Seismic source parameters for microearthquakes of the Granada basin (southern Spain)

• Published in: Tectonophysics Vol. 261; no. 1; pp. 51 - 66
• Main Authors: García-García, J.M., Vidal, F., Romacho, M.D., Martín-Marfil, J.M., Posadas, A., Luzón, F.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30-08-1996
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/0040-1951(96)00056-X

Ninety-five microearthquakes of the Granada basin (southern Spain) with duration magnitudes ranging from 1.3 to 3.5 (moment magnitude from 0.9 to 2.5) have been spectrally analyzed with digital recordings from ten stations of the Andalusian Seismic Network. The coda-
Q quality factor,
Q
c (assumed to be frequency dependent) was used instead of
Q
β
for the path correction and the
Q
α
adopted was equal to (
9
4
)
Q
c. The
k parameter for site attenuation correction had values in the range of 0.02–0.05. Fourier displacement spectra were calculated for P- and S-waves and analyzed with respect to the source model of Brune (1970, 1971). Spectral parameters were automatically determined by the method of Snoke (1987). The seismic moment ranged from 10
17 to 10
20 dyne cm, with average
M
0(P) to
M
0(S) ratio of 1.02, and the source radii spanned from 0.14 to 0.40 km, with average
r(P) to
r(S) ratio of 1.3. The seismic energy values ranged from 1 × 10
3 to 9 × 10
7 J, with P- to S-energy ratio from 1 to 10 for about 85% of the events, whereas the static stress drop varied from 0.02 to 2.6 bar. The scaling relation between the seismic moment and the stress drop indicates a decrease in stress drop with decreasing seismic moment. Apparent stress is linearly correlated with stress drop and have on average similar values, and this points out to a partial stress drop.