<br><font size=3 face="Times">Thank you all for agreeing to participate
in the PNW Fault Working Group. I have 'volunteered' to facilitate
the business of the group with the primary goal of helping it to come to
informed decisions that can be passed on to the national seismic hazard
mapping project. Secondarily, I hope this will be educational for
all involved. For those of you I have not met or only recently have
met, my principal qualification to do this is that I begin from a state
of nearly complete ignorance (and geologic expertise) and thus, can guarantee
that I have absolutely no biases! If it’s okay with all of you, I’d like
to try having our electronic exchanges using a listserv, which is basically
just a moderated email discussion group with the benefit of keeping an
online archive. As this listserv has already been set up, but was as yet
unused, I thought this might be a great way to both begin our discussions
and try out this tool (possibly for use more broadly). I’ve taken
the liberty of subscribing all of you to the listserv and have sent this
email through it; for more information about it please see the webpage
at</font>
<br><font size=3 color=blue face="Times"><u>http://geohazards.cr.usgs.gov/mailman/listinfo/pnw-earthquake-hazards</u></font><font size=3 face="Times">.
Please note that although described as for more general purposes, currently
only the Working Group is subscribed to it, so no one else will receive
our emails or be able to look at the archive (although I see no reason
why ultimately we shouldn’t use it as a means of helping to document the
basis of any recommendations). If you think this is not a good idea,
please don’t hesitate to let me know. If not, please send all email,
attachments, etc. to pnw-earthquake-hazards@geohazards.cr.usgs.gov, and
after I screen them (as the listserv moderator) the entire group will receive
them. </font>
<br>
<br><font size=3 face="Times">As you’ve all received Art’s emails, there’s
no need to repeat the PNW Fault Working Group’s current charge. 4
additions and 4 modifications to existing fault parameters are being considered
. These are listed below with a few comments about background information
with which to evaluate each. We hope that the person suggesting the change
and/or who is an obvious source of information about the particular fault
will provide the group with additional information. I have attached
the comments of Bob Yeats and responses from Rus Wheeler that you have
already been sent again for convenience. An overview of what fault parameters
are currently used, why, etc. is in the presentation under "Introduction:
Overview of scientific issues: why are we here?" by Frankel made at
the National Map workshop held this Spring. Most of the presentations
from the workshop and referenced below can be found at http://earthquake.usgs.gov/research/hazmaps/whats_new/workshops/pacNW_workshop.php.
</font>
<br>
<br><font size=3 face="Times">Please also note that Art emphasizes that
when thinking about deciding whether changes should be made, one should
consider the policy of the National Maps that only faults where a slip
rate or recurrence time has been estimated or determined from measurements
on that fault can be used (e.g. slip rates based entirely on analogs are
not sufficient). Please provide your contributions, using the listserv,
before the end of November (the earlier the better). When enough
information has been exchanged I will try to schedule a conference call,
or if it appears necessary, a face-to-face meeting. Please keep in
mind the goal of providing final recommendations my mid-January.</font>
<br>
<br><font size=3 face="Times">Thanks very much!</font>
<br><font size=3 face="Times">Joan Gomberg</font>
<br>
<br>
<br><font size=3 face="Times"><b>*** Changes to be Considered ***</b></font>
<br>
<br><font size=3 face="Times"><b>New additions:</b></font>
<br>
<br><font size=3 face="Times">The Stonewall anticline (Newport, OR)</font>
<br><font size=3 face="Times">This has been suggested by Bob Yeats and
is discussed by he and Rus Wheeler in the attachments.</font>
<br>
<br><font size=3 face="Times">More faults in Yakima fold belt</font>
<br><font size=3 face="Times">This has been suggested by Bob Yeats and
is discussed by he and Rus Wheeler in the attachments.</font>
<br>
<br><font size=3 face="Times">Boulder Creek fault (has multiple events
with age constraints)</font>
<br><font size=3 face="Times">Brian Sherrod has new information to share.</font>
<br>
<br><font size=3 face="Times">Little River fault (has multiple events with
age constraints)</font>
<br><font size=3 face="Times">See presentation under "Faults in the
Puget Sound region and elsewherein western Washington" by Alan Nelson.</font>
<br>
<br>
<br><font size=3 face="Times"><b>Slip rate changes:</b></font>
<br>
<br><font size=3 face="Times">Portland Hills fault</font>
<br><font size=3 face="Times">Change slip rate from 0.1 mm/yr (in 2002
maps) to 0.07 mm/yr; proposed by Ian Madin</font>
<br>
<br><font size=3 face="Times">Bolton fault</font>
<br><font size=3 face="Times">Change slip rate from 0.013 mm/yr (in 2002
maps) to 0.015 mm/yr; proposed by Ian Madin</font>
<br>
<br><font size=3 face="Times">Mt Angel fault</font>
<br><font size=3 face="Times">There is new information, noted by Bob Yeats
and and discussed by he and Rus Wheeler in the attachments, but it is not
clear that any change is being advocated in the treatment of this fault.</font>
<br>
<br><font size=3 face="Times">SWIF</font>
<br><font size=3 face="Times">Change fault geometry and dimensions; see
Art’s Introductory presentation that notes a change dip from 60 to 45
degrees,seismogenic layer thickness from 17.3 to 20 km, length from 63
to 86 km. Assuming the same uplift rate of 0.6 mm/yr this changes
the characteristic magnitude from M7.2 to M7.3 with Tchar from 3100 to
1700 yr, and for a M6.5 the recurrence time changes from 930 to 400 yr.
For 0.5 mm/yr strike slip component (derived assuming pure north-south
convergence): Tchar=2900 yr and the recurrence time for a M 6.5 becomes
680 yr. Combining these equally (1/2 reverse and 1/2 strike-slip
motion) results in Tchar= 1300 yr and a M 6.5 recurrence interval of 310
yr, which are much shorter times than used for the Seattle fault.</font>
<br><font size=3 face="Times">Also see presentations under "South
Whidbey Island Fault experience" by Rick Blakely</font>
<br>
<br>
<br>
<br>
<br><font size=2 face="sans-serif">Joan Gomberg<br>
US Geological Survey<br>
University of Washington<br>
Dept of Earth and Space Sciences<br>
Box 351310<br>
Seattle, Washington 98195-1310<br>
206-616-5581<br>
gomberg@usgs.gov</font>