(ABOVE: Bangladeshi locals look on as PASSCAL field engineer Alissa Scire and BIMA project member Celine Grall install a seismic station as part of the Tripartite-BIMA (Bangladesh-India-Myanmar Array) deployment. Photo credit: Leonardo Seeber, LDEO)
by Dr. Justin Sweet, IRIS PASSCAL
(Photo of the IRIS/PASSCAL Instrument Center on the New Mexico Tech campus in Socorro, NM. Photo credit: Derry Webb, PASSCAL)
The PASSCAL Instrument Center supports portable seismic deployments worldwide by providing instrumentation, equipment maintenance, software, data archiving, training, logistics, and field support. In a typical year, PASSCAL supports an average of 80-100 portable seismic deployments around the globe, including Arctic and Antarctic regions.
(PASSCAL nodes in yellow bags staged outside the Thwaites Glacier project tent near the West Antarctic Ice Sheet Divide camp. Photo credit: Galen Kaip, UTEP)
Since 1998, this IRIS facility has been located on the New Mexico Tech campus in Socorro, New Mexico, about an hour south of Albuquerque. A staff of approximately 30 individuals comprise a wealth of expertise that enables the facility to support a diverse group of users including students, faculty, government employees, and others who undertake temporary seismic deployments.
A central component of PASSCAL is the large instrument lending library, which contains thousands of seismometers of different classes and types.
(Members of the PASSCAL Standing Committee and IRIS staff review the many different types of seismic sensors and ancillary equipment staged in the PASSCAL warehouse. Photo credit: Justin Sweet, IRIS)
Different sensor types are sensitive to different frequencies of seismic energy, and thus a variety of sensors are often utilized by scientists for their field deployments depending upon the particular type of seismic signal they aim to record and analyze. For example, a deployment that aims to record signals from distant large earthquakes around the globe may install large “broadband” seismometers that are capable of recording signals across a broad band of frequencies. In contrast, a geophysics class that wants to image subsurface layers using active sources (e.g. hammer or small explosives) will likely deploy a linear string of smaller “geophone” seismic sensors to capture shorter-range, high-frequency signals over a small area of interest.
(A student swings a hammer as part of an active source seismic survey on the New Mexico Tech campus. Photo credit: Dave Thomas, PASSCAL)
Sensors are tested upon return from each deployment, and repairs are performed as needed to keep them in optimal condition. With careful handling, some of the sensors at PASSCAL have been in use for more than 25 years.
In addition to instrumentation, PASSCAL provides our users with support for their field deployments from beginning to end. Prior to the deployment, users often visit the facility to receive training on how to operate the instruments they will be deploying, as well as best practices for things like site selection, sensor emplacement, waterproofing techniques, and more. Shipping and logistics experts at PASSCAL work with our users to ensure that their equipment can be safely and efficiently sent where it needs to be. When the actual field deployment begins, PASSCAL staff can accompany users into the field to assist with on-site troubleshooting.
The seismometers themselves are usually buried a few feet below the ground surface with a station enclosure box placed on the surface that houses batteries and a small computer to record and store data from the buried sensor. Many stations also include solar panels to reduce the number of batteries needed. Deployment durations vary from 1-2 days to several years, depending on the science target. Once the field deployment has concluded, and equipment has been sent back to PASSCAL, maintenance staff test and evaluate all returning equipment to identify any problems that require attention. Meanwhile, the data group at PASSCAL works with deployment leaders to ensure that the data they collected is properly reviewed, formatted, and submitted to the IRIS data management center for archival. All data collected using PASSCAL instrumentation is required to be made freely and openly available to the public, sometimes after a 2-year embargo that allows faculty and students time to analyze their data and publish results.
(Louisiana State University PhD student Ritu Ghose installs a nodal seismometer during the LA BASIN project in Southern California. Photo credit: Patricia Persaud, LSU)
IRIS manages the PASSCAL Instrument Center with ongoing oversight from the seismologic community through the PASSCAL Standing Committee (PASC). The PASC meets twice each year to discuss issues of concern, and to plan out long-term strategic needs of the facility. This model of community governance ensures that PASSCAL is responsive to the ever-changing needs of our user community, and has been a big part of the reason for the success of the facility over the past two decades.
(A view of the reflected and refracted waves recorded from the hammer strike as part of an active source seismic survey on the New Mexico Tech campus. Photo credit: Dave Thomas, PASSCAL)