Applied an innovative method to determine the energy accumulation rate for the central Apennines faults through the use of geodetic and stress data.
Through an innovative multidisciplinary analysis, the result of geodetic observations of about 20 years and a large number of updated data on the direction of the tectonic stress, it is possible to quantify the speed of the movement of the active faults of the central Apennines. This approach could be decisive for better determining the speed of fault movement in a completely innovative and complementary way to the classic and reliable geological techniques
This is what was done in the study “Partitioning the Ongoing Extension of the Central Apennines (Italy): Fault Slip Rates and Bulk Deformation Rates from Geodetic and Stress Data” published in the 'Journal of Geophysical Research – Solid Earth'. The research, which involved geodetic, geological, and modeling expertise from the National Institute of Geophysics and Volcanology (INGV), was conducted in collaboration with the Department of Earth, Planetary, and Space Sciences of the University of California at Los Angeles (UCLA ).
As is known, earthquakes are generated by faults, large planes in correspondence with which portions of the earth's crust move in geological times with respect to each other parallel to the plane of the fault itself. The average speed over geological times with which this process takes place, called slip rate in the scientific literature, is a crucial parameter because it quantifies the potential of each fault within the models developed to evaluate the seismic hazard of a given region.
"This work”, explains Michele Carafa, author of the research, "was born during my stay at UCLA and developed within the "FIRB Abruzzo", an important project funded by MIUR between 2011 and 2016 and called 'High resolution surveys for the estimation of hazards' and seismic risk in the areas affected by the earthquake of 6 April 2009'. in my memory" continues Carafa, “this is the first research at European level which aims explicitly to determine the slip rate of all active faults present in an important seismic area, jointly using different types of information currently available in the field of geosciences, such as GPS data and those describe the orientation of the stress field in a viscoelastic material, such as the earth's crust. There are different techniques for determining the long-term slip rate: the simplest one to explain is based on the recognition of rock layers even hundreds of thousands of years old, placed at different altitudes often even hundreds of meters. According to a classic geological vision, these layers were initially at the same altitude, and it is conceivable that the current topographic difference is mainly the result of the repeated earthquakes that occurred in successive periods along the fault in question, often determinable with more or less complex techniques. And that was exactly the goal of our research group” continues Carafa, “have initial data to understand whether, over the last 15-20 years for which there are accurate geodetic measurements, the behavior of the rock volume adjacent to the fault is compatible with the available estimates of long-term slip rates, i.e. those based on geological methods. The response was essentially positive: the short-term and long-term estimates turned out to be congruent with each other. This result will allow us to better understand and estimate the forces responsible for the tectonic evolution of the Apennines and, therefore, in the future, to evaluate more accurately the seismic hazard of the region. Looking back, I can say that this was a really good scientific challenge. On the one hand, the geodesy researchers of our team have collected all the information necessary to define the average annual displacement of each of the GNSS stations distributed in the study area between the various seismic events, on the other, the tectonic researchers active have examined the scientific literature in detail in order to identify faults commonly accepted as active. Finally, the modelers synthesized the information obtained from the two groups to calculate the average slip rate of each fault, using a decidedly sophisticated method".
“To strengthen the result we analyzed the geodetic dataset together with that of the active stress field, available in the IPSI (Italian Present-day Stress Indicators) database, another product completely developed by INGV”, continues the research coordinator. "The results obtained, the result of our expertise, represent only a first step, and as such may be affected by uncertainties that can be overcome by continuing to work in each of the three areas involved: geodesics, geology and modelling".
If the first step of the study is the result exclusively of the skills of INGV, well directed by the experience of colleague Peter Bird of UCLA, the developments of this research, aimed at a better understanding of the geological evolution of the area, will see scientific collaborations with the University of L'Aquila and with the Gran Sasso Science Institute (GSSI).
“The method used for this research”, concludes the researcher, “it is completely innovative and requires interaction with additional skills such as, for example, mathematics and information technology. There is so much to do, but integrating different skills has been a winning choice and I think it is certainly the way forward to make this type of research useful for the community. In this regard, we are flattered that the Abruzzo Region itself immediately showed itself to be extremely interested in this research by adding to the regional geodetic network - under our scientific supervision - new GNSS stations located in strategic sites, precisely in order to be able to improve our model".
#ingv #centralappennino #faglie
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Investigating the large active faults of the central Apennines through an innovative multidisciplinary method
An innovative method allowed to determine the energy loading rate for the central Apennine faults by joint use of geodetic and stress data
Through an innovative multidisciplinary research, the result of 20 years of geodetic observations and a large number of updated data on the tectonic stress orientation, it is possible to quantify the slip rate of central Apennines active faults. This approach may be crucial for determining better fault slip rates in a completely innovative and complementary way relative to the classical and well-established geological techniques.
