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Tidal Behavior and Water‐Level Changes in Gravel Aquifers in Response to Multiple Earthquakes: A Case Study From New Zealand
Author(s) -
Weaver K. C.,
Doan M.L.,
Cox S. C.,
Townend J.,
Holden C.
Publication year - 2019
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr022784
Subject(s) - water level , aquifer , geology , hydrology (agriculture) , tidal force , oceanography , consolidation (business) , groundwater , environmental science , geotechnical engineering , geography , physics , cartography , accounting , business , astronomy
Earthquakes have been inferred to induce hydrological changes in aquifers on the basis of either changes to well water‐levels or tidal behavior, but the relationship between these changes remains unclear. Here, changes in tidal behavior and water‐levels are quantified using a hydrological network monitoring gravel aquifers in Canterbury, New Zealand, in response to nine earthquakes (of magnitudes M w 5.4 to 7.8) that occurred between 2008 and 2015. Of the 161 wells analyzed, only 35 contain water‐level fluctuations associated with “Earth + Ocean” (7) or “Ocean” (28) tides. Permeability reduction manifest as changes in tidal behavior and increased water‐levels in the near field of the Canterbury earthquake sequence of 2010–2011 support the hypothesis of shear‐induced consolidation. However, tidal behavior and water‐level changes rarely occurred simultaneously (~2%). Water‐level changes that occurred with no change in tidal behavior reequilibrated at a new postseismic level more quickly (on timescales of ~50 min) than when a change in tidal behavior occurred (~240 min to 10 days). Water‐level changes were more than likely to occur above a peak dynamic stress of ~50 kPa and were more than likely to not occur below ~10 kPa. The minimum peak dynamic stress required for a tidal behavior change to occur was ~0.2 to 100 kPa.