The strain rate map is produced using the 'analyze_strain' module of JPL's Quasi-Observation Combination Analysis (QOCA) software (http://http://qoca.jpl.nasa.gov).

The map input is the most recent SIO-JPL combined velocity map in the a region (32.5N-42N; 116E-125E) covering all of California (32.5N-42N; 116E-125E). The time period covered by the velocity estimate is… 

To produce the strain values shown in the map, 'analyze_strain' uses a least squares approach to estimate the strain rates, represented here as Dilatation and Maximum Shear rates, at given grid points based on velocities within a predefined distance from each grid point. These velocities are estimated from deformation GPS station time series using QOCA’s time series analysis tool that models annual and semiannual periodic variations, as well as offsets and postseismic deformation simultaneously with the inter-seismic velocity measured at GPS stations within a predefined distance from each grid point.  In this case, the strain estimate grid was set at 1/20 of a degree, and the radius of influence was set at 50km.  A Gaussian weighting scheme using a 10km Gaussian width around each grid point was implemented to give increased weight to GPS stations velocities closer to the grid point where the strain rate is calculated.  The color scale on the plot is saturated at 50% of the maximum strain rates observed in order to visually enhance the finer structure of the strain rate field.

In addition, The 'analyze_strain' output file, analyze_strain.gam, from which the map is derived with values used to generate map, is provided.

analyze_strain.gam contains the following information:

*    LON        LAT         GAMMA1   GAM1SIG    GAMMA2    GAM2SIG   GAM12COV  SHEARMAX  SHMAXSIG      PSI             PSISIG        SHPSICOV     DIL              DILSIG       EPOCH
*   (deg)       (deg)       (1e-6/yr)    (1e-6/yr)        (1e-6/yr)      (1e-6/yr)     (e-12/y^2)      (1e-6/yr)          (1e-6/yr)           (deg)          (deg)            (e-6*d/y^2)     (1e-6/yr)     (1e-6/yr)     (year)            corners
 242.3000   32.5000  1.94E+01  3.16E+02      9.38E+00   2.75E+02  -3.50E+02      2.16E+01        3.08E+02        122.1146   0.38E+03   1.29E+04        9.54E+00  1.58E+02   2000.0000   CORX-P475-PLO3
 242.3500   32.5000  1.94E+01  3.16E+02      9.37E+00   2.75E+02  -3.62E+02      2.16E+01        3.08E+02        122.1280   0.38E+03   1.29E+04        9.54E+00  1.58E+02   2000.0000   CORX-P475-PLO3
 242.4000   32.5000  1.94E+01  3.16E+02      9.37E+00   2.75E+02  -3.73E+02      2.16E+01        3.08E+02        122.1415   0.38E+03   1.29E+04        9.54E+00  1.58E+02   2000.0000   CORX-P475-PLO3
 242.4500   32.5000 -7.77E-01   3.55E+01    -6.39E-01    3.11E+01   3.92E+00      1.01E+00        3.39E+01           25.2962   0.94E+03   4.06E+03        -4.47E-01  1.78E+01   2000.0000   CORX-P475-PLO3-SIO3-SIO5
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Quantity	Units			Definition
LON		(deg)			Grid point longitude
LAT         	(deg)			Grid point latitude
GAMMA1	(1e-6/yr)		First engineering Shear strain rate
GAM1SIG    	(1e-6/yr)		First engineering Shear strain rate error
GAMMA2    	(1e-6/yr)		Second engineering Shear strain
GAM2SIG   	(1e-6/yr)		Second engineering Shear strain error
GAM12COV  (e-12/y^2)		Engineering Shear strain covariance 
SHEARMAX  (1e-6/yr) 		Maximum Shear rate
SHMAXSIG	(1e-6/yr) 		Maximum Shear rate error
PSI 		(deg) 			Maximum Shear direction
PSISIG        	(deg) 			Maximum Shear direction error
SHPSICOV 	(e-6*deg/y^2)	Covariance of Maximum Shear and Maximum Shear direction
DIL   		(1e-6/yr) 		Dilatation
DILSIG 	(1e-6/yr) 		Dilatation Error
EPOCH	(year)			Epoch of estimated strain rate in decimal year (IMPORTANT: Time is arbitrarily set to 2000.000 - The actual time period is that of the combined JPL-SIO velocity map time series used to produce the strain rate map estimate the inter-seismic/tectonic velocities that are the input to the strain estimation.)
		(names)		GPS stations used for the estimation of the strain rate at the specific grid point