scholarly journals The Italian Seismic Bulletin: strategies, revised pickings and locations of the central Italy seismic sequence

2016 ◽  
Vol 59 ◽  
Author(s):  
Alessandro Marchetti ◽  
Maria Grazia Ciaccio ◽  
Anna Nardi ◽  
Andrea Bono ◽  
Francesco Mariano Mele ◽  
...  
Keyword(s):  
Focal Mechanism ◽  
Main Shock ◽  
Moment Tensor ◽  
Central Italy ◽  
Seismic Sequence ◽  
Centroid Moment Tensor ◽  
Moment Tensors ◽  
Emergency Group ◽  
First Motion ◽  
New Procedures

<p>The central Italy seismic sequence, started with the Mw = 6.0 Amatrice earthquake on August 24th 2016, is the first significant one after the Italian Seismic Bulletin (BSI) changed its analysis strategies in 2015. These new strategies consist on the release of the BSI every four months, the review of the events with ML ≥ 1.5 and the priority on the review of events with ML ≥ 3.5. Furthermore, in the last year we improved the bulletin tools and made possible the analysis of all the stations whose data are stored in the European Integrated Data Archive (EIDA). The new procedures and software utilities allowed, during the first month of 2016 emergency, to integrate, in the Bulletin, the temporary stations installed by the emergency group SISMIKO, both in real–time transmission and in stand-alone recording. In the early days of the sequence many of the BSI analysts were engaged in the monitoring room shifts, nevertheless at the end of August all events occurred in those days with ML ≥ 4 were analyzed; the largest event recovered and localized is a ML = 4.5 event immediately following the main shock. In September 2016, 83 events with ML ≥ 3.5 were analyzed and re-checked, the number of pickings greatly improved. The focal mechanism of the main shock was evaluated using first motion polarities, and compared with the available Time Domain Moment Tensors and Regional Centroid Moment Tensor. The first eight hours of the day on August 24th, the most critical for the INGV surveillance room, were carefully analyzed: the number of located events increased from 133 to 408. The magnitude of completeness, after the analysis of the BSI, has dropped significantly from about 3.5 to 2.7. The mainshock focal mechanism and the relative locations of the first 8 hours’ aftershocks give clues on the initial fault activation. The seismic sequence in November 2016 is still ongoing; it included a mainshock of Mw = 6.5 on October 30th and 3 events of magnitude greater than 5.0 one on August 24th and two on October 26th.</p>

scholarly journals 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

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

<p>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.</p>

scholarly journals First-Motion Focal Mechanism Solutions for 2015–2019 M ≥ 4.0 Italian Earthquakes

2021 ◽  
Vol 9 ◽  
Author(s):  
Maria G. Ciaccio ◽  
Raffaele Di Stefano ◽  
Luigi Improta ◽  
Maria T. Mariucci ◽  
Keyword(s):  
Focal Mechanism ◽  
Carbonate Platform ◽  
Central Italy ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Seismic Sequence ◽  
Earthquake Parameters ◽  
Focal Mechanism Solutions ◽  
Initial Rupture ◽  
First Motion

A list of 100 focal mechanism solutions that occurred in Italy between 2015 and 2019 has been compiled for earthquakes with magnitude M ≥ 4.0. We define earthquake parameters for additional 22 seismic events with 3.0 ≤ M &lt; 4.0 for two specific key zones: Muccia, at the northern termination of the Amatrice–Visso–Norcia 2016–2018 central Italy seismic sequence, and Montecilfone (southern Italy) struck in 2018 by a deep, strike-slip Mw 5.1 earthquake apparently anomalous for the southern Apennines extensional belt. First-motion focal mechanism solutions are a good proxy for the initial rupture and they provide important additional information on the source mechanism. The catalog compiled in the present paper provides earthquake parameters for individual events of interest to contribute, as a valuable source of information, for further studies as seismotectonic investigations and stress distribution maps. We calculated the focal mechanisms using as a reference the phase pickings reported in the Italian Seismic Bulletin (BSI). We visually checked the reference picks to accurately revise manual first-motion polarities, or include new onsets when they are not present in the BSI dataset, for the selected earthquakes within the whole Italian region, with a separate focus on the Amatrice–Visso–Norcia seismic sequence area from August 24, 2016 to August 24, 2018. For the Montecilfone area, we combined the information on the geometry and kinematics of the source of the 2018 Mw 5.1 event obtained in this study with available subsurface and structural data on the Outer Apulia Carbonate Platform to improve understanding of this intriguing strike-slip sequence. Our analysis suggests that the Montecilfone earthquake ruptured a W–E trending strike-slip dextral fault. This structure is confined within the Apulia crystalline crust and it might represent the western prolongation of the Mattinata Fault–Apricena Fault active and seismogenic structures. The calculated focal mechanisms of the entire catalog are of good quality complementing important details on source mechanics from moment tensors and confirming the relevance of systematically including manually revised and more accurate polarity data within the BSI database.

