Earthquake data can clearly distinguish between ocean-ocean subduction and continental-ocean subduction.
the verdict
INSUFFICIENT LEANING
refutedsupported
the weight of evidence
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Available seismic and geological studies provide partial evidence regarding subduction characteristics, with some investigations demonstrating that seismic images can constrain slab composition and differentiate subducted oceanic versus continental crust, while other analyses indicate that distinguishing complex tectonic settings remains challenging.
The western Hellenic subduction zone (WHSZ) exhibits well‐documented along‐strike variations in lithosphere density (i.e., oceanic versus continental), subduction rates, and overriding plate extension. Differences in slab density are believed to drive deformation rates along the WHSZ; however, this hypothesis has been difficult to test given the limited seismic constraints on the structure of the WHSZ, particularly beneath northern Greece. Here, we present high‐resolution seismic images across northern and southern Greece to constrain the slab composition and mantle wedge geometry along the WHSZ. Data from two temporary arrays deployed across Greece in a northern line (NL) and southern line (SL) are processed using a 2D teleseismic migration algorithm based on the Generalized Radon Transform. Images of P‐ and S‐wave velocity perturbations reveal N60E dipping low‐velocity layers beneath both NL and SL. The ∼8 km thick layer beneath SL is interpreted as subducted oceanic crust while the ∼20 km thick layer beneath NL is interpreted as subducted continental crust. The thickness of subducted continental crust inferred within the upper mantle suggests that ∼10 km of continental crust has accreted to the overriding plate. The relative position of the two subducted crusts implies ∼70–85 km of additional slab retreat in the south relative to the north. Overall, our seismic images are consistent with the hypothesis that faster sinking of the denser, oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the WHSZ.
Seismotectonic characteristics of the transition area between the Zagros continental collision zone and the Makran ocean‐continent convergence zone (the ‘Oman Line’) are carefully examined. A northeast trending zone of earthquakes terminates the Zagros belt of seismicity just west of the Oman Line. This seismic zone extends northeastward beyond the Main Zagros Thrust and coincides with a surface escarpment clearly visible on LANDSAT imagery. Events with accurately determined depths along this seismic zone occurred in the upper 20 km of the crust and possibly show a shallow (<10°) northeastward dip. East of the Oman Line, the Zendan‐Minab fault system is relatively aseismic. The Oman Line region may be characterized by underthrusting of a wedge of Arabian shelf edge beneath Iranian crust or by an indentation of Arabia into the Iranian crustal block as a promontory. Available seismological and geological data cannot uniquely distinguish between these two possible tectonic settings. The area located to the northwest of the Oman Line region, now a zone of continental collision, appears to have been characterized by an episode of Neogene subduction. A well‐located, intermediate‐depth earthquake occurred in this area to the northeast of the Main Zagros Thrust on November 9, 1970. It was accurately located at 107‐km depth beneath a line of Quaternary volcanoes. Its focal mechanism may indicate downdip tension, with nodal planes that strike closely parallel to the trend of the Zagros
kilometres (1,500 mi) between Africa and Eurasia. Individual subductions thus varied between Oceanic and Continental, the current being Oceanic. This Hellenic
The Hellenic Trench (HT) is an oceanic trough located in the forearc of the Hellenic arc, an arcuate archipelago on the southern margin of the Aegean Sea plate, or Aegean Plate, also called Aegea, the basement of the Aegean Sea. The HT begins in the Ionian Sea near the mouth of the Gulf of Corinth and curves to the south, following the margin of the Aegean Sea. It passes close to the south shore o
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Seismic Consequences of Warm Versus Cool Subduction Metamorphism: Examples from Southwest and Northeast Japan | Science
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Contents
## Abstract
Warm and cool subduction zones exhibit differences in seismicity, seismic structure, and arc magmatism, which reflect differences in metamorphic reactions occurring in subducting oceanic crust. In southwest Japan, arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth; in northeast Japan, arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth. Thermal-petrologic models predict that oceanic crust subducting beneath southwest Japan is 300° to 500°C warmer than beneath northeast Japan, resulting in shallower eclogite transformation and slab dehydration reactions, and possible slab melting.
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## REFERENCES AND NOTES
1
Peacock S. M., Geol. Soc. Am. Bull. 105, 684 (1993).
2
Ahrens T. J., Schubert G., Rev. Geophys. Space Phys. 13, 383 (19
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