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  • 1
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    BRAVOSEIS Onshore Seismic Array (2020)
    GFZ Data Services
    Details
    Publication Date: 2024-02-21
    Description: Abstract
    Description: The Bransfield Strait is a seismically active extensional rift located between the Antarctic Peninsula and the South Shetland Islands. The Strait is partly located on continental crust including areas within the transition to seafloor spreading. The amphibious seismic network BRAVOSEIS is an international effort focused on the seismological research of submarine volcanoes and rift dynamics in the Bransfield Strait. This network is the onshore component of the entire network consisting of 15 broadband land stations deployed in the South Shetland Islands and Antarctic Peninsula between January 2018 and February 2020. The offshore components (network code ZX) include 9 broadband ocean bottom seismometers (OBS) across the Central Bransfield Basin and a group of 6 hydrophone moorings spanning the rift area of 200 x 100 km2, with inter-station distance of ~30 km. Additionally, a smaller offshore array consisting of 15 short-period OBSs with an aperture of 20 km and a narrow inter-station distance of ~4 km was deployed around the Orca submarine volcanic edifice south of King George Island. The data will be used to study the geodynamics of the Bransfield Strait and the evolution of the incipient rifting zone in the domain where extension has been suggested. Seismological methods will include earthquake location, source mechanism, surface wave analysis with ambient noise and earthquake data, receiver function and shear wave splitting. The results may shed light on the crustal structure and tectonic regime in the region and image the location and extent of magma accumulations related to submarine volcanic structures. Finally, the results should provide clues to assess the internal processes that occur in the submarine volcanoes of the area undergoing rifting. Waveform data are available from the GEOFON data centre, under network code 5M, and are embargoed until March 2024.
    Keywords: Broadband seismic waveforms ; Seismic monitoring ; temporary local seismic network ; Monitoring system ; Seismological stations ; In Situ/Laboratory Instruments 〉 Magnetic/Motion Sensors 〉 Seismometers ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS
    Type: Dataset , Seismic Network
    Format: ~1T
    Format: .mseed
    Format: XML
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    DATA GFZ
  • 2
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    Convection‐Permitting Simulations with the E3SM Global Atmosphere Model (2021)
    American Geophysical Union
    Details
    Publication Date: 2021-10-29
    Electronic ISSN: 1942-2466
    Topics: Geography , Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 3
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    Crustal and uppermost mantle structure of the NW Namibia continental margin and the Walvis Ridge derived from ambient seismic noise (2022)
    In:  Geophysical Journal International
    Details
    Publication Date: 2023-01-12
    Description: The Walvis Ridge (WR) is the most prominent hotspot track related to the opening in the South Atlantic Ocean. Several hypotheses have been developed to explain its origin and evolution. The presence of a massive magmatic structure at the landfall of the WR in Northwest Namibia raised speculation about the role of a hotspot during the opening of the South Atlantic ocean. To investigate its deeper velocity structure at the junction of the WR with the African continent was the focus of the amphibious seismological WALPASS experiment. In total 12 ocean-bottom seismometers and 28 broad-band land stations were installed between 2010 and 2012 to acquire seismological data. Here, we present the results of seismic ambient noise tomography to investigate to which extent the Tristan hotspot modified the crustal structure in the landward prolongation of the ridge and in the adjacent oceanic basins. For the tomography, vertical and hydrophone component cross correlations for 〉300 d for OBS stations and between 1 and 2 yr for land stations data were analysed. More than 49 000 velocity measurements (742 dispersion curves) were inverted for group velocity maps at 75 individual signal periods, which then had been inverted for a regional 3-D shear wave velocity model. The resulting 3-D model reveals structural features of the crust related to the continent–ocean transition and its disturbance caused by the initial formation of the WR ∼130 Ma. We found relatively thick continental crust below Northwest Namibia and below the near-shore part of the WR, a strong asymmetry offshore with typical, thin oceanic crust in the Namibe Basin (crossing over into the Angola Basin further offshore) to the North and a wide zone of transitional crust towards the Walvis Basin south of the WR.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
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    Structure and stress field of the lithosphere between Pamir and Tarim (2021)
    In:  Geophysical Research Letters
    Details
    Publication Date: 2023-01-04
    Description: The Pamir plateau protrudes ∼300 km between the Tajik- and Tarim-basin lithosphere of Central Asia. Whether its salient location and shape are caused by forceful indentation of a promontory of Indian mantle lithosphere is debated. We present a new local-seismicity and focal-mechanism catalog, and a P-wave velocity model of the eastern part of the collision system. The data suggest a south-dipping Asian slab that overturns in its easternmost segment. The largest principal stress at depth acts normal on the slab and is orientated parallel to the plate convergence direction. In front (south) of the Asian slab, a volume of mantle with elevated velocities and lined by weak seismicity constitutes the postulated Indian mantle indenter. We propose that the indenter delaminates and overturns the Asian slab, underthrusts the Tarim lithosphere along a compressive transform boundary, and controls the location and shape of the Pamir plateau.
