{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,19]],"date-time":"2026-10-19T03:16:46Z","timestamp":1792379806262,"version":"4.4.0"},"reference-count":60,"publisher":"American Geophysical Union (AGU)","issue":"B2","license":[{"start":{"date-parts":[[2012,9,20]],"date-time":"2012-09-20T00:00:00Z","timestamp":1348099200000},"content-version":"vor","delay-in-days":9719,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Geophys. Res."],"published-print":{"date-parts":[[1986,2,10]]},"abstract":"<jats:p>We have analyzed the focal mechanisms and depths of 10 moderately sized earthquakes along the Azores\u2010Gibraltar plate boundary by a variety of methods including formal inversion of the waveform and amplitude of teleseismic P and SH waves, first motion readings, and the identification of depth phases. Our data, together with a compilation of results reported for very large events from the past 30 years and for two recent events in 1983, place new constraints on the present\u2010day deformation of this boundary separating the Eurasian and African plates. The slow (\u223c2 to 3 mm\/yr) divergent plate motion near the Azores Islands at the western end of the boundary appears to be very similar to that of a typical ridge\u2010transform\u2010ridge configuration. A currently aseismic segment with presumed transcurrent motion separates the western end from a broad zone of ocean\u2010ocean convergence to the east. This convergence zone is characterized by scattered seismicity, complex bathymetry, and large positive geoid and gravity anomalies. The dispersed locations of the earthquakes and the lack of consistency in the orientation of their nodal planes and slip vectors all suggest that a single major plate boundary is not present there. We note that a regional stress field of north\u2010northwest\u2010south\u2010southeast compression can be inferred from the consistent P axis directions. The focal depths for earthquakes in this region reach a maximum of 50\u00b15 km beneath the seafloor. These events are among the deepest oceanic earthquakes which are apparently unrelated to a Benioff zone and their maximum depths are approximately limited by the position of the 600\u00b0C isotherm. We interpret the regional stress field and the focal depths as the result of the interaction of two sections of strong, cold oceanic lithosphere with nearly identical thermal structure. As the plate boundary crosses the passive continental margins of Iberia and Africa, the zone of ocean\u2010ocean convergence becomes that of continental collision. Two unusually deep events, one at 100 and another at 640 km, have occurred beneath southern Spain since the occurrence of the deep Spanish earthquake of 1954 in the same area. The configuration of a seismic upper crust and uppermost mantle straddling an aseismic lower crust resembles the distribution of focal depths in other areas of recent continental convergence. Based on the distribution of focal depths along the entire plate boundary and recent reconstructions of the history of relative motions between Eurasia and Africa, the very deep events beneath southern Spain are likely to have occurred within a detached piece of lithosphere which sank to its present depth during the current phase of plate convergence.<\/jats:p>","DOI":"10.1029\/jb091ib02p02029","type":"journal-article","created":{"date-parts":[[2008,2,6]],"date-time":"2008-02-06T16:36:55Z","timestamp":1202315815000},"page":"2029-2047","source":"Crossref","is-referenced-by-count":204,"title":["The Azores\u2010Gibraltar Plate Boundary: Focal mechanisms, depths of earthquakes, and their tectonic implications"],"prefix":"10.1029","volume":"91","author":[{"given":"Nina L.","family":"Grimison","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wang\u2010Ping","family":"Chen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"13","published-online":{"date-parts":[[2012,9,20]]},"reference":[{"key":"e_1_2_1_2_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB074i002p00632"},{"key":"e_1_2_1_3_1","unstructured":"Bowin C. W.Warsi andJ.Milligan Free\u2010air gravity anomaly atlas of the world Map Chart Ser. MC\u201046 Geol. Soc. of Am. Denver Colo. 1982."