Coupling Between Seismic Activity and Hydrogeochemistry at the Shillong Plateau, Northeastern India

Abstract

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 (M W = 5.3) and February 15, 2005 (M W = 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 M W = 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 M W = 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 M W 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 SumatraAndaman Islands Earthquake of December 26, 2004.

The Bortoluzzi Mud Volcano (Ionian Sea, Italy) and its potential for tracking the seismic cycle of active faults

“…Collectively, the geochemical, geophysical, and geologic data presented in this paper show that the BMV, like other onshore monitoring stations previously realized (e.g., Claesson et al, 2004;Skelton et al, 2014Skelton et al, , 2019Barberio et al, 2017;Huang et al, 2017), could be a proper site for installing a cabled submarine multiparametric station (Fig. 12) to study possible relationships between the seismic cycle of underlying active faults and geofluid emissions.…”

“…In 2012, anomalous increases in Ca, Mg, K, and Cl concentrations in groundwater, together with decreases in Na and SO 4 concentrations, started at least 20 to 30 d before the M w 7.1 Van earthquake, Turkey (20 km from the epicenter; Inan et al, 2012). In 2012, significant increases in Na, Si, and Ca concentrations were recorded in groundwater 4-6 months before two M w ≥ 5.5 earthquakes in northern Iceland (70-80 km from the epicenter; Skelton et al, 2014Skelton et al, , 2019 and Cl concentrations, began increasing 3-5 weeks before the M w 5.3 earthquake, whereas the Ba/Sr ratio began decreasing 3-6 d before the M w 5.0 earthquake (Skelton et al, 2008). In 2017, oxygen isotopic ratio anomalies of +0.24 ‰ relative to the local background were recorded in groundwater a few months before the M w 6.6 Tottori earthquake in southwest Japan (5 km from the epicenter; Onda et al, 2018).…”

“…Whether these precursors truly manifest before an earthquake is a different task that has to be accomplished with specific monitoring, as we will explain in the Discussion section. Our aim is nonetheless relevant for many geoscientists as noteworthy examples of earthquake geochemical precursors are documented in many previous works Igarashi et al, 1995;Claesson et al, 2004;Huang and Ding, 2012;Inan et al, 2012;Skelton et al, 2014Skelton et al, , 2019Sano et al, 2016;Barberio et al, 2017;Petitta et al, 2018;Boschetti et al, 2019) and are very promising for the science of earthquake forecasting.…”

CO2 Inflow and Elements Desorption Prior to a Seismic Sequence, Amatrice‐Norcia 2016, Italy

“…As a result, it is very difficult to relate the geochemical anomalies to a specific process and prove that are really associated with earthquakes. Despite this, water chemical anomalies are increasingly recorded at distances between 20 km and more than 200 km from strong earthquake epicenters (Andrén et al, 2016;Chen et al, 2015;Claesson et al, 2004;De Luca et al, 2018;Grant et al, 2011;Huang et al, 2012;Igarashi et al, 1995;Inan et al, 2012;Ingebritsen & Manga, 2014;Sano & Wakita, 2016;Skelton et al, 2008Skelton et al, , 2014Skelton et al, , 2019Wakita et al, 1988;Wang & Manga, 2010;Wästeby et al, 2014;Zeng et al, 2015).…”

Mechanisms of Earthquake‐Induced Chemical and Fluid Transport to Carbonate Groundwater Springs After Earthquakes

“…Coseismic hydrological and chemical response at groundwater springs following strong earthquakes is a significant concern worldwide, especially where groundwater is an important resource (Barberio et al, ; Pasvanoglu et al, ; Reddy et al, ; Skelton et al, , ).…”