scholarly journals Instrumental seismicity of the Amatrice earthquake epicentral area: a review 

2016 ◽  
Vol 59 ◽  
Author(s):  
Maria Grazia Ciaccio
Keyword(s):  
Moment Tensor ◽  
Central Italy ◽  
Central Area ◽  
Seismic Sequence ◽  
Centroid Moment Tensor ◽  
Fault Plane Solutions ◽  
Small Magnitude ◽  
Epicentral Area ◽  
Seismic Sequences ◽  
Seismogenic Structures

<p><em>This study presents a review of the instrumental seismicity of the Norcia-Amatrice area (central Italy) where a still on-going seismic sequence started on August 24th 2016 with a Mw6.0 earthquake.</em></p><p><em>The review is based on the analysis of the </em><em>seismic catalogs 1981-2016, the CMT (Centroid Moment Tensor) solutions and the TDMT (Time Domain Moment Tensor) solutions, dividing the area into three regions based on the main seismic sequences preceding the Amatrice 2016 mainshock.</em><em></em></p><p><em>The seismicity of this region is characterized by different types of activity: single events, minor sequences and swarms with hypocenters within the upper 15 km of the crust. </em><em>Small-magnitude seismic sequences on March 2007 with maximum Mw3.9, and one earthquake on March 2012, Mw37, not followed by significant seismicity, affected the area east of the Norcia, close to the Mw 5.4 aftershock of the Amatrice 2016 sequence. In the central area, near Accumoli, and in the southern sector close to Amatrice, minor seismic sequences occurred on February 2014 Ml3.5 and on November 2013 Mw3.7 respectively.</em><em></em></p><p><em>We integrated hypocentral locations and fault plane solutions to give a first look at the main features of the instrumental seismicity compared to the present seismic sequence in order to relate the seismicity patterns to seismogenic structures of this area of the central Italy.</em><em></em></p>

scholarly journals Quick regional centroid moment tensor solutions for the Emilia 2012 (northern Italy) seismic sequence

2012 ◽  
Vol 55 (4) ◽  
Author(s):  
Silvia Pondrelli ◽  
Simone Salimbeni ◽  
Paolo Perfetti ◽  
Peter Danecek
Keyword(s):  
Moment Tensor ◽  
Mediterranean Area ◽  
Northern Italy ◽  
Seismic Sequence ◽  
Centroid Moment Tensor ◽  
Strong Earthquakes ◽  
Magnitude Range ◽  
The Mediterranean ◽  
Centroid Moment Tensor Solutions

<p>In May 2012, a seismic sequence struck the Emilia region (northern Italy). The mainshock, of Ml 5.9, occurred on May 20, 2012, at 02:03 UTC. This was preceded by a smaller Ml 4.1 foreshock some hours before (23:13 UTC on May 19, 2012) and followed by more than 2,500 earthquakes in the magnitude range from Ml 0.7 to 5.2. In addition, on May 29, 2012, three further strong earthquakes occurred, all with magnitude Ml ≥5.2: a Ml 5.8 earthquake in the morning (07:00 UTC), followed by two events within just 5 min of each other, one at 10:55 UTC (Ml 5.3) and the second at 11:00 UTC (Ml 5.2). For all of the Ml ≥4.0 earthquakes in Italy and for all of the Ml ≥4.5 in the Mediterranean area, an automatic procedure for the computation of a regional centroid moment tensor (RCMT) is triggered by an email alert. Within 1 h of the event, a manually revised quick RCMT (QRCMT) can be published on the website if the solution is considered stable. In particular, for the Emilia seismic sequence, 13 QRCMTs were determined and for three of them, those with M &gt;5.5, the automatically computed QRCMTs fitted the criteria for publication without manual revision. Using this seismic sequence as a test, we can then identify the magnitude threshold for automatic publication of our QRCMTs.</p>

The Global Centroid Moment Tensor Catalog: Heterogeneities and improvements

2021 ◽  
Author(s):  
Álvaro González
Keyword(s):  
Subduction Zones ◽  
Moment Tensor ◽  
Statistical Seismology ◽  
Centroid Moment Tensor ◽  
Moment Tensors ◽  
Global Database ◽  
Intermediate Period ◽  
Data Compilation ◽  
Forecast Models ◽  
The Moment

