Effects of trench-zone scattering on receiver functions over a subduction zone: A 3-D finite-difference modelling study

Abstract. New combined P receiver functions and seismicity data obtained from the EGELADOS network employing 65 stations within the Aegean constrained new information on the geometry of the Hellenic subduction zone. The dense network and large dataset enabled us to accurately estimate the Moho of the continental Aegean plate across the whole area. Presence of a negative contrast at the Moho boundary indicating the serpentinized mantle wedge above the subducting African plate was clearly seen along the entire forearc. Furthermore, low seismicity was observed within the serpentinized mantle wedge. We found a relatively thick continental crust (30–43 km) with a maximum thickness of about 48 km beneath the Peloponnesus Peninsula, whereas a thinner crust of about 27–30 km was observed beneath western Turkey. The crust of the overriding plate is thinning beneath the southern and central Aegean (Moho depth 23–27 km). Moreover, P receiver functions significantly imaged the subducted African Moho as a strong converted phase down to a depth of 180 km. However, the converted Moho phase appears to be weak for the deeper parts of the African plate suggesting reduced dehydration and nearly complete phase transitions of crustal material into denser phases. We show the subducting African crust along 8 profiles covering the whole southern and central Aegean. Seismicity of the western Hellenic subduction zone was taken from the relocated EHB-ISC catalogue, whereas for the eastern Hellenic subduction zone, we used the catalogues of manually picked hypocenter locations of temporary networks within the Aegean. P receiver function profiles significantly revealed in good agreement with the seismicity a low dip angle slab segment down to 200 km depth in the west. Even though, the African slab seems to be steeper in the eastern Aegean and can be followed down to 300 km depth implying lower temperatures and delayed dehydration towards larger depths in the eastern slab segment. Our results showed that the transition between the western and eastern slab segments is located beneath the southeastern Aegean crossing eastern Crete and the Karpathos basin. High resolution P receiver functions also clearly resolved the top of a strong low velocity zone (LVZ) at about 60 km depth. This LVZ is interpreted as asthenosphere below the Aegean continental lithosphere and above the subducting slab. Thus the Aegean mantle lithosphere seems to be 30–40 km thick, which means that its thickness increased again since the removal of the mantle lithosphere about 15 to 35 Ma ago.

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Evidence of subduction zone segmentation: Finite-difference tomography and earthquake relocation along the Java margin

10.1002/essoar.10501631.1 ◽

2020 ◽

Author(s):

Anne Sirait ◽

Anne Meltzer ◽

Joshua Stachnik ◽

Mohamad Ramdhan ◽

Nova Heryandoko

Keyword(s):

Finite Difference ◽

Subduction Zone ◽

Earthquake Relocation

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Receiver function images of the Hellenic subduction zone and comparison to microseismicity

Solid Earth ◽

10.5194/se-6-135-2015 ◽

2015 ◽

Vol 6 (1) ◽

pp. 135-151 ◽

Cited By ~ 12

Author(s):

F. Sodoudi ◽

A. Brüstle ◽

T. Meier ◽

R. Kind ◽

W. Friederich ◽

...

Keyword(s):

Subduction Zone ◽

Mantle Wedge ◽

Receiver Functions ◽

Moho Depth ◽

Crustal Material ◽

Mantle Lithosphere ◽

African Plate ◽

Data Set ◽

Hellenic Subduction Zone ◽

Hypocentre Locations

Abstract. New combined P receiver functions and seismicity data obtained from the EGELADOS network employing 65 seismological stations within the Aegean constrained new information on the geometry of the Hellenic subduction zone. The dense network and large data set enabled us to estimate the Moho depth of the continental Aegean plate across the whole area. Presence of a negative contrast at the Moho boundary indicating the serpentinized mantle wedge above the subducting African plate was seen along the entire forearc. Furthermore, low seismicity was observed within the serpentinized mantle wedge. We found a relatively thick continental crust (30–43 km) with a maximum thickness of about 48 km beneath the Peloponnese Peninsula, whereas a thinner crust of about 27–30 km was observed beneath western Turkey. The crust of the overriding plate is thinning beneath the southern and central Aegean and reaches 23–27 km. Unusual low Vp / Vs ratios were estimated beneath the central Aegean, which most likely represent indications on the pronounced felsic character of the extended continental Aegean crust. Moreover, P receiver functions imaged the subducted African Moho as a strong converted phase down to a depth of about 100 km. However, the converted Moho phase appears to be weak for the deeper parts of the African plate suggesting nearly complete phase transitions of crustal material into denser phases. We show the subducting African crust along eight profiles covering the whole southern and central Aegean. Seismicity of the western Hellenic subduction zone was taken from the relocated EHB-ISC catalogue, whereas for the eastern Hellenic subduction zone, we used the catalogues of manually picked hypocentre locations of temporary networks within the Aegean. Accurate hypocentre locations reveal a significant change in the dip angle of the Wadati–Benioff zone (WBZ) from west (~ 25°) to the eastern part (~ 35°) of the Hellenic subduction zone. Furthermore, a zone of high deformation can be characterized by a vertical offset of about 40 km of the WBZ beneath the eastern Cretan Sea. This deformation zone may separate a shallower N-ward dipping slab in the west from a steeper NW-ward dipping slab in the east. In contrast to hypocentre locations, we found very weak evidence for the presence of the slab at larger depths in the P receiver functions, which may result from the strong appearance of the Moho multiples as well as eclogitization of the oceanic crust. The presence of the top of a strong low-velocity zone at about 60 km depth in the central Aegean may be related to the asthenosphere below the Aegean continental lithosphere and above the subducting slab. Thus, the Aegean mantle lithosphere seems to be 30–40 km thick, which means that its thickness increased again since the removal of the mantle lithosphere about 15 to 35 Ma ago.

