[PNW-Earthquake-Hazards] Please Ignore this Message (Sorry!)

[Joan S Gomberg]

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 
http://geohazards.cr.usgs.gov/mailman/listinfo/pnw-earthquake-hazards. 
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 at geohazards.cr.usgs.gov, 
and after I screen them (as the listserv moderator) the entire group will 
receive them.  

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
. 

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. 

Thanks very much! 
Joan Gomberg 


***  Changes to be Considered *** 

New additions: 

The Stonewall anticline (Newport, OR) 
This has been suggested by Bob Yeats and is discussed by he and Rus 
Wheeler in the attachments.

More faults in Yakima fold belt 
This has been suggested by Bob Yeats and is discussed by he and Rus 
Wheeler in the attachments.

Boulder Creek fault (has multiple events with age constraints)
Brian Sherrod has new information to share. 

Little River fault (has multiple events with age constraints) 
See presentation under "Faults in the Puget Sound region and elsewherein 
western Washington" by Alan Nelson. 


Slip rate changes: 

Portland Hills fault 
Change slip rate from 0.1 mm/yr (in 2002 maps) to 0.07 mm/yr; proposed by 
Ian Madin 

Bolton fault 
Change slip rate from 0.013 mm/yr (in 2002 maps) to 0.015 mm/yr; proposed 
by Ian Madin 

Mt Angel fault 
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. 

SWIF 
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.
Also see presentations under "South Whidbey Island Fault experience" by 
Rick Blakely 


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