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Combining stress transfer and source directivity: the case of the 2012 Emilia seismic sequence.

Convertito V, Catalli F, Emolo A - Sci Rep (2013)

Bottom Line: We find that static stress redistribution alone is not capable of explaining the locations of subsequent events.We conclude that dynamic triggering played a significant role in driving the sequence.This triggering was also associated with a variation in permeability and a pore pressure increase in an area characterized by a massive presence of fluids.

View Article: PubMed Central - PubMed

Affiliation: Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano, Via Diocleziano 328, 80124, Napoli, Italy.

ABSTRACT
The Emilia seismic sequence (Northern Italy) started on May 2012 and caused 17 casualties, severe damage to dwellings and forced the closure of several factories. The total number of events recorded in one month was about 2100, with local magnitude ranging between 1.0 and 5.9. We investigate potential mechanisms (static and dynamic triggering) that may describe the evolution of the sequence. We consider rupture directivity in the dynamic strain field and observe that, for each main earthquake, its aftershocks and the subsequent large event occurred in an area characterized by higher dynamic strains and corresponding to the dominant rupture direction. We find that static stress redistribution alone is not capable of explaining the locations of subsequent events. We conclude that dynamic triggering played a significant role in driving the sequence. This triggering was also associated with a variation in permeability and a pore pressure increase in an area characterized by a massive presence of fluids.

No MeSH data available.


Related in: MedlinePlus

Maps of dominant rupture direction.Overview of inferences obtained from the inversion of the peak-ground velocities for the main triggering events (black stars) considered in this study. In each panel, the dominant rupture directions (red arrows) and aftershock distributions (gray stars) up-to the next main event in the sequence (green stars), are shown. The orange arrow indicates the secondary rupture direction and its length depends on the ratio between the Pdf at the secondary maximum and the value at the absolute maximum (supplementary Figure S2). The uncertainties of the rupture directions are given in Table 1. The blue arrows indicate strike directions of the principal and auxiliary fault planes deduced from the corresponding focal mechanism3. The black triangles identify the stations at which PGVs data were available. In each panel the origin time and magnitude of the triggering event are specified, as well as the best value of the Mach number α and the available number of PGV data used. The figure was generated by using the Generic Mapping Tools (http://gmt.soest.hawaii.edu/)35.
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f2: Maps of dominant rupture direction.Overview of inferences obtained from the inversion of the peak-ground velocities for the main triggering events (black stars) considered in this study. In each panel, the dominant rupture directions (red arrows) and aftershock distributions (gray stars) up-to the next main event in the sequence (green stars), are shown. The orange arrow indicates the secondary rupture direction and its length depends on the ratio between the Pdf at the secondary maximum and the value at the absolute maximum (supplementary Figure S2). The uncertainties of the rupture directions are given in Table 1. The blue arrows indicate strike directions of the principal and auxiliary fault planes deduced from the corresponding focal mechanism3. The black triangles identify the stations at which PGVs data were available. In each panel the origin time and magnitude of the triggering event are specified, as well as the best value of the Mach number α and the available number of PGV data used. The figure was generated by using the Generic Mapping Tools (http://gmt.soest.hawaii.edu/)35.

Mentions: We use 22 hypocentral locations, moment magnitudes and focal mechanism solutions3 to estimate source dimensions45 and cumulative changes in the static stress field (ΔCFS). In addition, we use peak-ground velocities (PGVs) of the 8 largest earthquakes (Table 1) to estimate: i) rupture directivity, and ii) the peak-dynamic strain field. Combining i) and ii) results in an original representation of the dynamic strain field, whose amplitude and azimuthal distribution is modified by source directivity. The PGVs used in this study are those also used to produce ShakeMaps in Italy6. The waveforms are recorded by the Italian permanent seismic network (http://iside.rm.ingv.it) and Rete Accelerometrica Nazionale (http://www.protezionecivile.gov.it/jcms/it/ran.wp). The combination of the two datasets provides data with a reliable azimuthal coverage of stations. According to the automatic procedures implemented at INGV6, seismograms are corrected by the instrumental response, and processed applying a de-trending and a band-pass filtering in the range 0.01–30 Hz. At each station, the PGV corresponds to the largest value between the two horizontal components of the recorded velocity. The number of PGV data available for each earthquake is reported in Figure 2 where only those seismic stations located at epicentral distances less than 150 km are included. Moreover, we discarded peak velocity values differing more than 2σ from the predictions provided by the Ground-Motion Prediction Equation (GMPE)7, where σ is the standard error of the GMPE. This resulted in discarding about 18% on average, of available data.


