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  • 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals  (7)
  • 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
  • AGU  (11)
  • American Association for the Advancement of Science  (1)
  • Espoo : Geologian tutkimuskeskus
  • Irkutsk : Ross. Akad. Nauk, Sibirskoe Otd., Inst. Zemnoj Kory
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • Lower Hutt : Institute of Geological and Nuclear Sciences
  • 2005-2009  (12)
  • 1955-1959
Collection
Keywords
Publisher
Years
  • 2005-2009  (12)
  • 1955-1959
Year
  • 1
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    Geomagnetic jerks in the polar regions (2009)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The occurrence of geomagnetic jerks over the Arctic and Antarctic regions is here investigated. Maps of geomagnetic secular acceleration over the polar regions are produced from the CM4 and CHAOS models and the occurrence of geomagnetic jerks is associated with jumps in secular acceleration. The obtained results confirm that in Antarctica geomagnetic jerks systematically follow geomagnetic jerks in the Arctic region with a time delay from one to three years. Evidence is found of an abrupt change in secular acceleration in both polar regions around 1985, suggesting that the 1985 local jerk could actually be a worldwide event. Combining our results with the results previously obtained on the occurrence of a geomagnetic jerk at low-mid latitudes around 2003, we support the hypothesis of a global extension of an event occurred at the beginning of the 21st century.
    Description: Published
    Description: L15304
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: geomagnetic jerks ; magnetic global models ; geomagnetic secular variation ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.03. Global and regional models ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Multifractality and Punctuated Equilibrium in the Earth's Magnetic Field Polarity Reversals (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The Earth's magnetic field has reversed its polarity hundreds of times in the Earth's history. This phenomenon is generally viewed as due to a Poisson nonstationary process. Here, the geomagnetic chron time length sequence for the past 166 Ma, is analyzed using a multifractal approach, based on "singularity analysis". The existence of a multifractal structure is the signature of the occurrence of "punctuated equilibrium", which can be read as an indication of a critical configuration of the geodynamo. The results obtained are compared with those from a prototypical model of a dynamical system, introduced by Seki & Ito [1993], and are discussed in the context of fluid motions within the Earth's outer liquid core.
    Description: Published
    Description: 293-296
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Magnetic field polarity reversals ; Multifractal approach ; Punctuated equilibrium ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Assessing the timing of greigite formation and the reliability of the Upper Olduvai polarity transition record from the Crostolo River, Italy (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The Crostolo River section in Italy yielded a detailed record of the Upper Olduvai geomagnetic polarity transition that has been used to support the hypothesis of deep mantle control on the transitional geomagnetic field. The paleomagnetic record is carried by the authigenic iron sulphide, greigite, which was interpreted to have formed shortly after deposition. Our detailed scanning electron microscope investigations indicate the presence of at least 3 generations of pyrite, which usually forms with greigite as a precursor. This suggests that the total magnetization is a complex composite that produced a smoothed record of transitional field behaviour.
    Description: Published
    Description: L05307
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: greigite ; Upper Olduvai polarity transition ; Crostolo river ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    Tidal Modulation of Nonvolcanic Tremor (2008)
    American Association for the Advancement of Science
    Details
    Publication Date: 2017-04-04
    Description: Episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of Japan and Cascadia. In Cascadia, such episodes typically last a few weeks, and differ from “normal” earthquakes in their source location and momentduration scaling. The three most recent episodes in the Puget Sound/Southern Vancouver Island portion of the Cascadia subduction zone have been exceptionally well recorded. In each episode, we see clear pulsing of tremor activity with periods of 12.4 and 24-25 hours, the same as the principal lunar and lunisolar tides. This indicates that the small stresses associated with the solid-earth and ocean tides influence the genesis of tremor much more effectively than they do “normal” earthquakes. Because the lithostatic stresses are 105 times larger than those associated with the tides, we argue that tremor occurs on very weak faults.
    Description: Published
    Description: 186 -189
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Nonvolcanic ; tremor ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Worldwide character of the 1991 geomagnetic jerk (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: A recent examination of the geomagnetic element annual mean values fbr the European magnetic observatories, has shown the existence of a sudden change in the secular acceleration at about 1991. In this work the space time character of the 1991 impulse is investigated and its worldwide character is evidenced; an evaluation of the amplitude spatial distribution is given for the Y component, analysing data relative to 74 magnetic observatories. The external effects were removed from the annual mean data and successively the Y secular variation has been evaluated from the corrected annual means. Moreover the worldwide character of the intensity of the step in the second time derivative is compared with the character of the previous well known jerk events of 1969 and 1978.