},{"key":"e_1_2_1_4_1","doi-asserted-by":"publisher","DOI":"10.1126\/science.168.3939.1573"},{"key":"e_1_2_1_5_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB088iB05p04183"},{"key":"e_1_2_1_6_1","doi-asserted-by":"publisher","DOI":"10.1016\/0031-9201(76)90073-X"},{"key":"e_1_2_1_7_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246X.1966.tb03063.x"},{"key":"e_1_2_1_8_1","first-page":"400","article-title":"Il terremoto delle Azzore del 25 Nov. 1941","volume":"2","author":"DiFilipo D.","year":"1949","journal-title":"Ann. Geofis."},{"key":"e_1_2_1_9_1","doi-asserted-by":"publisher","DOI":"10.1016\/0031-9201(83)90140-1"},{"key":"e_1_2_1_10_1","doi-asserted-by":"publisher","DOI":"10.1016\/0031-9201(84)90001-3"},{"key":"e_1_2_1_11_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(80)90013-8"},{"key":"e_1_2_1_12_1","doi-asserted-by":"publisher","DOI":"10.1029\/TC001i001p00021"},{"key":"e_1_2_1_13_1","doi-asserted-by":"publisher","DOI":"10.1016\/0031-9201(82)90079-6"},{"key":"e_1_2_1_14_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(73)90058-7"},{"key":"e_1_2_1_15_1","first-page":"1028","article-title":"Seismotectonics of the eastern Azores\u2010Gibraltar ridge (abstract)","volume":"56","author":"Hadley D. M.","year":"1975","journal-title":"Eos Trans. AGU"},{"key":"e_1_2_1_16_1","unstructured":"Hatzfeld D. Etudes sismotectonique de la zone de collision Ibero\u2010Maghrebine D. Sci. thesis 281 pp. Univ. Sci. et M\u00e9dicale de Grenoble Grenoble France 1978."},{"key":"e_1_2_1_17_1","doi-asserted-by":"publisher","DOI":"10.1038\/292443a0"},{"key":"e_1_2_1_18_1","volume-title":"Gravity Field of the World's Oceans Recovered from SEASAT Altimeter Data","author":"Haxby W. F.","year":"1983"},{"key":"e_1_2_1_19_1","doi-asserted-by":"publisher","DOI":"10.1029\/GM027p0326"},{"key":"e_1_2_1_20_1","doi-asserted-by":"publisher","DOI":"10.1029\/GL007i007p00501"},{"key":"e_1_2_1_21_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.2153-3490.1956.tb01229.x"},{"key":"e_1_2_1_22_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB086iB07p06115"},{"key":"e_1_2_1_23_1","first-page":"361","article-title":"SEASAT derived gravity and geoid anomalies of the Azores\u2010Gibraltar plate boundary: A diffuse zone of ocean\u2010ocean convergence near Gibraltar (abstract)","volume":"66","author":"Karner G. D.","year":"1985","journal-title":"Eos Trans. AGU"},{"key":"e_1_2_1_24_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246X.1970.tb06046.x"},{"key":"e_1_2_1_25_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-94-010-2271-2_5"},{"key":"e_1_2_1_26_1","doi-asserted-by":"publisher","DOI":"10.1016\/0011-7471(75)90084-4"},{"key":"e_1_2_1_27_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246X.1985.tb05148.x"},{"key":"e_1_2_1_28_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246X.1972.tb02351.x"},{"key":"e_1_2_1_29_1","doi-asserted-by":"publisher","DOI":"10.1038\/2161276a0"},{"key":"e_1_2_1_30_1","doi-asserted-by":"publisher","DOI":"10.1016\/0079-1946(65)90017-0"},{"key":"e_1_2_1_31_1","doi-asserted-by":"publisher","DOI":"10.1038\/2221037a0"},{"key":"e_1_2_1_32_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB083iB11p05331"},{"key":"e_1_2_1_33_1","doi-asserted-by":"publisher","DOI":"10.1126\/science.189.4201.419"},{"key":"e_1_2_1_34_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(73)90104-0"},{"key":"e_1_2_1_35_1","first-page":"203","article-title":"Deep mantle convection plumes and plate motions","volume":"56","author":"Morgan W. J.","year":"1972","journal-title":"Bull. Am. Assoc. Pet. Geol."},{"key":"e_1_2_1_36_1","first-page":"1009","article-title":"An OBS study of microearthquakes in the median valley on the Mid\u2010Atlantic Ridge near 35\u00b0N (abstract)","volume":"65","author":"Murray M. H.","year":"1984","journal-title":"Eos Trans. AGU"},{"key":"e_1_2_1_37_1","unstructured":"N\u00e1b\u011blek J. L. Determination of earthquake source parameters from inversion of body waves Ph.D. thesis Mass. Inst. of Technol. Cambridge 1984."