Active fault-related folding in the epicentral area of the December 25, 1222 (Io=IX MCS) Brescia earthquake (Northern Italy): Seismotectonic implications

On May 20, 2012, a Ml 5.9 seismic event hit the Emilia Po Plain, triggering intense earthquake activity along a broad area of the Po Plain across the provinces of Modena, Ferrara, Rovigo and Mantova (Figure 1). Nine days later, on May 29, 2012, a Ml 5.8 event occurred roughly 10 km to the SW of the first main shock. These events caused widespread damage and resulted in 26 victims. The aftershock area extended over more than 50 km and was elongated in the WNW-ESE direction, and it included five major aftershocks with 5.1 ≤Ml ≤5.3, and more than 2000 minor events (Figure 1). In general, the seismic sequence was confined to the upper 10 km of the crust. Minor seismicity with depths ranging from 10 km to 30 km extended towards the southern sector of the epicentral area (ISIDe, http://iside.rm.ingv.it/). […]

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Searching for the effects of the May-June 2012 Emilia seismic sequence (northern Italy): medium-depth deformation structures at the periphery of the epicentral area

Annals of Geophysics ◽

10.4401/ag-6131 ◽

2012 ◽

Vol 55 (4) ◽

Author(s):

Lisa Borgatti ◽

Antonio Edoardo Bracci ◽

Stefano Cremonini ◽

Giovanni Martinelli

Keyword(s):

Ground Level ◽

Northern Italy ◽

Seismic Sequence ◽

Surface Phenomena ◽

Po River ◽

Epicentral Area ◽

Ground Fissures ◽

Groundwater Levels ◽

Geological Surveys ◽

Emilia Romagna Region

In 2012, a seismic sequence occurred in the lowlands of the Emilia-Romagna Region (northern Italy), between the borders of the Modena, Ferrara and Bologna Provinces. It consisted of seven mainshocks (5.9 > Ml > 5) that were recorded between May 20 and 29, 2012 [INGV 2012a] and 2,200 minor earthquakes [INGV 2012b]. An interferometric analysis [Bignami et al. 2012, Salvi et al. 2012, this volume] highlighted three main deformation areas, each of which was 12 km wide (from S to N) and 10 km to 20 km long in an ESE-WNW to E-W direction, thus affecting an area of about 600 km2 (Figure 1). Field and aerial geological surveys recorded numerous surficial effects, such as: (i) sediment liquefaction [Crespellani et al. 2012]; (ii) localized ground fissures resembling surficial faulting [Fioravante and Giretti 2012] (Figure 2); (iii) groundwater levels rising up to 400 cm above the local ground level in phreatic wells during the mainshocks (lower values were observed in confined aquifers); and (iv) dormancy of previously known sinkholes [Borgatti et al. 2010, Cremonini 2010a, and references therein]. Some of the observed surface phenomena were previously recorded as coseismic effects during the earthquakes of Ferrara (1570) and Argenta (1624) [Boschi et al. 1995, Galli 2000], together with the early rising of the water level of the Po River in the Stellata section. […]

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ER3D: a structural and geophysical 3-D model of central Emilia-Romagna (northern Italy) for numerical simulation of earthquake ground motion

Solid Earth ◽

10.5194/se-10-931-2019 ◽

2019 ◽

Vol 10 (3) ◽

pp. 931-949 ◽

Cited By ~ 1

Author(s):

Peter Klin ◽

Giovanna Laurenzano ◽

Maria Adelaide Romano ◽

Enrico Priolo ◽

Luca Martelli

Keyword(s):

