The USArray component of the NSF-funded EarthScope project ended its observational period in September 2021 and all remaining close-out tasks concluded in March 2022. Hundreds of seismic stations were transferred to other operators and continue to collect scientific observations. This website is now in an archival state and will no longer be updated. To learn more about this project and the science it continues to enable, please view publications here: and citations of the Transportable Array network DOI 10.7914/SN/TA.

To further advance geophysics support for the geophysics community, UNAVCO and IRIS are merging. The merged organization will be called EarthScope Consortium. As our science becomes more convergent, there is benefit to examining how we can support research and education as a single organization to conduct and advance cutting-edge geophysics. See our Joining Forces website for more information. The site will soon host the new EarthScope Consortium website.

A Continental-scale Seismic Observatory


Central Oregon Locked Zone Array

Principal Investigators and Institutions:

Anne Trehu, Oregon State University

Station Map

Funding Source:

NSF EarthScope

Field Dates: 

1/2008 – 12/2010

Equipment Used:

11 Broadband Stations   

Data Status:

Archive Complete

Data released

Network Code:  



Station MapHistorically, the subducting Juan de Fuca plate has produced very large thrust earthquakes along the Cascadia subduction zone. These events occur every few hundred years on average, with very little documented seismic activity in the interim. Since 2003, about 40 earthquakes have been detected in the nominally "locked" zone offshore central Oregon. Analysis of the two largest earthquakes suggests that they were low angle thrust events on the plate boundary. We are currently operating an onshore/offshore seismic array (COLZA – Central Oregon Locked Zone Array) to better constrain microseismic activity in this region. 

The COLZA experiment consists of six temporary land seismic stations from the FlexArray, part of EarthScope's USArray network of instuments, and two deployments of ocean bottom seismometers. Our data are collected and archived with the help of the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) and archived by the Incorporated Research Institutions for Seismology (IRIS).

Publications/ Abstracts

Tréhu, A.M., J. Braunmiller, J. L. Nabelek, Probable low-angle thrust earthquakes on the Juan de Fuca–North America plate boundary, Geology, Volume 36, Issue 2 (February 2008) pp. 127–130