<br><font size=3>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><u>http://geohazards.cr.usgs.gov/mailman/listinfo/pnw-earthquake-hazards</u>.
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>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>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>Thanks very much! </font>
<br><font size=3>Joan Gomberg </font>
<br>
<br>
<br><font size=3><b>*** Changes to be Considered ***</b> </font>
<br>
<br><font size=3><b>New additions:</b> </font>
<br>
<br><font size=3>The Stonewall anticline (Newport, OR) </font>
<br><font size=3>This has been suggested by Bob Yeats and is discussed
by he and Rus Wheeler in the attachments.</font>
<br>
<br><font size=3>More faults in Yakima fold belt </font>
<br><font size=3>This has been suggested by Bob Yeats and is discussed
by he and Rus Wheeler in the attachments.</font>
<br>
<br><font size=3>Boulder Creek fault (has multiple events with age constraints)</font>
<br><font size=3>Brian Sherrod has new information to share. </font>
<br>
<br><font size=3>Little River fault (has multiple events with age constraints)
</font>
<br><font size=3>See presentation under "Faults in the Puget Sound
region and elsewherein western Washington" by Alan Nelson. </font>
<br>
<br>
<br><font size=3><b>Slip rate changes:</b> </font>
<br>
<br><font size=3>Portland Hills fault </font>
<br><font size=3>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>Bolton fault </font>
<br><font size=3>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>Mt Angel fault </font>
<br><font size=3>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>SWIF </font>
<br><font size=3>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>Also see presentations under "South Whidbey Island
Fault experience" by Rick Blakely </font>
<br>
<br>
<br><img src=cid:_1_084D8DD0084D8A48005E26E088257219><img src=cid:_1_084D8F80084D8A48005E26E088257219><img src=cid:_1_084D9130084D8A48005E26E088257219><img src=cid:_1_084D92E0084D8A48005E26E088257219><img src=cid:_1_084D94BC084D8A48005E26E088257219>