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  • 1
    Electronic Resource
    Electronic Resource
    Stress distribution and geometry of the subducting Nazca plate in northern Chile using teleseismically recorded earthquakes (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 122 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The stress distribution along the subducting Nazca plate in northern Chile is analysed using focal mechanism solutions obtained from the inversion of long-period P, SV, and SH waveforms of 15 earthquakes (mb± 5.5), and from 212 events with reported focal mechanisms, which occurred between 1962 and 1993. A joint hypocentral determination was carried out to control the depth of 261 events (mb± 5.0) recorded at teleseismic distances. A change from tensional to compressional stress field along the upper part of the subducting slab is associated with the maximum depth extent of the coupled zone. This change occurs in northern Chile at ±200-250 km from the trench, at depths of ±60.10 km. This depth is larger than the maximum depth observed for the thrusting interplate events (40 ± 10 km), probably meaning that, at depths of between 40 and 60 km, large low-dip angle thrust events do not nucleate. Seismic slip, however, probably extends down to 40 km in depth. The shallow dip angle (up to 60 km in depth) of the Wadati-Benioff zone does not show variations along the strike of the trench. However, a gradual southward flattening of the slab is observed at distances greater than 200–250 km from the trench. This change, observed from about 21°S, could be associated with a younger and probably more buoyant lithosphere than that observed to the north of this latitude. There are two gaps located between the three main clusters of seismicity; these gaps are clearly not related to detachments in the descending litosphere. The first cluster is located in and beneath the seismogenic interplate contact, and is characterized by reverse and thrust faulting events over a scarce tensional activity. In the second cluster, the compressional seismicity is scarce for teleseismic events and is located beneath the normal faulting events. The third cluster corresponds to tensional events. Therefore, these gaps in seismicity could be associated with alternating changes from compressional to tensional stress field in the subducting slab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb07005.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Velocity structure in northern Chile: evidence of subducted oceanic crust in the Nazca Plate (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 117 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: 2-D P-wave velocity models were determined for the subduction zones near Iquique and Antofagasta in northern Chile, simultaneously inverting P- and S-wave arrival times from locally recorded earthquakes for velocity structure and hypocentral locations. A 2-D parametrization was used because of the paucity of data, but is justified by the lack of significant variations along the strike of the subduction zone observed from both refraction profiles and simple 3-D inversions. The crust and upper mantle are parameterized by constant velocity regions of irregular shape, with the size and boundaries of these regions governed by prior information about the structure and by the ability of the data to resolve P-wave velocities. Beneath the Antofagasta region there is evidence of an approximately 10 km thick layer of oceanic crust attached to the top of the subducting Nazca plate. This crust has a P-wave velocity of 7.3 ± 0.1 km s-1 and is observed down to a depth of 60 ± 10km. This depth also corresponds to the maximum depth of seismogenic coupling in the Chilean subduction zone. The subducted oceanic crust overlies an oceanic upper mantle with a P-wave velocity of 8.0 ± 0.1 km s-1. Apparently, oceanic crust is being subducted beneath Iquique as well. However, this feature is less constrained by the data available from this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb02458.x
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Spatio-temporal variations of seismicity in the southern Peru and northern Chile seismic gaps (1993)
    Springer
    Pure and applied geophysics 140 (1993), S. 317-330 
    Details
    ISSN: 1420-9136
    Keywords: Seismicity ; spatio-temporal variations ; seismic gaps ; southern Peru ; northern Chile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The spatio-temporal variation of seismicity in the southern Peru and northern Chile seismic gaps is analyzed with teleseismic data (m b ≥5.5) between 1965 and 1991, to investigate whether these gaps present the precursory combination of compressional outer-rise and tensional downdip events observed in other subduction zones. In the outer-rise and the inner-trench (0 to 100 km distance from the trench) region, lower magnitude (5.0≤m b 〈5.5) events were also studied. The results obtained show that the gaps in southern Peru and northern Chile do not present compressional outer-rise events. However, both gaps show a continuous, tensional downdip seismicity. For both regions, the change from compressional to tensional regime along the slab occurs at a distance of about 160 km from the trench, apparently associated with the coupled-uncoupled transition of the interplate contact zone. In southern Peru, an increase of compressional seismicity near the interplate zone and of tensional events (5.0≤m b ≤6.3) in the outer-rise and inner-trench regions is observed between 1987 and 1991. A similar distribution of seismicity in the outer-rise and inner-trench regions is observed with earthquakes (m b 〈5.5). In northern Chile there is a relative absence of compressional activity (m b ≥5.5) near the interplate contact since the sequence of December 21, 1967. After that, only a cluster of low-magnitude compressional events has been located in the area 50 to 100 km from the trench. The compressional activity occurring near the interplate zone in both seismic gaps represents that a seismic preslip is occurring in and near the plate contact. Therefore, if this seismic preslip is associated with the maturity of the gap, the fact that it is larger in southern Peru than in northern Chile may reflect that the former gap is more mature than the latter. However, the more intense downdip tensional activity and the absence of compressional seismicity near the contact zone observed in northern Chile, may also be interpreted as evidence that northern Chile is seismically more mature than southern Peru. Therefore, the observed differences in the distribution of stresses and seismicity analyzed under simple models of stress accumulation and transfer in coupled subduction zones are not sufficient to assess the degree of maturity of a seismic gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879410
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Reappraisal of great historical earthquakes in the northern Chile and southern Peru seismic gaps (1991)
    Springer
    Natural hazards 4 (1991), S. 23-44 
    Details
    ISSN: 1573-0840
    Keywords: Northern Chile and Southern Peru seismic gaps ; historical seismicity ; rupture length ; estimated magnitudes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A critical reappraisal of great historical interplate earthquakes in the occidental margin of South America, including southern Peru and northern Chile, is carried out. A spacetime distribution of the earthquakes associated to the seismotectonics regions defined by the rupture zones of the greatest events (1868, Mw = 8.8 and 1877, Mw = 8.8) is obtained. Both regions are seismic gaps that are in the maturity state of their respective earthquake cycles. The region associated to the 1868 earthquake presents a notable seismic quiescence in the present century.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00126557
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    Paper (German National Licenses)
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  • 5
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    Unknown
    3-D velocity structure and seismotectonics prior to the 2010 Chile earthquake (Mw 8.8) from an amphibious seismological network (2012)
    In:  [Talk] In: The Lübeck Retreat, Collaborative Research Centre SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters, 23.05.-25.05.2012, Lübeck . The Lübeck Retreat, Collaborative Research Centre SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters : final colloquium of SFB 574 ; May 23-25, 2012; program & abstracts ; p. 1 .