Numerical Simulations ◽

Ground Motion ◽

Northern Italy ◽

Peak Ground Velocity ◽

Earthquake Ground Motion ◽

Po River ◽

Epicentral Area ◽

River Bank ◽

Local Seismic Response ◽

D Model

Abstract. During the 2012 seismic sequence of the Emilia region (northern Italy), the earthquake ground motion in the epicentral area featured longer duration and higher velocity than those estimated by empirical-based prediction equations typically adopted in Italy. In order to explain these anomalies, we (1) build up a structural and geophysical 3-D digital model of the crustal sector involved in the sequence, (2) reproduce the earthquake ground motion at some seismological stations through physics-based numerical simulations and (3) compare the observed recordings with the simulated ones. In this way, we investigate how the earthquake ground motion in the epicentral area is influenced by local stratigraphy and geological structure buried under the Po Plain alluvium. Our study area covers approximately 5000 km2 and extends from the right Po River bank to the Northern Apennine morphological margin in the N–S direction, and between the two chief towns of Reggio Emilia and Ferrara in the W–E direction, involving a crustal volume of 20 km thickness. We set up the 3-D model by using already-published geological and geophysical data, with details corresponding to a map at scale of 1:250 000. The model depicts the stratigraphic and tectonic relationships of the main geological formations, the known faults and the spatial pattern of the seismic properties. Being a digital vector structure, the 3-D model can be easily modified or refined locally for future improvements or applications. We exploit high-performance computing to perform numerical simulations of the seismic wave propagation in the frequency range up to 2 Hz. In order to get rid of the finite source effects and validate the model response, we choose to reproduce the ground motion related to two moderate-size aftershocks of the 2012 Emilia sequence that were recorded by a large number of stations. The obtained solutions compare very well to the recordings available at about 30 stations in terms of peak ground velocity and signal duration. Snapshots of the simulated wavefield allow us to attribute the exceptional length of the observed ground motion to surface wave overtones that are excited in the alluvial basin by the buried ridge of the Mirandola anticline. Physics-based simulations using realistic 3-D geomodels show eventually to be effective for assessing the local seismic response and the seismic hazard in geologically complex areas.

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Seismic Performance of Industrial Sheds and Liquefaction Effects During May 2012 Emilia Earthquakes Sequence in Northern Italy

Journal of Earthquake and Tsunami ◽

10.1142/s1793431114500092 ◽

2014 ◽

Vol 08 (02) ◽

pp. 1450009 ◽

Cited By ~ 5

Author(s):

Gian Paolo Cimellaro ◽

Marco Chiriatti ◽

Hwasung Roh ◽

Andrei M. Reinhorn

Keyword(s):

Emergency Response ◽

Working Hours ◽

Northern Italy ◽

Seismic Sequence ◽

Epicentral Area ◽

Existing Structures ◽

Industrial Sites ◽

Emilia Earthquake ◽

Private Homes ◽

Seismic Area

On May 20, 2012 at 2:03 UTC, a Mw 6.1 earthquake occurred in Emilia Region of Northern Italy. The event was preceded by a Ml 4.1 foreshock on May 19, 2012 at 23:13 UTC, and followed by several aftershocks, twenty of them with a magnitude Mw greater than 4. The epicentral area of the seismic sequence covers alluvial lowland that is occupied by both agricultural and urbanized areas. Liquefaction effects were observed in several villages on the west side of Ferrara which were built upon former river beds such as the Reno River. The Emilia seismic sequence resulted in 27 casualties, several of whom were among the workers in the factories that collapsed during working hours, and there was extensive damage to monuments, public buildings, industrial sites and private homes. Almost no municipalities hit by 2012 earthquake were classified as seismic area before 2003; therefore, most of the existing structures had been designed without taking in account the seismic actions. The main aims of MCEER field mission was to document the emergency response and the most common damage mechanisms of industrial sheds during Emilia earthquake sequence which are shown and discussed in detail.

