Source modelling of the M5–6 Emilia-Romagna, Italy, earthquakes (2012 May 20–29)

Cesca, Simone; Braun, T.; Maccaferri, Francesco; Passarelli, Luigi; Rivalta, Eleonora; Dahm, Torsten

doi:10.1093/gji/ggt069

Cited by 37 publications

(35 citation statements)

References 28 publications

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“…As quantitatively discussed in Passarelli et al (2013a) and Cesca et al (2013a), positive variation of the Coulomb stress, even of a small intensity similar to what we find on northern portion of the Castrovillari fault (Fig. 4), leads to an increase of triggering probability.…”

Section: Focal Mechanisms and Coulomb Stress Transfersupporting

confidence: 88%

“…The magnitude of the increase of probability scales with the intensity of the Coulomb stress and decreases in time according to the decay rate of aftershocks (Dieterich 1994;Passarelli et al 2013). However, the possibility that a major tectonic event is triggered is mainly controlled by the tectonically pre-loaded stresses (Cesca et al 2013a;Passarelli et al 2013), so that the possibility that an earthquake on the Castrovillari fault is triggered due static stress interaction with seismic events in the Mercure basin cannot be excluded.…”

Section: Focal Mechanisms and Coulomb Stress Transfermentioning

confidence: 99%

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Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy

Passarelli¹,

Hainzl²,

Cesca³

et al. 2015

Geophysical Journal International

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S U M M A R YTectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency-magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg-Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude M w = 4.2 and M w = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the M l > 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been 'passive' features, with small fault patches failing on largely locked faults, or may have been accompanied by an 'active', largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area.

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Section: Focal Mechanisms and Coulomb Stress Transfersupporting

confidence: 88%

Section: Focal Mechanisms and Coulomb Stress Transfermentioning

confidence: 99%

Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy

Passarelli¹,

Hainzl²,

Cesca³

et al. 2015

Geophysical Journal International

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“…The up‐to‐date activity of this sector of the buried Apennine front was confirmed by the May 2012 Emilia seismic sequence [ Galli et al ., ; Ventura and Di Giovambattista , ; Cesca et al ., ]. During this seismic sequence, the vertical component of the deformation attained a relative maximum (112 mm) at the study site [ Borgatti et al ., ; Galli et al ., ].…”

Section: Geological Backgroundmentioning

confidence: 98%

Ground heating and methane oxidation processes at shallow depth in Terre Calde di Medolla (Italy): Observations and conceptual model

et al. 2015

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The toponym "Terre Calde di Medolla" (literally, "Warm Earths of Medolla") refers to a farming area, located near the town of Modena (Emilia-Romagna region, northern Italy), which has always been known by the local population for the relatively high temperatures of the soil. This phenomenon is particularly evident in wintertime when the snow cover over this area rapidly melts. A detailed investigation, carried out after the devastating 2012 Emilia earthquake that affected this area, showed soil temperatures up to 44°C, i.e., 20-25°C above the local background value, together with diffuse soil fluxes of CH 4 (0-2432 g × m, especially from subcircular (a few meters in diameter) zones. Ground heating and gas seepage appear spatially correlated, thus suggesting a close relationship between the two phenomena. The anomalous high ground temperature is not associated with an anomalous geothermal gradient or with the uprising of deep-seated hot fluids. According to the lateral and vertical distributions of the temperatures as well as the chemical and isotopic compositions of the soil gases, the most reliable explanation is the exothermic oxidation of diffusely uprising biogenic methane at very shallow levels (<1 m). Such a process occurs in the presence of free oxygen and methanotrophic bacteria and can then explain (i) the observed ground heating up, (ii) the diffuse emission from the soil of CO 2 characterized by an extremely negative isotopic ( 13 C/ 12 C) signature, and (iii) the lack of diffuse and low CH 4 fluxes. According to these hypotheses, the heating phenomena affecting the shallow groundwater and the ground surface, as described by several witnesses in the area of the May-June 2012 Emilia earthquake, could be related to either a coseismic or postseismic onset of new areas affected by CH 4 seepage or an increase in preexisting CH 4 fluxes.

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“…Several authors attributed the rupture either to a distinct adjacent thrust fault segment (i.e. the Mirandola thrust), located to the west, with a similar mechanism (Scognamiglio et al 2012;Bignami et al 2012;Govoni et al 2014) or to a different patch on the same blind low-angle thrust fault (Cesca et al 2013). Instead, a different interpretation was provided by Tizzani et al (2013), requiring the activation of three different fault segments and a block roto-translation of the Mirandola anticline.…”

Section: Introductionmentioning

confidence: 99%

“…Differently, Convertito et al (2013), evaluating cumulative changes in the static stress field, reported that static Coulomb stress changes did not significantly contribute to the triggering process, while dynamic triggering, caused by passing seismic waves and enhanced by source directivity, played a primary role in driving the sequence. Cesca et al (2013), by regional waveform inversion, inferred that the static stress perturbation associated with the May 20 earthquake can not be responsible for the rupture of the Mirandola fault, but it can have sped it up, being the event mature on that fault. Pezzo et al (2013), by means of geodetic data modeling and stress-transfer analysis, suggested that, although the May 20 event did not produce stress loading at the May 29 hypocenter, a triggering effect could be ascribed to additional stress load redistribution, owing to an aseismic slip occurred on the eastern sector of the Mirandola thrust in the time span between the two shocks.…”

Section: Introductionmentioning

confidence: 99%

The role of fluid migration and static stress transfer in searching connections between the May 2012 Emilia earthquakes through a fully 3D finite element modeling

Volpe

Piersanti

2016

Model. Earth Syst. Environ.

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On May 20 and 29, 2012, two earthquakes struck the Emilia Romagna region (Northern Italy), with similar mechanisms. The proximity in space and time between the two events required to investigate possible triggering effects in terms of stress transfer or fluid migration. Moreover, the debate concerning fluid extraction-injection activities brought to the appointment of an International Commission (ICHESE), for evaluating relationships between the hydrocarbon exploitation and the seismic activity near the focal zone: the ICHESE conclusive report did not exclude the possibility of a triggering effect associated with explorations, although this appears not supported by robust evidences. On the other hand, there is no agreement between published papers addressing classical triggering mechanisms and in this respect an improved analysis based on 3D numerical modeling is a valuable tool to provide new insights and outcomes. To this aim, we built up a 3D model honoring the complexities of the real Earth, to retrieve the slip patterns on both the rupture planes by implementing finite element computed Green's functions in a linear joint inversion scheme of geodetic data. Then, we inspected possible mechanisms which could have contributed to promote the second event, such as Coulomb stress transfer and natural fluid migration. Our findings suggest that both phenomena are not likely to be responsible for the May 29 earthquake, even if fluid migration was found to have a role in facilitating the rupture but without reaching hydrofracturing condition. Nevertheless a suprahydrostatic pore pressure is inferred which could have promoted the reactivation of the thrust fault.

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Source modelling of the M5–6 Emilia-Romagna, Italy, earthquakes (2012 May 20–29)

Cited by 37 publications

References 28 publications

Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy

Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy

Ground heating and methane oxidation processes at shallow depth in Terre Calde di Medolla (Italy): Observations and conceptual model

The role of fluid migration and static stress transfer in searching connections between the May 2012 Emilia earthquakes through a fully 3D finite element modeling

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