    Details
    Publication Date: 2019-09-23
    Description: Within the project SFB574, an “amphibious” network of 15 ocean bottom seismometers and 27 land stations was operated from April to October 2008 along 350 km from the outer-rise to the magmatic arc. Additional readings from 11 permanent stations of the Chilean Seismological Service were included in the database improving onshore coverage. One of the main goals of the project is to gain a detailed image of the crustal and upper mantle structure and the seismogenic zone by analyzing earthquake distribution and combined passive and active source seismic tomographic images. To achieve precise earthquake locations and to serve as an initial model for local earthquake tomography, we derived a P- and S-wave minimum-1D model using a very high-quality subset of 340 events (GAP ! 180°, at least 10 P-wave and 5 S-wave arrivals) and velocity information from a wideangle profile shot in the area. Most of the ~1200 earthquakes recorded in our target area were originated within the subducting slab down to ~140 km depth, with a higher concentration beneath the main cordillera, at depths of 80-110 km. Fewer events were generated at the outer-rise, at depths of ~20-40 km, closely following the NE-SW trend of the oceanic plate faulting. The database was relocated using the minimum 1-D model and a subset of 400 events (GAP ! 180°, at least 8 P-wave arrivals) with ~7000 observations was selected to perform a P-wave tomography. Our results confirm the strong, lateral velocity gradient in the forearc seen in previous works along the margin, interpreted as the transition between a paleoaccretionary complex and the seaward edge of the Paleozoic continental framework. The downdip limit of the interplate seismicity previous to the great earthquake was aparently controlled by a low-velocity anomaly at ~40 km depth, shallower than the deeper extent estimated by geodetic modeling of the rutpture and from aftershocks relocation for the Maule earthquake. The interplate seismicity nucleated from ~40 up to ~20 km depth, and did not extend up to the 100°C isotherm. It was sparse except for a cluster of ~1200 km2 offshore and SW of Pichilemu town, within an area where a locking " 75 % before the great earthquake has been estimated. The deep outer-rise seismicity and the low velocities on top suggest considerable hydration of the downgoing plate.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 6
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    Unknown
    Seismic velocity structure of the slab and continental plate in the region of the 1960 Valdivia (Chile) slip maximum - insights into fluid release and plate coupling (2012)
    Elsevier
    In:  Earth and Planetary Science Letters, 331-332 . pp. 164-176.
    Details
    Publication Date: 2019-09-23
    Description: The south-central Chilean subduction zone has witnessed some of the largest earthquakes in history, making this region particularly important for understanding plate coupling. Here we present the results of a local earthquake tomography study from a temporary local seismic network in the Villarrica region between 39 and 40°S, where the largest coseismic displacement of the 1960 Valdivia earthquake occurred. A lowvelocity anomaly and high Vp/Vs values occur under the coastal region, indicating mantle serpentinisation and/or underthrusting of forearc material. Further east, a high-velocity anomaly is observed, interpreted as “normal” high-velocity mantle. Under the active volcanic arc a low-velocity anomaly together with high Vp/Vs ratios (1.8 and higher) likely images fluid ascent beneath the volcanoes. Close to the subducting Valdivia Fracture Zone, the coastal low-velocity anomaly extends further inland, where it interrupts and shifts the high-velocity anomalies associated with “normal” fast mantle velocities. This may indicate enhanced fluid presence along this part of the margin, probably caused by a stronger hydration of the incoming plate along the Valdivia Fracture Zone. This is consistent with geochemical fluid proxies (U/Th, Pb/Ce, Ba/Nb) in young volcanic rocks displaying peak values along the volcanic front at Llaima and Villarrica Volcanoes, and with recent GPS measurements, which suggested a local reduction in plate coupling in this region. The shift in the high-velocity anomaly underlying the central part may be caused by a north to south decrease in plate age and hydration across the Valdivia Fracture Zone, and may explain why a Central Valley is absent in this segment of the margin. The low La/Yb ratios in the volcanic rocks from Villarrica and Llaima suggest that the high slab-derived fluid flux causes elevated degrees of melting beneath these volcanoes, providing an explanation as to why these are amongst the most active volcanoes in South America.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2012.02.006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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