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  • 1
    Electronic Resource
    Electronic Resource
    Subduction and collision processes in the Central Andes constrained by converted seismic phases (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 958-961 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Central Andes are the Earth's highest mountain belt formed by ocean–continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35050073
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    Paper (German National Licenses)
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  • 2
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    Analysis and modelling of tsunami-induced tilt for the 2007, M = 7.6, Tocopilla and the 2010, M = 8.8 Maule earthquakes, Chile, from long-base tiltmeter and broadband seismometer records (2013)
    Oxford University Press
    Details
    Publication Date: 2013-06-11
    Description: We present a detailed study of tsunami-induced tilt at in-land sites, to test the interest and feasibility of such analysis for tsunami detection and modelling. We studied tiltmeter and broadband seismometer records of northern Chile, detecting a clear signature of the tsunamis generated by the 2007 Tocopilla ( M  = 7.6) and the 2010 Maule ( M  = 8.8) earthquakes. We find that these records are dominated by the tilt due to the elastic loading of the oceanic floor, with a small effect of the horizontal gravitational attraction. We modelled the Maule tsunami using the seismic source model proposed by Delouis et al. and a bathymetric map, correctly fitting three tide gauge records of the area (Antofagasta, Iquique and Arica). At all the closest stations (7 STS2, 2 long-base tiltmeters), we correctly modelled the first few hours of the tilt signal for the Maule tsunami. The only phase mismatch is for the site that is closer to the ocean. We find a tilt response of 0.005–0.01 μm at 7 km away from the coastline in response to a sea level amplitude change of 10 cm. For the Maule earthquake, we observe a clear tilt signal starting 20 min before the arrival time of the tsunami at the nearest point on the coastline. This capability of tilt or seismic sensors to detect distant tsunamis before they arrive has been successfully tested with a scenario megathrust in the southern Peru-northern Chile seismic gap. However, for large events near the stations, this analysis may no longer be feasible, due to the large amplitude of the long-period seismic signals expected to obscure the loading signal. Inland tilt measurements of tsunamis smooth out short, often unmodelled wavelengths of the sea level perturbation, thus providing robust, large-scale images of the tsunami. Furthermore, tilt measurements are not expected to saturate even for the largest run-ups, nor to suffer from near-coast tsunami damages. Tiltmeters and broadband seismometers are thus valuable instruments for monitoring tsunamis in complement with tide gauge arrays.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
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    Source parameters of the Sarez-Pamir earthquake of 1911 February 18 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-25
    Description: The M s ~ 7.7 Sarez-Pamir earthquake of 1911 February 18 is the largest instrumentally recorded earthquake in the Pamir region. It triggered one of the largest landslides of the past century, building a giant natural dam and forming Lake Sarez. As for many strong earthquakes from that time, information about source parameters of the Sarez-Pamir earthquake is limited due to the sparse observations. Here, we present the analysis of analogue seismic records of the Sarez-Pamir earthquake. We have collected, scanned and digitized 26 seismic records from 13 stations worldwide to relocate the epicentre and determine the event's depth (~26 km) and magnitude ( m B 7.3 and M s 7.7). The unusually good quality of the digitized waveforms allowed their modelling, revealing an NE-striking sinistral strike-slip focal mechanism in accordance with regional tectonics. The shallow depth and magnitude ( M w 7.3) of the earthquake were confirmed. Additionally, we investigated the possible contribution of the landslide to the waveforms and present an alternative source model assuming the landslide and earthquake occurred in close sequence.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 4
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    Applicability and Bias of VP/VS Estimates by P and S Differential Arrival Times of Spatially Clustered Earthquakes (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-06-10
