Volume unbalance on the 2016 Amatrice - Norcia (Central Italy) seismic sequence and insights on normal fault earthquake mechanism

The Apenninic chain, in central Italy, has been recently struck by the Norcia 2016 seismic sequence. Three mainshocks, in 2016, occurred on August 24 (MW6.0), October 26 (MW 5.9) and October 30 (MW6.5) along well-known late Quaternary active WSW-dipping normal faults. Coseismic fractures and hypocentral seismicity distribution are mostly associated with failure along the Mt Vettore-Mt Bove (VBF) fault. Nevertheless, following the October 26 shock, the aftershock spatial distribution suggests the activation of a source not previously mapped beyond the northern tip of the VBF system. In this area, a remarkable seismicity rate was observed also during 2017 and 2018, the most energetic event being the April 10, 2018 (MW4.6) normal fault earthquake. In this paper, we advance the hypothesis that the Norcia seismic sequence activated a previously unknown seismogenic source. We constrain its geometry and seismogenic behavior by exploiting: 1) morphometric analysis of high-resolution topographic data; 2) field geologic- and morphotectonic evidence within the context of long-term deformation constraints; 3) 3D seismological validation of fault activity, and 4) Coulomb stress transfer modeling. Our results support the existence of distributed and subtle deformation along normal fault segments related to an immature structure, the Pievebovigliana fault (PBF). The fault strikes in NNW-SSE direction, dips to SW and is in right-lateral en echelon setting with the VBF system. Its activation has been highlighted by most of the seismicity observed in the sector. The geometry and location are compatible with volumes of enhanced stress identified by Coulomb stress-transfer computations. Its reconstructed length (at least 13 km) is compatible with the occurrence of MW≥6.0 earthquakes in a sector heretofore characterized by low seismic activity. The evidence for PBF is a new observation associated with the Norcia 2016 seismic sequence and is consistent with the overall tectonic setting of the area. Its existence implies a northward extent of the intra-Apennine extensional domain and should be considered to address seismic hazard assessments in central Italy.

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Heterogeneous Behavior of the Campotosto Normal Fault (Central Italy) Imaged by InSAR GPS and Strong-Motion Data: Insights from the 18 January 2017 Events

Remote Sensing ◽

10.3390/rs11121482 ◽

2019 ◽

Vol 11 (12) ◽

pp. 1482 ◽

Cited By ~ 5

Author(s):

Daniele Cheloni ◽

Nicola D’Agostino ◽

Laura Scognamiglio ◽

Elisa Tinti ◽

Christian Bignami ◽

...

Keyword(s):

Central Italy ◽

Sampling Rate ◽

Strong Motion ◽

Normal Fault ◽

Slip Distribution ◽

Fault System ◽

Time Interval ◽

Seismic Sequence ◽

Main Shocks ◽

Heterogeneous Behavior

On 18 January 2017, the 2016–2017 central Italy seismic sequence reached the Campotosto area with four events with magnitude larger than 5 in three hours (major event MW 5.5). To study the slip behavior on the causative fault/faults we followed two different methodologies: (1) we use Interferometric Synthetic Aperture Radar (InSAR) interferograms (Sentinel-1 satellites) and Global Positioning System (GPS) coseismic displacements to constrain the fault geometry and the cumulative slip distribution; (2) we invert near-source strong-motion, high-sampling-rate GPS waveforms, and high-rate GPS-derived static offsets to retrieve the rupture history of the two largest events. The geodetic inversion shows that the earthquake sequence occurred along the southern segment of the SW-dipping Mts. Laga normal fault system with an average slip of about 40 cm and an estimated cumulative geodetic moment of 9.29 × 1017 Nm (equivalent to a MW~6). This latter estimate is larger than the cumulative seismic moment of all the events, with MW > 4 which occurred in the corresponding time interval, suggesting that a fraction (~35%) of the overall deformation imaged by InSAR and GPS may have been released aseismically. Geodetic and seismological data agree with the geological information pointing out the Campotosto fault segment as the causative structure of the main shocks. The position of the hypocenters supports the evidence of an up-dip and northwestward rupture directivity during the major shocks of the sequence for both static and kinematic inferred slip models. The activated two main slip patches are characterized by rise time and peak slip velocity in the ranges 0.7–1.1 s and 2.3–3.2 km/s, respectively, and by ~35–50 cm of slip mainly concentrated in the shallower northern part of causative fault. Our results show that shallow slip (depth < 5 km) is required by the geodetic and seismological observations and that the inferred slip distribution is complementary with respect to the previous April 2009 seismic sequence affecting the southern half of the Campotosto fault. The recent moderate strain-release episodes (multiple M~5–5.5 earthquakes) and the paleoseismological evidence of surface-rupturing events (M~6.5) suggests therefore a heterogeneous behavior of the Campotosto fault.

