Aquifer permeability change caused by a near‐field earthquake, Canterbury, New Zealand

Abstract

The M W 7.1 Darfield (Canterbury) earthquake, 4 September 2010, generated widespread hydrological effects in New Zealand ranging from instantaneous changes of piezometric levels, to more sustained postseismic changes in spring flow, river discharge and groundwater levels, and increased turbidity and declined yields of water abstracted from wells. Four years later, piezometric levels remained elevated in deeper (>40 m) aquifers along the north-western (upper) side of the Canterbury Plains near the Greendale Fault, with changes in mean piezometric level reaching 113 m. Linear reservoir modeling (eigen modeling) suggests that sustained high groundwater was not the result of changes in abstraction or land surface recharge.Step-drawdown tests at six wells within 15 km of Greendale Fault were carried out prior to the earthquake and were retested following fault rupture. Eden-Hazel analysis of discharge/drawdown relationships discriminates potential sources of head losses, and how these changed (or otherwise) as a result of the earthquake. Objective application of Eden-Hazel analysis provided confidence levels for the interpretation, including when step tests provide reliable/unreliable estimates of transmissivity change. Increases in both aquifer losses and well losses were observed in four wells, reflecting both a change in sediment transmissivity and decrease in well efficiency. At two locations, the data were unable to provide results that can be interpreted with confidence. As the majority of local groundwater flow occurs through high-permeability open framework gravel lenses, we suggest that reduction in the permeability of these gravels, due to finesediment incursion, is the cause of the reduction in transmissivity and increase in well losses.

Changes in Permeability Caused by Two Consecutive Earthquakes—Insights From the Responses of a Well‐Aquifer System to Seismic Waves

“…Far‐field changes induced by transient stresses in fractured rock commonly involve permeability increases and have been attributed to mobilization of fine particles (Manga et al, ). Rutter et al () analyzed permeability reduction in open‐framework gravels caused by a near‐field earthquake in New Zealand and suggested that fine‐sediment incursion reduced transmissivity and increased piezometric levels. Laboratory observations also show that permeability can both increase and decrease under the effect of dynamic stress (Elkhoury et al, ; Liu & Manga, ).…”

“…The shaking caused by seismic waves can change the permeability of an aquifer, causing increases (Candela et al, 2014;Elkhoury et al, 2006;Fischer et al, 2017;Rojstaczer et al, 1995) or decreases (Rutter et al, 2016;Shi et al, 2018) and resulting in changes in stream flow, spring discharge, and groundwater or piezometric levels. Different mechanisms trigger responses at various distances from epicenters.…”

“…Far-field changes induced by transient stresses in fractured rock commonly involve permeability increases and have been attributed to mobilization of fine particles (Manga et al, 2012). Rutter et al (2016) analyzed permeability reduction in open-framework gravels caused by a near-field earthquake in New Zealand and suggested that fine-sediment incursion reduced transmissivity and…”

Tidal Behavior and Water‐Level Changes in Gravel Aquifers in Response to Multiple Earthquakes: A Case Study From New Zealand

“…Permeability reduction is mainly documented in the interseismic environment involving chemical processes such as clay alteration (Menzies et al, ), fault healing (Aben et al, ; Gratier & Gueydan, ), and cementation (Dempsey et al, ). Coseismic reduction of permeability has been observed in the field as a result of clogging of fractures (Shi et al, ; Yan et al, ) and can be associated with processes requiring a high level of shaking (Vucetic, ), notably shear‐induced consolidation (Rutter et al, ; Wang et al, ) or liquefaction (Wang, ).…”

Heterogeneous Permeability Changes along a Fault Zone Caused by the Xingwen M5.7 Earthquake in SW China

“…Early hydrogeologists and geophysicists tended to consider permeability enhancement to be an important factor in risk assessment, such as assessing the effects of earthquakes on underground landfills (Carrigan et al, 1991), oil well production (Beresnev & Johnson, 1994), triggered earthquakes (Hill & Prejean, 2015), and geothermal development (Elkhoury et al, 2006). However, rock experiments have shown that it is possible for permeability to decrease under dynamic stress (Liu & Manga, 2009), a finding that has recently been supported by field observations (Rutter et al, 2016;Shi, Zhang et al, 2018;Zhang et al, 2019).…”