Earthquakes at the deep roots of arc volcanos

Abstract

The most conspicuous and spectacular volcanic features on Earth are the graceful volcanic arcs that parallel the deep oceanic trenches where cold and strong surface plates descend into the Earth's mantle. More than three‐quarters of the volcanos that erupt above sea level are found at these regions, called subduction zones. Inclined bands of earthquakes trace the descent of plates into trenches, beneath the arc volcanos, and ultimately down to depths as great as 690 km. Earthquakes at depths below about 40–60 km represent seismic failure within the sinking plate rather than the slipping motion between plates. Some of those earthquakes have been large and very damaging, and future quakes of this type pose a significant seismic hazard in northwest Washington state, Central America, and elsewhere. Most earlier studies have emphasized the role of the sinking force that accompanies the cold thermal structure, as well as the resultant higher density of descending plates in producing stresses that lead to seismic failure of the plate.

Stress distribution and geometry of the subducting Nazca plate in northern Chile using teleseismically recorded earthquakes

“…The double plane seismicity pattern in northern Chile is observed beneath the volcanic Andean belt, and is thus probably associated with the process involved in the production of arc volcanoes. The distribution of stress in northern Chile supports recent numerical models (Engebretson & Kirby 1992;Kirby & Hacker 1993) which suggest that, at depths of between 90 and 150km, the basalt-toeclogite transformation of the oceanic slab may induce tensional deformation in the upper part of the subducting slab and compressional deformation in the underlying mantle (Comte & Suiirez 1994). Bearing in mind that the microseismic experiments cover only two small zones of the 1877 rupture area, the aim of this study is to make a global and integrated analysis of the .stress distribution along the subducting Nazca plate in northern Chile using accurately determined depths and focal mechanism solutions obtained from teleseismically recorded events in combination with the locally recorded microearthquakes.…”

“…The distribution of stresses observed in the second cluster has been properly explained by phase transformations occurring in the layered descending slab (Kirby & Hacker 1993;Comte & Suarez 1994). The tensional stress field observed in the third cluster is well associated with the effect of the slab pull acting in the deeper part of the intermediate-depth seismic activity.…”

Pseudotachylytes Generated During Seismic Faulting and Eclogitization of the Deep Crust

“…Likewise. the transition from basalt to eclogite has been used to explain earthquakes at depths of about 100 km in sub duction zones (24,25). The eclogitization process involved several mechanisms that have been proposed to cause earthquakes.…”

Transition from interplate slip to double seismic zone along the Kuril‐Kamchatka arc

“…The gabbro-eclogite transition has also been suggested as a possible mechanism for generating earthquakes at intermediate depth [e.g., Pennington, 1983]. Kirby and Hacker [1993] along the Tonga arc [Kawakatsu, 1985[Kawakatsu, , 1986 If the transitional thrust zone is embedded in a low-velocity zone, we interpret that the transitional thrust zone occurs below the plate interface, within subducted oceanic crust. In this case, the occurrence of thrust faulting on moderate-dipping planes below the plate interface might be an indication of a locked interplate thrust zone at depths of 30-50 km.…”