NSFGEO-NERC: Collaborative Research: The Central Apennines earthquake Cascade under a New Microscope
DESCRIPTION: A series of powerful earthquakes rocked the Apennine mountains in central Italy, between August 2016 and January 2017 causing loss of life and inflicting heavy damage to the historic towns of Amatrice, Accumoli and Norcia. This sequence produced six strong earthquakes over a period of five months as response and recovery operations were underway. This rapidly evolving seismic crisis underscores the pressing need to better understand how earthquake sequences unfold. The goal of this joint project, funded by the National Science Foundation in the U.S. and the National Environmental Research Council in the U.K., in coordination with the Istituto Nazionale di Geofisica e Volcanologia in Italy, will deepen knowledge of earthquake interaction by studying these devastating earthquakes. An international team of earthquake experts will use high-quality seismic data recorded during the sequences to develop new approaches that can address current obstacles that not only impede deep understanding of the earthquake processes, but also delay the scientific response in the post-earthquake disaster environment. The observational capability to detect, locate and characterize even the smallest magnitude events within few hours developed in this project will be directly applicable to tectonic, induced, geothermal and volcanic seismicity in the U.S. and around the world. Findings of this research will enable improved and scientifically-informed response to the next earthquake crisis to strike the U.S. through existing partnership with the U. S. Geological Survey and support international collaboration amongst US and European earthquake researchers. This study investigates the physics of complex earthquake sequences through the analysis of high-resolution earthquake catalogs to test increasingly sophisticated earthquake forecasting models. To reach this goal this project will: 1) Use state-of-the-art techniques to develop a comprehensive high-resolution earthquake catalog for the devastating earthquake sequence that struck the Italian Apennines in 2016-2017; 2) Investigate the physics of earthquake triggering and the evolution of large-magnitude events within this sequence; 3) Develop and provide testable forecast models that can support decision-making process for future earthquake sequences. The reseach will use the unparalleled seismic data set recorded by more than 85 high-quality broadband sensors deployed in the epicentral region to analyze how each earthquake in the sequence contributes to the evolution of seismicity in space and time. This sequence is particularly rich in this regard, with spatially intertwined episodes on August 24, 2016, October 26-28, 2016 and January 18, 2017. The seismograms of both large and small events will enable us to develop and test new full-waveform based algorithms for event detection, location and characterization that will yield precise source parameters and faulting mechanisms for even the smallest magnitude events. By improving the quality of seismic source parameters across the magnitude spectrum it will be possible to apply process-based models of earthquake nucleation and interaction, including the role of fault complexity, fault loading, relaxation, stress interaction, and fault susceptibility to stress perturbation to understand the evolution of this sequence. The improved fault mechanical understanding will help to develop innovative physics-based forecast models. Currently, real-time earthquake forecasts that describe short-term clustering probabilities are based predominantly on statistical/empirical models. However, these models lack an underlying physical model and therefore have limited predictability if no precursory seismicity exists. A common challenge for both physics- based and statistical forecasts that are based on routine catalogues is the low-probability and high-uncertainty nature of the resulting probabilities. Decision-making and scientific advice are all severely hampered under these conditions. Thus, using this new state-of the art earthquake catalog of the 2016-2017 Italian sequence to test physical, statistical and hybrid (physical and statistical) forecasts in space and time will help (a) to test physical models for earthquake occurrences in sequences, and (b) improve the resolution, accuracy and skill of the forecasts. The broader impacts of this project include improvement on seismic risk assessment as well as fostering collaboration between US and European seismologists.