    Description: Estimating small-scale V P / V S variations at depth can be a powerful tool to infer lithology and hydration of a rock, with possible implications for frictional behavior. In principle, from the differential arrival times of P and S phases from a set of spatially clustered earthquakes, an estimate of the local V P / V S can be extracted, because the V P / V S is the scaling factor between the P and S differential times for each pair of earthquakes. We critically review the technique proposed by Lin and Shearer (2007) , in which the mean value over all stations is subtracted from the differential arrival times of each pair of events in order to make the method independent of a priori information on origin times. The demeaned differential P and S arrival times are plotted on a plane, and the V P / V S ratio is estimated by fitting the points on this plane. We tested the method by both theoretical analysis and numerical simulations of P and S travel times in several velocity models. We found that the method returns exact values of V P / V S only in the case of a medium with homogeneous V P / V S , whereas, when a V P / V S gradient is present, the estimates are biased as an effect of systematic differences between P and S takeoff angles. We demonstrated that this bias arises from the demeaning of the arrival times over the stations. In layered models with V P / V S decreasing with depth, we found that V P / V S is overestimated or underestimated, respectively, for takeoff angles larger or smaller than 90°. Moreover, we calculated analytically the dependence of this bias on the takeoff angles. Our simulations also showed that the difference between the calculated and the expected V P / V S is reduced for simple horizontally layered velocity structures (〈0.06), whereas it is 0.27 in a more realistic velocity model mimicking a subduction zone.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 5
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    A Magnitude Attenuation Function Derived for the 2014 Pisagua (Chile) Sequence Using Strong-Motion Data (2014)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2014-12-05
    Description: In this note, we derive an attenuation function for computing magnitude values equivalent to M w using strong-motion data. We analyze 106 earthquakes of the 1 April 2014 M w  8.1 Pisagua sequence, which occurred along the 1877 seismic gap in northern Chile. We considered both foreshocks and aftershocks with moment magnitude available from moment tensor inversion in the GEOFON bulletin and recorded by the Integrated Plate boundary Observatory Chile strong-motion network. The maximum peak displacement measured over the double integrated traces is used to construct the magnitude scale, following a nonparametric approach. A bootstrap analysis is performed to assess the uncertainty of the model parameters, and cross-validation tests are performed to proof the suitability of the derived model in predicting the M w in the analyzed area, with an uncertainty of 0.2 magnitude units. The derived scale is applied to an early aftershock, which occurred about 155 s after the mainshock, initially missed in bulletins published by rapid global earthquake monitoring agencies (e.g., National Earthquake Information Center and GEOFON), because its phase arrivals at regional/teleseismic distances mix with those of the mainshock and its later arrivals. The estimated magnitude equivalent to M w is 6.6±0.3, which rank this event as the second largest aftershock of the sequence, after the M w  7.6 earthquake that occurred on 3 April 2014.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    High-resolution relocation and mechanism of aftershocks of the 2007 Tocopilla (Chile) earthquake (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-05
    Description: We study the distribution of the aftershocks of Tocopilla M w 7.7 earthquake of 2007 November 14 in northern Chile in detail. This earthquake broke the lower part of the seismogenic zone at the southern end of the Northern Chile gap, a region that had its last megathrust earthquake in 1877. The aftershocks of Tocopilla occurred in several steps: the first day they were located along the coast inside the co-seismic rupture zone. After the second day they extended ocean-wards near the Mejillones peninsula. Finally in December they concentrated in the South near the future rupture zone of the Michilla intermediate depth earthquake of 2007 December 16. The aftershock sequence was recorded by the permanent IPOC (Integrated Plate Boundary Observatory in Chile) network and the temporary task force network installed 2 weeks after the main event. A total of 1238 events were identified and the seismic arrival times were directly read from seismograms. Initially we located these events using a single event procedure and then we relocated them using the double-difference method and a cross-correlation technique to measure time differences for clusters of aftershocks. We tested a 1-D velocity model and a 2-D one that takes into account the presence of the subducted Nazca Plate. Relocation significantly reduced the width of the aftershock distribution: in the inland area, the plate interface imaged by the aftershocks is thinner than 2 km. The two velocity models give similar results for earthquakes under the coast and a larger difference for events closer to the trench. The surface imaged by the aftershocks had a length of 160 km. It extends from 30 to 50 km depth in the northern part of the rupture zone; and between 5 and 55 km depth near the Mejillones peninsula. We observed a change in the dip angle of the subduction interface from 18° to 24° at a depth of 30 km. We propose that this change in dip is closely associated with the upper limit of the rupture zone of the main event. We also studied the focal mechanisms of the aftershocks, most of them were thrust events like the mainshock. As the aftershock activity was significantly reduced, on 2007 December 13, an M L 6.1 event occurred offshore of the Mejillones peninsula reactivating the seismicity. Three days later the Michilla intraslab earthquake of M w 6.8 ruptured an almost vertical fault with slab-push mechanism. The aftershocks locations of this event define a planar zone about 11 km in depth, situated right bellow the subduction interface.