PNSN Logo PNSN | Winter 2008 Tremor Episode | Fall 2006 Tremor Episode | Summer 2005 deep tremor

Map of tremor epicenters for five-minute intervals

Tremor epicenters are automatically generated for every 5 minutes of the previous day and ploted on a map of north-west Washington. This experimental, automatic procedure is being developed by Aaron Wech and was changed on April 27, 2008 to give a different output. It produces a location for every 5 minute time period using an envelope cross-correlation tecnique to determine relative timing and then a regular location program using S-wave velocities to invert for a location. A boot-strap method is used to try and determine reliability of locations. If a location passes this error check it will be ploted only if at least 10 minutes (2 locations) of tremor locates in the same 0.1 x 0.1 degree area. Thus each red circle on the plot is the epicenter for a 5 minute tremor location in which at least one other location is within 0.1 degrees. Areas where there are larger concentrations of points are areas where longer tremor has occurred. The previous plotting techique of contouring the number of tremor locations within an area has been depricated.
Use these locations with caution, particularly north of the Straights of Juan de Fuca where stations available to the PNSN are limitted and biases due to station distribution is unknown.

Previous days automatic locations

  • Directory of archived locations contain plots for previous days.

    The location position maps have been turned into a short animated movie