic reflection lines (Ghisetti & Sibson 2012;Jongens et al 2012). Ghisetti & Sibson (2012) discuss the reactivation in terms of the regional principal compressive stress orientation quoted as 115958, which is broadly perpendicular to the northeast-striking thrust system.…”

“…Ghisetti & Sibson (2012) discuss the reactivation in terms of the regional principal compressive stress orientation quoted as 115958, which is broadly perpendicular to the northeast-striking thrust system. The east-striking anisotropic planes of weakness are optimally oriented for strike-slip movement (Sibson et al 2011) but have non-vertical, possibly listric, dips in the basement (Ghisetti & Sibson 2012). If this regional stress were the only controlling factor, then these faults should propagate to the surface independently of other structures.…”

“…Upthrown on the south side, it reverses throw east of the Okuku River where uplift is on the north side. The ridge itself is underlain by a flower structure of faults over older Cretaceous structures (Ghisetti & Sibson 2012;Jongens et al 2012).…”

“…Since Nicol (1993a) first described the transpressive inversion of the Birch Fault, a Cretaceous normal fault, it has been recognised that other similarly oriented faults were probably reactivated inherited faults, a view now supported by seismic reflection data (Ghisetti & Sibson 2012;Jongens et al 2012). The emergence of these faults as active surface traces is observed to be closely associated with the location of thrust faults and their associated anticlines.…”