Transportable Array (TA)

After covering the lower 48 United States from coast to coast with a grid of nearly 1700 sites, the last seismic station of the EarthScope Transportable Array has finally been installed in Alaska. IRIS has commemorated the event with a post titled "EarthScope’s Transportable Array Spans Alaska, the Last Frontier." The IRIS article includes a detailed map of the Alaska TA stations, highlighting the location of the final station A19K. 

March 7th, 2017

With the expansion of TA Alaska into even more remote regions of Alaska and Canada it was necessary to develop and construct an extremely lightweight, high performance helicopter portable air rotary drill weighing less than 1700 lbs and capable of installing a 6” steel casing 2.7m deep in any type of ground including solid rock, frost shattered overburden, cobbles and frozen soils.  Based on these parameters, a custom drill rig system was commissioned and tested by IRIS for specific use on the project.  At PASSCAL we had the opportunity to be among the first testing locations for the newly constructed third generation Purple Drill.  Ryan Bierma, and Max Enders along with Bob Busby from IRIS and Mike Lundgren  from Lundgren Systems (rig developer) operated the rig, and then Ryan and Max demonstrated a mock installation of an STS-5A seismic sensor at the test site behind PASSCAL in Socorro, NM.

A November 5th article in the prestigious journal Nature discusses a major milestone in the Transportable Array project. In her article "US seismic array eyes its final frontier," Nature's Alexandra Witze writes

On Maine’s rugged coast, just north of the tourist town of Boothbay, an underground seismometer is listening for earthquakes. Engineers activated it on 26 September, completing the US$90-million Transportable Array, an ambitious effort to blanket the contiguous United States with a moveable grid of seismic monitors ... "As the array has moved, the whole picture of what’s under North America has gotten much sharper," says Andy Frassetto, a seismologist at the Incorporated Research Institutions for Seismology (IRIS) in Washington DC, which operates the stations.

The Transportable Array (TA) is a gridwork of broadband seismic instruments that are being installed across the continental United States (see a map of TA stations that have been installed to date).  They are laid out in a rectangular array with approximately 75 kilometer spacing between stations stretching from Canada to Mexico and from the Pacific Ocean eastward.

The Flexible Array is a pool of portable seismic instruments supported by the Array Operations Facility at the PASSCAL Instrument Center. The instruments are available for PI-driven research projects associated with the goals of Earthscope. The pool consists of broadband (325), short-period (100), accelerometer (20), and controlled source (1700) stations.