Slow Slip and Tremor Observations and Research at the PNSN
CURRENT ACTIVITY (or last major ETS)
Slow Slip episodes affecting southern British Columbia and northern Washington have been occurring every 14 months or so since at least the 1990s. The PNSN monitors the non-volcanic tremor associated with slow slip and has deployed additional seismometers from time to time to record expected tremor events to gain insight into the process and into the stresses that eventually will lead to the region's next major earthquake.
Many different techniques are used to study this phenomenon. The two primary areas of research the PNSN and related researchers are involved in include; 1. A semi-automatic tremor detection and location process that uses continuous waveform data from the PNSN and cooperating networks and has a web interface called, Interactive Tremor Map; 2. Experimental algorithms applied to waveform data from special installed small aperture arrays to better characterize the space and time distribution of tremor. The latest experiment was called an Array of Arrays.
Episodic Tremor and Slip (ETS) periods in northern Washington have been individually studied over a number of years. During each of these periods web pages were constructed at the time describing the events and the research efforts made to study them. Here we list references to the original pages as then constructed.
Tremor log index:
- ETS event of Winter 2003
- ETS event of Spring 2004
- ETS event of Summer 2005
- ETS event of Fall-winter 2006
- ETS event of Winter 2008
- ETS event of Summer 2009
- ETS event of Summer 2010
- ETS event of Summer 2011
- ETS event of Summer-Fall 2012
- ETS event of Fall 2013
- ETS event of Winter 2014
We have made some comparative tremor map snapshots showing tremor locations by week of several previous northern Washington ETS events. There is also a set of comparative density maps for the past three ETS episodes.
Some background information:
- Fairly comprehensive list of journal publications by ESS researchers on ETS
- One page simple explanation (paraphrased from PGC web page)
- Original Paper describing ETS by Rogers & Dragert, 2003
- Thorough review of slow slip in Physics Today by Vidale & Houston, 2012
- Web page from Pacific Geoscience Centre of the Geological Survey of Canada
- A Canadian tremor location system for northern Cascadia tremor called TAMS
- Web page from Geodesy Labs of Central Washington University
UW Press Releases about ETS studies:
- Mar 13, 2003 - Parts of Washington, British Columbia in the midst of a 'silent earthquake'
- May 13, 2004 - Scientists hope current silent earthquake will help to understand big quakes
- Spring 2007 - EarthScope info sheet about ETS and UW research
- Nov 22, 2007 - Rising tides intensify non-volcanic tremor in Earth's crust
- Nov 22, 2007 - 2002 Alaskan quake left seven areas of California stirred but not shaken
- Mar 5, 2008 - This is not a drill: The earth actually is moving beneath western Washington
- Mar 6, 2008 - Special KOMO TV report on current slow slip event
- Jan 29, 2009 - Research links seismic slip and tremor, with implications for subduction zone
- Dec 15, 2009 - Tremors between slip events: More evidence of great quake danger to Seattle
- Aug 10, 2010 - Slow-moving ‘earthquake’ under Olympic Peninsula will be well recorded
- Dec 13, 2010 - ‘Array of arrays’ coaxing secrets from unfelt seismic tremor events
- May 22, 2011 - Scientists find odd twist in slow ‘earthquakes’: tremor running backwards