&lt;p&gt;Statistical seismology relies on earthquake catalogs as homogeneous and complete as possible. However, heterogeneities in earthquake data compilation and reporting are common and frequently are not adverted.&lt;/p&gt;&lt;p&gt;The Global Centroid Moment Tensor Catalog (www.globalcmt.org) is considered as the most homogeneous global database for large and moderate earthquakes occurred since 1976, and it has been used for developing and testing global and regional forecast models.&lt;/p&gt;&lt;p&gt;Changes in the method used for calculating the moment tensors (along with improvements in global seismological monitoring) define four eras in the catalog (1976, 1977-1985, 1986-2003 and 2004-present). Improvements are particularly stark since 2004, when intermediate-period surface waves started to be used for calculating the centroid solutions.&lt;/p&gt;&lt;p&gt;Fixed centroid depths, used when the solution for a free depth did not converge, have followed diverse criteria, depending on the era. Depth had to be fixed mainly for shallow earthquakes, so this issue is more common, e.g. in the shallow parts of subduction zones than in the deep ones. Until 2003, 53% of the centroids had depths calculated as a free parameter, compared to 78% since 2004.&lt;/p&gt;&lt;p&gt;Rake values have not been calculated homogenously either. Until 2003, the vertical-dip-slip components of the moment tensor were assumed as null when they could not be constrained by the inversion (for 3.3% of the earthquakes). This caused an excess of pure focal mechanisms: rakes of -90&amp;#176; (normal), 0&amp;#176; or &amp;#177;180&amp;#176; (strike-slip) or +90&amp;#176; (thrust). Even disregarding such events, rake histograms until 2003 and since 2004 are not equivalent to each other.&lt;/p&gt;&lt;p&gt;The magnitude of completeness (&lt;em&gt;M&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt;) of the catalog is analyzed here separately for each era. It clearly improved along time (average &lt;em&gt;M&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; values being ~6.4 in 1976, ~5.7 in 1977-1985, ~5.4 in 1986-2003, and ~5.0 since 2004). Maps of &lt;em&gt;M&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; for different eras show significant spatial variations.&lt;/p&gt;

scholarly journals Coulomb stress transfer and fault interaction over millennia on non-planar active normal faults: the Mw 6.5–5.0 seismic sequence of 2016–2017, central Italy

2017 ◽  
Vol 210 (2) ◽  
pp. 1206-1218 ◽  
Author(s):  
Zoe K. Mildon ◽  
Gerald P. Roberts ◽  
Joanna P. Faure Walker ◽  
Francesco Iezzi
Keyword(s):  
Main Shock ◽  
Central Italy ◽  
Stress Transfer ◽  
Historical Record ◽  
Normal Faults ◽  
Coulomb Stress ◽  
Seismic Sequence ◽  
Fault Interaction ◽  
Slip Rates ◽  
Stress Changes

Abstract In order to investigate the importance of including strike-variable geometry and the knowledge of historical and palaeoseismic earthquakes when modelling static Coulomb stress transfer and rupture propagation, we have examined the August–October 2016 A.D. and January 2017 A.D. central Apennines seismic sequence (Mw 6.0, 5.9, 6.5 in 2016 A.D. (INGV) and Mw 5.1, 5.5, 5.4, 5.0 in 2017 A.D. (INGV)). We model both the coseismic loading (from historical and palaeoseismic earthquakes) and interseismic loading (derived from Holocene fault slip-rates) using strike-variable fault geometries constrained by fieldwork. The inclusion of the elapsed times from available historical and palaeoseismological earthquakes and on faults enables us to calculate the stress on the faults prior to the beginning of the seismic sequence. We take account the 1316–4155 yr elapsed time on the Mt. Vettore fault (that ruptured during the 2016 A.D. seismic sequence) implied by palaeoseismology, and the 377 and 313 yr elapsed times on the neighbouring Laga and Norcia faults respectively, indicated by the historical record. The stress changes through time are summed to show the state of stress on the Mt. Vettore, Laga and surrounding faults prior to and during the 2016–2017 A.D. sequence. We show that the build up of stress prior to 2016 A.D. on strike-variable fault geometries generated stress heterogeneities that correlate with the limits of the main-shock ruptures. Hence, we suggest that stress barriers appear to have control on the propagation and therefore the magnitudes of the main-shock ruptures.

scholarly journals Identifikasi Sesar di Wilayah Gorontalo dengan Analisis Mekanisme Bola Fokus

Jurnal MIPA ◽  
2014 ◽  
Vol 3 (1) ◽  
pp. 40
Author(s):  
Nurfitriani . ◽  
Guntur Pasau ◽  
Slamet Suyitno Raharjo
Keyword(s):  
Focal Mechanism ◽  
Active Fault ◽  
Moment Tensor ◽  
Earthquake Catalog ◽  
Centroid Moment Tensor ◽  
Geological Map ◽  
Fault Structures

