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

Abstract

Plate boundary deformation creates a south-easterly advancing, repetitive structural pattern in Canterbury dominated by the propagation of northeast-striking thrust assemblages. This pattern is regularly segmented by east-striking faults inherited from reactivated Cretaceous normal faults. The more evolved and deeply exposed structures in the foothills of north Canterbury provide insights into the tectonic processes of the blind structures now emerging from under the northern and eastern Canterbury Plains, where thrust and strike-slip fault activity are closely linked. The east-striking faults separate relative motion between thrust segments and accommodate oblique transpressive shear. Early stages of thrust emergence are dominated by anticlinal growth and blind, or partially buried, thrusts and backthrusts. The east-striking transecting faults therefore record timing of coseismic episodes of uplift and shortening with variable horizontal to vertical ratios and displacement rates on the hidden adjacent thrusts. The Greendale and blind Port Hills faults, with their associated aftershock patterns, are compatible with this style.

Faulting and folding beneath the Canterbury Plains identified prior to the 2010 emergence of the Greendale Fault

“…These observations suggest that the bulk of late Cenozoic deformation on the Ashley Fault has transferred south-westwards onto the Cust Anticline (see also Campbell et al 2012), although we infer that some late Cenozoic deformation on the Ashley Fault zone continues westward onto the Glentui Fault zone (Fig. 1).…”

“…The Ashley Fault may be a more emergent but similar structure to that of the Greendale Fault (see Campbell et al 2012). Both faults are optimally oriented for strike-slip movement under the contemporary stress field (Ghisetti & Sibson 2012).…”

“…Cust Anticline). In contrast to southern Canterbury, late Cenozoic structures below the north-western Canterbury Plains are contractional, although a component of strike-slip movement is suspected, particularly on those faults with easterly strike (Campbell et al 2012). …”

“…The regional geologic and tectonic setting of the Canterbury Plains is described by Browne et al (2012) and Campbell et al (2012).…”

High‐resolution relocation of aftershocks of the Mw 7.1 Darfield, New Zealand, earthquake and implications for fault activity

“…New Zealand's seismicity and faulting are mainly focused on the Hikurangi margin beneath the North Island, the Marlborough Fault system in the northern portion of the South Island, the Alpine Fault in the western portion of the South Island, and along the Puysegur subduction zone at the southwestern end of the South Island. Known faults exist to the north of the region of the Darfield earthquake [ Dorn et al ., ; Jongens et al ., ] and to its west [ Campbell et al ., ; Jongens et al ., ], but there was limited previous knowledge of faults in this portion of the Canterbury plains prior to the 2010 main shock, mainly due to the low strain rate in the area [ Beavan and Haines , ], the lack of historic seismicity that ruptured the surface [ Downes and Yetton , ], the relatively recent end of glaciation (~18,000 years ago), and the young alluvial cover [ Forsyth et al ., ] that would have covered previous surface ruptures.…”