After receiving the InSAR results as a high-resolution KMZ file from Sang-Ho Yun (JPL), Tim Dawson (CGS) and I first checked at the Napa County Airport yesterday (Wed.) afternoon, and we did find one runway with clearly tectonic fractures but no measurable displacement (see photos attached).

After that, Tim went south and I went north to perform additional checks. Essentially, neither of us found anything else as good as the airport site yesterday.

In all, I took 208 photos on Wed.-Thurs. but attached here are just a couple of samples. I loaded the InSAR KMZ onto my laptop in Google Earth, then plugged my Garmin into the laptop and did real-time navigation and used that to locate myself on the InSAR results as I drove around.

Today, I continued searching and also went to a list of other sites that needed to be checked. Some turned out to be duplicated efforts with what Ron Rubin (CGS) has already reported this evening, at the Alston Park and Dry Creek driveway sites. Not bad to have multiple assessments.

My GPS track is attached here in KML formats (GPX upload is not allowed so e-mail me if you prefer the GPX file) so that others can see the localities that I have checked. Mostly, these are from tracking down features that looked interesting in the InSAR.

In any case, overall these checks did not turn out to reveal any additional significant slip on newly recognized strands. I think the InSAR is sensitive to small (<1-2 cm) slip that is absorbed by shear in shallow soils. We saw this, too, for the Brawley Swarm.

Carol Prentice and colleagues from USGS Menlo Park found, on Tues., several additional strands that lie farther east than had been recognized on Sun.-Mon. and these were included in the v.6 AOI for the LiDAR acquisition plan.

Alex Morelan led us to the site at 3051 Redwood Creek Road that does have tectonic slip of ~10 mm (see photos attached). These breaks take off at N25W through the vineyard, but we did not follow them today. Maybe someone else will get a chance to do so - that would be good.

On the basis of these newly identified and confirmed 'definitive' displacement of tectonic origin (found on Tues., Wed. and Thurs.), I revised the polygon for the LiDAR and finalized it this afternoon, with the help of the cost-share partner group via e-mail and phone calls (see earlier note).

Tomorrow morning, I will check the strand that Carol Prentice and colleagues found and work southwards along it to see if it warrants LiDAR coverage (it is not all included in v.6 and has not yet been field-checked to my knowledge).

Thanks for your interest, feel free to ask questions here or else via e-mail to hudnut@usgs.gov or call or text me at 626-672-6295. I'll be in the field through next Tues., perhaps longer, from now on working more with Ben Brooks on laser scanning.

     Ken

 The cracking noted early on at Alston Park has been looked at by Tim and I, as well as several others who are mapping the rupture to the east. The consensus is they are non-tectonic cracks that have been enhanced by shaking. The orientation of the longer crack is not favorable, and the other appeared to be one of many pre-existing irregular cracks in clayey soil. No cracks were observed in the area of our trench, and no other evidence of tectonic rupture has been observed nearby. 

It is also worth pointing out that in contrast to the commentary in the original post here, the lack of tectonic deformation is consistent with the results of our trench across the slope. It was over 3 m deep and exposed Pleistocene and possibly older sediments, un-faulted. We held a trench review and the consensus concurred with that conclusion.

I have taken the Cosmo-Skymed interferogram that Sang-Ho Yun and the ARIA project have kindly provided, and uploaded it to the 'Visible Earthquakes' tool. This is an interactive InSAR modeling website that I have been developing along with Rowan Cockett of 3 point Science, with financial support provided by UNAVCO:

The site is here: http://www.3ptscience.com/earthquake

The Visible Earthquakes tool allows you to make a simple uniform-slip model of an earthquake, by allowing you to manually adjust individual fault parameters within the web interface, and to see how that changes a model interferogram. By comparing this model side-by-side with the real data, you can fine-tune it until you reach an acceptable match. If you are happy with the model, you can submit it, and we can collect statistics on the results. 

The tool is still in beta testing, and has only limited supporting documentation, but the controls are easy to learn and use, so please try it out. Setting up an account (which is required to access the modeling functions), means that we can keep track of your models. Hopefully even non-InSAR specialists can have a go at modeling the earthquake!

The attached figure shows the flight lines from the inital aerial photography done on Monday (8/25/2014) morning by USGS and CHP in light blue.

The planned airborne LiDAR acquisition polygon (v.6) is overlain as a white line bounded area that covers all faults that broke with significant and clearly tectonic rupture that have been identified at this time. This additional imagery will be acquired soon, hopefully within the next few days (pending funding arrangements). This is being cost-shared by a coalition of federal and state agencies including CGS, USGS, PEER/GEER, DWR and potentially others.

Please feel free to ask questions about all of this. I've been busy with field work, racing to get things done before the pavement grinders destroy evidence.

