Tectonic regimes and earthquake size distribution: new evidence f or PSHA

Earthquake catalogues, seismotectonic zonations and ground-motion prediction equations (GMPE) are the basic ingredients for probabilistic seismic hazard assessment (PSHA). Seismotectonic zones are commonly defined considering the style-of-faulting; contemporary GMPE’s also differentiate by the style-of-faulting. Here we present a case study for Italy to show that style-of-faulting should also be incorporated into the recurrence rates estimation. In the past 40 years many studies relating b-values of the Gutenberg and Richter law to physical properties have been performed, from laboratory rock specimens to observations in different tectonic regimes. Various authors analyzed the correlation between b-value and tectonic regimes and the results are generally consistent: as power laws indicate scale invariance, the inverse dependence of the b-value on the differential stress is universally valid and the parameter can therefore be interpreted as a ‘stressmeter’ in the Earth’s crust. A consequence of the inverse dependency of the b-value on differential stress is that tectonics regimes with different dominant faulting styles should exhibit significantly different b-values, in particular the highest values for normal events (bNR), followed by strike-slip ( bSS) and reverse (bTH): bTH < bSS < bNR. In this study, we evaluate this hypothesis for the first time, using data from the Italian Peninsula, whose complex geology is reflected in a strongly variable stress field and distinctly different faulting regimes. Extensional, compressional and strike-slip regimes are simultaneously present. T he study region fulfils two other critical requirements: 1)the regional seismic monitoring of the microseismicity of the past two decades was good enough to allow detailed mapping of the b-value and 2) a rich catalogue of focal mechanism exists that allows a detailed seismotectonic zonation. Because the b–value is a critical parameter in PSHA, linking it firmly to regional faulting style has significant implications for future regional PSHA studies. At present the b-values are not used for zonation purposes, but they are either assigned regionally or computed for each zone, where zones are in general defined based on expert judgment. We suggest that future seismotectonic zonation models should take into account the knowledge on faulting style dependence of b-values. T here are a variety of way how this can be achieved, for example using high resolution mapping of b as an input for zonation, or by using the b-values of the large scale tectonic zones as a prior, deviating only if local b-values are found to be significantly different from the regional ones

HALM: A Hybrid Asperity Likelihood Model for Italy

The Asperity Likelihood Model (ALM), first developed and currently tested for California, hypothesizes that small-scale spatial variations in the b-value of the Gutenberg and Richter relationship play a central role in forecasting future seismicity (Wiemer and Schorlemmer, SRL, 2007). The physical basis of the model is the concept that the local b-value is inversely dependent on applied shear stress. Thus low b-values (b < 0.7) characterize the locked paches of faults –asperities- from which future mainshocks are more likely to be generated, whereas the high b-values (b > 1.1) found for example in creeping section of faults suggest a lower seismic hazard. To test this model in a reproducible and prospective way suitable for the requirements of the CSEP initiative (www.cseptesting.org), the b-value variability is mapped on a grid. First, using the entire dataset above the overall magnitude of completeness, the regional b-value is estimated. This value is then compared to the one locally estimated at each grid-node for a number of radii, we use the local value if its likelihood score, corrected for the degrees of freedom using the Akaike Information Criterion, suggest to do so. We are currently calibrating the ALM model for implementation in the Italian testing region, the first region within the CSEP EU testing Center (eu.cseptesting.org) for which fully prospective tests of earthquake likelihood models will commence in Europe. We are also developing a modified approach, ‘hybrid’ between a grid-based and a zoning one: the HALM (Hybrid Asperity Likelihood Model). According to HALM, the Italian territory is divided in three distinct regions depending on the main tectonic elements, combined with knowledge derived from GPS networks, seismic profile interpretation, borehole breakouts and the focal mechanisms of the event. The local b-value variability was thus mapped using three independent overall b-values. We evaluate the performance of the two models in retrospective tests using the standard CSEP likelihood test

Comment on “High-Definition Mapping of the Gutenberg–Richter b-Value and Its Relevance: A Case Study in Italy” by M. Taroni, J. Zhuang, and W. Marzocchi

Taroni et al. (2021) published a statistical framework to reliably estimate the b-value and its uncertainties, with the goal being the interpretation in a seismotectonic context and improving earthquake forecasting capabilities. In this comment, we show that the results presented for the Italian region and the conclusions drawn by the authors, are heavily biased due to quarry-blast events in the Italian earthquake catalog used in the analysis. Without removing this anthropogenic component in the data, a meaningful analysis of the earthquake- size distribution for natural seismicity is, in our opinion, not possible. This comment highlights the need for basic data quality analysis before sophisticated statistical tools are applied to a dataset