Combining stress transfer and source directivity: the case of the 2012 Emilia seismic sequence.

Convertito V, Catalli F, Emolo A - Sci Rep (2013)

Maps of dominant rupture direction.Overview of inferences obtained from the inversion of the peak-ground velocities for the main triggering events (black stars) considered in this study. In each panel, the dominant rupture directions (red arrows) and aftershock distributions (gray stars) up-to the next main event in the sequence (green stars), are shown. The orange arrow indicates the secondary rupture direction and its length depends on the ratio between the Pdf at the secondary maximum and the value at the absolute maximum (supplementary Figure S2). The uncertainties of the rupture directions are given in Table 1. The blue arrows indicate strike directions of the principal and auxiliary fault planes deduced from the corresponding focal mechanism3. The black triangles identify the stations at which PGVs data were available. In each panel the origin time and magnitude of the triggering event are specified, as well as the best value of the Mach number α and the available number of PGV data used. The figure was generated by using the Generic Mapping Tools (http://gmt.soest.hawaii.edu/)35.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814900&req=5

f2: Maps of dominant rupture direction.Overview of inferences obtained from the inversion of the peak-ground velocities for the main triggering events (black stars) considered in this study. In each panel, the dominant rupture directions (red arrows) and aftershock distributions (gray stars) up-to the next main event in the sequence (green stars), are shown. The orange arrow indicates the secondary rupture direction and its length depends on the ratio between the Pdf at the secondary maximum and the value at the absolute maximum (supplementary Figure S2). The uncertainties of the rupture directions are given in Table 1. The blue arrows indicate strike directions of the principal and auxiliary fault planes deduced from the corresponding focal mechanism3. The black triangles identify the stations at which PGVs data were available. In each panel the origin time and magnitude of the triggering event are specified, as well as the best value of the Mach number α and the available number of PGV data used. The figure was generated by using the Generic Mapping Tools (http://gmt.soest.hawaii.edu/)35.
Mentions: We use 22 hypocentral locations, moment magnitudes and focal mechanism solutions3 to estimate source dimensions45 and cumulative changes in the static stress field (ΔCFS). In addition, we use peak-ground velocities (PGVs) of the 8 largest earthquakes (Table 1) to estimate: i) rupture directivity, and ii) the peak-dynamic strain field. Combining i) and ii) results in an original representation of the dynamic strain field, whose amplitude and azimuthal distribution is modified by source directivity. The PGVs used in this study are those also used to produce ShakeMaps in Italy6. The waveforms are recorded by the Italian permanent seismic network (http://iside.rm.ingv.it) and Rete Accelerometrica Nazionale (http://www.protezionecivile.gov.it/jcms/it/ran.wp). The combination of the two datasets provides data with a reliable azimuthal coverage of stations. According to the automatic procedures implemented at INGV6, seismograms are corrected by the instrumental response, and processed applying a de-trending and a band-pass filtering in the range 0.01–30 Hz. At each station, the PGV corresponds to the largest value between the two horizontal components of the recorded velocity. The number of PGV data available for each earthquake is reported in Figure 2 where only those seismic stations located at epicentral distances less than 150 km are included. Moreover, we discarded peak velocity values differing more than 2σ from the predictions provided by the Ground-Motion Prediction Equation (GMPE)7, where σ is the standard error of the GMPE. This resulted in discarding about 18% on average, of available data.

Bottom Line: We find that static stress redistribution alone is not capable of explaining the locations of subsequent events.We conclude that dynamic triggering played a significant role in driving the sequence.This triggering was also associated with a variation in permeability and a pore pressure increase in an area characterized by a massive presence of fluids.

View Article: PubMed Central - PubMed

Affiliation: Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano, Via Diocleziano 328, 80124, Napoli, Italy.

ABSTRACT
The Emilia seismic sequence (Northern Italy) started on May 2012 and caused 17 casualties, severe damage to dwellings and forced the closure of several factories. The total number of events recorded in one month was about 2100, with local magnitude ranging between 1.0 and 5.9. We investigate potential mechanisms (static and dynamic triggering) that may describe the evolution of the sequence. We consider rupture directivity in the dynamic strain field and observe that, for each main earthquake, its aftershocks and the subsequent large event occurred in an area characterized by higher dynamic strains and corresponding to the dominant rupture direction. We find that static stress redistribution alone is not capable of explaining the locations of subsequent events. We conclude that dynamic triggering played a significant role in driving the sequence. This triggering was also associated with a variation in permeability and a pore pressure increase in an area characterized by a massive presence of fluids.

No MeSH data available.


Related in: MedlinePlus