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Imaging the megathrust in subduction zones: lessons from Greece, Ecuador and the Lesser Antilles

10.5194/egusphere-egu2020-14636 ◽

2020 ◽

Author(s):

Mireille Laigle ◽

Hans Agurto-Detzel ◽

Anne Bécel ◽

Milton Boucard ◽

Caroline Chalumeau ◽

...

Keyword(s):

Subduction Zone ◽

Subduction Zones ◽

Convergence Rates ◽

Complex Structure ◽

Receiver Functions ◽

Lesser Antilles ◽

Damage Effect ◽

Physical Parameters ◽

Strain Partitioning ◽

The Impact

Understanding the physical parameters and processes that control the seismogenic behavior of subduction zones megathrust faults remains one of the outstanding challenges in Earth Sciences.Here we present important results from several large seismic experiments aimed at addressing this question. These experiments focused on the three subduction zones off Greece, the Lesser Antilles islands, and Ecuador, with different convergence rates and seismic activities. Surveys included multibeam bathymetry, multichannel reflection seismic (MCS) and wide-angle seismic (WAS) acquisitions over the forearc domain, as well as teleseismic receiver-functions and local earthquakes monitoring with temporary deployments of seismological networks.Our results demonstrate the needs of both dense and extensive geophysical investigations.In the central Lesser Antilles subduction zone, the interplate has been imaged down to the backstop at 12-15 km depth over the 350-km-long Antigua to Martinique islands segment. The outer forearc crust is strongly faulted in response to the two subducting Tiburon and Barracuda ridges (SISMANTILLES1-and-2 surveys). Two WAS profiles constrained the deeper geometry of the interplate down to the forearc Moho located at 28 km depth (TRAIL survey). The OBS networks deployed over several months (OBSANTILLES and OBSISMER surveys) revealed mantle wedge supraslab earthquakes and M4-5 possible repeaters with flat-trust mechanisms. The joint active-source/local earthquake seismic tomography let us to unveil the Vp and Vp/Vs heterogeneity along the slab surface and derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. Farther northwest, where the convergence obliquity strongly increases, we constrained the geometry of the interplate down to the forearc Moho at 25 km depth. Strain partitioning localizes on inherited major structures within the forearc domain, like the left-lateral partitioning system of the Anegada Passage and the 850-km-long Bunce fault, located along the backstop (ANTITHESIS survey).On the southwestern Hellenic subduction zone, MCS and WAS acquisitions highlight the existence of an outer forearc crust beneath the forearc Matapan Trough, but its highly complex structure prevented us to image the interplate (ULYSSE survey). Acquisition by the R/V Marcus Langseth with its 8-km-long streamer finally made it possible (SISMED survey). Dense receiver-function acquisition on a 300-km-long mobile seismic network constrained the 3D geometry of the slab top underneath central Greece. This imaging revealed that the subducting oceanic crust and backstop updip limit are segmented by 9 trench-normal subvertical faults, seismically active at intermediate depths and possibly of inherited origin (THALES WAS RIGHT survey).South of the 1906 M8.8 Ecuador-Columbia rupture area, the April 2016 Mw7.8 Pedernales subduction earthquake and its ensuing postseismic phase revealed a combination of seismic/aseismic slip behavior. Fluid-enriched parts of the megathrust fault and structural margin segmentation are hypothesized to play a major role in controlling slip behavior but direct observations are still lacking. Previous MCS acquisitions revealed very locally a fluid-rich subduction channel along with severe damage effect of the forearc margin due to seamounts subduction (SISTEUR survey). Forthcoming 3D seismic acquisition along this segment will examine the impact of the along-strike and along-dip variations of the physical properties and fluid content on the slip mode (HIPER survey).

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