D. Giardini, G. Grünthal, K.M. Shedlock, and P. Zhang, The GSHAP Global Seismic Hazard Map, Ann. Geofisica, 42, 1225-1230, 1999.


The volcanism in subduction zones is caused primarily by water that is carried down with the subducted slab to depths on the order of 100 kilometers. This water eventually fluxes into the mantle wedge above the slab, lowering the melting temperature of the rocks and producing a small fraction of melt that rises into shallow magma chambers, which erupt to form the andesitic volcanoes characteristic of the island arcs.


S. Uyeda and H. Kanamori, Back-arc opening and the mode of subduction, J. Geophys. Res., 84, 1049-1061, 1979.


L. Ruff and H. Kanamori, Seismicity and the subduction process, Phys. Earth Planet. Int., 23, 240-252, 1980.


W.R. McCann, S.P. Nishenko, L.R. Sykes, and J. Krause, Seismic gaps and plate tectonics: Seismic potential for major boundaries, Pure Appl. Geophys., 117, 1082-1147, 1979. Offshore of Java, the subduction zone has produced only major earthquakes (M = 7.5) in the 450-year-long historic record, whereas offshore of Sumatra, giant earthquakes (M 8.5 to 8.8) have occurred. Future geodetic measurements across subduction zones will enable better quantification of the degree of coupling and, hence, better estimates of seismic potential.


T.J. Fitch, Plate convergence, transcurrent faults and deformation in Asia and Pacific, J. Geophys. Res., 77, 4432-4460, 1972.


A.Y. Le Dain, B. Robineau, and P. Tapponnier, The tectonic effects of the seismic and volcanic event of November 1978 in the Asia-Ghubbet Rift, Soc. Gèol. France Bull., 22, 817-822, 1979; T. Forslund and A. Gudmundsson, Crustal spreading due to dikes and faults in southwest Iceland, J. Struct. Geol., 13, 443-457, 1991; R.S. Stein, P. Briole, J.-C. Ruegg, P. Tapponnier, and F. Gasse, Contemporary, Holocene, and Quaternary deformation of the Asal Rift, Djibouti: Implications for the mechanics of slow spreading ridges, J. Geophys. Res., 96, 21,789-21,806, 1991.


Several million years of normal faulting in the million-square-kilometer Basin and Range Province have led to a northwest-southeast extension of more than 100 kilometers and the creation of dozens of tilted, 10- to 30-kilometer-wide crustal blocks that form the alternating basins and ranges. Although late Cenozoic normal faults are distributed relatively uniformly across this region, historical and instrumental seismicity is concentrated in two zones: the central Nevada seismic zone, which extends along the western margin of the province in eastern California and western Nevada, and the intermountain seismic zone, along the eastern edge of the province from southern Nevada across central Utah to southwestern Montana. The large (>M 7) earthquakes of 1872, 1915, and 1954 occurred within the former zone and the large events of 1959 and 1983 within the latter. Paleoseismic studies of normal faults in the Basin and Range Province suggest that many of the faults produce such big earthquakes only every few thousand years and that the current level of activity is abnormally high in the central Nevada seismic zone and abnormally low in the intermountain seismic belt. This possibility is of particular importance to Carson City and Salt Lake City, the capitals of Nevada and Utah, respectively, which sit on the edges of the province.


Examples include the 1987 Edgecomb earthquake (M 6.6) caused by failure of several normal faults within the volcanic arc of North Island, New Zealand, as well as dozens of historically important earthquakes in Greece and western Turkey that have occurred in the broad extensional back-arc setting of the Aegean Sea, for example, in the Bay of Corinth in 1861 and 1981, on the Pelopponese near Kalamata in 1981 and 1998, and probably an earthquake that destroyed Sparta in 464 B.C. (R. Armijo, H. Lyon-Caen, and D. Papanastassiou, A possible normal-fault rupture for the 464 BC Sparta earthquake, Nature, 351, 137-139, 1991).


An alternative explanation for this type of normal faulting involves behind-the-arc divergence associated with changes in the curvatures of the plate boundary thrust faults.

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