Pacific Northwest Geodetic Array
Central Washington University

Tilt Monitoring of 2008 ETS

 What is an ETS?

ETS onset around 05/05/08 at 08:00 UTC
(see Shelton N-S)

Below are the preliminary Baytap-G tilt 1-hour solutions for select segments of the Cascadia Tiltmeter Array showing up to 4.5 months of tilt data. Shelton Tiltmeter is very stable with less than 25nrad of drift over 3.5 months proceeding the 2008 ETS. On May 5th, 2008 the data show obvious signs of ETS onset with an approximate 300nrad E-W and 100nrad N-S over the past month. The Sequim Tiltmeter also recorded ETS intiation at around the same time where 3.5 months of steady 100nrad drift abruptly changes to 500nrad on the north-south arm. Mt. Vernon shows comparable time onset, however the drift is much larger and tilt characteristics are confused by other signals. For comparison, the January 2007 ETS event is plotted at the bottom. This penultimate event had almost twice the tilt amplitude in less than half the time interval.

Data trace "down" means south/west down. *Note: trend is smoothed data residual after subtracting theoretical tides.

 Shelton Data
Shelton East-Center Baytap-G Solution

Shelton North-South Baytap-G Solution

 Sequim Data
Sequim East-West Baytap-G Solution

Sequim North-South Baytap-G Solution

 Vernon Data
Mt. Vernon East-West Baytap-G Solution

2007 ETS Event w/ ~700nrad tilt: Shelton East-Center Trend

2007 ETS Event w/ ~150nrad tilt: Shelton North-South Trend

2005-2008.5 Shelton C-E Trend w/ tides, pressure, temperature and local hydro-geo signals removed

Tiltmeter Home