Asperity-based earthquake likelihood models for Italy

The Asperity Likelihood Model (ALM) hypothesizes that small-scale spatial variations in the b-value of the Gutenberg-Richter relationship have a central role in forecasting future seismicity. The physical basis of the ALM is the concept that the local b-value is inversely dependent on the applied shear stress. Thus low b-values (b 1.1), which can be found, for example, in creeping sections of faults, suggest a lower probability of large events. To turn this hypothesis into a forecast model for Italy, we first determined the regional b-value (b = 0.93 ±0.01) and compared it with the locally determined b-values at each node of the forecast grid, based on sampling radii ranging from 6 km to 20 km. We used the local b-values if their Akaike Information Criterion scores were lower than those of the regional b-values. We then explored two modifications to this model: in the ALM.IT, we declustered the input catalog for M ≥2 and smoothed the node-wise rates of the declustered catalog with a Gaussian filter. Completeness values for each node were determined using the probability-based magnitude of completeness method. In the second model, the hybrid ALM (HALM), as a «hybrid» between a grid-based and a zoning model, the Italian territory was divided into eight distinct regions that depended on the main tectonic regimes, and the local b-value variability was thus mapped using the regional b-values for each tectonic zone

Metodologie per il miglioramento delle stime di pericolosità sismica in Italia

In questo lavoro di dottorato sono stati analizzati differenti strumenti impiegati per le stime di pericolosità sismica. Facendo riferimento alla Mappa di Pericolosità Sismica Italiana MPS04 (Gruppo di Lavoro MPS, 2004), redatta dall’Istituto Nazionale di Geofisica e Vulcanologia (INGV) e adottata come mappa di riferimento per il territorio nazionale ai sensi dell’Ordinanza PCM 3519 del 28 aprile 2006, All. 1b, è stato approfondito il calcolo dei tassi di sismicità attraverso la relazione di Gutenberg e Richter (1944). In particolare, si è proceduto attraverso un confronto tra i valori ottenuti dagli autori della Mappa (Gruppo di Lavoro MPS, 2004) e i valori ottenuti imponendo un valore costante e unico al parametro b della relazione (Gutenberg e Richter, 1944). Il secondo tema affrontato è stato l’analisi della presenza di eventi di origine non tettonica in un catalogo. Nel 2000 Wiemer e Baer hanno proposto un algoritmo che identifica e rimuove gli eventi di origine antropica. Alla metodologia di Wiemer e Baer (2000) sono state apportate delle modifiche al fine di limitare la rimozione di eventi naturali. Tale analisi è stata condotta sul Catalogo Strumentale della Sismicità Italiana (CSI 1.1; Castello et al., 2006) e sui cataloghi Europei disponibili online: Spagna e Portogallo, Francia, Nord Europa, Repubblica Ceca, Romania, Grecia. L’ultimo argomento trattato ha riguardato la presunta correlazione tra i meccanismi di fagliazione e il parametro b della relazione di Gutenberg e Richter (1944). Nel lavoro di Schorlemmer et al. (2005), tale correlazione è dimostrata calcolando il b-value su una griglia a scala mondiale raggruppando i terremoti in funzione dell’angolo di rake: i valori maggiori del parametro sono misurati per i terremoti che si originano in un regime distensivo, seguono quelli in un regime trascorrente mentre i valori minori si registrano nelle aree a regime compressivo. Il principale ostacolo per una applicazione del metodo al territorio italiano è rappresentato dal numero ridotto di terremoti per i quali è possibile avere indicazioni circa il meccanismo focale della sorgente: la correlazione è stata così valutata calcolando il b-value all’interno delle zone sismogenetiche definite per la realizzazione di MPS04 (Gruppo di Lavoro MPS, 2004), alle quali è stato nuovamente assegnato un meccanismo di fagliazione prevalente attraverso la somma del tensore momento. Sono inoltre allegati lavori altri lavori prodotti nell’ambito della pericolosità sismica

Asperity-based earthquake likelihood models f or Italy

T he Asperity Likelihood Model (ALM) was first developed for forecasting earthquakes in California (Wiemer and Schorlemmer, SRL, 2007) and is now being tested for performance in the US testing center of the Collaboratory for the Study of Earthquake Predictability (CSEP). T he model hypothesizes that small-scale spatial variations in b-value of the Gutenberg and Richter relationship play a central role in forecasting future seismicity. T he physical basis of the model is the concept that the local b-value depends inversely on applied shear stress. T hus, low b-values (b<0.7) characterize locked patches of faults—asperities—from which future main shocks are more likely to nucleate, whereas high b-vaues (b>1.1), found for example in creeping sections of faults, suggest a lower probability of nucleating large events. Here, we calibrate this model for the Italian testing region, the first region in the CSEP European testing center. Italian seismicity is lower, more distributed, and less fault-centric than seismicity in California. Comparison of forecasts of the same model in different regions is a key element in making progress in the study of earthquake forecast models. We also explore two modified versions of this model: in the ALM.IT model, we in addition decluster the input catalog and smooth the node-wise rates of the declustered catalog with a gaussian filter. Completeness values for each node are determined using the probability-based magnitude of completeness method (Schorlemmer and Woessner,BSSA, 2008). In the HALM (Hybrid Asperity Likelihood Model), a ‘hybrid’ between a grid-based and a zoning model, the Italian territory is divided into 8 distinct regions depending on the main tectonic regime, and the local b-value variabilily is thus mapped using regional b-values for each tectonic zone

