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  • 1
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    Relationships between fault geometry, slip rate variability and earthquake recurrence in extensional settings (2015)
    Details
    Publication Date: 2017-04-04
    Description: Field observations and modelling indicate that elastic interaction between active faults can lead to variations in earthquake recurrence intervals measured on timescales of 102–104 yr. Fault geometry strongly influences the nature of the interaction between adjacent structures as it controls the spatial redistribution of stress when rupture occurs. In this paper, we use a previously published numerical model for elastic interaction between spontaneously growing faults to investigate the relationships between fault geometry, fault slip rate variations and the statistics of earthquake recurrence. These relationships develop and become systematic as a long-term consequence of stress redistribution in individual rupture events even though on short timescales earthquake activity appears to be stochastic. We characterize fault behaviour using the coefficient of variation (CV) of earthquake recurrence intervals and introduce a new measure, slip-rate variability (SRV) that takes into account the size and time ordering of slip events. CV generally increases when the strain is partitioned on more than one fault but the relationship between long-term fault slip rate (SRmean) and CV is poorly defined. In contrast, SRV increases systematically where faulting is more distributed and SRmean is lower. To first order, SRV is inversely proportional to SRmean. We also extract earthquake recurrence statistics and compare these to previously published probability density functions used in earthquake forecasting. The histograms of earthquake recurrence vary systematically as a function of fault geometry and are best characterized by a Weibull distribution with fitting parameters that vary from site to site along the fault array. We explain these phenomena in terms of a time-varying, geometrical control on stress loading of individual faults arising from the history of elastic interactions and compare our results with published data on SRV and earthquake recurrence along normal faults in New Zealand and in the Italian Apennines. Our results suggest that palaeoseismic data should be collected and analysed with structural geometry in mind and that information on SRV, CV and SRmean should be integrated with data from earthquake catalogues when evaluating seismic hazard.
    Description: Published
    Description: 143-160
    Description: 3T. Pericolosità sismica e contributo alla definizione del rischio
    Description: N/A or not JCR
    Description: restricted
    Keywords: Palaeoseismology;Continentaltectonics:extensional;Dynamicsandmechanics of faulting. ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    High-resolution seismic and ground penetrating radar - geophysical profiling of a thermokarst lake in the western Lena Delta, Northern Siberia (2002)
    In:  EPIC3Permafrost and periglacial processes, 13, 4, pp. 259-269
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Regulation of core body temperature during whole body hyperthermia by oesophageal temperature feedback (1980)
    Springer
    Medical & biological engineering & computing 18 (1980), S. 299-302 
    Details
    ISSN: 1741-0444
    Keywords: Cancer ; Hyperthermia ; Programmable calculator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The use of whole-body hyperthermia as an adjuvant mode of therapy for metastatic cancer requires an accurate control of core body temperature so that the high temperatures encountered during treatment may be safely employed. Heating of the patient is accomplished by use of high-perfusion water-heated blankets. The temperature of the water circulating through the blankets is regulated by digital feedback control, using patient oesophageal temperature as a reference. A forced air heat exchanger is used to cool the circulating water once the control temperature is reached. Patient core body temperatures are currently being maintained at 41·8°C±0·1°C for time periods of up to four hours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02443383
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    Paper (German National Licenses)
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  • 4
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    Deformation and submarine landsliding caused by seamount subduction beneath the Costa Rica continental margin -- new insights from high-resolution sidescan sonar data (2007)
    In:  Geological Society Special Publication 244: 195-205.
    Details
    Publication Date: 2007-10-08
    Description: Subduction of seamounts at destructive sedimented plate margins results in spectacular deformation of the overriding plate. High-resolution sidescan sonar imagery from the Costa Rica margin show the tracks of five individual seamounts, of which four are described in this paper. These were subducted at various times during the last 690 ka and each represents a different stage in the subduction process. Each subducted seamount leaves a parallel-sided depression in its wake, that can be traced for up to 55 km landward of the deformation front. This wake is created by deformation and uplift of the continental slope as the seamount passes beneath it, followed by collapse due to landsliding as support for the uplifted area is withdrawn. Areas of uplift above seamounts are characterized by complex normal and strike-slip fault patterns. Collapse of the uplift along the trailing edge of the seamount creates a zone of slope failure (landsliding) that migrates upslope (or landward) with the seamount. Landslide processes are dominated by debris flow, but also include sliding of coherent blocks and debris avalanche. Erosion occurs by repeated landslides, which produce a series of overlapping debris flows. Downslope sediment transport typically extends over limited distances, resulting in partial backfilling' of the scar as its headwall moves up slope. The amount of margin material disrupted by seamount subduction is four to five times the volume of the subducting seamount, of which about three quarters seems to be recycled downslope, backfilling the scar, and nearly one quarter is subducted with the seamount.
