Fig. DR1: Projection, on a Schmidt’s lower hemisphere net, of faults (a), extension fractures (b) and dikes (c) planes; (d) frequency distribution of the pitch values on the WNW-ESE trending faults; percentage of data taken from literature is indicated in brackets (from Madeira, 1998).

Fig. DR2: (a) view of a dike (N 200°, 80°) located in Ponta dos Capelinhos (site 1, Fig. 4); (b) a dike (N 126°, 81°) feeding a scoria cone near Horta Harbour (site 18, Fig. 4); rose diagram showing the frequency (%) of dike orientations in the Pedro Miguel Graben area (c) and in Ponta dos Capelinhos (d), as well as their location (e).

Fig. DR3: examples of orthogonal Zijderveld diagram, indicating demagnetization step values in degrees Celsius (one sample for each paleomagnetic site; sampling locations indicated in Fig. 2).

Fig. DR4: Wind roses showing the azimuth frequencies (in %) of fault planes (a), T Axes (b) and P Axes (c) collected from focal mechanisms of 38 earthquakes occurred in the Azores region from 1939 to 2013; the earthquake data are listed in Table DR2. The gaussian parameters are also shown; sd = standard deviation.

Fig. DR5: (a) Comparison among the mean azimuths of data obtained from the fieldwork (faults, dikes and extension fractures), remote sensing (lineaments) and focal mechanisms of earthquakes (faults). Orientation and lengths of lines are extracted from the wind roses related to each dataset (Fig. 3 for lineaments, Fig. 5 for field data and Fig. DR4a for focal mechanisms). The length of the lines indicates the amount of data corresponding to each orientation. (b) Comparison between the mean opening direction calculated from field data (gray arrow for faults = N51°E; black arrow for extension fractures = N18°E; white arrow for dikes = N41°E) and the azimuth distribution of the tension axes (mainly N40°W) obtained from focal mechanisms of earthquakes (grey ellipses). Opening directions for field data are those of Fig. 10; the distribution of T Axis azimuths is extracted from Fig. DR4b (see also Tab. DR2).

Site ID Locality N S0 D, I

(b.t.c.)

95 K D, I

(a.t.c.)

95 K K/Ar ages *

FY04 Lomba Grande 10 (10) 355, 18 311, 57 10 23 343, 68 9 28 389 +/- 7

FY09 Riberinha 9 (9) 338, 25 342, 47 4 155 6, 39 4 157 358 +/- 7

FY10 Espalamanca 10 (8) 138, 12 192, -40 6 90 186, -50 6 90 846 +/- 12

N = number of measured specimens (used for statistics in parentheses); S0 = mean bedding attitude (strike and dip values); D, I (b.t.c.) = Paleomagnetic declination and inclination before tectonic correction;

D, I (a.t.c.) = Paleomagnetic declination and inclination after tectonic correction;

95, K = semi-angle of 95% cone of confidence and precision parameter after Fisher (1953);

* radiometric ages in ka from Hildenbrand et al. (2012).

Table DR1: List of paleomagnetic mean directions computed at each site, before and after tectonic corrections.

1- McKenzie, 1972; 2-Udìas et al., 1976; 3- Hirn et al., 1980; 4- Udìas, 1980; 5- Grimison and Chen, 1986; 6- Udìas et al.,

1986; 7- Buforn et al., 1988; 8- Moreira, 1991; 9- Nunes, 1991; 10- Miranda et al., 1998; 11- Madeira et al., 1998a; 12-

Vales et al., 2000; 13- Fernandes et al., 2002; 14- Borges et al., 2007; 15- Matias et al., 2007.

Table DR2: List of 38 earthquakes (M>3.0) occurred in the Central and Eastern Azores region from 1939 to 2013. For each event, the parameters obtained from the focal mechanism solutions and the relative references are indicated. The earthquakes with M>5.0 are included in Fig. 1, with the corresponding event number shown nearby. Num. = number of the event; MAG.= magnitude.

REFERENCES CITED

Borges, J.F., Bezzeghoud, M., Buforn, E., Pro, C., and Fitas, A., 2007, The 1980, 1997 and 1998 Azores earthquakes and some seismo-tectonic implications: Tectonophysics, v. 435, p. 37–54, doi:10.1016/j.tecto.2007.01.008.

Buforn, E., Udìas, A., and Colombas, M.A., 1988, Seismicity, source mechanisms and tectonics of the Azores-Gibraltar plate boundary: Tectonophysics, v. 152, p. 89–118, doi:10.1016/0040-1951(88)90031-5.

