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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

Geographical distribution of peak-dynamic strain.Peak-dynamic strain field (microstrain) obtained by using the peak-ground velocity as a proxy (ε ≈ PGV/Vs). In each panel, the black and green stars indicate the triggering and target event, respectively. The red and orange arrows represent the dominant and the secondary rupture directions, respectively. Black rectangles represent the surface fault projections estimated through PGVs inversion (in some cases dimensions are very small and then dimly visible).
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f4: Geographical distribution of peak-dynamic strain.Peak-dynamic strain field (microstrain) obtained by using the peak-ground velocity as a proxy (ε ≈ PGV/Vs). In each panel, the black and green stars indicate the triggering and target event, respectively. The red and orange arrows represent the dominant and the secondary rupture directions, respectively. Black rectangles represent the surface fault projections estimated through PGVs inversion (in some cases dimensions are very small and then dimly visible).

Mentions: Figure 4 shows that the major events of the Emilia seismic sequence occurred in areas where the peak-dynamic strain values are in the range of the dynamic triggering12 (from a few microstrain up to tens of microstrain). Moreover, the corresponding local dynamic stress changes (~0.1–1 MPa, assuming a rigidity of 30 GPa) are about one order of magnitude higher than the cumulative static stress changes (Figure 3b and 3a). This might suggest that the dynamic effect played a significant role in the evolution of this seismic sequence.


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

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

Geographical distribution of peak-dynamic strain.Peak-dynamic strain field (microstrain) obtained by using the peak-ground velocity as a proxy (ε ≈ PGV/Vs). In each panel, the black and green stars indicate the triggering and target event, respectively. The red and orange arrows represent the dominant and the secondary rupture directions, respectively. Black rectangles represent the surface fault projections estimated through PGVs inversion (in some cases dimensions are very small and then dimly visible).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Geographical distribution of peak-dynamic strain.Peak-dynamic strain field (microstrain) obtained by using the peak-ground velocity as a proxy (ε ≈ PGV/Vs). In each panel, the black and green stars indicate the triggering and target event, respectively. The red and orange arrows represent the dominant and the secondary rupture directions, respectively. Black rectangles represent the surface fault projections estimated through PGVs inversion (in some cases dimensions are very small and then dimly visible).
Mentions: Figure 4 shows that the major events of the Emilia seismic sequence occurred in areas where the peak-dynamic strain values are in the range of the dynamic triggering12 (from a few microstrain up to tens of microstrain). Moreover, the corresponding local dynamic stress changes (~0.1–1 MPa, assuming a rigidity of 30 GPa) are about one order of magnitude higher than the cumulative static stress changes (Figure 3b and 3a). This might suggest that the dynamic effect played a significant role in the evolution of this seismic sequence.

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