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ER3D: a structural and geophysical 3D model of central Emilia-Romagna (Northern Italy) for numerical simulation of earthquake ground motion

10.5194/se-2019-1 ◽

2019 ◽

Author(s):

Peter Klin ◽

Giovanna Laurenzano ◽

M. Adelaide Romano ◽

Enrico Priolo ◽

Luca Martelli

Keyword(s):

Numerical Simulations ◽

Ground Motion ◽

High Performance ◽

3D Model ◽

Northern Italy ◽

Peak Ground Velocity ◽

Earthquake Ground Motion ◽

Po River ◽

Epicentral Area ◽

Local Seismic Response

Abstract. During the 2012 seismic sequence of Emilia region (Northern Italy), the earthquake ground motion in the epicentral area featured longer duration and higher velocity than those estimated by empirical-based prediction equations typically adopted in Italy. In order to explain these anomalies, we (1) build up a structural and geophysical 3D digital model of the crustal sector involved in the sequence, (2) reproduce the earthquake ground motion at some seismological stations through physics-based numerical simulations and (3) compare the observed recordings with the simulated ones. In this way we investigate how the earthquake ground motion in the epicentral area is influenced by local stratigraphy and geological structure buried under the Po Plain alluvium. Our study area covers approximately 5000 km2 and extends from the Po river right bank to the Northern Apennines morphological margin in N-S direction, and between the two chief towns of Reggio Emilia and Ferrara in W-E direction, involving a crustal volume with 20 km of thickness. We set up the 3D model by using already published geological and geophysical data, with a detail corresponding to a map at scale 1:250 000. The model depicts the stratigraphic and tectonic relationships of the main geological formations, the known faults and the spatial pattern of the seismic properties. Being a digital vector structure, the 3D model can be easily modified or refined locally for future improvements or applications. We exploited high performance computing to perform numerical simulations of the seismic wave propagation in the frequency range up to 2 Hz. In order to get rid of the finite source effects and validate the model response, we choose to reproduce the ground motion related to two moderate-size aftershocks of the 2012 Emilia sequence that were recorded by a large number of stations. The obtained solutions compare very well to the recordings available at about 30 stations, in terms of peak ground velocity and signal duration. Snapshots of the simulated wavefield allow us to explain the exceptional length of the observed ground motion as due to surface waves overtones that are excited in the alluvial basin by the buried ridge of the Mirandola anticline. Physics-based simulations using realistic 3D geo-models show eventually to be effective for assessing the local seismic response and the seismic hazard in geologically complex areas.

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Is blind faulting truly invisible? Tectonic-controlled drainage evolution in the epicentral area of the May 2012, Emilia-Romagna earthquake sequence (northern Italy)

Annals of Geophysics ◽

10.4401/ag-6182 ◽

2012 ◽

Vol 55 (4) ◽

Author(s):

Pierfrancesco Burrato ◽

Paola Vannoli ◽

Umberto Fracassi ◽

Roberto Basili ◽

Gianluca Valensise

Keyword(s):

Urban Areas ◽

Power Plants ◽

Active Faults ◽

Northern Italy ◽

Industrial Districts ◽

Large Power ◽

Epicentral Area ◽

The Earth ◽

October 17 ◽

Large Earthquakes

For decades, alluvial plains have been the areas of the fastest population growth over most of the globe. Modern societies demand growing extensions of flat and easily accessible land to accommodate the swelling urban areas, booming industrial districts, large power plants, and multi-runway airports. But how can we tell if such flat areas hide large active faults? How can we assign a significant pre-instrumental earthquake to its causative source? In other words, how can modern societies deal with buried, that is to say, 'invisible' faults, and with the elusiveness of the hazards they can pose? The issue of blind faulting became widely debated in the Earth sciences community in 1989, following the publication of a summary on a sequence of 'hidden earthquakes' that hit central and southern California, USA, between 1983 and 1987, and following the October 17, 1989, Loma Prieta, California, earthquake (Mw 6.9). These earthquakes shattered the accepted belief that large earthquakes are associated with large topographic contrasts; i.e., that they usually take place in mountainous terrains, and that their causative faults are expressed at the surface. Stein and Yeats [1989] spelled out clearly that "...large earthquakes can take place not only on faults that cut the Earth's surface, but also on 'blind' faults under folded terrain". Due to the growing concentrations of population and infrastructures in low topography areas, although such earthquakes might pose comparable hazards, they can come with substantially greater risk than earthquakes that occur in hilly or mountainous terrains. [...]