Fernandes, R.M.S., Miranda, J.M., Catalão, J., Luís, J.F., Bastos, L., and Ambrosius, B.A.C., 2002, Coseismic displacements of the MW=6.1, July 9, 1998, Faial earthquake (Azores, North Atlantic): Geophysical Research Letters, v. 29, p. 21-1–21-4, doi:10.1029/2001GL014415.

Fisher, R., 1953, Dispersion on a Sphere: Proceedings of the Royal Society of London, Series A, v. 217, p. 295–305.

Grimison, N.L., and Chen, W.P., 1986, The Azores-Gibraltar plate boundary: focal mechanisms, depths of earthquakes and their tectonic implications: Journal of Geophysical Research, v. 91, p. 2029–2047, doi:10.1029/JB091iB02p02029.

Hildenbrand, A., Marques, F.O., Costa, A.C.G., Sibrant, A.L.R., Silva, P.F., Henry, B., Miranda, J.M., and Madureira, P., 2012, Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: The Faial Island example (Azores): Journal of Volcanology and Geothermal Research, v. 241-242, p. 39–48.

Hirn, A., Haessler, H., Hoang-Trong, P., Wittlinger, P., and Mendesvictor, L., 1980, Aftershock sequence of the January 1st, 1980 earthquake and present-day tectonics in the Azores: Geophysical Research Letters, v. 7, p. 501–504, doi:10.1029/GL007i007p00501.

Madeira, J., 1998, Estudos de neotectónica nas ilhas do Faial, Pico e S. Jorge: uma contribuição para o conhecimento geodinâmico da junção tripla dos Açores [Ph.D. Thesis]: Lisbon University, Lisbon, 481 p.

Madeira, J., Brum da Silveira, A., and Serralheiro, A., 1998a, Efeitos geológicos do sismo do Faial de 9 de Julho de 1998: Protecção Civil, v. 14, p. 12–20.

Matias, L., Dias, N.A., Morais, I., Vales, D., Carrilho, F., Madeira, J., Gaspar, J.L., Senos, L., and Silveira, A.B., 2007, The 9th of July 1998 Faial Island (Azores, North Atlantic) seismic sequence: Journal of Seismology, v. 11, p. 275–298, doi:10.1007/s10950-007-9052-4.

McKenzie, D., 1972, Active tectonics of the Mediterranean region: Geophysical Journal of the Royal Astronomical Society, v. 30, p. 109–185, doi:10.1111/j.1365-246X.1972.tb02351.x.

Miranda, J.M., Mendes Victor, L.A., Simões, J.Z., Luis, J.F., Matias, L., Shimamura, H., Shiobara, H., Nemoto, H., Mochizuki, H., Hirn, A., and Lépine, J.C., 1998, Tectonic setting of the Azores Plateau deduced from a OBS survey: Marine Geophysical Researches, v. 20, p. 171–182, doi:10.1023/A:1004622825210.

Moreira, V.S., 1991, Historical seismicity and seismotectonics of the area situated between the Iberian Peninsula, Morocco, Selvagens and Azores islands, in Seismicity, Seismotectonics and Seismic Risk of the Ibero-Maghrebian Region, edited by Mezcua J. and Udìas A. (Instituto Geografico Nacional, Madrid), Série Monografia: v. 8, p. 213–225.

Nunes, J.C., 1991, Microssismos e neotectónica: contribuição para o seu estudo nos Açores [M.Sc. thesis]: Azores University, 245 p.

Udìas, A., Lopezarroyo, A., and Mezcua, J., 1976, Seismotectonics of the Azores-Alboran region: Tectonophysics, v. 31, p. 259–289, doi:10.1016/0040-1951(76)90121-9.

Udìas, A., 1980, Seismic stresses in the region AzoresGibraltar-Western Mediterranean: Rock Mechanics, v. 9, suppl., p. 75–84.

Udìas, A., Espinoza, A.F., Mezcua, J., Buforn, E., Vegas, R., Nishenko, S.P., Martinez-Solares, J.M., and Lopez-Arroyo, A., 1986, Seismicity and tectonics of the North African-Eurasian plate boundary (Azores-Iberia-Tunisia), U.S. Geological Survey Open-File Report 86-626.

Vales, D., Matias, L., Carrilho, F., Madeira, J., Morais, I., and Senos, L., 2000, Focal mechanisms and source parameters of earthquake sequence following the 9th July 1998 Faial (Azores) event, in Book of Abstracts and Papers of the XXVII General Assembly of the European Seismological Commission, Lisbon, September 2000, p. 53.