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