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  • 5
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    Downgoing plate topography stopped rupture in the A.D. 2005 Sumatra earthquake (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-12-24
    Description: Earthquakes in subduction zones rupture the plate boundary fault in discrete segments. One factor that may control this segmentation is topography on the downgoing plate, although it is controversial whether this is by weakening or strengthening of the fault. We use multichannel seismic and gravity data to map the top of the downgoing oceanic crust offshore central Sumatra, Indonesia. Our survey spans a complex segment boundary zone between the southern termination of the M w = 8.7, A.D. 2005 Simeulue-Nias earthquake, and the northern termination of a major 1797 earthquake that was partly filled by an M w = 7.7 event in 1935. We identify an isolated 3 km basement high at the northern edge of this zone, close to the 2005 slip termination. The high probably originated at the Wharton fossil ridge, and is almost aseismic in both local and global data sets, suggesting that while the region around it may be weakened by fracturing and fluids, the basement high locally strengthens the plate boundary, stopping rupture propagation.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 6
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    Fault interactions and reactivation within a normal-fault network at Milne Point, Alaska (2014)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2014-09-27
    Description: A normal-fault network from Milne Point, Alaska, is investigated focusing on characterizing geometry, displacement, strain, and different fault interactions. The network, constrained from three-dimensional seismic reflection data, comprises two generations of faults: Cenozoic north-northeast–trending faults and Jurassic west-northwest–trending faults, which highly compartmentalize Upper Triassic to Lower Cretaceous reservoirs. The west-northwest–trending faults are influenced by a similarly oriented underlying structural grain. This influence is characterized by increases in throw on several faults, strain localization, reorientation of faults and an increase in linkage maturity. Reconstructing fault plane geometries and mapping spatial variations in throw identified key characteristic features in their interactions and reactivation of pre-existing structures. Faults are divided into isolated, abutting, and splaying faults. Isolated faults exhibit a range of displacement profiles depending on the degree of restriction at fault tips. Fault splays accommodate step-like decreases in throw along larger main faults with a throw maximum at the intersection with the main fault. Throw profiles of abutting faults are divided into two groups: early stage abutting faults with throw minima at both the isolated and abutting tips, and developed abutting faults with throw maxima near the abutting tip. Developed abutting faults accumulate throw after initial abutment, locally reactivating and transferring throw onto the pre-existing fault. Two abutting faults can link kinematically by reactivating a segment of the pre-existing fault forming a trailing fault. The motion sense of the trailing fault can be synthetic or antithetic to the reactivated pre-existing fault, producing increases or decreases in the throw of the pre-existing fault, respectively.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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  • 7
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    Pervasive deformation of an oceanic plate and relationship to large 〉Mw 8 intraplate earthquakes: The northern Wharton Basin, Indian Ocean (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-03-24
    Description: Large-magnitude intraplate earthquakes within the ocean basins are not well understood. The M w 8.6 and M w 8.2 strike-slip intraplate earthquakes on 11 April 2012, while clearly occurring in the equatorial Indian Ocean diffuse plate boundary zone, are a case in point, with disagreement on the nature of the focal mechanisms and the faults that ruptured. We use bathymetric and seismic reflection data from the rupture area of the earthquakes in the northern Wharton Basin to demonstrate pervasive brittle deformation between the Ninetyeast Ridge and the Sunda subduction zone. In addition to evidence of recent strike-slip deformation along approximately north-south–trending fossil fracture zones, we identify a new type of deformation structure in the Indian Ocean: conjugate Riedel shears limited to the sediment section and oriented oblique to the north-south fracture zones. The Riedel shears developed in the Miocene, at a similar time to the onset of diffuse deformation in the central Indian Ocean. However, left-lateral strike-slip reactivation of existing fracture zones started earlier, in the Paleocene to early Eocene, and compartmentalizes the Wharton Basin. Modeled rupture during the 11 April 2012 intraplate earthquakes is consistent with the location of two reactivated, closely spaced, approximately north-south–trending fracture zones. However, we find no evidence for WNW-ESE–trending faults in the shallow crust, which is at variance with most of the earthquake fault models.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Local Earthquake Magnitude Scale and b-Value for the Danakil Region of Northern Afar (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-03-23