Thanks for your interest and support!

     - Ken

From Mike Oskin (UC Davis) 8/28/14 3:28pm PDT:

Hi all,

This may be somewhat peripheral, but in case anyone is interested, it appears that this earthquake triggered some tremor (low frequency earthquakes, LFEs) along the San Andreas near Parkfield.   There was a small sequence mostly just north of Parkfield (-20 to -15 along-strike position on the attached plot) that started within minutes of the waves passing.  A much larger sequence that started ~10 hours later near Cholame (15-40 km along-strike position) may also have been triggered, as there was a bit of activity in this zone earlier, and these episodes are relatively rare (every few months).  These observations are not too surprising given the history of triggered activity in this zone (including apparent triggering by the 2007 M 5.4 Alum Rock earthquake), though the possibility of delayed triggering of a major tremor episode is interesting.

More notes on the plot:  Along strike position goes from NW (top, -85 km) to SE (bottom, 65 km) - zero position is the town of Parkfield.  Color represents the estimated depth of the LFE family.  For more details see Shelly and Hardebeck, GRL, 2010 or Shelly et al., Nature Geoscience, 2011. 

Best,

David

 Attached are co-seismic offsets from the PBO combined GPS analysis (Central Washington and New Mexico Tech) which used 2-days before the earthquake and 2 days after the earthquake and an updated MIT analysis which uses the same 2-day pairs plus the day of the earthquake split around the time of the earthquake.  Time series plots do not show large post-seismic motions compared the error bars on the daily position estimates.

The attached PDF plot shows the results with the Green vectors being the JPL ARIA project results, red vectors PBO combined results and black vectors MIT results.  MIT results have error bars based on the RMS scatter of the phase residuals from each sites and the PBO results have a blend of this error model with a site independent  constant error model. 

Tom Herring

Thanks, Mike. I'll have a look today. It sounds as if David Schwartz checked it on Sunday but that with the possibility of afterslip, it would be worth checking again.

I have compiled a list of sites that I plan to check today as we try to work towards completeness, partly in order to fine-tune the area-of-interest for the airborne LiDAR.

     Ken

Thank you, Sang-Ho, it was helfpul. Yesterday, Tim Dawson (CGS) and I met at Napa County Airport to check the break from your InSAR for possible surface rupture.

At the airport, we did find en echelon fractures of tectonic origin at one place. We then split up, with Tim checking south and me checking north from there along the tear in phase in the interferogram.

Neither of us found other localities along that lineament with clear tectonic slip.

On the basis of this new evidence, I am working on revising the area-of-interest polygon for use in the airborne LiDAR acquisition planning.

Thank you for the timely InSAR results. It was very helpful.

Regards,

     Ken

Below is the link to a KMZ of surface rupture locations documented by the UC Davis team (myself and Chad Trexler). One CSV file contains the locations of each photo as well as a look direction. Another CSV contains a summary of the observations we made. The KMZ contains the sites that we visited, the data collected at each site, and a link to the rest of the pictures associated with the site.

 https://ucdavis.box.com/s/9zsz84638fp90grhikzx

- Alex Morelan

The NEIC has updated the event page on the USGS website to include recent slip distributions (one seismic from Doug Dreger, one geodetic from Bill Barnhart). 

http://earthquake.usgs.gov/earthquakes/eventpage/nc72282711#scientific_f...

I am posting this again, as I cannot find the "edit" button I used to see. The COSMO-SkyMed coseismic interferogram URL has changed. The new URL is as follows. The zoomable wrapped interferogram can help locating surface ruptures. For example, there could to be one about 2.5 km east from the epicenter, running parallel to what Mike Oskin mapped. 

http://aria-share.jpl.nasa.gov/events/20140824-south_napa/interferogram/...

http://aria-share.jpl.nasa.gov/events/20140824-south_napa/interferogram/...

Caption: Interferometric Synthetic Aperture Radar (InSAR) map of coseismic displacement (wrapped interferogram) in the radar line-of-sight (LOS, 29 degrees from vertical and roughly west) caused by the 2014/08/24 M6.0 South Napa Earthquake, California. Derived from COSMO-SkyMed data acquired on 2014/07/26 and 2014/08/27. One color cycle represents 1.56 cm of LOS displacement. Processed by ARIA team at JPL-Caltech in collaboration with the Italian Space Agency (ASI) and University of Basilicata. The epicenter indicated with the red star is from USGS NEIC. The white line indicates the North Bay Aqueduct. COSMO-SkyMed data (c) ASI 2014.

Contact aria@jpl.nasa.gov or aria@caltech.edu for more information.

-- Sang-Ho Yun, JPL-Caltech ARIA project