PROSPECTIVE AFTERSHOCK FORECASTING OF THE NORCIA 2016 EARTHQUAKE SEQUENCE, CENTRAL APENNINES, ITALY
Lead Research Organisation:
BRITISH GEOLOGICAL SURVEY
Abstract
On 24/08/2016, 01:36:33 UTC an earthquake of magnitude M=6.2 occurred at Norcia, Italy, killing more than 290 people, injuring 500 more, and leaving some 2,500 local inhabitants without a home. The earthquake resulted from movement on a normal fault in the Apennines mountain chain that runs along the Italian peninsula. Large destructive earthquakes of similar rupture style have occurred throughout this region in the past, most recently the 2009 M=6.4 L'Aquila event, 43 km S of the recent epicenter.
Immediately after the Norcia earthquake, a UK scientific team led by the British Geological Survey, together with the University of Edinburgh, coordinated with the Instituto Nationale Geophysica e Vulcanologia (INGV) to enable the deployment of a high -density temporary seismic network to study the aftershock sequence. To date, 26 UK seismic recording stations are fully integrated with the INGV network and this will enable a high-accuracy updated earthquake catalogue to be derived with a greater regional coverage and improved magnitude sensitivity.
The dataset collected within the next 6 months will be the basis of the development of aftershock forecast models and their transparent testing following international protocols. Aftershock forecasts are based on our understanding of earthquake triggering mechanisms and the empirical knowledge from previous aftershock sequence in the broader region. A validation of our forecasts using widely accepted statistical metrics is necessary in order to determine the strengths and weaknesses behind our triggering hypothesis and ensure that new knowledge will be passed on to improve operational aftershock forecasting world-wide.
Immediately after the Norcia earthquake, a UK scientific team led by the British Geological Survey, together with the University of Edinburgh, coordinated with the Instituto Nationale Geophysica e Vulcanologia (INGV) to enable the deployment of a high -density temporary seismic network to study the aftershock sequence. To date, 26 UK seismic recording stations are fully integrated with the INGV network and this will enable a high-accuracy updated earthquake catalogue to be derived with a greater regional coverage and improved magnitude sensitivity.
The dataset collected within the next 6 months will be the basis of the development of aftershock forecast models and their transparent testing following international protocols. Aftershock forecasts are based on our understanding of earthquake triggering mechanisms and the empirical knowledge from previous aftershock sequence in the broader region. A validation of our forecasts using widely accepted statistical metrics is necessary in order to determine the strengths and weaknesses behind our triggering hypothesis and ensure that new knowledge will be passed on to improve operational aftershock forecasting world-wide.
Planned Impact
Operational earthquake forecasting benefits wider society in affected areas primarily by supporting decision makers on the ground at times when felt aftershocks continue to rattle the population. It can also aid in increase awareness of the risks on different timescales, and hence can help to promote the development of resilience to future events.
Our research will engage a range of professionals working at the interface between research and impact in the British Isles, including social scientists, educationalists and humanities researchers and the humanitarian organisations they are already engaged with. The network already has an established track record of applying contemporary earthquake science to emergency earthquake response. It has, at its heart, the aim of doing world-leading research and using it to increase the resilience of earthquake-threatened communities. The overall practical aim in our proposal is to improve current practice in operational forecasting, in consultation with a variety of end users, so the results can be transferred quickly to operational utility, and used ultimately to support decision-making in a crisis. Such Impact is at the core of our scientific motivation. We will continue to engage with NGO Concern Worldwide, since their input and collaboration over the last years has helped constrain our research focus and continues to shape our thinking, and seek to develop and extend this best practice in collaboration with NGOs to other organisations. We will also seek to engage with decision makers with delegated authority from Government, on issues of policy development and practical implementation of Operational Forecasting at a special Impact-dedicated event involving the Italian Department of Civil Protection (DPC) and the National Institute of Geophysics and Volcanology (INGV) in Italy. This will explicitly include discussion on how the scientific discoveries and outputs could be further used to increase resilience in a post-disaster environment.
