Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006geoji.166..322f&link_type=abstract
Geophysical Journal International, Volume 166, Issue 6, pp. 322-338.
Astronomy and Astrophysics
Astronomy
4
Circular Crack, Directivity, Fault Plane Solution, Non-Linear Inversion, Polarities, Rise Time
Scientific paper
A two-step technique has been developed with the aim of retrieving the fault plane orientation of a small-magnitude earthquake. The technique uses a set of non-linear equations, which relate the rise times of first P waves to source parameters (source dimension L, dip δ and strike φ of the fault) and intrinsic Qp. At the first step of the technique, the inversion of P polarities provides two fault plane orientations for each focal mechanism solution. At the second step, the inversion of rise times is carried out to retrieve L and Qp by fixing δ and φ to the values of the fault plane orientation inferred at the first step. A robust analysis, based on the random deviates technique, allows us to evaluate if one fault plane exists which systematically better fits data and can be considered the `true' fault plane. A parameter is introduced to quantify the level of resolution of the `true' fault plane. A probabilistic approach, based on the assumption that errors on data are Gaussian distributed, allows us to a posteriori validate or reject the `true' fault plane. The technique has been applied to 47 small earthquakes (1.3 < ML < 3.9) occurred below the town of Sellano, during the 1997 Umbria-Marche (Central Italy) seismic crisis. The strike of the inferred fault planes is generally along the Apennine direction. Fault plane solutions can be mainly subdivided into two groups: a first group of SW-dipping faults and a second group of NE-dipping faults. These results agree with the present day knowledge of the fault systems in the area. An average Qp equal to 354 +/- 63 has been estimated, in agreement with previous attenuation studies.
Boschi Enzo
de Lorenzo Salvatore
Filippucci Marilena
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