Fault plane orientations of microearthquakes at Mt. Etna from the inversion of P-wave rise times |
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| Authors: | Salvatore de Lorenzo Elisabetta Giampiccolo Carmen Martinez-Arevalo Domenico Patanè Annalisa Romeo |
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| Institution: | 1. Dipartimento di Scienze della Terra e Geoambientali, via Orabona 4, 70125, Bari, Italy;2. IDPA-CNR, via Mario Bianco 9, Milan, Italy;3. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Piazza di Porta S. Donato 1, 40126, Bologna, Italy;4. Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092, Zurich, Switzerland;1. Fault Analysis Group, School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland;2. Department of Geological Sciences, University of Canterbury, Private bag 4800, Christchurch, New Zealand |
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| Abstract: | A crucial point in the analysis of tectonic earthquakes occurring in a volcanic area is the inference of the orientation of the structures along which the ruptures occur. These structures represent zones of weakness which could favor the migration of melt toward the surface and the assessment of their geometry is a fundamental step toward efficient evaluation of volcanic risk. We analyzed a high-quality dataset of 171 low-magnitude, tectonic earthquakes that occurred at Mt. Etna during the 2002–2003 eruption. We applied a recently developed technique aimed at inferring the source parameters (source size, dip and strike fault) and the intrinsic quality factor Qp of P waves from the inversion of rise times. The technique is based on numerically calibrated relationships among the rise time of first P waves and the source parameters for a circular crack rupturing at a constant velocity. For the most of the events the directivity source effect did not allow us to constrain the fault plane orientation. For a subset of 45 events with well constrained focal mechanisms we were able to constrain the “true” fault plane orientation. The level of resolution of the fault planes was assessed through a non linear analysis based on the random deviates technique. The significance of the retrieved fault plane solutions and the fit of the assumed source model to data were assessed through a χ-square test. Most of the retrieved fault plane solutions agree with the geometrical trend of known surface faults. The inferred source parameters and Qp are in agreement with the results of previous studies. |
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