    Description: Published
    Description: 377-380
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Geomagnetic field ; Secular variation ; Geomagnetic jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Reply to Comment by M. Dumberry (2008)
    AGU
    In:  Reply to Comment on “Could the Mw = 9.3 Sumatra Earthquake Trigger a Geomagnetic Jerk?”
    Details
    Publication Date: 2017-04-04
    Description: We thank M. Dumberry for providing the opportunity to discuss further the article [Florindo et al., 2005] in which we suggested that the Sumatra earthquake could have triggered a geomagnetic jerk. Dumberry is against our hypothesis for different reasons: (1) The displacement pattern produced by this earthquake is incompatible with the core-mantle boundary (CMB) deformations required for a torsional oscillation; (2) most of the deformations occurred locally, producing an actual mass displacement that has not involved the entire Earth; and (3) no abrupt change in the length of day (LOD) has been observed after this event. Although we agree with some of the considerations proposed by Dumberry, we think that these do not rule out the possibility that a jerk has been triggered by the Sumatra earthquake or that in the future, other earthquakes could induce a change in the flow pattern near the CMB leading to a geomagnetic jerk. On the contrary, we retain that this hypothesis is plausible, although it is more correct to talk about the existence of a possible link between geomagnetic jerks and earthquakes where the earthquake magnitude is not the only discriminating parameter.
    Description: Published
    Description: 343
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: 3.4. Geomagnetismo
    Description: N/A or not JCR
    Description: reserved
    Keywords: Sumatra Earthquake ; Geomagnetic Jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
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    Holocene eruptive history of the Stromboli volcano: Constraints from paleomagnetic dating (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: We report on paleomagnetic directions gathered from 33 sites from (mostly Holocene) volcanics from Stromboli, loosely dated at present by few K/Ar and 14C ages. In order to provide dating, the paleomagnetic directions were compared to the Holocene paleosecular variation of the geomagnetic field for the Mediterranean region, derived from direct geomagnetic observations and several archeomagnetic-paleomagnetic data sets. Petrochemical analyses from the paleomagnetic specimens revealed that each Holocene eruptive cycle of Stromboli was characterized by peculiar chemical characteristics. We suggest that before the 20th century AD paroxysms, powerful spatter-forming eruption(s) occurred during the 17th century AD, followed by three centuries of less energetic eruptions, when spattering was limited to the summit cones. A robust data set (4 sites, 52 samples) from the S. Bartolo flow, partially buried below the Stromboli village, constrains its age to 360 BC to 7 AD, in Greek-Roman times. The ca. 6200 years BP age inferred for a scoria exposed below a characteristic pyroclastic succession suggests its correlation with the Secche di Lazzaro pyroclastics, a major phreatomagmatic eruption occurring during the 6th millennium BP, synchronous with the major volcanotectonic collapse of the Sciara del Fuoco. Ages were provided for many lavas from the Neostromboli sequence (including the Labronzo, Nel Cannestrà, and Ginostra flows), indicating that huge effusive activity from lateral fissures fed by an evolving magma chamber occurred in the 6200–8000 years BP time window. The absence of volcanics with ages comprised between the 6th millennium BP and 400 BC implies a puzzling three-millennia "eruption gap" at Stromboli.
    Description: Published
    Description: B09101
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Stromboli ; palaeomagnetism ; Holocene eruptive history ; secular variation of the geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
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    A double branching model for earthquake occurrence (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The purpose of this work is to put forward a double branching model to describe the spatio-temporal earthquake occurrence. The model, applied to two worldwide catalog in different time-magnitude windows, shows a good fit to the data, and its earthquake forecasting performances are superiors to what obtained by ETAS (first-step branching model) and by Poisson model. The results obtained provide also interesting insights about the physics of the earthquake generation process, and the time evolution of seismicity. In particular, the so-called background seismicity, i.e., the catalog after removing short-time clustered events, is described by a further (second-step model) branching characterized by a longer time-space clustering maybe due to long-term seismic interaction. Notably, this branching highlights a long-term temporal evolution of the seismicity that is never taken into account in seismic hazard assessment, or to define reference seismicity models for large earthquakes occurrence. Another interesting issue is related to the parameters of the short-term clustering that appear constant in different magnitude window, supporting some sort of universality for the generating process.
