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  • mfloyd
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    As Gareth has previously informed the community, he and I (with equipment and field assistants from UC Riverside and Berkeley) set up 11 GPS receivers at previously observed survey marks around the epicentral region within about 15 hours of the event.

    Yesterday, I added two more sites (MADR and M139) and, given the mapped rupture, we removed some sites (X552 and 6908) to place them further north (B468 and VETH).

    See attached KML and screen shot of current UCR-MIT survey GPS. The USGS has been working in parallel with us to reoccupy sites that they have previous observations from (see http://earthquake.usgs.gov/monitoring/gps/NCalifornia_SGPS/ or http://earthquake.usgs.gov/monitoring/gps/data/networks/USGS_campaign_da...).

    Cheers,
    Mike

  • eqadmin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    From Steve DeLong (USGS) 6/26/14 06:05 PDT:

    Hi Dan, Interesting. Has anyone checked the attached location, it may be a bit farther south and across Buhman from what you describe? Photo and kmz attached. Observed from helicopter. If verified, it would change the trace mapped through to Henry Rd a bit, shifting it eastward. This photo is from shared photos on google drive DeLongOverflightPhotosAug24. DSC_0583

    Best,

    Steve

  • eqadmin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    From Dan Ponti (USGS) 8/26/14 01:36 PDT:

    All -

    Tom Holzer, Tim Dawson and I observed well-expressed right-lateral and transpressive faulting in natural ground just west of Buhman Ave between Twin Oaks Drive and Congress Valley Rd. Right lateral displacement within the ~0.4 km long zone that we were able to access is the largest observed to date, and is on the order of 40 cm, with the maximum displacement measured at 46 cm. Over the region we examined, strike of the fault rupture changed from ~345 deg. northward to nearly 0 deg. As the strike changes to the northerly trend, displacement sense changes from nearly pure strike-slip to a more transpressive rupture with notable vertical offset on the order of 15-20 cm (down to the east) and E-W shortening estimated at 10-15 cm. This observation would indicate a clockwise rotation in the slip vector to a N-NE orientation in association with the change in fault strike.

    Although we were unable to walk out the zone today farther to the north and south due to time and access constraints, the zone of fault rupture projects to the north to where UC Davis investigators reported offsets at Oak Rock and Leaning Oak Drives, and to the White Cliff Circle area where the deformation zone trends N-NE and several investigators have reported dominantly compressive deformation, evidenced by pavement buckling and tented sidewalks. To the south these large ruptures likely connect with cracking and small displacements noted at Henry Road near the intersection of Buhman Ave. In the vineyards to the south of the zone we mapped, the fault zone appears to become broader, and more diffuse although this needs to be verified with additional mapping. Some afterslip may be occurring, based on anecdotal comments from residents who described several cracks as growing in width on the order of 1 inch since the earthquake. Based on these same accounts, however, we would infer that most of the observed displacement is coseismic.

    The region of large displacement occurs approximately 8.4 km NW of the epicenter of the mainshock, which is in the region where the preliminary finite fault model from UC Berkeley shows high slip within a few km of the surface. It also appears to be coincident with a bedrock fault shown by Graymer that juxtaposes Cretaceous and Paleogene sediment.

    I've attached an image showing the location of rupture zone we documented in red, along with a couple of photographs to give you the flavor of the rupture character. Tom and I have a lot more photos and measurements that we will upload onto the Google Drive Tuesday.

    Dan

  • huynht
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    Emailed by Ian Dixon (SAS Chief, R9 RRCC), and circulated via USGS response email list:

    The red tag list has grown to 64 structures. As of 1445 PDT, 25 August, 2014:

    http://cityofnapa.org/index.php?option=com_content&view=article&id=1835%3Ared-tagged-structures-list-as-of-245pm-aug-25&catid=1%3Alatest&Itemid=30

  • huynht
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago
    Kenneth W Hudnut (USGS) wrote 8/26/14 12:15am:

     

    Latest situation report from FEMA R9. I spoke at length with Jon Bartlett this evening to ensure that critical lifelines operators are aware of the afterslip that has been observed by USGS. He is passing that info along to Don Boland so that all are advised and can perform repairs accordingly.

