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.