    Description: The Danakil region of northern Afar is an area of ongoing seismic and volcanic activity caused by the final stages of continental breakup. To improve the quantification of seismicity, we developed a calibrated local earthquake magnitude scale. The accurate calculation of earthquake magnitudes allows the estimation of b -values and maximum magnitudes, both of which are essential for seismic-hazard analysis. Earthquake data collected between February 2011 and February 2013 on 11 three-component broadband seismometers were analyzed. A total of 4275 earthquakes were recorded over hypocentral distances ranging from 0 to 400 km. A total of 32,904 zero-to-peak amplitude measurements ( A ) were measured on the seismometer’s horizontal components and were incorporated into a direct linear inversion that solved for all individual local earthquake magnitudes ( M L ), 22 station correction factors ( C ), and 2 distance-dependent factors ( n , K ) in the equation M L =log( A )–log( A 0 )+ C . The resultant distance correction term is given by –log( A 0 )=1.274336log( r /17)–0.000273( r –17)+2. This distance correction term suggests that attenuation in the upper and mid-crust of northern Afar is relatively high, consistent with the presence of magmatic intrusions and partial melt. In contrast, attenuation in the lower crust and uppermost mantle is anomalously low, interpreted to be caused by a high melt fraction causing attenuation to occur outside the seismic frequency band. The calculated station corrections serve to reduce the M L residuals significantly but do not show a correlation with regional geology. The cumulative seismicity rate produces a b -value of 0.9±0.06, which is higher than most regions of continental rifting yet lower than values recorded at midocean ridges, further supporting the hypothesis that northern Afar is transitioning to seafloor spreading. Electronic Supplement: List of all local earthquakes used in the study with calculated local magnitudes and associated magnitude error.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 9
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    Lithosphere structure and upper mantle characteristics below the Bay of Bengal (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-28
    Description: The oceanic lithosphere in the Bay of Bengal (BOB) formed 80–120 Ma following the breakup of eastern Gondwanaland. Since its formation, it has been affected by the emplacement of two long N-S trending linear aseismic ridges (85°E and Ninetyeast) and by the loading of ca . 20-km of sediments of the Bengal Fan. Here, we present the results of a combined spatial and spectral domain analysis of residual geoid, bathymetry and gravity data constrained by seismic reflection and refraction data. Self-consistent geoid and gravity modelling defined by temperature-dependent mantle densities along a N–S transect in the BOB region revealed that the depth to the lithosphere–asthenosphere boundary (LAB) deepens steeply from 77 km in the south to 127 km in north, with the greater thickness being anomalously thick compared to the lithosphere of similar-age beneath the Pacific Ocean. The Geoid-Topography Ratio (GTR) analysis of the 85°E and Ninetyeast ridges indicate that they are compensated at shallow depths. Effective elastic thickness ( T e ) estimates obtained through admittance/ coherence analysis as well as the flexural modelling along these ridges led to the conclusions: (i) 85°E Ridge was emplaced in off-ridge environment ( T e  = 10–15 km); (ii) the higher T e values of ~25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, (iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher T e values (25–30 km). Furthermore, the admittance analysis of geoid and bathymetry revealed that the admittance signatures at wavelengths 〉800 km are compensated by processes related to upper mantle convection.
    Keywords: Marine Geosciences and Applied Geophysics
    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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  • 10
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    Increased Fluid Flow Activity in Shallow Sediments at the 3 km Long Hugin Fracture in the Central North Sea (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-01-01
    Description: The North Sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species, such as methane, from the Earth's interior to its exterior. Here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered, 3 km long Hugin Fracture in the Central North Sea. Although venting of gas bubbles was not observed, concentrations of dissolved methane were significantly elevated (up to six-times background values) in the water column at various locations above the fracture, and microbial mats that form in the presence of methane were observed at the seafloor. Seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane. Sediment porewaters recovered in close proximity to the Hugin Fracture indicate the presence of fluids from two different shallow (〈550 m) sources: (i) a reduced fluid characterized by elevated methane concentrations and/or high levels of dissolved sulfide (up to 6 mmol L−1), and (ii) a low-chlorinity fluid (Cl ∼305 mmol L−1) that has low levels of dissolved methane and/or sulfide. The area of the seafloor affected by the presence of methane-enriched fluids is similar to the footprint of seepage from other morphological features in the North Sea. © 2017. American Geophysical Union. All Rights Reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Geophysical Union
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