    Ken Hudnut(626)672-6295
  • eqadmin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    From Fred Pollitz (USGS) responding to Tom Brocher inquire about resurvey of campaign GPS sites near the epicenter: (8/25/14 5:25pm):

    There are 11 campaign stations that we have been re-surveying over the past day and a half. These are shown in the attached figure which I also put on the google drive page. We are discussing re-surveying more stations throughout the area, but the ones given on the figure are the closest to the rupture.

    We do not have results from this campaign yet but hope to soon, and these will be posted online.

    Bill Barnhart has a preliminary `geodetic' slip distribution based on essentially the cGPS results plotted in the figure, which were derived from Jerry's 24 hour time series. Bill's slip distribution has predominantly shallow slip on the northern end of the rupture.

    Fred

  • aemorelan
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    Doug,

    Chad and I were in the field again today to check some measurements and confirm observations from yesterday. We are planning to compile data for distribution tomorrow morning. We will include a summary with lat, lon, and slip in cm.

    Alex

  • eqadmin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

     From Bob Dollar (USGS) 8/24/14 4:39am:

    All,

    I have set up a magnitude counter, using COMCAT, for the Napa area.

    http://tejon.gps.caltech.edu/stats/magcount/nc_napa.php

    Hit refresh to update.

    Surprisingly few aftershocks.

    bob

  • yule
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

     Very cool! I will show all of this great information to my class tomorrow on Day 1 of 'Living with Earthquakes in California'. 

  • yule
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    Looks to me like the surface rupture locations are west of the USGS' mapped trace of the (Late Quaternary) fault, and systematically farther away at the north (~50 m) than to the south (~10 m). Is this correct?

  • owen
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

     

    All,

    Posting coseismic GPS offsets (and figure showing horizontal vectors). The pre-event positions are based on 7 days of daily positions. The post-event positions are based on a static solution using ~13.5 hours of data after the earthquake.

    We will monitor subdaily positions to see if GPS sites show additional postseismic movement, especially given reports that surface ruptures have increased significantly since they were first observed. 

    Thanks,

    Sue Owen, Angie Moore, Zhen Liu & ARIA team. 

  • dreger
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    I have updated the preliminary UCB finite-source slip model. The rupture extends approximately 12 km N-NW of the epicenter and updip from 11 km to 2 km depth. There is shallower slip in the model that is not as well resolved. The location of the shallowest slip is consistent with the reported  locations of peak surface offsets. The kinematics of the rupture process would produce a strong directivity effect in Napa, CA.

  • barnhartwd
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

     We've derived a fault slip model from regional GPS. Slip distribution and location map/information are attached below. Please email wbarnhart@usgs.gov to request further details on the fault source model. We will continue to update on this forum as the GPS positions improve.

     

  • arrowsmi
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

     I ran the kmz Mike Oskin posted last night through my GlobalMapper and exported it as attached txt file. Might need a bit of cleanup for your purposes.

  • oskin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

     Locations in kmz are in utm meters and accurate to a few meters. 

  • ccrosby
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    There is coverage of the epicentral region in the 2003 Napa Watershed lidar dataset collected by NCALM, available from OpenTopography here:  http://opentopography.org/id/OTLAS.052010.26910.1

    There is also a 2010 San Francisco Bay lidar dataset available from NOAA that appears to cover the EQ extent: http://www.csc.noaa.gov/dataviewer/index.html?action=advsearch&qType=in&qFld=ID&qVal=584#

    -cc

  • ybock
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    The READI group has been analyzing 1 Hz GPS data collected in real time from stations within 75 km of the epicenter. At SOPAC we have produced 1 Hz displacements using PPP-AR analysis (Geng et al., G-cubed, 2013). Attached is a slide with 1 Hz displacements from 6 stations. The complete set of plots and displacements will be posted on GPS Explorer (http://geoapp03.ucsd.edu/gridsphere/gridsphere?cid=Earthquakes) later this afternoon, or contact jgeng@ucsd.edu for a tar file. We've heard from UNAVCO that they are downloading 5 Hz GPS data from PBO stations within 300 km of the epicenter.