    Type: info:eu-repo/semantics/article
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  • 5
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    Full Waveform Inversion beneath the Central Andes: Insight into the dehydration of the Nazca slab and delamination of the back‐arc lithosphere (2021)
    In:  Journal of Geophysical Research: Solid Earth
    Details
    Publication Date: 2023-01-04
    Description: We present a new seismic tomography model for the crust and upper-mantle beneath the Central Andes based on multi-scale full seismic waveform inversion, proceeding from long periods (40–80 s) over several steps down to 12–60 s. The spatial resolution and trade-offs among parameters are estimated through the multi-parameter point-spread functions. P and S wave velocity structures with spatial resolution of 30–40 km for the upper mantle and 20 km for the crust could be resolved in the central study region. In our study, the subducting Nazca slab is clearly imaged in the upper mantle, with dip-angle variations from the north to the south. Bands of low velocities in the crust and mantle wedge indicate intense crustal partial melting and hydration of the mantle wedge beneath the frontal volcanic arc, respectively and they are linked to the vigorous dehydration from the subducting Nazca plate and intermediate depth seismicity within the slab. These low velocity bands are interrupted at 19.8°–21°S, both in the crust and uppermost mantle, hinting at the lower extent of crustal partial melting and hydration of the mantle wedge. The variation of lithospheric high velocity anomalies below the backarc from North to South allows insight into the evolutionary foundering stages of the Central Andean margin. A high velocity layer beneath the southern Altiplano suggests underthrusting of the leading edge of the Brazilian Shield. In contrast, a steeply westward dipping high velocity block and low velocity lithospheric uppermost mantle beneath the southern Puna plateau hint at the ongoing lithospheric delamination.
    Type: info:eu-repo/semantics/article
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  • 6
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    Earthquake and Moment Tensor Catalogs of the 2015-2017 Pamir Earthquake Sequence (2022)
    GFZ Data Services
    Details
    Publication Date: 2023-01-10
    Description: A sequence of three strong (M W 7.2–6.4) and several moderate (M W 4.4–5.7) earthquakes struck the Pamir Plateau and surrounding mountain ranges of Tajikistan, China, and Kyrgyzstan in 2015–2017. With a local seismic network in operation in the Xinjiang province since August 2015, an aftershock network on the Pamir Plateau of Tajikistan since February 2016, and additional permanent regional seismic stations, we were able to record the succession of the fore-, main-, and aftershock sequences at local distances with good azimuthal coverage. We located 11,784 seismic events and determined the moment tensor for 33 earthquakes. The seismicity delineates the major tectonic structures of the Pamir, i.e., the thrusts that absorb shortening along the plateau thrust front, and the strike-slip and normal faults that dissect the Plateau into a westward extruding and a northward advancing block. Fault ruptures were activated subsequently at increasing distances from the initial M W 7.2 Sarez. All mainshock areas but the initial one exhibited foreshock seismicity which was not modulated by the occurrence of the earlier earthquakes. The tabular ASCII data of the seismic event catalog consist of origin date, time, location, depth and magnitude of the events, along with the quality measures: number of P- and S-wave arrival time picks, location root-mean-square misfit and localization method. The tabular ASCII data of the moment tensor catalog consist of origin date, time, location, the six independent components of the moment tensor, the moment magnitude, and the orientation of the preferred fault plane parameterized as fault strike, dip and rake.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 7
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    Seismicity catalog, focal mechanism catalog and P-wave velocity structure between Pamir and Tarim (2021)
    GFZ Data Services
    Details
    Publication Date: 2023-01-28
    Description: The Pamir plateau protrudes ~300 km between the Tajik- and Tarim-basinlithosphere of Central Asia. We present a new local-seismicity catalog, a focal-mechanism catalog, and a P-wave velocity model of the of the collision system between the Pamir plateau and the Tarim basin. The data suggest a south-dipping Asian slab that overturns in its easternmost segment. The largest principal stress at depth acts normal on the slab and is orientated parallel to the plate convergence direction. In front (south) of the Asian slab, a volume of mantle with elevated velocities and lined by weak seismicity constitutes the postulated Indian mantle indenter. The data set consists of an earthquake catalog, an earthquake focal mechanism catalog and a subsurface P-wave velocity model of the central and eastern Pamir plateau and the adjacent north-western Tarim basin; between 36.8–40.0 °N and 72.2–78.0 °E. It was collected to identify the deep tectonic structures that determine the lithospheric architecture of the Pamir plateau. Earthquakes were recorded by two temporary seismic deployments. Earthquakes that occurred between 1st August 2008 and 6th June 2010 were primarily recorded by the TIPAGE network (Yuan et al., 2008); those, between 3rd August 2015 and 23rd June 2017 