},{"key":"e_1_2_1_38_1","first-page":"805","article-title":"Source mechanisms of twenty\u2010six large, shallow earthquakes (MS \u2265 6.5) during 1980 from P\u2010wave first motion and long\u2010period Rayleigh wave data","volume":"74","author":"Nakanishi I.","year":"1984","journal-title":"Bull. Seismol. Soc. Am."},{"key":"e_1_2_1_39_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB082i005p00803"},{"key":"e_1_2_1_40_1","doi-asserted-by":"publisher","DOI":"10.1130\/0016-7606(1972)83[619:SSITNA]2.0.CO;2"},{"key":"e_1_2_1_41_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246X.1975.tb06206.x"},{"key":"e_1_2_1_42_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4684-3033-2_12"},{"key":"e_1_2_1_43_1","volume-title":"NOAA Atlas","author":"Rona P. A.","year":"1980"},{"key":"e_1_2_1_44_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(75)90186-7"},{"key":"e_1_2_1_45_1","first-page":"591","article-title":"Rare earth abundances in DSDP sites 332A, 332B, 334, 335 and inferences on the Azores mantle blob activity with time","volume":"37","author":"Schilling J. G.","year":"1977","journal-title":"Init. Rep. Deep Sea Drill. Proj."},{"key":"e_1_2_1_46_1","first-page":"190","article-title":"Iberian plate kinematics: Jumping plate boundaries, an alternative to ball\u2010bearing plate tectonics (abstract)","volume":"65","author":"Schouten H.","year":"1984","journal-title":"Eos Trans. AGU"},{"key":"e_1_2_1_47_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(80)90221-6"},{"key":"e_1_2_1_48_1","unstructured":"Searle R. C. D.Monahan andG. L.Johnson General bathymetric chart of the oceans (GEBCO) sheet 5.08 5th ed. Can. Hydrogr. Serv. Ottawa Canada 1982."},{"key":"e_1_2_1_49_1","first-page":"759","article-title":"Earthquakes and tectonics at Mid\u2010ocean ridge axes (abstract)","volume":"64","author":"Solomon S. C.","year":"1983","journal-title":"Eos Trans. AGU"},{"key":"e_1_2_1_50_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(84)90143-2"},{"key":"e_1_2_1_51_1","doi-asserted-by":"publisher","DOI":"10.1029\/JZ072i008p02131"},{"key":"e_1_2_1_52_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB090iB07p05443"},{"key":"e_1_2_1_53_1","doi-asserted-by":"publisher","DOI":"10.1007\/BF00286147"},{"key":"e_1_2_1_54_1","doi-asserted-by":"publisher","DOI":"10.1016\/0040-1951(67)90031-5"},{"key":"e_1_2_1_55_1","doi-asserted-by":"publisher","DOI":"10.1029\/GD007p0075"},{"key":"e_1_2_1_56_1","doi-asserted-by":"publisher","DOI":"10.1016\/0040-1951(70)90034-X"},{"key":"e_1_2_1_57_1","doi-asserted-by":"publisher","DOI":"10.1016\/0040-1951(76)90121-9"},{"key":"e_1_2_1_58_1","doi-asserted-by":"publisher","DOI":"10.1038\/scientificamerican0485-50"},{"key":"e_1_2_1_59_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(78)90004-3"},{"key":"e_1_2_1_60_1","doi-asserted-by":"publisher","DOI":"10.1029\/JB088iB08p06455"},{"key":"e_1_2_1_61_1","doi-asserted-by":"publisher","DOI":"10.1016\/0012-821X(81)90135-7"}],"container-title":["Journal of Geophysical Research: Solid Earth"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/api.wiley.com\/onlinelibrary\/tdm\/v1\/articles\/10.1029%2FJB091iB02p02029","content-type":"unspecified","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/agupubs.onlinelibrary.wiley.com\/doi\/pdf\/10.1029\/JB091iB02p02029","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,9,22]],"date-time":"2023-09-22T18:00:59Z","timestamp":1695405659000},"score":1,"resource":{"primary":{"URL":"https:\/\/agupubs.onlinelibrary.wiley.com\/doi\/10.1029\/JB091iB02p02029"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1986,2,10]]},"references-count":60,"journal-issue":{"issue":"B2","published-print":{"date-parts":[[1986,2,10]]}},"alternative-id":["10.1029\/JB091iB02p02029"],"URL":"https:\/\/doi.org\/10.1029\/jb091ib02p02029","archive":["Portico"],"relation":{},"ISSN":["0148-0227"],"issn-type":[{"value":"0148-0227","type":"print"}],"subject":[],"published":{"date-parts":[[1986,2,10]]}}}