Our research will engage a range of professionals working at the interface between research and impact in the British Isles, including social scientists, educationalists and humanities researchers and the humanitarian organisations they are already engaged with. The network already has an established track record of applying contemporary earthquake science to emergency earthquake response. It has, at its heart, the aim of doing world-leading research and using it to increase the resilience of earthquake-threatened communities. The overall practical aim in our proposal is to improve current practice in operational forecasting, in consultation with a variety of end users, so the results can be transferred quickly to operational utility, and used ultimately to support decision-making in a crisis. Such Impact is at the core of our scientific motivation. We will continue to engage with NGO Concern Worldwide, since their input and collaboration over the last years has helped constrain our research focus and continues to shape our thinking, and seek to develop and extend this best practice in collaboration with NGOs to other organisations. We will also seek to engage with decision makers with delegated authority from Government, on issues of policy development and practical implementation of Operational Forecasting at a special Impact-dedicated event involving the Italian Department of Civil Protection (DPC) and the National Institute of Geophysics and Volcanology (INGV) in Italy. This will explicitly include discussion on how the scientific discoveries and outputs could be further used to increase resilience in a post-disaster environment.
Publications
Spallarossa D
(2021)
An automatically generated high-resolution earthquake catalogue for the 2016-2017 Central Italy seismic sequence, including P and S phase arrival times
in Geophysical Journal International
Milena Moretti
(2016)
SISMIKO: emergency network deployment and data sharing for the 2016 central Italy seismic sequence
in Annals of Geophysics
| Description | The objective of the project was to develop aftershock forecast model using preliminary information available following the large earthquake in the Apennines. The evolving sequence was characterised by the occurrence of 9 earthquakes above magnitude M=5.0. Three principle earthquakes of magnitude M=5.9 occurred within a 50 km distance along the Apennines mountain chain in a period of just over 2 months. The first occurred on 24th August with a magnitude of M=6.0 near Amatrice and killed 297 people, destroying the medieval villages of Amatrice, Accumoli and Pescara di Tronto. It was followed almost one hour after by a M=5.7 triggered event near Norcia. On 26th October two large shocks of M=5.4 and M=5.9 (32 minutes after) struck ~30 km further north. Four days later on 30th October the largest (M=6.5) event to date struck, devastating Norcia and its historical cathedral of San Benedetto. Few months later in January 18, 2017 4 events above magnitude M=5.0 occurred at the south prolongation of the fault near L'Aquila that suffered a M=6.4 earthquake in 2009 with devastating consequences. All the above make clear that the occurrence of large magnitude events within a limited time period under a well instrumented area gives scientists the opportunity to develop and test aftershock forecast models that can inform us about the evolution of the sequence. These models do not only have a great scientific value enhancing our understanding about under which conditions hazard occurs but are expected to play in the future an important role in developing emergency strategies in disaster settings. We find that stress transfer hypothesis, supporting the existence of triggering seismicity due to rapid elastic stress loading of near-by faults following a large earthquake, reasons the occurrence of the largest earthquake in the sequence. However, at small scales (few km) the triggering mechanisms are unknown and they are subject to large uncertainties related to the source models, used to described co-seismic fault slip. In the future, we seek to incorporate influence from large and small magnitude earthquakes to enhance the performance of aftershock forecast models in different scales. |
| Exploitation Route | The preliminary forecast models, products of the first year of research that describe our knowledge for aftershock occurrence immediately after the large earthquakes of the Apennines, will be the benchmark forecast models against which the best models, products of the next 3 years of research, will be compared against within the now starting NERC-NSF project (UK PI Margarita Segou). The evolution of our research on the subject of earthquake forecasting in the Central Apennines continues and any new findings and outcomes are reported in the award NE/R000794/1 - NSFGEO-NERC: The central Apennines earthquake cascade under a new microscope. |