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High resolution morphometric analysis of the Cordone del Vettore normal fault scarp (2016 Central Italy seismic sequence): Insights into age, earthquake recurrence and throw rates

Geomorphology ◽

10.1016/j.geomorph.2021.107784 ◽

2021 ◽

pp. 107784

Author(s):

S. Pucci ◽

L. Pizzimenti ◽

R. Civico ◽

F. Villani ◽

C.A. Brunori ◽

...

Keyword(s):

High Resolution ◽

Morphometric Analysis ◽

Central Italy ◽

Normal Fault ◽

Fault Scarp ◽

Seismic Sequence ◽

Earthquake Recurrence

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Failure Analysis of Apennine Masonry Churches Severely Damaged during the 2016 Central Italy Seismic Sequence

Buildings ◽

10.3390/buildings11020058 ◽

2021 ◽

Vol 11 (2) ◽

pp. 58 ◽

Cited By ~ 2

Author(s):

Francesco Clementi

Keyword(s):

Case Studies ◽

Central Italy ◽

Numerical Data ◽

Sensitivity Study ◽

Nonlinear Material ◽

Seismic Sequence ◽

Nonlinear Approach ◽

Nonlinear Static ◽

Masonry Churches ◽

Global And Local

This paper presents a detailed study of the damages and collapses suffered by various masonry churches in the aftermath of the seismic sequence of Central Italy in 2016. The damages will first be analyzed and then compared with the numerical data obtained through 3D simulations with eigenfrequency and then nonlinear static analyses (i.e., pushover). The main purposes of this study are: (i) to create an adequately consistent sensitivity study on several definite case studies to obtain an insight into the role played by geometry—which is always unique when referred to churches—and by irregularities; (ii) validate or address the applicability limits of the more widespread nonlinear approach, widely recommended by the Italian Technical Regulations. Pushover analyses are conducted assuming that the masonry behaves as a nonlinear material with different tensile and compressive strengths. The consistent number of case studies investigated will show how conventional static approaches can identify, albeit in a qualitative way, the most critical macro-elements that usually trigger both global and local collapses, underlining once again how the phenomena are affected by the geometry of stones and bricks, the texture of the wall face, and irregularities in the plan and elevation and in addition to hypotheses made on the continuity between orthogonal walls.

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Exceedance of design actions in epicentral areas: insights from the ShakeMap envelopes for the 2016–2017 central Italy sequence

Bulletin of Earthquake Engineering ◽

10.1007/s10518-021-01192-z ◽

2021 ◽

Author(s):

Iunio Iervolino ◽

Pasquale Cito ◽

Chiara Felicetta ◽

Giovanni Lanzano ◽

Antonio Vitale

Keyword(s):

Earthquake Engineering ◽

Structural Damage ◽

Structural Engineering ◽

Central Italy ◽

Civil Defense ◽

Point Of View ◽

Seismic Sequence ◽

Ground Shaking ◽

Motion Effect ◽

Observed Damage

AbstractShakeMap is the tool to evaluate the ground motion effect of earthquakes in vast areas. It is useful to delimit the zones where the shaking is expected to have been most significant, for civil defense rapid response. From the earthquake engineering point of view, it can be used to infer the seismic actions on the built environment to calibrate vulnerability models or to define the reconstruction policies based on observed damage vs shaking. In the case of long-lasting seismic sequences, it can be useful to develop ShakeMap envelopes, that is, maps of the largest ground intensity among those from the ShakeMap of (selected) events of a seismic sequence, to delimit areas where the effects of the whole sequence have been of structural engineering relevance. This study introduces ShakeMap envelopes and discusses them for the central Italy 2016–2017 seismic sequence. The specific goals of the study are: (i) to compare the envelopes and the ShakeMap of the main events of the sequence to make the case for sequence-based maps; (ii) to quantify the exceedance of design seismic actions based on the envelopes; (iii) to make envelopes available for further studies and the reconstruction planning; (iv) to gather insights on the (repeated) exceedance of design seismic actions at some sites. Results, which include considerations of uncertainty in ShakeMap, show that the sequence caused exceedance of design hazard in thousands of square kilometers. The most relevant effects of the sequence are, as expected, due to the mainshock, yet seismic actions larger than those enforced by the code for structural design are found also around the epicenters of the smaller magnitude events. At some locations, the succession of ground-shaking that has excited structures, provides insights on structural damage accumulation that has likely taken place; something that is not accounted for explicitly in modern seismic design. The envelopes developed are available as supplemental material.

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Along-strike rupture directivity of earthquakes of the 2009 L'Aquila, central Italy, seismic sequence

Geophysical Journal International ◽

10.1093/gji/ggv275 ◽

2015 ◽

Vol 203 (1) ◽

pp. 399-415 ◽

Cited By ~ 26

Author(s):

G. Calderoni ◽

A. Rovelli ◽

Y. Ben-Zion ◽

R. Di Giovambattista

Keyword(s):

Central Italy ◽

Seismic Sequence ◽

Rupture Directivity

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Iconic crumbling of the clock tower in Amatrice after 2016 central Italy seismic sequence: advanced numerical insight

Procedia Structural Integrity ◽

10.1016/j.prostr.2018.11.041 ◽

2018 ◽

Vol 11 ◽

pp. 314-321 ◽

Cited By ~ 12

Author(s):

M. Poiani ◽

V. Gazzani ◽

F. Clementi ◽

G. Milani ◽

M. Valente ◽

...