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The May 2012 Emilia (Italy) earthquakes: preliminary interpretations on the seismogenic source and the origin of the coseismic ground effects

Annals of Geophysics ◽

10.4401/ag-6171 ◽

2012 ◽

Vol 55 (4) ◽

Author(s):

Alberto Pizzi ◽

Vittorio Scisciani

Keyword(s):

Seismic Reflection ◽

Field Survey ◽

Epicentral Distance ◽

Northern Italy ◽

Seismic Reflection Profile ◽

Epicentral Area ◽

Preliminary Model ◽

Seismogenic Source ◽

Emilia Romagna Region ◽

Ground Effects

On May 20, 2012, a Ml 5.9 earthquake (T1) occurred in the Emilia-Romagna Region of northern Italy. This was preceded by a Ml 4.1 foreshock on May 19, 2012, and followed by several aftershocks, including two Ml 5.1 events, both on the same day. On May 29, 2012, a second strong event of Ml 5.8 (T2) hit the same region, with its epicenter ca. 12 km to the WSW of the first mainshock, T1. The epicentral area of the seismic sequence covers an alluvial lowland that is occupied by both agricultural and urbanized areas, and there were 17 casualties and about 14,000 people left homeless. […] In the present study, we provide a preliminary model of the seismogenic source(s) responsible for the two mainshocks, by comparing the seismic reflection profile interpretation with the available seismological and interferometric data. Furthermore, we show the coseismic ground effects that were observed in the epicentral area during two field survey campaigns: the first conducted after the May 20, 2012, event and the second soon after the May 29, 2012, earthquake, when several sites were revisited to observe the occurrence of newly formed or 're-activated' liquefaction features. Hence, we discuss the origin and location of the coseismic features observed in the context of the local geological–geomorphological setting and with respect to the epicentral distance. Finally, we provide our interpretation for the question: "Why did the mainshock ruptures not break the surface?" […]

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Liquefaction phenomena along the paleo-Reno River caused by the May 20, 2012, Emilia (northern Italy) earthquake

Annals of Geophysics ◽

10.4401/ag-6147 ◽

2012 ◽

Vol 55 (4) ◽

Author(s):

Giorgos Papathanassiou ◽

Riccardo Caputo ◽

Dimitra Rapti-Caputo

Keyword(s):

Structural Damage ◽

Northern Italy ◽

Seismic Profiles ◽

Ground Acceleration ◽

Po River ◽

Maximum Acceleration ◽

Epicentral Area ◽

Industrial Buildings ◽

Moderate Earthquake ◽

Dense Grid

On the May 20, 2012 (04:03:52 local time; 02:03:52 UTC), a moderate earthquake (Ml 5.9) [Scognamiglio et al. 2012, this volume] with a focal mechanism showing E-W-trending, S-dipping, reverse-faulting occurred in the eastern sector of the alluvial plain of the Po River, close to the border between the Regions of Emilia-Romagna and Lombardia (northern Italy). The tectonic structure is completely blind, but it was well known from a dense grid of seismic profiles for hydrocarbon explorations [e.g., Pieri and Groppi 1981, Toscani et al. 2009]. The earthquake triggered extensive liquefaction-induced ground effects at the surface, and caused severe structural damage to nonreinforced masonry and precast industrial buildings within the broader epicentral area. The hypocenter was at 44.89 ˚N, 11.23 ˚E, at a depth of 6.3 km [Scognamiglio et al. 2012], while the maximum acceleration was recorded in Mirandola, with peak ground acceleration 310 cm/s2 and 264 cm/s2 along the vertical and horizontal components, respectively [Bozzoni et al. 2012, this volume]. In this report, we focus on a zone including the Sant'A-gostino, San Carlo and Mirabello villages (west Ferrara Province), which were built along an abandoned reach of the Reno River and where liquefaction phenomena were particularly diffuse, with very intense local effects. […]

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