When an earthquake occurs, there are only few seconds between the rupture beginning and its effect on population and buildings. A real-time, reliable image of the finite seismic source is crucial for producing realistic ground shaking maps. Currently the automatic determination of the focal mechanism is generally available within minutes after the earthquake occurrence. Here, we present a straightforward and robust methodology for the real-time determination of the focal mechanism form the azimuthal distribution of the initial P-wave amplitude. The inverse problem is solved in a Bayesian framework, to easily account for a-priori constraints based on the local tectonic information. In the proposed methodology, as soon as few seconds of P-wave signals are available at a set of recording stations, the observed P-wave amplitude spatial distribution is compared to the theoretical P-wave radiation pattern, in an Octree model space exploration scheme. Then, the procedure evolves in time as further stations record the earthquake. The best solution (in terms of strike, dip and slip angles) is obtained from the characterization of the posterior probability density function, while the errors on each parameter are inferred from the confidence ellipsoid. The algorithm has been first validated offline through a set of synthetic tests, in which we changed number, density and azimuthal coverage of available stations, for two different fault plane geometries and in presence of different levels of Gaussian noise. Then we applied the methodology to a selection of 12 real earthquakes (moment magnitude ranging from 4.7 to 6.5) belonging to the 2016-2017 Central Italy seismic sequence. Both for the synthetic tests and for the real earthquake scenarios, we found consistent focal mechanisms with respect to the catalogue solutions. We conclude that our procedure is stable and provides robust results, also in the case of not optimal azimuthal coverage and small number of recording stations.
Earthquake focal mechanism determination from the initial P-wave amplitude distribution for real-time applications / Colombelli, Simona; Emolo, Antonio; Tarantino, Stefania; Zollo, Aldo. - (2018). (Intervento presentato al convegno 2018 Fall Meeting of the American Geophysical Union tenutosi a Washington, D.C. (USA) nel 10-14 December, 2018).
Earthquake focal mechanism determination from the initial P-wave amplitude distribution for real-time applications
Simona Colombelli;Antonio Emolo;Stefania Tarantino;and Aldo Zollo
2018
Abstract
When an earthquake occurs, there are only few seconds between the rupture beginning and its effect on population and buildings. A real-time, reliable image of the finite seismic source is crucial for producing realistic ground shaking maps. Currently the automatic determination of the focal mechanism is generally available within minutes after the earthquake occurrence. Here, we present a straightforward and robust methodology for the real-time determination of the focal mechanism form the azimuthal distribution of the initial P-wave amplitude. The inverse problem is solved in a Bayesian framework, to easily account for a-priori constraints based on the local tectonic information. In the proposed methodology, as soon as few seconds of P-wave signals are available at a set of recording stations, the observed P-wave amplitude spatial distribution is compared to the theoretical P-wave radiation pattern, in an Octree model space exploration scheme. Then, the procedure evolves in time as further stations record the earthquake. The best solution (in terms of strike, dip and slip angles) is obtained from the characterization of the posterior probability density function, while the errors on each parameter are inferred from the confidence ellipsoid. The algorithm has been first validated offline through a set of synthetic tests, in which we changed number, density and azimuthal coverage of available stations, for two different fault plane geometries and in presence of different levels of Gaussian noise. Then we applied the methodology to a selection of 12 real earthquakes (moment magnitude ranging from 4.7 to 6.5) belonging to the 2016-2017 Central Italy seismic sequence. Both for the synthetic tests and for the real earthquake scenarios, we found consistent focal mechanisms with respect to the catalogue solutions. We conclude that our procedure is stable and provides robust results, also in the case of not optimal azimuthal coverage and small number of recording stations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
