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| Titel |
Thresholds for earthquake-induced hydrological changes in sedimentary
aquifers: a record from 9 earthquakes and 107 boreholes in central New
Zealand |
| VerfasserIn |
Konrad Weaver, Simon Cox, Caroline Holden, John Townend |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124209
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| Publikation (Nr.) |
 EGU/EGU2016-3603.pdf |
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| Zusammenfassung |
| A dense hydrogeological network in central New Zealand has recorded groundwater
fluctuations from 12 years of seismic events. Hydrological data over the past 15 years were
assessed in 107 boreholes at depths of 4 – 405 m. Nine seismic events (M≥5.9) occurred at
near- to far-field distances of 10 – 913 km, shaking the sedimentary aquifers at a wide range
of 10−4 to 103 J/m3 seismic energy densities.
The earthquakes produced 258 detectable hydrological responses, exhibiting different
polarities (rise or fall), amplitudes (2 to 820 mm, -859 to -2 mm) and timescales (15 min to
day [s]). Shaking parameters were calculated from 28 proximal GeoNet broadband
seismometers, providing local estimates of peak ground acceleration (PGA) and velocity
(PGV), Arias intensity, and spectral amplitudes. ShakeMap model solutions, utilising ground
motion prediction equations (GMPEs), were also acquired at borehole sites. Continuous
oceanic tidal responses of 38 boreholes were derived using Baytap08, with temporal
transmissivity and earthquake-induced changes estimated from tidal properties. The
earthquake-induced changes to groundwater level and tidal response are used to infer those
events which caused aquifer deformation and changes to the groundwater flow
regime.
A transient (15 min to 2 hr) / permanent (15 min to day [s]) deformation boundary is
observed when shaking reaches ∼1 %g PGA. As well as defining thresholds at which
hydrological changes occurred, the central New Zealand dataset provided an opportunity to
examine aquifer ability in resistance to the effects induced by earthquakes. Where
monitoring is dense and continuous, the absence of responses under certain levels of shaking
is equally informative and helps delineate causative processes. On-going work utilises
data mining to assess the contribution of seismic, hydrological, and geological
parameters to earthquake-induced hydrological changes in sedimentary aquifer systems. |
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