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Coupling Between Seismic Activity and Hydrogeochemistry at the Shillong Plateau, Northeastern India
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
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2008 (English)In: Pure and Applied GeophysicsArticle in journal (Other (popular science, discussion, etc.)) Published
Abstract [en]

Transient hydrogeochemical anomalies were detected in a granite-hosted aquifer, which is

located at a depth of 110 m, north of the Shillong Plateau, Assam, India, where groundwater chemistry is mainly

buffered by feldspar alteration to kaolinite. Their onsets preceded moderate earthquakes on December 9, 2004

(MW = 5.3) and February 15, 2005 (MW = 5.0), respectively, 206 and 213 km from the aquifer. The

ratios [Na+K]/Si, Na/K and [Na+K]/Ca, conductivity, alkalinity and chloride concentration began increasing

3–5 weeks before the MW = 5.3 earthquake. By comparison with field, experimental and theoretical studies, we

interpret a transient switchover between source aquifers, which induced an influx of groundwater from a second

aquifer, where groundwater chemistry was dominantly buffered by the alteration of feldspar to smectite.

This could have occurred in response to fracturing of a hydrological barrier. The ratio Ba/Sr began decreasing

3–6 days before the MW = 5.0 earthquake. We interpret a transient switchover to anorthite dissolution caused

by exposure of fresh plagioclase to groundwater interaction. This could have been induced by microfracturing,

locally within the main aquifer. By comparison with experimental studies of feldspar dissolution, we interpret

that hydrogeochemical recovery was facilitated by groundwater interaction and clay mineralization, which could

have been coupled with fracture sealing. The coincidence in timing of these two hydrogeochemical events with

the only two MW C 5 earthquakes in the study area argues in favor of cause-and-effect seismichydrogeochemical

coupling. However, reasons for ambiguity include the lack of similar hydrogeochemical

anomalies coupled with smaller seismic events near the monitoring station, the >200 km length scale of inferred

seismic-hydrogeochemical coupling, and the potential for far-field effects related to the Great Sumatra–

Andaman Islands Earthquake of December 26, 2004.

Place, publisher, year, edition, pages
Keyword [en]
Hydrogeochemistry, seismic-hydrogeochemical coupling, water-rock interaction, Shillong Plateau
National Category
Geosciences, Multidisciplinary
URN: urn:nbn:se:su:diva-15758DOI: doi:10.1007/s00024-007-0288-2ISI: 000253897400004OAI: diva2:182278
Available from: 2008-12-10 Created: 2008-12-10 Last updated: 2011-01-10Bibliographically approved

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Skelton, AlasdairClaesson, LillemorRouth, Joyanto
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Department of Geology and Geochemistry
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