This is an update on the status of an NSF RAPID proposal to support airborne lidar data collection. Ramon Arrowsmith and I are taking the lead on this. Dave Fountain (NSF program director for tectonics) has expressed some support for the project. Right now our chief concerns in assembling the proposal are logistical. These fall into four categories:

(1) Permission from the Mexican government. Contacts have been made with faculty at CICESE and UABCS, and these persons are willing to work with us to get permission through the Mexican national cartographic agency, INEGI. Other permits will likely be needed as well.

(2) Permission from the US government. Importing the IMU for the airborne lidar is a huge issue. It will probably be much easier if we can fly in/out of a U.S. airport. None the less permission from the State Department will be needed. I don't know yet whether a survey flown from the U.S. side will cause a problem on the Mexican side.

(3) GPS support. We need dGPS base stations in the survey area. No plan has been formulated yet for getting instruments into and back out of Mexico. This is probably simpler than (1) and (2), but is none the less a task likely to consume some time. Coordination with SIO may help here.

(4) Rupture location. Hopefully we will know a lot more about this after tomorrow's helicopter recon flight. We need this information to design the lidar survey.
 

UNAVCO has GPS, borehole strainmeter, pore pressure and seismic data available for download at the links below.  UNAVCO also has a suite of GPS equipment ranging from campaign systems to permanent GPS stations that can be deployed rapidly.  You can view UNAVCO community event response coordination at: http://www.unavco.org/voce/viewforum.php?sid=111da1d89bb668f726e7ca0adfa...

GPS Data: UNAVCO is downloading and archiving 5 Hz data from all Plate Boundary Observatory GPS stations within 200 km of the northern end of the April 4, 2010 Baja California earthquake rupture.  The time period covered will be April 2 through April 6, although the later endpoint might be extended if there are significant aftershocks .  These data will be made available via anonymous FTP at data-out.unavco.org/highrate/rinex/2010/, organized by day-of-year and by site ID.

BSM Data: PBO 1-sps strain data  for the M7.2 Baja Earthquake are available from UNAVCO in ASCII format from http://borehole.unavco.org/bsm/earthquakes/BajaCalifornia_20100404/ .
PBO strain (20-sps, 1-sps), seismic (100-sps, 1-sps) and pore pressure (1-sps) data data are available in SEED format from the Northern California Earthquake Data Center and the IRIS DMC
(network code PB).  Plots of automatically processed strain data with tides, trends and barometric pressure signals can be viewed from http://pboweb.unavco.org/strain_data .
The Anza strainmeters have PBO codes B081(Keene Wilde) B082 (Pathfinder 1), B084 (Pinyon Flat), B086 (Santa Rosa), B087 (Ford Ranch), B088 (Sky Oaks) B089 (Pathfinder 2) and B093 (Tripp Flat). For example the Keene Wilde plots may be viewed at
http://pboweb.unavco.org/shared/scripts/stations/?checkkey=B081&sec=time...

Seismic Data: PBO seismic data view and download: http://wiggle.unavco.org/eqs/baja_10.php

UNAVCO Equipment: Below is what is currently available:
20 TopCon GB1000 ready to go and available for 5 weeks
12 NetR8s available for 10 days
4 Trimble 5700s
8-26 Short drilled-braced monument (SDBM) permanent stations (2 panel DC systems) – NetRS and Trimble chokering antennas. 

UNAVCO also has Tripod Laser Scanners including the new Riegl system for tectonic geomorphic/paleoseismic studies. 

To request UNAVCO support please use the online form at:
http://achaia.unavco.org/public/newproject/supportform.aspx
 

Tom Rockwell called to relay info from John Fletcher who made the following field observation.

Some of this same info has just been posted already on the SCEC response web site by Mark Benthien after Rockwell also called him.

Then, John Fletcher called me as well and provided more information. Here is a summary of the latest info we have from John now.

A narrow zone of breaks across hwy. 2 - in all about 12 breaks and each having 10-20 cm of offset, for a total cumulative offset of about 1.2 meters with some east-down but mostly right-lateral slip at the highway crossing. At the hwy 2 crossing, the trend of the 140 m wide zone of fractures is about N 20° W overall.

Coordinates of the location:     32.578621° ; -115.725814°  (KML attached)

To the north of the highway, John observed a nearly north-south oriented zone of fractures with dominantly east-down sense of displacement, totaling perhaps just over 2 meters.

More work is in progress. John reports road crew said there are more fault offsets in Yuhas desert area so they're going there next to check it out.

Rockwell said that this offset at the highway is apparently on the Borrego fault (not the Laguna Salada fault, exactly).

Later, Fletcher said it's probably an un-named fault but he's leaning toward naming it the Centinela fault (for the tall peak immediately to the north that is a well-known landmark in the area). John would like to hold off on giving this a name until it can be further studied -- need to see if it wraps to the east or west around El Centinela.

Furthermore, Tom suggested what perhaps others are also thinking and discussing by now -- perhaps the early subevent is a normal fault break on the north-south oriented range front fault system, followed 10-15 sec later by a strike-slip sub-event much farther northwest along the fault that broke hwy. 2 (call it Borrego or, better yet, Centinela fault for the time being).

Here is an interesting abstract that says the range fault along the east side of the Sierra El Mayor has an uplift rate of 2.1 to 2.7 mm/yr.

    http://cat.inist.fr/?aModele=afficheN&cpsidt=22351031

Regards,

    Ken
 

I think that the gap in the aftershock distribution is real.  The catalog is complete except for smaller events that are detected as subnet triggers or if more than one event is in the same data file, called clones.

Attached is a map of aftershock relocations. 

Egill

VP14 - IVPN 114  32.7402545, 244.285766

PV02 - IVPN 02 32.664567, 244.41398489

At the request of Prof. John Fletcher of CICESE, USGS has activated the International Charter and will support helicopter reconnaissance along the fault tomorrow.

The plan is to meet John and also Tom Rockwell at Mexicali airport early to begin the recon. They are meeting in the field this evening to compare initial findings.

     Ken

From Ross Stein and Shinji Toda

People here are wondering about whether the pronounced difference between seismicity near Signal Mtn in the north and the epicenter is entirely a catalog completeness issue, or if those of you more familiar with the catalog think there might be a real concentration in seismicity to the north of the rupture.

 I made a map to look at the aftershock zone and the USGS active faults. Looks similar to lots of the other maps out there...

http://stockdale.sese.asu.edu/baja_eq/bajaeq.png

http://stockdale.sese.asu.edu/baja_eq/bajaeq.pdf

I have been in touch with Yuri Fialko and David Sandwell regarding campaign GPS response.  Since USGS folks are not at this point allowed to do field work in Mexico, I will send two field crew personnel to reoccupy the sites Duncan listed that are north of the border.  They will drive down tomorrow and begin work Wednesday.

Gavin Hayes at NEIC is working on a finite-source model. Harley Benz indicated last night that the source-time function is rather complicated so progress was very difficult.

Several media outlets have asked to accompany any scientists goin in the field.  If you are interested, email me at jones@usgs.gov and I will connect you.

Lucy