Relative Noise Level Comparison Of Portable Broadband Seismometer Installation Techniques Used By PASSCAL And Flexible Array
Abstract:Multiple methods of broadband seismometer emplacement are used on portable experiments. Techniques range from a typical IRIS PASSCAL vault (~1-m deep vault with a decoupled pier), to an EarthScope USArray Flexible Array (FA) vault (~1-m deep narrow vault with a cement plug in the bottom coupled to the vault), both using traditional vault (pier) sensors, as well as direct burial emplacement of both sensors purpose-built for direct burial and standard vault sensors. The selection of the appropriate sensor emplacement technique for a given environment has often relied on anecdotal assessment or personal preference. We have performed an inter-comparison of these various emplacement techniques, for diverse environments. Our goal is to provide quantitative information that will facilitate choosing deployment strategies that best meet an experiment’s scientific goals and logistical constraints.
For our analysis, a total of 15 networks (781 stations) from PASSCAL and FA are analyzed using SQLX, which utilizes the ambient noise analysis methods of McNamara and Buland*. Using this analysis, a comparison of the mean of the monthly mode (MMM) of each component of the networks is performed to evaluate the various emplacement methods currently used. We have used a total of 182 PASSCAL stations (5 networks using PASSCAL vaults and 1 network using direct burial installs) and 365 FA stations (5 networks with FA vaults, 2 networks using direct burial installs, and 2 networks with a mix of installation types). The installations span a variety of environments. For our analysis the MMM has been calculated for each component separately (Z, N and E) and these results are compared to similar results already computed for EarthScope USArray Transportable Array (TA) stations. To evaluate the relative network performance, we use three separate period bands: short period (< 1 s), microseism band (1-10 s) and long period (10 -100 s). Using the TA baseline as a reference, each network is ranked from quietest to noisiest. Results of this comparison will be presented.
* (McNamara, D.E. and R.P. Buland, Ambient Noise Levels in the Continental United States, Bull. Seism. Soc. Am., 94, 4, 1517-1527, 2004).
1 – Independent Contractor for IRIS 2- IRIS/PASSCAL