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
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    Strain partitioning at the eastern Pamir-Alai revealed through SAR data analysis of the 2008 Nura earthquake (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-22
    Description: On 2008 October 5, a magnitude 6.6 earthquake struck the eastern termination of the intermontane Alai valley between the southern Tien Shan and the northern Pamir of Kyrgyzstan. The shallow thrust earthquake occurred in the footwall of the Main Pamir thrust, where the Pamir orogen is colliding with the southern Tien Shan mountains. We measure the coseismic surface displacements using SAR (Synthetic Aperture RADAR) data; the results show clear gradients in the vertical and horizontal directions along a complex pattern of surface ruptures and active faults. To integrate and to interpret these observations in the context of the regional tectonics, we complement the SAR data analysis with seismological data and geological field observations. While the main moment release of the Nura earthquake appears to be on the Pamir Frontal thrust, the main surface displacements and surface rupture occurred in the footwall along the NE–SW striking Irkeshtam fault. With InSAR data from ascending and descending tracks along with pixel offset measurements, we model the Nura earthquake source as a segmented rupture. One fault segment corresponds to high-angle brittle faulting at the Pamir Frontal thrust and two more fault segments show moderate-angle and low-friction thrusting at the Irkeshtam fault. Our integrated analysis of the coseismic deformation argues for rupture segmentation and strain partitioning associated to the earthquake. It possibly activated an orogenic wedge in the easternmost segment of the Pamir-Alai collision zone. Further, the style of the segmentation may be associated with the presence of Palaeogene evaporites.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Seismicity Structure of the Northern Chile Forearc From 〉100,000 Double-Difference Relocated Hypocenters (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-05-01
    Description: In this study, we present high-resolution seismicity images of the northern Chile subduction zone forearc. We used 8 years of continuous seismic waveform data from the Integrated Plate Boundary Observatory Chile network and auxiliary stations to produce an extensive earthquake catalog containing 101,601 double-difference relocated earthquake hypocenters using automatic event detection and phase picking routines. The minimum magnitude of retrieved events is 〈2, and the catalog is estimated to be complete at magnitudes above ∼2.8. Intraslab seismicity makes up the majority of detected earthquakes. Where the seismogenic zone of the megathrust is active, a clear separation of seismicity into three distinct planes can be observed. The uppermost plane corresponds to the plate interface, which is observed to terminate downdip at a depth of 50–55 km. The other two planes, located ∼7 and ∼26 km below the slab surface, dip at a constant angle of about 20° until they are absorbed by a 25 km thick highly active cluster of intermediate-depth seismicity at depths of 80–120 km. Downdip of this cluster, the slab steepens and lower plate seismicity is considerably sparser, even absent in the northern part of the study area. Upper plate seismicity is also considerable, with a segment between 21 and 21.6°S standing out for featuring pervasive activity occurring all the way down to the plate interface. Here the seismicity resembles a wedge in west-east profile view and occurs where the upper plate crust is coldest based on thermal models. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 9
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    Probing the Northern Chile Megathrust With Seismicity: The 2014 M8.1 Iquique Earthquake Sequence (2019)
    American Geophysical Union
    Details
    Publication Date: 2019-12-01
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    The 2007 M7.7 Tocopilla northern Chile earthquake sequence: Implications for along-strike and downdip rupture segmentation and megathrust frictional behavior (2012)
    American Geophysical Union
    Details
    Publication Date: 2012-05-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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