Keyword(s):

Central Italy ◽

Seismic Sequence

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The first month of the 2016 central Italy seismic sequence: fast determination of time domain moment tensors and finite fault model analysis of the ML 5.4 aftershock

Annals of Geophysics ◽

10.4401/ag-7246 ◽

2016 ◽

Vol 59 ◽

Author(s):

Laura Scognamiglio ◽

Elisa Tinti ◽

Matteo Quintiliani

Keyword(s):

Time Domain ◽

Moment Tensor ◽

Central Italy ◽

Model Analysis ◽

Fault Model ◽

Normal Faults ◽

Seismic Sequence ◽

Moment Tensors ◽

Finite Fault ◽

Finite Fault Model

We present the revised Time Domain Moment Tensor (TDMT) catalogue for earthquakes with M_L larger than 3.6 of the first month of the ongoing Amatrice seismic sequence (August 24th - September 25th). Most of the retrieved focal mechanisms show NNW–SSE striking normal faults in agreement with the main NE-SW extensional deformation of Central Apennines. We also report a preliminary finite fault model analysis performed on the larger aftershock of this period of the sequence (M_w 5.4) and discuss the obtained results in the framework of aftershocks distribution.

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Assessing soil-structure interaction during the 2016 Central Italy seismic sequence (Italy): preliminary results

Annals of Geophysics ◽

10.4401/ag-7250 ◽

2016 ◽

Vol 59 ◽

Author(s):

Arrigo Caserta ◽

Fawzi Doumaz ◽

Antonio Costanzo ◽

Anna Gervasi ◽

William Thorossian ◽

...

Keyword(s):

Soil Structure ◽

Central Italy ◽

Seismic Energy ◽

Soil Structure Interaction ◽

Seismic Sequence ◽

Structure Interaction ◽

Preliminary Results ◽

The Church ◽

Moderate Magnitude

We used the moderate-magnitude aftershocks succeeding to the 2016 August 24th, Mw = 6.0, Amatrice (Italy) mainshok to asses, specially during an ongoing seismic sequence, the soil-structure interaction where cultural Heritage is involved. We have chosen as case study the San Giovanni Battista church (A.D. 1039) in Acquasanta Terme town, about 20 Km northeast of Amatrice. First of all we studied the soil shaking features in order to characterize the input to the monument. Then, using the recordings in the church, we tried to figure out how the input seismic energy is distributed over the different monument parts. Some preliminary results are shown and discussed.

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Seismogenesis in Central Apennines, Italy: an integrated analysis of minor earthquake sequences and structural data in the Amatrice-Campotosto area

Annals of Geophysics ◽

10.4401/ag-3371 ◽

2009 ◽

Vol 47 (6) ◽

Author(s):

P. Boncio ◽

G. Lavecchia ◽

G. Milana ◽

B. Rozzi

Keyword(s):

Late Quaternary ◽

Central Italy ◽

Normal Fault ◽

Structural Data ◽

Integrated Analysis ◽

Fault Plane Solutions ◽

Small Magnitude ◽

Fault Surface ◽

Displacement Profile ◽

Earthquake Sequences

We present a seismotectonic study of the Amatrice-Campotosto area (Central Italy) based on an integrated analysis of minor earthquake sequences, geological data and crustal rheology. The area has been affected by three small-magnitude seismic sequences: August 1992 (M=3.9), June 1994 (M=3.7) and October 1996 (M=4.0). The hypocentral locations and fault plane solutions of the 1996 sequence are based on original data; the seismological features of the 1992 and 1994 sequences are summarised from literature. The active WSWdipping Mt. Gorzano normal fault is interpreted as the common seismogenic structure for the three analysed sequences. The mean state of stress obtained by inversion of focal mechanisms (WSW-ENE-trending deviatoric tension) is comparable to that responsible for finite Quaternary displacement, showing that the stress field has not changed since the onset of extensional tectonics. Available morphotectonic data integrated with original structural data show that the Mt. Gorzano Fault extends for ~28 km along strike. The along-strike displacement profile is typical of an isolated fault, without significant internal segmentation. The strong evidence of late Quaternary activity in the southern part of the fault (with lower displacement gradient) is explained in this work in terms of displacement profile readjustment within a fault unable to grow further laterally. The depth distribution of seismicity and the crustal rheology yield a thickness of ~15 km for the brittle layer. An area of ~530 km2 is estimated for the entire Mt. Gorzano Fault surface. In historical times, the northern portion of the fault was probably activated during the 1639 Amatrice earthquake (I = X, M~ 6.3), but this is not the largest event we expect on the fault. We propose that a large earthquake might activate the entire 28 km long Mt. Gorzano Fault, with an expected Mmax up to 6.7.

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