| Sectors | Other |
| Description | The findings, summarized in Mancini et al. (2019), sheds light on the scientific progress and the much-required developments to support decision-making for stakeholders. |
| First Year Of Impact | 2017 |
| Sector | Energy,Environment |
| Impact Types | Societal Policy & public services |
| Description | NERC-NSFGEO Standard Grant |
| Amount | £800,000 (GBP) |
| Organisation | Natural Environment Research Council |
| Sector | Public |
| Country | United Kingdom |
| Start | 01/2018 |
| End | 01/2021 |
| Title | One year of continuous waveforms of 24 broadband stations located in the Central Apennines |
| Description | Our emerging dataset consists of seismic records from 89 stations deployed soon after the first event2; 28 permanent and 23 temporary stations deployed by Istituto Nationale Geofisica e Vulcanologia (INGV), 24 temporary stations by the British Geological Survey (BGS), and 19 accelerometer stations operated by the Italian Civil Protection. The network has an average station spacing ~5 km and it will continue to be fully operational until at least September 2017. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2017 |
| Provided To Others? | Yes |
| Impact | An International project is now just starting (Jan, 2018-Jan. 2021) focusing on the laborious processing of the continuous waveform and harvesting source parameters for even the smallest magnitude earthquakes within the earthquake sequence. |
| Title | Physics-based forecast models |
| Description | Two different approaches have been developed to face the problem of forecasting the spatiotemporal evolution of an earthquake sequence. The first involves the use of Rate-and-State laboratory derived friction models based on the calculation of the static stress transfer in the crust following a mainshock (Toda et al., 2005; Cocco et al., 2010; Toda & Enescu, 2011; Parsons et al., 2012, 2014; Segou et al., 2016; Segou & Parsons, 2016, among others). The second entails a statistical modelling of the cascade of triggered events based on empirical observations (e.g. Werner et al., 2011; Lombardi & Marzocchi, 2010; Marzocchi, 2012). Given their ability to capture different characteristics of the evolution of a sequence, it is not rare to use both of these two methods and then compare the results, or to use a hybrid approach. Immediately following the 24th August 2016 Amatrice earthquake (Central Apennines, Italy) we started producing and testing physics-based forecast models, that is, those belonging to the first of the two aforementioned categories. As earthquakes redistribute the stresses acting on the surrounding crust, according to the static stress transfer hypothesis seismicity is generally promoted in crustal volumes where the shear stress increases, while it is inhibited where the stress is reduced. The simulation of a mainshock rupture (aka source fault) and the subsequent effect of stress perturbation onto neighbouring active faults (aka receiver faults) represent the key feature of physics-based models. To do that, the so-called "static Coulomb stress change" is calculated with the following equation: Where is the shear stress change on a given receiver fault plane (positive in direction of fault slip), is the change in normal stress, and is the effective coefficient of friction on a candidate receiver fault plane on which aftershocks could nucleate. Estimated stresses are used to derive the time-dependent evolution of seismicity by following the rate-and-state friction laws (Dieterich, 1994). According to this theory, in the absence of a relevant stress change in the crustal volume of interest, the seismicity rate is simply equal to its characteristic background seismicity rate of the region. However, if a the crustal static stress field is perturbed, the new expected aftershocks rate depends on a set of parameters (the so-called Rate-and-State parameters): the stress change itself, the contribution of the intrinsic background rate and two parameters describing the fault behavior, namely the effective normal stress clamping (or unclamping) the receiver faults and the secular shear stressing rate acting on them. |
| Type Of Material | Computer model/algorithm |
| Year Produced | 2018 |
| Provided To Others? | Yes |
| Impact | We have presented the model in the final meeting of the project, summarising the first year results in INGV, Rome. Experts attending suggested to incorporate the physics-based approach to operational forecasting model for Italy nationwide. |