In search of evidence of deep fluid discharges and pore pressure evolution in the crust to explain the seismicity style of the Umbria-Marche 1997-1998 seismic sequence (Central Italy)

Starting soon after the first main-shocks of the long seismic sequence which has occurred along the Umbria-Marche boundary since September 1997, fluid geochemistry surveying was accomplished (around 200 samples) over the epicentre area as a whole, collecting information on hydrological variations too. The collected experimental data allowed to discuss the spatial and temporal evolution of the circulating fluids, either in the chemistry or in the dynamic paths, during the different stages of the seismic sequence. All the geo-structural, seismological and fluid geochemistry information gathered in this sector of the Central Apennines are discussed together in an attempt to speculate about the possible role and evolution of pore-pressure at depth up to surface within the seismogenic process recalling the "Fault Valve Activity Model", the "Coseismic Strain Model", the "frictional heating-frictional stress coupling model" and the "Dilatancy Model". This overview may also explain the geochemical and hydrological experimentally observed anomalies, in occurrence of the seismic sequence. The seismic style of the long sequence is revised in terms of pore-pressure regime down to seismogenic depth (2-10 km), within the poly-phase Evaporite Triassic Basement (ETB) and the Paleozoic Crystalline Basement (PCB), corresponding to the horizons of transient dehydration reactions: process triggered and enhanced during the seismogenic process, involving further fluid overpressure, and consequently further seismicity (chain effect). All the recalled processes and models may explain fluid remobilization and over-pressuring in the upper crust starting soon after the main-shocks, along relict low angle planes (close Apennine and anti-Apennine fault segments), rendering the Umbria-Marche boundary a "transiently weakened frictional instability zone", for a period spanning more than one year.

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Spatio-temporal variation of Anaelastic and Scattering Seismic Attenuation during the 2016-2017 Central Italy Seismic Sequence

10.5194/egusphere-egu21-8802 ◽

2021 ◽

Author(s):

Simona Gabrielli ◽

Aybige Akinci ◽

Ferdinando Napolitano ◽

Luca De Siena ◽

Edoardo Del Pezzo ◽

...

Keyword(s):

Wave Attenuation ◽

Central Italy ◽

Temporal Variations ◽

Seismic Attenuation ◽

Coda Wave ◽

Seismic Sequence ◽

Rock Fracturing ◽

Low Frequencies ◽

Main Shocks ◽

Stress Changes

Between August and October 2016, the Central Apennines in Italy have been struck by a long-lasting seismic sequence, known as the Amatrice (Mw 6.0) - Visso (Mw 5.9) - Norcia (Mw 6.5) sequence. The cascading ruptures occurred in this sequence have been considered connected to the fluid migration in the fault network, as suggested by previous studies. The behaviour of fluids in the crust is crucial to understand earthquakes occurrence and stress changes since fluids reduce fault stability. It has long been understood that the seismic attenuation is strongly controlled by the structural irregularity and heterogeneities; micro-cracks and cavities, either fluid-filled or dry, temperature and pressure variations cause a decrease in seismic wave amplitude and pulse broadening. Hence seismic attenuation imagining is a powerful tool to be a relevant provenance of information about the influence and abundance of fluids in a seismic sequence.The aim of this work is to separate scattering and absorption contributions to the total attenuation of coda waves and to provide their spatial and temporal variations at different frequency bands of these quantities using two datasets: the first one comprising 592 earthquakes occurred before the sequence (March 2013-August 2016) and the second one comprising 763 events (ML > 2.8) from the Amatrice-Visso-Norcia sequence. Scattering and absorption have been measured through peak-delay and coda-wave attenuation parameters (the latter inverted using frequency-dependent sensitivity kernels).The preliminary results show a clear difference between the pre-sequence and sequence images, mainly at low frequencies (1.5 Hz), where we can define a spatial increase of scattering with time attributed to rock fracturing and fluid circulation. The coda attenuation tomography also demonstrates a clear variation between the pre-sequence and the sequence over series of time windows being before and after the largest main shocks of the seismic sequence, with an increase of the attenuation in space with decreasing time. The peak delay indicates a high scattering area corresponding to the Gran Sasso massif and L&#8217;Aquila zone, where an important seismic sequence (Mw 6.3) occurred in 2009.

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Analysis of a database of landslides triggered by the 2016 Central Italy seismic sequence

10.5194/egusphere-egu21-1597 ◽

2021 ◽

Author(s):

Giovanni Forte ◽

Melania De Falco ◽

Federica Iannicelli ◽

Antonio Santo

Keyword(s):

