This directory contains focal mechanisms for southern California earthquakes 1984-2003, computed from P-wave first motion polarities and S-wave/P-wave amplitude ratios.

A publication on this dataset has not yet appeared.  For now, please reference our technique paper:

Hardebeck, J. L. and P. M. Shearer, Using S/P Amplitude Ratios to Constrain the Focal Mechanisms of Small Earthquakes, Bull. Seismo. Soc. Am., 93, 2434-2444, 2003.

You can also download the source code and user's manual for the focal mechanism program at: http://quake.wr.usgs.gov/research/software/#HASH.


FILES:

README.txt : this file.

socal_1984_2003.hash : a text file containing the focal mechanism dataset (2.6 MB).

socal_hash_poster.pdf : a poster-sized map showing the high-quality (A and B) focal mechanisms from this dataset (3.4 MB).


FORMAT:
         1         2         3         4         5         6         7         8         9        10        11
123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234

2003 12 31 20  8 53.600 14018116  33.91133 -117.06300  17.180  1.260  308  79  165  39  40   20  0.16    6  0.75 D

year mo dy hr mn  sec    cuspid     lat       lon       dep     mag   str  dp  rak un1 un2   np  pmis  nsp  spms qual

2003 = year
12 = month
31 = day
20 = hour
 8 = minute
53.600 = second
14018116 = SCSN cuspid
33.91133 = latitude (3D locations from Egill Hauksson)
-117.06300 = longitude
17.180 = depth (km)  
1.260 = magnitude (from SCSN)
308 = strike (degrees E of N)
79 = dip (degrees, dip to right when facing in strike direction)
165 = rake (degrees, -90=normal; 0=left-lateral; 90=thrust; 180/-180=right-lateral)
39 = RMS uncertainty of given fault plane (degrees)
40 = RMS uncertainty of second fault plane (degrees)
20 = number of P-wave polarities
0.16 = weighted misfit of P-wave polarities 
6 = number of S/P amplitude ratios
0.75 = average log10(S/P) misfit 
D = quality (A=best; D=worst)


Notes:

- No attempt has been made to resolve the nodal plan ambiguity and identify the fault plane and auxiliary plane.  The listed fault plane is chosen arbitrarily.

- Please do not consider this to be an authoritative catalog of earthquake locations or magnitudes.  The values given here were taken from other sources and used unaltered.

- Focal mechanism quality is assigned based on the average fault plane uncertainty, and the probability of the preferred mechanism as compared to any multiples:

        quality   RMS fault plane    mechanism 
        (qual)    uncertainty        probability	
        ----------------------------------------
        A         <=25 degrees       >=0.8
        B         <=35 degrees       >=0.6
        C         <=45 degrees       >= 0.5
        D         maximum azimuthal gap <90 degrees and
                  maximum takeoff angle gap <60 degrees