Real-Time Estimation of Earthquake Location, Magnitude and Rapid Shake map Computation for the Campania Region, Southern Italy

A prototype system for earthquake early warning and rapid shake map evaluation is being developed and tested in southern Italy based on a dense, wide dynamic-range seismic network (accelerometers + seismometers) under installation in the Apenninic belt region (Irpinia Seismic Network). This system forms a regional Earthquake Early Warning System consisting of a seismic sensor network covering a portion of the expected epicentral area for large earrthquakes. Considering a warning window ranging from tens of seconds before to hundred of seconds after an earthquake, several public infrastructures and buildings of strategic relevance (hospitals, gas pipelines, railways, railroads, ...) of the Regione Campania are potential test-sites for testing innovative technologies for data acquisition, processing and transmission. A potential application of an early warning system in the Campania region based on the Irpinia network, should consider an expected time delay to the first energetic S wave train varying between 14-20 sec at 40-60 km distance to 26-30 sec at about 80-100 km, from a crustal earthquake occurring in the source region. The latter is the typical time window available for mitigating earthquake effects through early warning in the city of Naples (about 2 million of inhabitants including suburbs). We have developed a method for real time earthquake location following a probabilistic approach. The earthquake location is expressed as a probability density function for the hypocenter location in 3D space based on the concept of equal differential-time (EDT). It provides a location as the maximum of a stack over quasi-hyperbolic surfaces. On each surface the difference of calculated travel-times at a pair of stations is equal to the difference of observed arrival times at the same pair of stations. For an increasing number of P-wave readings, progressively acquired in the short time after the occurrence of an earthquake, the EDT method can be generalized by introducing an evolutionary strategy which is aimed at obtaining a more and more refined estimate of the maximum probability volume as the time goes on. The real time magnitude estimate will take advantage from the high spatial density of the network in the source region and the wide dynamic range of installed instruments. Based on the offline analysis of high quality strong-motion data bases recorded in Italy and worldwide, several methods will be checked and validated , using different observed quantities (peak amplitude, dominant frequency, square velocity integral, .) to be measured on seismograms, as a function of time. Following the ElarmS methodology (Allen,2004), peak ground attenuation relations can be used to predict the distribution of maximum ground shaking, as updated estimates of earthquake location and magnitude are progressively available from the Early Warning system starting from the time of first P-wave detection. As measurements of peak ground quantities for the current earthquake become available from the network, these values are progressively used to adjust an "ad hoc" determined attenuation relation for the Campania region using the stochastic approach proposed by Boore (1993).