Gorontalo menjadi salah satu daerah rawan bencana gempa bumi dan ecara tektonik berada di wilayah pertemuan 2 lempeng besar, yakni lempeng Pasifik dan Eurasia serta lempeng-lempeng mikro. Peta Geologi Gorontalo menunjukkan adanya struktur sesar yang memotong wilayah kota Gorontalo. Adapun tujuan penelitian ini adalah mengidentifikasi keberadaan struktur sesar di wilayah Gorontalo dengan menggunakan metode mekanisme bola fokus kejadian gempa bumi di wilayah daratan Gorontalo periode 1963-2013 dengan sumber data dari katalog gempa bumi USGS, Global Centroid Momen Tensor, dan BMKG. Analisis bola fokus menunjukkan adanya 3 daerah dugaan sesar aktif, dengan tipe sesar cenderung oblique, dengan panjang 24,54 km sampai 27,54 km dan lebar rupture 8,51 km sampai 9,22 km. Hasil analisis ini juga mendeteksi adanya satu daerah dugaan sesar aktif yang tidak teridentifikasi pada peta geologi.Gorontalo is one of the earthquake prone areas and is tectonically located at the junction of two major plates and some microplates. Geological map indicated the presence of fault structures across Gorontalo. This study was aimed to identify the presence of fault structures in the Gorontalo area using focal mechanism of earthquakes in the mainland region of Gorontalo at the period of 1963-2013 with data sourced from the USGS earthquake catalog, the Global Centroid Moment Tensor, and BMKG. The analysis showed that there were 3 suspected active fault area having oblique-type fault with length of 24,54 to 27,54 km and rupture width of 8,51 to 9,22 km. The analysis also detected the presence of a suspected active fault area which was not identified on the geological map.

The Global Importance of Continental Seismic Sequences

2020 ◽  
Author(s):  
Richard Walters ◽  
Tim Craig ◽  
Laura Gregory ◽  
Russell Azad Khan
Keyword(s):  
Structural Control ◽  
Initial Conditions ◽  
Moment Tensor ◽  
Central Italy ◽  
Relative Number ◽  
Strike Slip ◽  
Normal Faults ◽  
Centroid Moment Tensor ◽  
Multiple Faults ◽  
Seismic Sequences

&lt;p&gt;Large continental earthquakes necessarily involve cascading rupture of multiple faults or segments (e.g. El Mayor-Cucapah 2010). But these same critically-stressed systems sometimes rupture in drawn-out sequences of smaller earthquakes over days or years (e.g. Central Italy 2016), instead of in a single large event. Due to the similarity in the initial conditions of both scenarios, seismic sequences may be considered as &amp;#8216;failed&amp;#8217; multi-segment earthquakes, whereby cascading rupture is prematurely halted before all available slip deficit is released.&lt;/p&gt;&lt;p&gt;These two modes of strain-release have vastly different implications for seismic hazard. Recent work on the 2016 Central Italy earthquake sequence, which is the first seismic sequence to be studied with modern high-quality geodetic and seismological datasets, showed that complexity in fault structure appeared to exercise a dual control on both the timing and sizes of events throughout this sequence. However, it is unclear if this structural control is common for all continental seismic sequences, how important seismic sequences are for the global seismic moment budget, and how this contribution to moment budget may vary between different tectonic regions.&lt;/p&gt;&lt;p&gt;Here we select shallow crustal continental earthquakes from the Global Centroid Moment Tensor catalog, and identify seismic sequences as agglomerates of clustered pairs of earthquakes where the summed moment (M&lt;sub&gt;0&lt;/sub&gt;) of all aftershocks is greater than 50% of the M&lt;sub&gt;0&lt;/sub&gt; of the first event in the sequence. We analyse the relative number of seismic sequences compared to other earthquakes for normal, reverse, and strike-slip faulting regions, and also calculate the relative M&lt;sub&gt;0&lt;/sub&gt; release of seismic sequences and other earthquakes in these three regimes.&lt;/p&gt;&lt;p&gt;We find that although seismic sequences are equally common by number in all continental tectonic regimes, seismic sequences account for a much higher proportion of M&lt;sub&gt;0&lt;/sub&gt; release for normal faults (~20%) than for reverse faults (~10%), with strike-slip faults intermediate between these two end-members. We also find that the proportion of M&lt;sub&gt;0&lt;/sub&gt; release in seismic sequences is higher for events that occur in regions characterised by a diversity of different earthquake types (e.g. both reverse and strike-slip faulting) than for events that occur in regions characterised by a single earthquake type (e.g. strike-slip faulting only). Together these findings imply that complexity of fault network is an important factor in controlling the occurrence of large-M&lt;sub&gt;0&lt;/sub&gt; seismic sequences, and that &amp;#8216;failed&amp;#8217; multi-segment earthquakes and therefore large-M&lt;sub&gt;0&lt;/sub&gt; seismic sequences are more likely to occur in regions with complex fault networks.&lt;/p&gt;

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