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Improvements in Seismic Station Noise Levels Through Budget Boreholes

Description: 

It has been known for decades that the noise performance of seismic stations at both high (1 Hz) and low (<0.05 Hz) frequencies can be improved through installing the seismometer within deep (>30 m) boreholes. However, the cost of these installations has historically been prohibitive for their widespread use in regional and national seismic networks. Consequently, most of the Advanced National Seismic System (ANSS) and aftershock stations operated by the Albuquerque Seismological Laboratory (ASL) utilize seismometers placed in shallow (<3 m) vaults. The development of direct bury, posthole seismometers has enabled a handful of these vault stations to be converted at low cost to posthole (<5 m) and shallow (< 10 m) boreholes in the past few years using a gas-powered, hydraulic auger. We examine the change in noise performance at these stations that were converted from vaults to posthole installations, including changes in sensitivity to atmospheric pressure variations. We suggest that the USArray Transportable Array vaults were often emplaced on top of sediment, which exacerbates low-frequency noise generated by pressure changes.

We additionally investigate how the emplacement material around the seismometer in a posthole or borehole installation impacts noise performance. Using best practices from the borehole strainmeter community, we successfully grouted in a seismometer at 10 m depth within fractured granite at ASL in the summer of 2023. By using a Nanometrics T120 Slim and forgoing borehole casing, we were able to contract a commercial water well driller to complete the station within a timeframe and budget comparable to a traditional vault installation. We present analysis from 1.5 years of this grouted-in data and discuss the potential benefits and drawbacks for incorporating this installation method into ANSS networks.

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned [Poster]

Type: Poster

Date: 4/15/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Robert

Student Presenter: No

Invited Presentation: 

Poster Number: 18

Authors