The Vrancea seismogenic zone in Romania represents a peculiar source of seismic hazard, which is also a major concern for neighboring countries Bulgaria, Serbia and Republic of Moldavia. Earthquakes in the Carpathian-Pannonian region are confined within the crust, except for the Vrancea zone, where earthquakes occur at focal depth down to 200 km. Situated at 140-170 km distance from the Vrancea epicentral zone, Bucharest has suffered many damages due to high energy Vrancea intermediate-depth earthquakes; the March 4, 1977 event (Mw 7.2) caused the collapse of 36 buildings, and more than 150 were seriously damaged.
We present an approach for a regional Earthquake Early Warning for Romania. It is based on the PRESTo (PRobabilistic and Evolutionary early warning SysTem) software platform. PRESTo was tested in simulation, offline mode, by playing back the 3-component accelerometric waveforms recorded by the stations of the Romanian Seismic Network (RoNet). The system performs P-waves arrival detection and, once an event has been detected, it first provides location and magnitude estimations. The earthquake location is obtained through an evolutionary, real-time probabilistic approach based on an equal differential time formulation that uses information from both triggered and not-yet-triggered stations. The earthquake magnitude is estimated exploiting its empirical correlation with the peak displacement measured on the first 2-4s of P-waves. The peak ground motion at sites of interest can be finally estimated by specific ground motion prediction equations once that the hypocenter and magnitude are known. All estimates are provided as probability density functions, with an uncertainty that typically decreases with time, and can be sent as alarm messages that can reach the vulnerable structures before the arrival of destructive S waves. PRESTo will be implemented in real-time in the near future on the live data streams from the existing RoNet seismic stations. PRESTo has been tested off-line with recorded events of magnitude greater than Mw 4, but smaller than Mw 6.0 occurred between 2004 and 2011. The tests performed have shown that a stable solution is generally reached within 10-25s from the origin time, depending on the depth of the earthquakes.