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Seismic Noise Tests in Mammoth Cave, USA

Session: Network Seismology: Keeping the Network Running While Integrating New Technologies [Poster]

Type: Poster

Date: 4/22/2021

Presentation Time: 11:30 AM Pacific

Description: 

Caves can offer environmentally stable and seismically quiet locations for recording small seismic signals. In September 2020, the Kentucky Geological Survey began testing locations in Mammoth Cave National Park, Kentucky, USA, to determine if they are suitable for the installation of a permanent broadband seismograph. To date, broadband instruments have occupied three candidate locations in the cave at subsurface depths of 71‒88 m. They operated at each location for approximately 30‒40 days, and one to three more stations are planned. To investigate sources of local cultural noise and to quantify the effects of shallow stratigraphy on ground motions, an additional station was installed at the surface directly above the quietest site to date. Power spectral densities of the recordings were used to quantify noise levels and were compared with each other and with recordings from other permanent regional stations. At short periods (0.08‒1 s), noise levels at the cave sites are comparable to levels observed at regional seismic stations in caves but quieter than levels at regional surface stations. Daytime short-period (0.08‒0.4 s) noise levels at the cave sites increased by approximately 4‒5 dB compared to noise levels at night. Daytime short-period noise increases at cave sites closer to Interstate 65 (ranging from 5.5 ‒7.5 km away) suggest that the highway is a principal source of short-period noise. At long periods (> 10 s), the quietest cave site has noise levels comparable to those from other cave stations in the region and is quieter than the regional surface stations. Once the quietest cave site has been identified, it will be monitored for one year to test the installation and communications, in preparation for establishing the permanent station. Once the station is established, it will contribute to regional seismic monitoring efforts by KGS and to national and global monitoring through real-time data sharing.

Presenting Author: Jonathan P. Schmidt

Student Presenter: Yes

Authors