Hydrochemical Response of Groundwater Following the 2020 Monte Cristo Range Earthquake Sequence within Mineral and Esmeralda Counties, NV
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Authors
Morlang, Dylan
Issue Date
2022
Type
Thesis
Language
Keywords
Earthquakes , Geochemistry , Geodesy , Hydrogeology , Hydrology
Alternative Title
Abstract
The 2020 Monte Cristo Earthquake sequence in western Nevada began with a M 6.5 shock on 5/15/2020, and was the largest to occur in Nevada since 1954. The event exhibited left-lateral slip along an eastward extension of the Candelaria fault and extensive distributed surface faulting in the epicentral area. Groundwater monitoring and strain analysis were conducted to evaluate hydrochemical effects on the regional groundwater systems following the introduction of both static and dynamic strain. Physiochemical monitoring, began on 5/16/2020 and included measurements of temperature (temp), pH, specific conductance (SpC), flow rate, alkalinity and collection of samples for isotopic and elemental analysis. Since sites had not been monitored prior to the initial shock, measurements were evaluated against a year of post-event data to gauge response to seismicity. Four sites were monitored: a well from Columbus Marsh (CM) located 5 km from the epicenter; an artesian thermal well from Fish Lake Valley (FLV); a well at Willow Ranch (WR) tapping cool water above the FLV waters; and a spring along Mina Dump Road (MD) located 15 km north of the Candelaria fault on the Benton Springs Fault. GPS and InSAR measurements were used to create a model of the slip of the M 6.5 event, from which coseismic static strain was calculated at each sampling location. All but one sample site, MD, experienced positive dilatation and CM experienced the greatest amount of static strain (1.2E6 nanostrains). Hydrologic and chemical changes were observed following the initial shock and aftershocks >M 4, varying between sites and event. CM had significantly lower SpC values in the week following the May 15th event. During the early part of the seismic series, a period of high frequency and intensity aftershocks, MD showed a suppressed flow rate. Several aftershock sequences that were host to >M 4 events were also modeled in an elastic half space to estimate coseismic static strain as a result of less intense earthquakes. Clear physiochemical responses were observed throughout three aftershock sequences (6/30/2020, 11/13/2020, and 12/2/2020) and show a high correlation to the sign and magnitude of strain each site experienced. The clearest of these responses were recorded as a result of the 11/13/2020 and 12/2/2020 aftershock sequences. Between these two events, differential stress correlated well with the differential response seen as an increase in the temp of CM and WR trending with an increase in stress at these sites leading up to 11/13/2020. SpC dropped at CM and FLV and pH at CM after dilatational strain was modeled at both sites as a result of the 11/13/2020 event. The trend in SpC and pH at CM was reversed following contractional static strain the site on 12/2/2020. The trend in FLV also reversed on 12/2/2020, but instead, due to the location of dilatational static strain relative to the site. This study provides the framework of a new method to better analyze the impacts earthquakes have on the hydrogeological environment. Elemental chemical analysis is planned to further the understanding of earthquake mechanisms and their response in the Basin and Range.
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Creative Commons Attribution-NoDerivatives 4.0 United States