Air pollution in Delhi: A review of past and current policy approaches

Delhi National Capital Region (Delhi NCR) is facing serious challenges linked to worrying levels of air pollution (mainly NO2, PM10 and PM2.5). The CADTIME prject (Clean Air in Delhi through Implementation, Mitigation and Engagement) aims to understand what is required to deliver significant reductions in levels of air pollution. This paper presents the results of the first stage of the project: it firstly contextualises the challenges of air quality management in Delhi within the broader evolution of environmental policies and governance in India, with particular consideration to the tensions between environmental protection and the country's development objectives. Secondly, it sets out how CADTIME will combine multiple source qualitative and quantitative data to develop an air quality action plan and an implementation strategy. In particular, through two workshops with local and national experts and stakeholders, and two rounds of focus groups with citizens of Delhi we will contrast stakeholders' priorities and preferences for existing and potential solutions to air pollution with citizens' lived experiences, thus assessing the political/technical feasibility and public acceptability of current and proposed measures. Furthermore, we will complement the primary qualitative data with a critical review examining the successes and failures of UK and European policies to draw lessons that can be relevant for Delhi and to avoid ineffective policies and achieve cost-effective solutions for the city in the shortest possible time

Air Pollution in Delhi: A Review of Past and Current Policy Approches

Delhi National Capital Region (Delhi NCR) is facing serious challenges linked to worrying levels of air pollution (mainly NO2, PM10 and PM2.5). The CADTIME prject (Clean Air in Delhi through Implementation, Mitigation and Engagement) aims to understand what is required to deliver significant reductions in levels of air pollution. This paper presents the results of the first stage of the project: it firstly contextualises the challenges of air quality management in Delhi within the broader evolution of environmental policies and governance in India, with particular consideration to the tensions between environmental protection and the country’s development objectives. Secondly, it sets out how CADTIME will combine multiple source qualitative and quantitative data to develop an air quality action plan and an implementation strategy. In particular, through two workshops with local and national experts and stakeholders, and two rounds of focus groups with citizens of Delhi we will contrast stakeholders’ priorities and preferences for existing and potential solutions to air pollution with citizens’ lived experiences, thus assessing the political/technical feasibility and public acceptability of current and proposed measures. Furthermore, we will complement the primary qualitative data with a critical review examining the successes and failures of UK and European policies to draw lessons that can be relevant for Delhi and to avoid ineffective policies and achieve cost-effective solutions for the city in the shortest possible time

Detection of quarry and mine blast contamination in European regional catalogues

The presence of quarry and mine blasts in seismic catalogues is detected using the Wiemer and Baer (Bull Seism Soc Am 90(2):525\u2013530, 2000) algorithm. The procedure is based on the observation that quarry blasts generally take place during daytime hours: the areas with a high ratio of daytime and night-time events are likely to be regions with quarry activity. In the first part of this work we have tested the method, using both a synthetic and a regional catalogue; in the second part the procedure has been applied to some of the European regional catalogues available on line. The comparison between the results obtained and the location of known quarries and mines for the analysed catalogues confirms the reliability of the methodology in identifying mining areas

Distribuzione del carbonio organico nelle acque del lago di Massaciuccoli e rilascio dai sedimenti

Sono state analizzate due sezioni verticali complete (intera colonna d'acqua, interfaccia sedimento-acqua, e i primi 50 cm di sedimento) del lago di Massaciuccoli, per studiare il rilascio dei sedimenti di un lago eutrofìzzato. Come punti di campionamento sono stati scelti il canale Burlamacca, unico emissario del lago, e il fosso Barra, di fronte all'idrovora di Massaciuccoli, entrambi ricchi di sostanze nutrienti, causa dell'eutrofizzazione, a seguito di forti input estemi. Le diversità granulometriche e composizionali dei sedimenti analizzati hanno fornito l'opportunità di osservare due comportamenti ben distinti e rappresentativi dell'intero lago. È stata inoltre eseguita una campagna di raccolta dati tra maggio e settembre 2003, consistita nel prelievo di campioni di acqua all'interfaccia acqua-aria, acqua- sedimento e almeno un punto intermedio, in quattordici stazioni distribuite sia nell'interno del lago, sia nei canali. Particolare attenzione è stata rivolta al contenuto di carbonio organico totale (TOC), parametro già ampiamente utilizzato per questi scopi nell'ambito della comunità scientifica nazionale e intemazionale. I risultati ottenuti hanno fornito un quadro dello stato attuale della qualità delle acque del lago e del loro grado di eutrofizzazione e permesso di definire i diversi rilasci di TOC dalle differenti tipologie di sedimenti