Entiat-Chelan region of Washington: High resolution relocation of
earthquakes
Recent research using felt reports suggests the the 1872 magnitude 7+
earthquake in central Washington was in fact centered in the Entiat
region
on the east flank of the Cascade range, just south of Lake Chelan
(Bakun
et al., 2003).
My research in this region aims to refine the characterization
of earthquakes recorded instrumentally since 1980 in the Entiat region
in order to see if contemporary seismicity may reflect the after
effects
of the 1872 earthquake, and also reveal the nature of faulting and
tectonics that may have given rise to the 1872 earthquake.
Using the program HYPODD described by Waldhauser and Ellsworth (2001),
I have relocated approximately 1000 earthquakes in the Entiat cluster.
The relocations, using only catalog data, significantly reduce the
scatter of initial locations,
suggesting the presence of a SW dipping fault plane.
Subsequent analysis of focal
mechanisms of well recorded earthquake in this cluster indicate that
the
fault may be a thrust dipping to the southwest. It is a reasonable
hypothesis
that the Entiat sequence reflects faulting that occurred in the 1872
earthquake.
The results, both before relocation
(using a standard relocation technology) and after relocation (using
HYPODD), can be viewed in a 3-D viewer using
the LiveGraphics3D java program from the link:
entiat3D.
If you are unfamiliar with LiveGraphics3D, I have prepared an
abbreviated
usage page
extracted from the full documentation by Martin Kraus.
If you are interested in complete information about LiveGraphics3D,
see the home page link in the abbreviated documentation.
R.S. Crosson
Earth and Space Sciences
University of Washington