Array of Arrays (AofA) Project Plan
Spring 2009

We are running an Array of Arrays (AofA) experiment to study tremor with unprecedented resolution in an active and relatively predictable portion of the Cascadia SZ. Our plan has two field seasons of temporary seismic deployments, augmented by an inexpensive extension of the already successful CAFE experiment. The first year, the temporary deployment will embed about 180 short-period sensors, half vertical and half three-component, in seven new dense arrays to run with two existing arrays to catch the expected mid-summer 2009 and 2010 ETS episodes. The second year, we will strive to re-capture interesting patterns to measure the degree to which ETS repeats in detail.

The AofA will enable specialized array processing techniques such as high-resolution beamforming and spectrograms, which we demonstrated in an 84-station pilot experiment this past spring, to pinpoint tremor and LFE location and character in space and time. We expect to study the location and depth of tremor, its migration, its spectral content at high frequencies, as well as better resolution of source spectra from earthquakes through LFEs to tremor. Examples of array processing from this previous test array illustrate how tremor moves with time. We hope the analysis of data from this set of up to nine dense arrays will answer many key questions about tremor and further elucidate the physics of the ETS process.

NOTE:The ETS expected for summer of 2009 came over two months early, in early May. Equipment was not even shipped to Seattle until early June thus this ETS was missed by the planned Array of Arrays. The equipment will be left in place over the next year to be ready for the 2010 ETS and to capture any small tremor periods in the meantime.

A general map of the areas we plan to install arrays on the Olympic Peninsula.
Red line surounds the stippled area which usually contains the main part of tremor as an ETS passes under this area.

A map of installed arrays with their array codes.

The 10 day install process

Abhijit and Justin spent several days in a couple of different siting trips in the spring of 2009 to locate and mark stations for six new arrays. Below are some sample photos of the array install process that took place in mid June, 2009. Up to 12 people, mostly in teams of 2-4 worked long days installing approximately 75 Reftek RT-130 short-period, 3-component (Mark Products L-28) stations with aircells and 70 single-component, short-period Reftek RT-125 ("Texan") stations. The Texans were serviced once and then removed to wait for the next ETS.

The whole AofA team

carbo loading

before the first install.

Heading out with a station.

Planting the seismometer.

Lets see. Tab A into slot B?

Connect up the batteries.

A well hidden station.

A little crazy after 59 installs.

Heading to the truck after an 11 hour day.

Pizza and beer after a 12 hour day.