caa a22 4500 463172140 CHVBK 20180406164816.0 cr unu---uuuuu 170326e20070701xx s 000 0 eng 10.1007/s10950-007-9052-4 doi (NATIONALLICENCE)springer-10.1007/s10950-007-9052-4 The 9th of July 1998 Faial Island (Azores, North Atlantic) seismic sequence [Elektronische Daten] [L. Matias, N. Dias, I. Morais, D. Vales, F. Carrilho, J. Madeira, J. Gaspar, L. Senos, A. Silveira] The Faial earthquake (M L 5.8) that occurred on the 9th of July, 1998, in the Azores region (north Atlantic), caused nine casualties and severe destruction affecting more than 5,000 people. The main shock was located at sea, 10km NE of the Faial Island, and triggered a seismic sequence that lasted for several weeks and was characterized by an unusual high p-value of 1.40 for the modified Omori law. We present here the results of a joint inversion of hypocenters and 1D velocity model performed on the data collected by the permanent network complemented with a temporary network installed shortly after the occurrence of the main event. The 1D velocity model shows a heterogeneous upper crust, testified by the observed differences in site effects at the stations, while the middle crust from ∼2.5 to 8km in depth is quite homogeneous. The Moho is located at a depth of about 12-13km and the Vp/Vs ratio is found to be around 1.78. The events at depth are mainly concentrated in the middle-lower crust (8-12km), while their spatial distribution shows a main cluster, visible after relocation, SSE trending. This direction of elongation is consistent with one of the fault planes (N151°E) of the centroid moment tensor (CMT) solution for the main shock. The same plane is the preferred main shock fault plane inferred after a Coulomb failure function analysis on the aftershock distribution. The main event relocation points to a focal depth shallower than 5km. The aftershocks pattern shows that several fault systems were reactivated by the stress perturbation induced by the main shock. Besides the two main tectonic directions, trending WNW-ESE and NNW-SSE, observed in the tectonics of Faial, Pico, and S. Jorge, there is also evidence of a new tectonic direction trending WSW-ENE. Springer Science+Business Media, Inc., 2007 Aftershocks nationallicence Hypocenter relocation nationallicence Velocity models nationallicence Omori fit nationallicence Focal mechanisms nationallicence Azores nationallicence Matias L. University of Lisbon, CGUL, IDL, Lisbon, Portugal aut Dias N. University of Lisbon, CGUL, IDL, Lisbon, Portugal aut Morais I. University of Lisbon, CGUL, IDL, Lisbon, Portugal aut Vales D. Instituto de Meteorologia, IM, Lisbon, Portugal aut Carrilho F. Instituto de Meteorologia, IM, Lisbon, Portugal aut Madeira J. University of Lisbon, LATTEX, IDL, Lisbon, Portugal aut Gaspar J. University of Azores, CVARG, Ponta Delgada, Azores, Portugal aut Senos L. Instituto de Meteorologia, IM, Lisbon, Portugal aut Silveira A. University of Lisbon, LATTEX, IDL, Lisbon, Portugal aut Journal of Seismology Kluwer Academic Publishers 11/3(2007-07-01), 275-298 1383-4649 11:3<275 2007 11 10950 https://doi.org/10.1007/s10950-007-9052-4 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10950-007-9052-4 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Matias L. University of Lisbon, CGUL, IDL, Lisbon, Portugal aut NATIONALLICENCE 700 1- Dias N. University of Lisbon, CGUL, IDL, Lisbon, Portugal aut NATIONALLICENCE 700 1- Morais I. University of Lisbon, CGUL, IDL, Lisbon, Portugal aut NATIONALLICENCE 700 1- Vales D. Instituto de Meteorologia, IM, Lisbon, Portugal aut NATIONALLICENCE 700 1- Carrilho F. Instituto de Meteorologia, IM, Lisbon, Portugal aut NATIONALLICENCE 700 1- Madeira J. University of Lisbon, LATTEX, IDL, Lisbon, Portugal aut NATIONALLICENCE 700 1- Gaspar J. University of Azores, CVARG, Ponta Delgada, Azores, Portugal aut NATIONALLICENCE 700 1- Senos L. Instituto de Meteorologia, IM, Lisbon, Portugal aut NATIONALLICENCE 700 1- Silveira A. University of Lisbon, LATTEX, IDL, Lisbon, Portugal aut NATIONALLICENCE 773 0- Journal of Seismology Kluwer Academic Publishers 11/3(2007-07-01), 275-298 1383-4649 11:3<275 2007 11 10950 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer