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  • 1
    Publication Date: 2018-05-02
    Description: We investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity (PGV) from moderate to large earthquakes occurring in the southern Apennines (Italy). Simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the PGV, following an evolutionary, probabilistic approach. The system performance is measured through the Effective Lead-Time (ELT), i.e., the time interval between the arrival of the first S-wave and the time at which the probability to observe the true PGV value within one standard deviation becomes stationary, and the Probability of Prediction Error (PPE), which provides a measure of PGV prediction error. The regional maps of ELT and PPE show a significant variability around the fault up to large distances, thus indicating that the system's capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault.
    Keywords: ddc:550
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 2
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    In:  Bulletin of the Seismological Society of America ; Year: 2011 ; Volume: 101 ; Pages: 447-463
    Publication Date: 2018-12-21
    Description: We studied the correlation between the final event magnitude and four parameters obtained from the early portion of P and S phases for a set of high quality subduction events. These relationships are used in the framework of earthquake early-warning systems for real-time magnitude estimation. The investigated parameters are the low-pass-filtered peak displacement (PD), the integral of the velocity squared (IV2), and the predominant and characteristic periods (τp and τc). We created a dataset from the continuous records of the first two weeks following the 14 November 2007 Mw 7.8 Tocopilla (Chile) earthquake. The dataset includes 69 events with magnitudes greater than 4, among them the main event (Mw 7.8), the main aftershocks of Mw 6.7 occurred on November 15, and 4 events with magnitude greater than 6. The low-pass-filtered PD read on short P-phase and S-phase windows is well correlated with the final magnitude, confirming previous results. Indeed when examining 2-s time windows of P waves, we did not observe any saturation effect for magnitudes greater than 6.5; however, there is a slope change in the regression curve. A similar result is obtained from the integral of squared velocity computed over short windows around P and S waves. The characteristic and predominant periods are correlated with magnitudes up to Mw 6; but they clearly do not scale with the magnitude for the stronger events. Our observations offer insight into the feasibility of an early-warning system in Chile.
    Keywords: ddc:550
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 3
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    In:  Geophysical Journal International ; Year: 2012 ; Volume: 189 ; Pages: 469-480
    Publication Date: 2018-12-21
    Description: We study the scaling of spectral properties of a set of 68 aftershocks of the 2007 November 14 Tocopilla (M 7.8) earthquake in northern Chile. These are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments. The seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega-square spectral decay; radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect. Using a graphical approach, we test the scaling of seismic spectrum, and the scale invariance of the apparent stress drop with the earthquake size. To test whether the Tocopilla aftershocks scale with a single parameter, we introduce a non-dimensional number, graphic, that should be constant if earthquakes are self-similar. For the Tocopilla aftershocks, Cr varies by a factor of 2. More interestingly, Cr for the aftershocks is close to 2, the value that is expected for events that are approximately modelled by a circular crack. Thus, in spite of obvious differences in waveforms, the aftershocks of the Tocopilla earthquake are self-similar. The main shock is different because its records contain large near-field waves. Finally, we investigate the scaling of energy release rate, Gc, with the slip. We estimated Gc from our previous estimates of the source parameters, assuming a simple circular crack model. We find that Gc values scale with the slip, and are in good agreement with those found by Abercrombie and Rice for the Northridge aftershocks.
    Keywords: ddc:550
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 4
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    In:  Bulletin of the Seismological Society of America ; Year: 2011 ; Volume: 101 ; Pages: 447-463
    Publication Date: 2018-12-21
    Description: We studied the correlation between the final event magnitude and four parameters obtained from the early portion of P and S phases for a set of high quality subduction events. These relationships are used in the framework of earthquake early-warning systems for real-time magnitude estimation. The investigated parameters are the low-pass-filtered peak displacement (PD), the integral of the velocity squared (IV2), and the predominant and characteristic periods (τp and τc). We created a dataset from the continuous records of the first two weeks following the 14 November 2007 Mw 7.8 Tocopilla (Chile) earthquake. The dataset includes 69 events with magnitudes greater than 4, among them the main event (Mw 7.8), the main aftershocks of Mw 6.7 occurred on November 15, and 4 events with magnitude greater than 6. The low-pass-filtered PD read on short P-phase and S-phase windows is well correlated with the final magnitude, confirming previous results. Indeed when examining 2-s time windows of P waves, we did not observe any saturation effect for magnitudes greater than 6.5; however, there is a slope change in the regression curve. A similar result is obtained from the integral of squared velocity computed over short windows around P and S waves. The characteristic and predominant periods are correlated with magnitudes up to Mw 6; but they clearly do not scale with the magnitude for the stronger events. Our observations offer insight into the feasibility of an early-warning system in Chile.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 5
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    In:  Geophysical Journal International ; Year: 2012 ; Volume: 189 ; Pages: 469-480
    Publication Date: 2018-12-21
    Description: We study the scaling of spectral properties of a set of 68 aftershocks of the 2007 November 14 Tocopilla (M 7.8) earthquake in northern Chile. These are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments. The seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega-square spectral decay; radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect. Using a graphical approach, we test the scaling of seismic spectrum, and the scale invariance of the apparent stress drop with the earthquake size. To test whether the Tocopilla aftershocks scale with a single parameter, we introduce a non-dimensional number, graphic, that should be constant if earthquakes are self-similar. For the Tocopilla aftershocks, Cr varies by a factor of 2. More interestingly, Cr for the aftershocks is close to 2, the value that is expected for events that are approximately modelled by a circular crack. Thus, in spite of obvious differences in waveforms, the aftershocks of the Tocopilla earthquake are self-similar. The main shock is different because its records contain large near-field waves. Finally, we investigate the scaling of energy release rate, Gc, with the slip. We estimated Gc from our previous estimates of the source parameters, assuming a simple circular crack model. We find that Gc values scale with the slip, and are in good agreement with those found by Abercrombie and Rice for the Northridge aftershocks.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 6
    Publication Date: 2018-05-02
    Description: We investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity (PGV) from moderate to large earthquakes occurring in the southern Apennines (Italy). Simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the PGV, following an evolutionary, probabilistic approach. The system performance is measured through the Effective Lead-Time (ELT), i.e., the time interval between the arrival of the first S-wave and the time at which the probability to observe the true PGV value within one standard deviation becomes stationary, and the Probability of Prediction Error (PPE), which provides a measure of PGV prediction error. The regional maps of ELT and PPE show a significant variability around the fault up to large distances, thus indicating that the system's capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 7
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    In:  Geophysical Journal International ; Year: 2013 ; Volume: 194 ; Issue: 2 ; Pages: 1216-1228
    Publication Date: 2018-12-21
    Description: We study the distribution of the aftershocks of Tocopilla Mw 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 ML 6.1 event occurred offshore of the Mejillones peninsula reactivating the seismicity. Three days later the Michilla intraslab earthquake of Mw 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.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 8
    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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  • 9
    Publication Date: 2011-04-01
    Description: We studied the correlation between the final event magnitude and four parameters obtained from the early portion of P and S phases for a set of high quality subduction events. These relationships are used in the framework of earthquake early-warning systems for real-time magnitude estimation. The investigated parameters are the low-pass-filtered peak displacement (PD), the integral of the velocity squared (IV2), and the predominant and characteristic periods ({tau}p and{tau} c). We created a dataset from the continuous records of the first two weeks following the 14 November 2007 Mw 7.8 Tocopilla (Chile) earthquake. The dataset includes 69 events with magnitudes greater than 4, among them the main event (Mw 7.8), the main aftershocks of Mw 6.7 occurred on November 15, and 4 events with magnitude greater than 6. The low-pass-filtered PD read on short P-phase and S-phase windows is well correlated with the final magnitude, confirming previous results. Indeed when examining 2-s time windows of P waves, we did not observe any saturation effect for magnitudes greater than 6.5; however, there is a slope change in the regression curve. A similar result is obtained from the integral of squared velocity computed over short windows around P and S waves. The characteristic and predominant periods are correlated with magnitudes up to Mw 6; but they clearly do not scale with the magnitude for the stronger events. Our observations offer insight into the feasibility of an early-warning system in Chile.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2011-03-22
    Description: We studied the correlation between the final event magnitude and four parameters obtained from the early portion of P and S phases for a set of high quality subduction events. These relationships are used in the framework of earthquake early-warning systems for real-time magnitude estimation. The investigated parameters are the low-pass-filtered peak displacement (PD), the integral of the velocity squared (IV2), and the predominant and characteristic periods (tau (sub p) and tau (sub c) ). We created a dataset from the continuous records of the first two weeks following the 14 November 2007 M (sub w) 7.8 Tocopilla (Chile) earthquake. The dataset includes 69 events with magnitudes greater than 4, among them the main event (M (sub w) 7.8), the main aftershocks of M (sub w) 6.7 occurred on November 15, and 4 events with magnitude greater than 6. The low-pass-filtered PD read on short P-phase and S-phase windows is well correlated with the final magnitude, confirming previous results. Indeed when examining 2-s time windows of P waves, we did not observe any saturation effect for magnitudes greater than 6.5; however, there is a slope change in the regression curve. A similar result is obtained from the integral of squared velocity computed over short windows around P and S waves. The characteristic and predominant periods are correlated with magnitudes up to M (sub w) 6; but they clearly do not scale with the magnitude for the stronger events. Our observations offer insight into the feasibility of an early-warning system in Chile.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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