    Description: Published
    Description: B08317
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: stochastic model ; earthquake forecasting ; seismic interaction ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    Could the Mw = 9.3 Sumatra Earthquake Trigger a Geomagnetic Jerk? (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The magnetic field observed at the Earth’s surface is not a stationary feature. It is characterized by time variations ranging from milliseconds (micropulsations) to millions of years (the time interval between field reversals). Time variations with periods of a year or longer are related to Earth’s outer core sources, whereas for shorter timescales an external origin is invoked (i.e., solar activity). One of the most interesting time variations of the geomagnetic field is represented by the “geomagnetic jerk.” It is idealized as a rapid change in the slope of the secular variation, defined as the first derivative of the geomagnetic field. This means that the secular variation roughly appears as a series of straightline segments separated by geomagnetic jerks.
    Description: Published
    Description: 123
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: 3.4. Geomagnetismo
    Description: N/A or not JCR
    Description: reserved
    Keywords: Sumatra Earthquake ; Geomagnetic Jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    Evidence of clustering and nonstationarity in the time distribution of large worldwide earthquakes (2007)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: 1The purpose of this paper is to characterize the statistical distribution of worldwide largest earthquakes. We analyze the distribution of worldwide shallow events with Ms 7.0+ since 1900, by following the Occam’s razor philosophy; we start from the simplest possible model (stationary Poisson process), and we inspect more complicated models only if the data show significant departures from the simplest one. The results show two important characteristics; first, worldwide Ms 7.0+ earthquakes tend to cluster in time and space, with features similar to smaller events. Second, for some seismic regions there is evidence in favor of long-term fluctuations of the earthquake rate. These results support the hypothesis of universality, suggesting that an ETAS model with a background varying with time can be considered reliable to describe the seismicity distribution over a wide space-time-magnitude window. From a practical point of view, our findings suggest that the paradigm that seismic zones are stationary systems, implicitly assumed in seismic hazard assessment, should be regarded with caution.
    Description: Published
    Description: B02303
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: ETAS model ; cluster ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 11
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    Source and Qp parameters from pulse width inversion of microearthquake data in southeastern Sicily, Italy (2005)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: Source and Qp parameters were estimated from the inversion of first arrival P waveform durations of about 300 microearthquakes recorded at a digital seismic network operating in southeastern Sicily. The average risetime and pulse width at each station do not show large differences, allowing us to exclude significant differential attenuation site effects. A first Qp estimate was obtained by applying the classical risetime method, under the assumption of a point-like source time function. In order to investigate the effect of directivity due to the finiteness of seismic sources, new nonlinear relationships, based on a circular crack model rupturing at a constant velocity, were numerically built. These relationships were used to formulate a nonlinear inverse method for retrieving source (radius, dip, and strike of the circular crack) and Qp parameters from the inversion of risetime and pulse width data. The application of the method produced a better fit of the observed data and a Qp value higher than that obtained by applying the risetime method. The discrepancy between the different Q estimates may be due to a trade-off among source dimension and Qp, as we inferred from a test on a subset of low-magnitude events (Ml ≤ 2.5). A good agreement with independent estimates of fault plane solutions, as inferred from P polarities and S polarizations, was found. The estimated stress drops are generally very low (0.1–10 bars). This suggests that the background seismic activity in southeastern Sicily is related to fault segments and/or weakened zones where great stress accumulations are hindered.
    Description: Published
    Description: 1-14
    Description: partially_open
    Keywords: source and Qp parameters ; risetime ; pulse width ; attenuation ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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    Format: 654914 bytes
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  • 12
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    Variations of southern California seismicity: Empirical evidence and possible physical causes (2005)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: We investigate southern California seismicity in order to characterize its temporal evolution during the last decades. We analyze the time series composed of the number of events per year and the focal mechanisms of earthquakes since 1933. The results show a statistically significant nonstationarity, with a change that occurred in the 1960s in both time series. The seismicity before the change point is mostly characterized by a strike-slip focal mechanism of San Andreas type; after the 1960s the seismicity appears to show more scattered focal mechanisms and a lower seismicity rate. We provide a possible physical explanation of the significant nonstationarity by modeling the postseismic stress perturbation field induced by the two strongest earthquakes of the last century, the Chile (1960) and Alaska (1964) earthquakes, which both occurred in the 1960s. To first order, the postseismic stress rate seems to be in agreement with the observed changes in seismicity, supporting a causality hypothesis. The model also foretells the future behavior of the trend of southern California seismicity; this forward prediction provides an important opportunity to validate the causal hypothesis of a remote (and long-term) coupling between earthquakes.
    Description: Published
    Description: reserved
    Keywords: lon-term interaction ; post-seismic field ; nonstationarities ; southern california ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 339642 bytes
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