Natural Seismicity Arrays

Monitoring the background seismicity of Tompkins county is essential to revealing if and where seismic activity is occurring, prior to any subsurface drilling activities relating to ESH. Data collected before drilling will be compared to data collected during and after drilling to monitor any possible impacts subsurface drilling activities related to ESH may have on the regional seismicity.  Drilling of the exploratory borehole that will not involve circulating fluids or extraction of heat is scheduled for Fall 2021.  Because existing national and regional seismic networks are not sensitive enough to detect seismic activity in Tompkins County, several studies have been undertaken to install new temporary instruments in Tompkins County to detect seismic events — both natural and

To measure background seismicity, a first network of 12 passive seismometers called CorNET16 (Cornell Network 2016) was deployed from 2015 to 2016. This network provided valuable data about the background seismicity, including 17 events detected in Tompkins County, and is summarized in an online report available here. At the conclusion of the CorNET16 study, it was decided that another background seismicity array covering a larger area and for a longer period of time would be beneficial.

Following the recommendations of CorNET16, CorNET21 was installed in July 2019 and is expected to be in operation until at least 2022. CorNET21 is operated through a contract with an independent company, Weston Geophysical Group. This array of 17 stations includes both surface (buried 2 feet or 0.5 meters) and borehole stations (buried 30 feet or 10 meters).  Preliminary analysis of CorNET21 indicates that between August 2019 and January 2021, 359 seismic events were detected in Tompkins County described in this online report.

For the seismic events detected in Tompkins County, it is important to determine which events are caused by human activities, known as anthropogenic events, as these events should not be included in the background seismicity. Many events recorded by CorNET21 have been categorized as anthropogenic, possibly relating to Cornell’s North Campus Residential Expansion project and activities around the Cargill Salt Mine, but further analysis is needed to separate these events from natural seismicity.

Future work will focus on systematically differentiating anthropogenic events and natural events, and determining the smallest magnitude events that can be reliably located for the CorNET21 network. Continued seismicity monitoring throughout installation and geothermal fluid circulation is also essential.

An analysis of CorNET16 is reported by McLeod et al. (2020) at https://hdl.handle.net/1813/69609. An examination of the CorNET16 data and analysis of CorNET21 (Suhey et al., 2021) is available at https://hdl.handle.net/1813/103518.

map with locations of microseismic events

Map of CorNET21 events (August 2019-January 2021) reviewed by a Weston Geophysical Group seismologist. Daytime events are yellow, nighttime events are blue, the hatched pattern represents the approximate extent of the salt mine (Veaner, 2017), green triangles represent CorNET21 seismic stations, and the distance to the proposed borehole site (red circle) is shown. In addition to the folds mapped by Wedel (1932), a possible north-south fault along Cayuga Lake (Murphy, 1981) and an observed thrust fault near Portland Point (McKendree and Isachsen, 1977) are also shown.

Sources Referenced

McKendree, W., and Y. W. Isachsen, 1977, Preliminary brittle structures map of New York, 1:250,000 and 1:500,000 and generalized map of recorded joint systems in New York, 1:1,000,000: New York State Museum and Science Service Map and Chart Series No.3. http://www.nysm.nysed.gov/researchcollections/geology/gis

Murphy, P. J. 1981. Detachment structures in south-central New York. Northeastern Geology, 3(2), 105-115. National Research Council. 2013. Induced Seismicity Potential in Energy Technologies. Washington, DC: The National Academies Press. https://doi.org/10.17226/13355

Veaner, D., 2017, Mine Shaft Neighbors Meet With Cargill, Lansing Star, https://www.lansingstar.com/around-town/13732-mine-shaft-neighbors-meet-with-cargill

Wedel, A. A., 1932, Geologic structure of the Devonian strata of south – central New York: New York State Museum Bulletin 294, 74 p.

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