    Attached is a list of stations and the slide.

  • dreger
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    If possible could you post a ascii file with lat,lon, slip for all surveyed points? I would like to use your observations as a constraint in a finite-source inversion. I can get some of it from the figure and kmz, but it would be better if I had all of the observations.

     

    Best

    Doug

  • eqadmin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago

    From Doug Dreger (UC Berkeley) 8/25 11:25am:

    This is a preliminary finite-source model. It uses BDM, BKS, HOPS, CVS, MNRC, MCCM, FARB, and JRSC. The model is unilateral to the NW and updip. I used the UCB TDMT focal mechanism (155,82,-172). Single time window, rise time 0.6 seconds. Data and GFs were filtered between 0.02 to 1 Hz.

    I am working on filling in the Green's function data base that was used, and will then better explore the moment minimization and smoothing constraints, and will send you an update.

    Jack, how does this compare with your results?

    I have asked Ingrid for static GPS, which I can incorporate, and will send her a follow up email in a minute.

    Best
    Doug

  • huynht
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 49 weeks ago
  • huynht
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 50 weeks ago

    An EERI Virtual Clearinghouse has been established at: http://www.eqclearinghouse.org/2014-08-24-south-napa/. It has interactive ArcGIS data map.

  • oskin
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 50 weeks ago

     Alex and Chad found a lot of N to NE striking strands at the northern rupture termination. The LL offset is clear in the pavement but rotation of slabs of pavement could cause that. In any case the zone if rupture is quite wide in brown's valley.

  • Treiman
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 50 weeks ago
    If the left-lateral offset you mention is that noted at "Redwood Rd 2" I wonder if that wasn't just an artifact of rotation of the pavement slabs? I note in the photo that it looks like a nice left-step in the fractures that cross the road, suggestive of right-lateral shear.
  • jrmurray
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 50 weeks ago

     Field personnel from USGS Menlo Park began deploying instruments yesterday (8/24) at sites in the epicentral region where we have pre-earthquake data.  USGS and UCR/MIT are coordinating on the field response.  The attached map shows target locations for campaign measurements.

  • gareth
    2014.08.24 - M6.0 South Napa Earthquake, California   7 years 50 weeks ago

    Serendipitously, Mike Floyd and I are in the region on a GPS campaign and have diverted to the Napa area. We have 5 receivers each (i.e. 10 in total) and are planning to deploy them all at sites around Napa this afternoon.

    More when I have better internet.

    Update 15.15 PDT

    Our target sites are the following (see attached kmz):

    SPRR -122.1863 38.2086
    AMER -122.1992 38.1686
    6908 -122.1144 38.1569
    04KH -122.2535 38.1548
    SKAG -122.3806 38.1588
    04KF -122.4677 38.2452
    04LF -122.4786 38.3025
    04LG -122.2994 38.2711
    TRAN -122.3091 38.321
    HAGG -122.2592 38.3239 

    All bar one site (HAGG) were measured by us six weeks ago, so will have good pre-event coordinates. We intend to leave these sites out for the next few days to capture any early postseismic transient deformation.

    Update 21.00 PDT

    All of the above sites were occupied as planned, before 16.30 on Sunday afternoon, by our team (me, Mike Floyd and grad student Jerlyn Swiatlowski). Mike, in addition, occupied one more in the evening using additional equipment supplied by UC Berkeley:

    X552 122.28723W 38.10720N

    There are several more of our campaign sites in the area that could be usefully surveyed, particularly at the north end of the rupture, along highway 29 and parallel roads. If there are any other GPS receivers that can be loaned to the effort, please let us know!