This approach is described in the paper “Partitioning the Ongoing Extension of the Central Apennines (Italy): Fault Slip Rates and Bulk Deformation Rates from Geodetic and Stress Data”, published in 'Journal of Geophysical Research - Solid Earth'. The research involved several working groups of the National Institute of Geophysics and Volcanology (INGV), holding complementary expertise in geodesy, geology, and numerical modeling. The experiments were conducted in collaboration with the Department of Earth, Planetary, and Space Sciences of the University of California at Los Angeles (UCLA).
As known, earthquakes occur on faults, which can be described as surfaces along which the nearly-rigid viscous blocks of crust on either side have moved relative to one another parallel to the fracture over geological times. The average slipping rate over geological times of this process, referred to as slip rate in the scientific literature, is a crucial parameter for quantifying the seismogenic potential of each fault, and hence to assess the seismic hazard of a given region.
"This work", explains Michele Carafa, author of the research, "was conceived when I was a visiting researcher at UCLA, and was later developed within 'FIRB Abruzzo' an important project funded by the Italian Ministry of Research between 2011 and 2016, entitled 'High resolution analyzes for the estimation of the seismic hazard and risk in the areas hit by the 6 April 2009 earthquake')". Carafa maintains that “this is the first article in Italy - if not in the broader Mediterranean region - that explicitly aimed to determine the slip rate of active faults crossing an important seismogenic area, based on the joint use of different kind of observations such as GPS measurements and data determining the stress orientations in the viscoelastic Earth crust. Different techniques have been used to determine the average long-term slip rate: the elementary technique is based on the recognition of rock layers that are hundreds of thousands of years old, placed at different altitudes, often even hundreds of meters. According to the classical geological method, these layers were once placed at the same altitude, and it is conceivable the present-day topographic offset is due to the past earthquakes, whose age can be determined in different ways”. Carafa goes on recalling that “This was exactly the goal of our research group: to have some initial data to understand if, over the past 15-20 years for which accurate geodetic measurements exist, the behavior of the rock volume adjacent to the fault is compatible with the available estimates of long-term slip rates, ie those based on geological methods. The first results confirm such agreement exists, as the short and long term estimates were consistently found to be compatible with each other. In perspective, this result allows us to understand better what are the forces responsible for the current tectonic evolution of the Apennines and to improve the assessment of the region's seismic hazard. Looking back, I can say that our work was - and still is - an intriguing scientific challenge. On the one hand, geodesists of our group collected all the information necessary to define the secular annual displacement of each of the GNSS stations distributed in the study area, while on the other hand, the active tectonics researchers scrutinized the scientific literature to find out which faults are believed to be active. Finally, modelists synthesized all the information into a sophisticated method that determines the average slip rate of each fault".
The INGV scientist went on to explain that "To improve the overall compatibility with the geological settings of the region, we included the orientation of the principal stress axes available in the INGV database named 'Italian Present-day Stress Indicators', or IPSI". He also added that "The results we obtained, result of our skills, must necessarily be regarded as a first step: they are affected by uncertainties that may be reduced by replicating the experiment using the three scientific areas: geodesic, geological and modeling".
The published research is mainly the outcome of work conducted by INGV scientists, but it took advantage from the experience of Professor Emeritus Peter Bird of UCLA. Further developments will also entail a collaboration with the University of L'Aquila and with the Gran Sasso Science Institute (GSSI).
“Our research method”concludes Carafa, “requires a highly varied expertise, and indeed we are willing to collaborate with mathematicians and HPC (High Performance Computing) experts. There is still a lot to do, but integrating different skills is the only possibility to move forward and to make this type of research useful for the community. In this regard, we were very pleased by the enthusiastic response of the Abruzzo Region, whose officials - under our scientific supervision - promoted the extension of the regional GNSS network with four strategically located stations that will certainly improve our future results".
#ingv #centralApennines #faults
Photo - A GPS station installed near Bojano (CB) to study the slip rate of the Matese fault.
Photo - Temporary GPS station installed in the proximity of Bojano for investigating the slip rate of the Matese fault.
Figure 1 - Slip rate estimated using data relating to the last 15-20 years for the main faults of the central Apennines.
Figure 1 – Preferred slip rate values obtained for the main active faults of the central Apennines using 15-20 years of GPS measurements.
Figure 2 - Central Apennines: comparison between the loading rates (slip rates) of the main active faults obtained with GPS data (grey horizontal bars) and obtained as the relative slip rate of the crustal blocks on the sides of each fault from the geological studies available in literature (three or four depending on the case: blue bars).
Figure 2 - Central Apennines: comparison between geodetic slip rates (gray stripes) and the corresponding geological estimates available in the literature (three or four, depending on cases: blue bars) for the main active faults of the central Apennines.