by the East Pamir and Sarez aftershock networks (Yuan et al., 2018a, b). The earthquake catalog contains 1,493 seismic events at depth 〉50 km. They were localized in the present 3-D velocity model. Some events were re-located with hypoDD. The focal mechanism catalog consists of double-couple fault-slip parameters for 38 events, 29 of which are newly determined using the HASH algorithm and 9 are moment tensors from Kufner et al. (2016). The P wave-velocity model has been determined using simulps from 2,264 seismic events with well-constrained P- and S-wave arrivals. It is parameterized as velocity gradients between nodes with a horizontal and vertical spacing of 40 and 15 km, respectively. Unresolved nodes were masked using a checkerboard resolution test. The full description of the methods is provided in the data description file.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 8
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    Seismic discontinuities in the lithospheric mantle at the dead sea transform (2020)
    In:  Geophysical Journal International
    Details
    Publication Date: 2023-01-28
    Description: The Dead Sea Transform (DST) was formed in the Mid-Cenozoic, about 18 Myr ago, as a result of the breakaway of the Arabian plate from the African plate. Higher resolution information about the sub-Moho structure is still sparse in this region. Here we study seismic discontinuities in the mantle lithosphere in the region of the DST using a modified version of the P- and S-receiver function method. We use open data from permanent and temporary seismic stations. The results are displayed in a number of depth profiles through the study area. The Moho is observed on both sides of the transform at nearly 40 km depth by S-to-p and in P-to-s converted signals. The lithosphere-asthenosphere boundary (LAB) on the eastern side of the DST is observed near 180–200 km depth, which is according to our knowledge the first LAB observation at that depth in this region. This observation could lead to the conclusion that the thickness of the Arabian lithosphere east of the DST is likely cratonic. In addition, we observe in the entire area a negative velocity gradient (NVG) at 60–80 km depth, which was previously interpreted as LAB.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 9
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    Back‐arc extension of the Central Bransfield Basin induced by ridge–trench collision: Implications from ambient noise tomography and stress field inversion (2021)
    In:  Geophysical Research Letters
    Details
    Publication Date: 2023-01-28
    Description: The Bransfield Basin is a young (∼4 Ma) back-arc basin related to the remnant subduction of the Phoenix Plate that once existed along the entire Pacific margin of the Antarctic Peninsula. Based on a recently deployed amphibious seismic network, we use ambient noise tomography to obtain the S-wave velocity structure in the Central Bransfield Basin (CBB). Combining with the stress-field inverted from focal mechanisms, our images reveal that the CBB suffers a significant extension in the northwest-southeast direction. The extension is strongest in the northeastern CBB with associated mantle exhumation and weakens to the southwest with decoupled deformations between the upper crust and lithospheric mantle. Such an along-strike variation of extension can be explained by slab window formation and forearc rotation, which are associated with the Phoenix Plate detachment during the ridge–trench collisions at the southwest of the Hero Fracture Zone.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 10
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    Topography of mountain belts controlled by rheology and surface processes (2022)
    In:  Nature
    Details
    Publication Date: 2023-08-18
    Description: It is widely recognized that collisional mountain belt topography is generated by crustal thickening and lowered by river bedrock erosion, linking climate and tectonics. However, whether surface processes or lithospheric strength control mountain belt height, shape and longevity remains uncertain. Additionally, how to reconcile high erosion rates in some active orogens with long-term survival of mountain belts for hundreds of millions of years remains enigmatic. Here we investigate mountain belt growth and decay using a new coupled surface process and mantle-scale tectonic model. End-member models and the new non-dimensional Beaumont number, Bm, quantify how surface processes and tectonics control the topographic evolution of mountain belts, and enable the definition of three end-member types of growing orogens: type 1, non-steady state, strength controlled (Bm 〉 0.5); type 2, flux steady state, strength controlled (Bm ≈ 0.4−0.5); and type 3, flux steady state, erosion controlled (Bm 〈 0.4). Our results indicate that tectonics dominate in Himalaya–Tibet and the Central Andes (both type 1), efficient surface processes balance high convergence rates in Taiwan (probably type 2) and surface processes dominate in the Southern Alps of New Zealand (type 3). Orogenic decay is determined by erosional efficiency and can be subdivided into two phases with variable isostatic rebound characteristics and associated timescales. The results presented here provide a unified framework explaining how surface processes and lithospheric strength control the height, shape, and longevity of mountain belts.
    Language: English
    Type: info:eu-repo/semantics/article
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