Central Italy ◽

Google Earth ◽

Mountain Range ◽

Seismic Sequence ◽

Large Area ◽

Geometrical Characterization ◽

Seismic Parameters ◽

Main Shocks ◽

Ground Effects ◽

Transportation Routes

The seismic sequence that struck Central Italy in 2016 was characterized by three main shocks respectively occurred on August 24th Mw 6.0; October 26th Mw5.9 and October 30th Mw 6.5. The seismic sequence caused several ground effects over a large area of &#8203;&#8203;the central Apennine mountain range, mainly affecting transportation routes.In the aftermath of the sequence, several research groups mapped around 820 landslides involving road cuts in rock and fill slopes over an area of about 2000 km2 (GEER,ISPRA, C.E.R.I. by Roma La Sapienza). These data are summarized in the CEDIT catalog by Martino et al., (2017), where almost 150, 250 and 420 instability phenomena were respectively triggered by each mainshock. Further updates were carried out by the Authors in the framework of the Reluis projects of the Department of Civil Protection. In particular, other 550 phenomena were mapped by interpretation of aero photos provided by google-earth. For some of the largest ones, field surveys were carried out for mechanical, structural, and geometrical characterization.The dataset distribution was analyzed with geological, geomorphological, and seismic parameters, such as lithology, fault distance, landslide run-out, estimates of mobilized volumes, distance from the epicenter, PGA, and damages.The triggered events are mainly characterized by Category I of Keefer (1984) classification, namely rockfalls and rockslides. The maximum triggering distance resulted as high as 50 km far from the epicenter. The most affected areas are characterized by ridge crests or flanks of valleys in carbonate rocks.This study permitted to highlight the most relevant parameters for the assessment of earthquake-triggered susceptibility for the study area and identify some meaningful and critical case studies for the future development of the research.&#160;

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Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

Tectonics ◽

10.1002/2017tc004652 ◽

2017 ◽

Vol 36 (11) ◽

pp. 2370-2387 ◽

Cited By ~ 65

Author(s):

A. Pizzi ◽

A. Di Domenica ◽

F. Gallovič ◽

L. Luzi ◽

R. Puglia

Keyword(s):

Central Italy ◽

Seismic Sequence ◽

Fault Segmentation ◽

Main Shocks

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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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Spatio-temporal seismic velocity variations associated to the 2016–2017 central Italy seismic sequence from noise cross-correlation

Geophysical Journal International ◽

10.1093/gji/ggz429 ◽

2019 ◽

Vol 219 (3) ◽

pp. 2165-2173

Author(s):

Gaia Soldati ◽

Lucia Zaccarelli ◽

Licia Faenza

Keyword(s):

Seismic Waves ◽

Seismic Velocity ◽

Linear Trend ◽

Central Italy ◽

Fault System ◽

Seismic Sequence ◽

Sedimentary Deposits ◽

Main Shocks ◽

Spatio Temporal ◽

Velocity Changes

SUMMARY We investigate the temporal changes of crustal velocity associated to the seismic sequence of 2016–2017, which struck central Italy with a series of moderate to large earthquakes. We cross-correlate continuous recordings of 2 yr of ambient seismic noise from a network of 28 stations within a radius of 90 km around Amatrice town. We then map the spatio-temporal evolution of the velocity perturbations under the effect of subsequent earthquakes. Coinciding with each of the three main shocks of the sequence we observe a sudden drop of seismic velocity which tends to quickly recover in the short term. After the end of the strongest activity of the sequence, the coseismic velocity changes display gradual healing towards pre-earthquake conditions following a quasi-linear trend, such that by the end of 2017 about 75 per cent of the perturbation is recovered. The spatial distribution of the velocity drop fluctuates with time, and the area that shows the most intense variations beyond the ruptured fault system elongates in the NE direction. This zone roughly corresponds to a region of foredeep sedimentary deposits consisting of highly hydrated and porous sandstones, which respond to the passage of seismic waves with increased pore pressure and crack number, leading to a reduction of the effective relative velocity.

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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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Seismic Performance Assessment of Existing Steel Buildings: A Case Study

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.763.1067 ◽

2018 ◽

Vol 763 ◽

pp. 1067-1076 ◽

Cited By ~ 1

Author(s):

Luigi di Sarno ◽

Fabrizio Paolacci ◽

Anastasios G. Sextos

Keyword(s):

Numerical Study ◽

Central Italy ◽

Steel Structures ◽

Eurocode 8 ◽

Building Structures ◽

Steel Buildings ◽

Seismic Performance Assessment ◽

Masonry Infills ◽

Main Shocks

Numerous existing steel framed buildings located in earthquake prone regions world-wide were designed without seismic provisions. Slender beam-columns, as well as non-ductile beam-to-column connections have been employed for multi-storey moment-resisting frames (MRFs) built before the 80’s. Thus, widespread damage due to brittle failure has been commonly observed in the past earthquakes for steel MRFs. A recent post-earthquake survey carried out in the aftermath of the 2016-2017 Central Italy seismic swarm has pointed out that steel structures may survive the shaking caused by several main-shocks and strong aftershocks without collapsing. Inevitably, significant lateral deformations are experienced, and, in turn, non-structural components are severely damaged thus inhibiting the use of the steel building structures. The present papers illustrates the outcomes of a recent preliminary numerical study carried out for the case of a steel MRF building located in Amatrice, Central Italy, which experienced a series of ground motion excitations suffering significant damage to the masonry infills without collapsing. A refined numerical model of the sample structure has been developed on the basis of the data collected on site. Given the lack of design drawings, the structure has been re-designed in compliance with the Italian regulations imposed at the time of construction employing the allowable stress method. The earthquake performance of the case study MRF has been then investigated through advanced nonlinear dynamic analyses and its structural performance has been evaluated according to Eurocode 8-Part 3 for existing buildings. The reliability of the codified approaches has been evaluated and possible improvements emphasized.

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